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OT a bit: K3 Ant Tuner

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Rich-4

OT a bit: K3 Ant Tuner

To minimize emails direct replies would be nice. I searched the web and
could not find an answer. I know there are a ton of smart folks on
this list so I thought I would ask.

On Field Day at typical setup is :

K3 (or any radio) - bandpass filter - External Antenna Tuner - Antenna

So the antenna was tuned via the external tuner, but saw a guy then
using the K3 ant tuner to touch up the SWR between the radio and the
bandpass filter. Is that an acceptable practice?

I would think not?

Rich

K3RWN

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Don Wilhelm

Re: OT a bit: K3 Ant Tuner

Rich,

Yes and no. With 2 antenna tuners in-line, there will be a bit more
loss due to inductor winding resistance, but other than that, it should
do harm.

Several bandpass filters indicate that they should be between the rig
and the tuner (so the bandpass filters are not run at a high SWR).
If the power rating of the bandpass filter is marginal with respect to
the rig power, then I would observe that caution. Refer to the bandpass
filter specs.

73,
Don W3FPR

On 7/5/2019 10:57 AM, Rich wrote:

> To minimize emails direct replies would be nice. I searched the web and
> could not find an answer. I know there are a ton of smart folks on
> this list so I thought I would ask.
>
> On Field Day at typical setup is :
>
> K3 (or any radio) - bandpass filter - External Antenna Tuner - Antenna
>
> So the antenna was tuned via the external tuner, but saw a guy then
> using the K3 ant tuner to touch up the SWR between the radio and the
> bandpass filter. Is that an acceptable practice?
>

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Mark Goldberg

Re: OT a bit: K3 Ant Tuner

I could not let this go. I've done a lot of work with bandpass filters. The
mismatch will degrade the filter.

For an example, I used Elsie, which is a filter calculator. Using the
example 20 Meter bandpass filter, the passband loss is about .25 dB with
matched 50 ohms in and out. Changing the output impedance to 38+j12 (38
ohms plus 135 nH inductor at 14.15 MHz, about 1.5:1 SWR), the passband
losses increase to about 0.4 - .44 dB and vary more over the band.

Here are the schematics and plots, anyone is welcome to check my
calculations, as I do make mistakes!

https://drive.google.com/file/d/1kj31IL_px6nVyRadW4nOi_c6FLgyaRyk/view?usp=sharing

The loss in the filter will almost double. For 100W in, the loss goes from
about 6W to about 10W. So, it is not a good idea. A worse match will result
in even more losses, perhaps overheating and destroying the filter.

73,

Mark
W7MLG

On Fri, Jul 5, 2019 at 8:32 AM Don Wilhelm <[hidden email]> wrote:

> Rich,
>
> Yes and no. With 2 antenna tuners in-line, there will be a bit more
> loss due to inductor winding resistance, but other than that, it should
> do harm.
>
> Several bandpass filters indicate that they should be between the rig
> and the tuner (so the bandpass filters are not run at a high SWR).
> If the power rating of the bandpass filter is marginal with respect to
> the rig power, then I would observe that caution. Refer to the bandpass
> filter specs.
>
> 73,
> Don W3FPR
>
> On 7/5/2019 10:57 AM, Rich wrote:
> > To minimize emails direct replies would be nice. I searched the web and
> > could not find an answer. I know there are a ton of smart folks on
> > this list so I thought I would ask.
> >
> > On Field Day at typical setup is :
> >
> > K3 (or any radio) - bandpass filter - External Antenna Tuner - Antenna
> >
> > So the antenna was tuned via the external tuner, but saw a guy then
> > using the K3 ant tuner to touch up the SWR between the radio and the
> > bandpass filter. Is that an acceptable practice?
> >
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

David Gilbert

Re: OT a bit: K3 Ant Tuner

In reply to this post by Don Wilhelm

It's not just a power issue. A filter only achieves its design goals if
the impedance feeding it and the load impedance it sees are as
expected. Most filters are going to want to be fed by 50 ohms and see a
load of 50 ohms. Most rigs (not sure about the K3) don't actually
present a pure 50 ohm output impedance, so using the internal tuner in
the K3 supposedly would assure that the filter sees the correct feed
impedance, and for an operation like Field Day having a properly
performing filter might be more important than a bit of power loss in
the K3 tuner inductor.

On the other hand, I'm not sure that the SWR meter in the K3 is a
perfect indicator of a match to a 50 ohm load. I recently did some SWR
measurements on a new antenna setup for five different bands (three
different antennas) using four different indicators ... the SWR meter in
the K3, an AEA HF-CIA, an Elecraft W2, and a new FA-VA5. All four
instruments were located in the same spot on the transmission line for
each band (I swapped them in and out), and I plotted the SWR curves for
frequencies across each band band. The readings with the most deviation
from the others came from the K3, and for certain cable lengths (I did
readings with and without an additional 7 foot length of feedline
inserted) it was significant.

73,
Dave AB7E

On 7/5/2019 8:32 AM, Don Wilhelm wrote:

> Rich,
>
> Yes and no. With 2 antenna tuners in-line, there will be a bit more
> loss due to inductor winding resistance, but other than that, it
> should do harm.
>
> Several bandpass filters indicate that they should be between the rig
> and the tuner (so the bandpass filters are not run at a high SWR).
> If the power rating of the bandpass filter is marginal with respect to
> the rig power, then I would observe that caution. Refer to the
> bandpass filter specs.
>
> 73,
> Don W3FPR
>
> On 7/5/2019 10:57 AM, Rich wrote:
>> To minimize emails direct replies would be nice. I searched the web
>> and could not find an answer. I know there are a ton of smart folks
>> on this list so I thought I would ask.
>>
>> On Field Day at typical setup is :
>>
>> K3 (or any radio) - bandpass filter - External Antenna Tuner - Antenna
>>
>> So the antenna was tuned via the external tuner, but saw a guy then
>> using the K3 ant tuner to touch up the SWR between the radio and the
>> bandpass filter. Is that an acceptable practice?
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Wes Stewart-2

Re: OT a bit: K3 Ant Tuner

In reply to this post by Mark Goldberg

You're offering a scenario different from the original. As I read it,
originally a tuner was used to flatten the load that terminates the BPF output.
Your analysis assumes a matched driver and a mismatch on the output of the BPF.

Then the OP mentioned a second tuner between the TX output and the input of the
BPF, which can be assumed to match the BPF input. The BPF is now matched at
both ends.

To answer the OP's question, the answer is, IMHO of course, yes.

Wes N7WS

On 7/5/2019 10:18 AM, Mark Goldberg wrote:

> I could not let this go. I've done a lot of work with bandpass filters. The
> mismatch will degrade the filter.
>
> For an example, I used Elsie, which is a filter calculator. Using the
> example 20 Meter bandpass filter, the passband loss is about .25 dB with
> matched 50 ohms in and out. Changing the output impedance to 38+j12 (38
> ohms plus 135 nH inductor at 14.15 MHz, about 1.5:1 SWR), the passband
> losses increase to about 0.4 - .44 dB and vary more over the band.
>
> Here are the schematics and plots, anyone is welcome to check my
> calculations, as I do make mistakes!
>
> https://drive.google.com/file/d/1kj31IL_px6nVyRadW4nOi_c6FLgyaRyk/view?usp=sharing
>
> The loss in the filter will almost double. For 100W in, the loss goes from
> about 6W to about 10W. So, it is not a good idea. A worse match will result
> in even more losses, perhaps overheating and destroying the filter.
>
> 73,
>
> Mark
> W7MLG
>
> On Fri, Jul 5, 2019 at 8:32 AM Don Wilhelm <[hidden email]> wrote:
>
>> Rich,
>>
>> Yes and no. With 2 antenna tuners in-line, there will be a bit more
>> loss due to inductor winding resistance, but other than that, it should
>> do harm.
>>
>> Several bandpass filters indicate that they should be between the rig
>> and the tuner (so the bandpass filters are not run at a high SWR).
>> If the power rating of the bandpass filter is marginal with respect to
>> the rig power, then I would observe that caution. Refer to the bandpass
>> filter specs.
>>
>> 73,
>> Don W3FPR
>>
>> On 7/5/2019 10:57 AM, Rich wrote:
>>> To minimize emails direct replies would be nice. I searched the web and
>>> could not find an answer. I know there are a ton of smart folks on
>>> this list so I thought I would ask.
>>>
>>> On Field Day at typical setup is :
>>>
>>> K3 (or any radio) - bandpass filter - External Antenna Tuner - Antenna
>>>
>>> So the antenna was tuned via the external tuner, but saw a guy then
>>> using the K3 ant tuner to touch up the SWR between the radio and the
>>> bandpass filter. Is that an acceptable practice?

Elecraft mailing list

Re: OT a bit: K3 Ant Tuner

In reply to this post by Mark Goldberg

Lets step back a bit and look at the system here. The K3, with ATU, drives into the BPF, when then drives into the external ATU and finally the antenna.
The external ATU takes care of the antenna matching, and should present a 50 ohm load to the BPF. The BPF, because of its design, should present a 50 ohm load to the ATU as well, so everything is matched there.
Before anyone jumps on this, remember the signals go both ways, outbound for transmit, inbound for receive. Also, we have a fundamental principal thrown at every EE student, that for best transmission of signal, the source and load impedances should match.

OK, so let’s look at the K3 side. The K3 antenna port connects directly to the BPF’s radio port. Again, we are presuming the BPF is designed for 50 ohms resistive source/load. The K3 is designed to transmit into a 50 ohm load, but it may not itself be a 50 ohm source. And, the receiver input may not be 50 ohms as well. Adding a tuned ATU does bring this to 50 ohms, providing a proper match into the BPF, so that optimum signal flows both ways. So it could actually be beneficial for the ATU to be in-line and properly tuned. The best way to perform the tune would be to tune the ATU into a 50 ohm dummy load, but tuning into the BPF at low power should work also. The exception to this would be if the BPF changes impedance when power is applied, but then if this happens the best place for that BPF is the trash can.

Now having said this, the ATU can also be bypassed in the K3, and that circuit may provide a proper 50 ohm source/load for the BPF. I would probably take this approach myself (and in fact do so in my station). The reason I take this approach is to avoid the small loss that the internal ATU presents. In contesting, every db matters.

Note that we are talking nits at this point. Unless the ATU was tuned for a load quite a bit off 50 ohms resistive, (quite possible), then retuning won’t make much difference. Perhaps the op had this situation, and thought it better to return the ATU than to bypass it, or he didn’t even think to bypass it. The point is, both methods will work, and I doubt he did anything wrong it performing the tune.

73!
Jack, W6FB

> On Jul 5, 2019, at 10:18 AM, Mark Goldberg <[hidden email]> wrote:
>
> I could not let this go. I've done a lot of work with bandpass filters. The
> mismatch will degrade the filter.
>
> For an example, I used Elsie, which is a filter calculator. Using the
> example 20 Meter bandpass filter, the passband loss is about .25 dB with
> matched 50 ohms in and out. Changing the output impedance to 38+j12 (38
> ohms plus 135 nH inductor at 14.15 MHz, about 1.5:1 SWR), the passband
> losses increase to about 0.4 - .44 dB and vary more over the band.
>
> Here are the schematics and plots, anyone is welcome to check my
> calculations, as I do make mistakes!
>
> https://drive.google.com/file/d/1kj31IL_px6nVyRadW4nOi_c6FLgyaRyk/view?usp=sharing
>
> The loss in the filter will almost double. For 100W in, the loss goes from
> about 6W to about 10W. So, it is not a good idea. A worse match will result
> in even more losses, perhaps overheating and destroying the filter.
>
> 73,
>
> Mark
> W7MLG
>
> On Fri, Jul 5, 2019 at 8:32 AM Don Wilhelm <[hidden email]> wrote:
>
>> Rich,
>>
>> Yes and no. With 2 antenna tuners in-line, there will be a bit more
>> loss due to inductor winding resistance, but other than that, it should
>> do harm.
>>
>> Several bandpass filters indicate that they should be between the rig
>> and the tuner (so the bandpass filters are not run at a high SWR).
>> If the power rating of the bandpass filter is marginal with respect to
>> the rig power, then I would observe that caution. Refer to the bandpass
>> filter specs.
>>
>> 73,
>> Don W3FPR
>>
>> On 7/5/2019 10:57 AM, Rich wrote:
>>> To minimize emails direct replies would be nice. I searched the web and
>>> could not find an answer. I know there are a ton of smart folks on
>>> this list so I thought I would ask.
>>>
>>> On Field Day at typical setup is :
>>>
>>> K3 (or any radio) - bandpass filter - External Antenna Tuner - Antenna
>>>
>>> So the antenna was tuned via the external tuner, but saw a guy then
>>> using the K3 ant tuner to touch up the SWR between the radio and the
>>> bandpass filter. Is that an acceptable practice?
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

David Gilbert

Re: OT a bit: K3 Ant Tuner

In reply to this post by Mark Goldberg

I think you misread the situation. The question isn't whether to put a
single antenna tuner between the antenna and filter versus putting it
between the rig and the filter. The question is whether putting an
ADDITIONAL tuner (the one internal to the K3) at the input of the filter
is a good idea. And to me it seems the answer is yes.

I think we all agree that the right feed impedance and load impedance
for a filter is important. And as I pointed out, not just for power
handling, but also for the filter to actually filter as it was intended.

73,
Dave AB7E

On 7/5/2019 10:18 AM, Mark Goldberg wrote:

Wes Stewart-2

Re: OT a bit: K3 Ant Tuner

In reply to this post by David Gilbert

Good points, some of which I considered making in my last post. Regarding the
SWR measurement capabilities of the K3 (or many other devices) I wrote about
this too in another thread:

http://elecraft.365791.n2.nabble.com/K3-SWR-Numerical-Indication-td7643839.html

Wes N7WS

On 7/5/2019 10:37 AM, David Gilbert wrote:

>
> It's not just a power issue. A filter only achieves its design goals if the
> impedance feeding it and the load impedance it sees are as expected. Most
> filters are going to want to be fed by 50 ohms and see a load of 50 ohms.
> Most rigs (not sure about the K3) don't actually present a pure 50 ohm output
> impedance, so using the internal tuner in the K3 supposedly would assure that
> the filter sees the correct feed impedance, and for an operation like Field
> Day having a properly performing filter might be more important than a bit of
> power loss in the K3 tuner inductor.
>
> On the other hand, I'm not sure that the SWR meter in the K3 is a perfect
> indicator of a match to a 50 ohm load. I recently did some SWR measurements
> on a new antenna setup for five different bands (three different antennas)
> using four different indicators ... the SWR meter in the K3, an AEA HF-CIA, an
> Elecraft W2, and a new FA-VA5. All four instruments were located in the same
> spot on the transmission line for each band (I swapped them in and out), and I
> plotted the SWR curves for frequencies across each band band. The readings
> with the most deviation from the others came from the K3, and for certain
> cable lengths (I did readings with and without an additional 7 foot length of
> feedline inserted) it was significant.
>
> 73,
> Dave AB7E
>

Mark Goldberg

Re: OT a bit: K3 Ant Tuner

In reply to this post by David Gilbert

I stand corrected.

I made an assumption, probably incorrectly, that the reason they had a
second tuner was that the first did not successfully tune the antenna. They
just decided to put the bandpass filter between the two tuners, which would
have provided a mismatch at both the filter input and output. I just used a
mismatch at the output as an example. I just provided an example of filter
performance degradation with even what would be considered a reasonable SWR.

I prefer Jack's solution of bypassing the internal K3 tuner. I do have a
situation where my antenna tuner can't tune my antenna on 160. Rather than
try to use two tuners in series with the requisite losses, I added a shunt
inductor on a big ferrite core to provide most of the required inductance
for a match. It gets hot.

73,

Mark
W7MLG

On Fri, Jul 5, 2019 at 10:57 AM David Gilbert <[hidden email]>
wrote:

>
> I think you misread the situation. The question isn't whether to put a
> single antenna tuner between the antenna and filter versus putting it
> between the rig and the filter. The question is whether putting an
> ADDITIONAL tuner (the one internal to the K3) at the input of the filter
> is a good idea. And to me it seems the answer is yes.
>
> I think we all agree that the right feed impedance and load impedance
> for a filter is important. And as I pointed out, not just for power
> handling, but also for the filter to actually filter as it was intended.
>
> 73,
> Dave AB7E
>
> On 7/5/2019 10:18 AM, Mark Goldberg wrote:
> > I could not let this go. I've done a lot of work with bandpass filters.
> The
> > mismatch will degrade the filter.
> >
> > For an example, I used Elsie, which is a filter calculator. Using the
> > example 20 Meter bandpass filter, the passband loss is about .25 dB with
> > matched 50 ohms in and out. Changing the output impedance to 38+j12 (38
> > ohms plus 135 nH inductor at 14.15 MHz, about 1.5:1 SWR), the passband
> > losses increase to about 0.4 - .44 dB and vary more over the band.
> >
> > Here are the schematics and plots, anyone is welcome to check my
> > calculations, as I do make mistakes!
> >
> >
> https://drive.google.com/file/d/1kj31IL_px6nVyRadW4nOi_c6FLgyaRyk/view?usp=sharing
> >
> > The loss in the filter will almost double. For 100W in, the loss goes
> from
> > about 6W to about 10W. So, it is not a good idea. A worse match will
> result
> > in even more losses, perhaps overheating and destroying the filter.
> >
> > 73,
> >
> > Mark
> > W7MLG
> >
> > On Fri, Jul 5, 2019 at 8:32 AM Don Wilhelm <[hidden email]>
> wrote:
> >
> >> Rich,
> >>
> >> Yes and no. With 2 antenna tuners in-line, there will be a bit more
> >> loss due to inductor winding resistance, but other than that, it should
> >> do harm.
> >>
> >> Several bandpass filters indicate that they should be between the rig
> >> and the tuner (so the bandpass filters are not run at a high SWR).
> >> If the power rating of the bandpass filter is marginal with respect to
> >> the rig power, then I would observe that caution. Refer to the bandpass
> >> filter specs.
> >>
> >> 73,
> >> Don W3FPR
> >>
> >> On 7/5/2019 10:57 AM, Rich wrote:
> >>> To minimize emails direct replies would be nice. I searched the web
> and
> >>> could not find an answer. I know there are a ton of smart folks on
> >>> this list so I thought I would ask.
> >>>
> >>> On Field Day at typical setup is :
> >>>
> >>> K3 (or any radio) - bandpass filter - External Antenna Tuner -
> Antenna
> >>>
> >>> So the antenna was tuned via the external tuner, but saw a guy then
> >>> using the K3 ant tuner to touch up the SWR between the radio and the
> >>> bandpass filter. Is that an acceptable practice?
> >>>
> >> ______________________________________________________________
> >> Elecraft mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >> Help: http://mailman.qth.net/mmfaq.htm
> >> Post: mailto:[hidden email]
> >>
> >> This list hosted by: http://www.qsl.net
> >> Please help support this email list: http://www.qsl.net/donate.html
> >> Message delivered to [hidden email]
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> > Message delivered to [hidden email]
> >
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

K9MA

Re: OT a bit: K3 Ant Tuner

In reply to this post by Elecraft mailing list

On 7/5/2019 12:55, Jack Brindle via Elecraft wrote:
> OK, so let’s look at the K3 side. The K3 antenna port connects directly to the BPF’s radio port. Again, we are presuming the BPF is designed for 50 ohms resistive source/load. The K3 is designed to transmit into a 50 ohm load, but it may not itself be a 50 ohm source. And, the receiver input may not be 50 ohms as well. Adding a tuned ATU does bring this to 50 ohms, providing a proper match into the BPF, so that optimum signal flows both ways.

Bandpass filters are generally designed for 50 Ohm source and load
resistances, mainly because the actual source and load impedances are
usually unknown. These filters will only perform as advertised with a 50
Ohm source and load. With real world impedances, you just have to hope
for the best. It's easy enough to use a tuner or other matching network
to get the load impedance close to 50 Ohms in the passband, but even
then, the impedance outside the passband may be far different, so filter
performance will not match the ideal case. It might be better, or it
might be worse. Unless you know the actual impedances, you can't predict it.

The source impedance is another matter. The output impedance of a
transmitter is almost certainly NOT 50 Ohms. It's probably much lower.
After all, an ideal voltage source has an output impedance of zero, and
is 100 percent efficient. The ATU matches the LOAD to 50 Ohms, so the
transmitter sees a 50 Ohm load, but does NOT necessarily match the
output impedance to 50 Ohms. This is another reason real world filter
performance almost certainly differs from the ideal. Again, unless you
know the source and load impedances over the whole range of frequencies
of interest, you can't predict the filter performance. While it's
unlikely to happen by accident, it's possible to find a source impedance
for any reflective filter which will result in zero (or very little)
attenuation at any frequency. It's called a conjugate match.

In reality, though, we seem to get pretty good results with these 50 Ohm
filters. You can actually measure the parameters that are really
important, like harmonic attenuation, and see whether it is good
enough. Even then, though, there's uncertainty, as that measurement is
usually made with a dummy load. What if the impedance of your antenna at
a harmonic isn't 50 Ohms?

73,

Scott K9MA

--
Scott K9MA

[hidden email]

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K9MA

Re: OT a bit: K3 Ant Tuner

In reply to this post by Mark Goldberg

One reason to use the internal ATU with an external tuner is so the
transmitter can see a low SWR over a range of frequencies, without
retuning the external filter. Also, if the external tuner can only get
down to, say 2:1, the internal ATU will get it down to 1:1, and the
transmitter will be happier.

73,
Scott K9MA

On 7/5/2019 13:20, Mark Goldberg wrote:

> I stand corrected.
>
> I made an assumption, probably incorrectly, that the reason they had a
> second tuner was that the first did not successfully tune the antenna. They
> just decided to put the bandpass filter between the two tuners, which would
> have provided a mismatch at both the filter input and output. I just used a
> mismatch at the output as an example. I just provided an example of filter
> performance degradation with even what would be considered a reasonable SWR.
>
> I prefer Jack's solution of bypassing the internal K3 tuner. I do have a
> situation where my antenna tuner can't tune my antenna on 160. Rather than
> try to use two tuners in series with the requisite losses, I added a shunt
> inductor on a big ferrite core to provide most of the required inductance
> for a match. It gets hot.
>
> 73,
>
> Mark
> W7MLG
>
>
> On Fri, Jul 5, 2019 at 10:57 AM David Gilbert <[hidden email]>
> wrote:
>
>> I think you misread the situation. The question isn't whether to put a
>> single antenna tuner between the antenna and filter versus putting it
>> between the rig and the filter. The question is whether putting an
>> ADDITIONAL tuner (the one internal to the K3) at the input of the filter
>> is a good idea. And to me it seems the answer is yes.
>>
>> I think we all agree that the right feed impedance and load impedance
>> for a filter is important. And as I pointed out, not just for power
>> handling, but also for the filter to actually filter as it was intended.
>>
>> 73,
>> Dave AB7E
>>
>> On 7/5/2019 10:18 AM, Mark Goldberg wrote:
>>> I could not let this go. I've done a lot of work with bandpass filters.
>> The
>>> mismatch will degrade the filter.
>>>
>>> For an example, I used Elsie, which is a filter calculator. Using the
>>> example 20 Meter bandpass filter, the passband loss is about .25 dB with
>>> matched 50 ohms in and out. Changing the output impedance to 38+j12 (38
>>> ohms plus 135 nH inductor at 14.15 MHz, about 1.5:1 SWR), the passband
>>> losses increase to about 0.4 - .44 dB and vary more over the band.
>>>
>>> Here are the schematics and plots, anyone is welcome to check my
>>> calculations, as I do make mistakes!
>>>
>>>
>> https://drive.google.com/file/d/1kj31IL_px6nVyRadW4nOi_c6FLgyaRyk/view?usp=sharing
>>> The loss in the filter will almost double. For 100W in, the loss goes
>> from
>>> about 6W to about 10W. So, it is not a good idea. A worse match will
>> result
>>> in even more losses, perhaps overheating and destroying the filter.
>>>
>>> 73,
>>>
>>> Mark
>>> W7MLG
>>>
>>> On Fri, Jul 5, 2019 at 8:32 AM Don Wilhelm <[hidden email]>
>> wrote:
>>>> Rich,
>>>>
>>>> Yes and no. With 2 antenna tuners in-line, there will be a bit more
>>>> loss due to inductor winding resistance, but other than that, it should
>>>> do harm.
>>>>
>>>> Several bandpass filters indicate that they should be between the rig
>>>> and the tuner (so the bandpass filters are not run at a high SWR).
>>>> If the power rating of the bandpass filter is marginal with respect to
>>>> the rig power, then I would observe that caution. Refer to the bandpass
>>>> filter specs.
>>>>
>>>> 73,
>>>> Don W3FPR
>>>>
>>>> On 7/5/2019 10:57 AM, Rich wrote:
>>>>> To minimize emails direct replies would be nice. I searched the web
>> and
>>>>> could not find an answer. I know there are a ton of smart folks on
>>>>> this list so I thought I would ask.
>>>>>
>>>>> On Field Day at typical setup is :
>>>>>
>>>>> K3 (or any radio) - bandpass filter - External Antenna Tuner -
>> Antenna
>>>>> So the antenna was tuned via the external tuner, but saw a guy then
>>>>> using the K3 ant tuner to touch up the SWR between the radio and the
>>>>> bandpass filter. Is that an acceptable practice?
>>>>>
>>>>
>>

--
Scott K9MA

[hidden email]

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Bob McGraw - K4TAX

Re: OT a bit: K3 Ant Tuner

In reply to this post by Rich-4

A bandpass filter is designed for optimum rejection and pass frequencies
only when operated at 50 ohms. Thus both ends of the filter need to see
50 ohms. If the antenna has a SWR issue, no matter how small, it is not
likely 50 ohms. And if one uses the transceiver internal ATU to the
input of the filter, likewise the filter input doesn't see 50 ohms.

Correctly used the bandpass filter must be in the path between the PA
output and the ATU input. With an internal ATU, this isn't likely
possible.

And most filters are designed for a certain power level when operated
from a source and into a load of 50 ohms. Should one depart from the
correct source and load impedance, then the filter my fail due to
excessive voltage.

If the K3 is seeing an SWR of 2:1 or less, don't bother. If the
operator feels good about "touching it up" that is only good for the
operator. The radio doesn't care one way of the other.

Use a bandpass filter correctly or don't use one. For if you do, you'll
likely let the smoke out of the box.

73

Bob, K4TAX

On 7/5/2019 9:57 AM, Rich wrote:

> To minimize emails direct replies would be nice. I searched the web
> and could not find an answer. I know there are a ton of smart folks
> on this list so I thought I would ask.
> TU
> On Field Day at typical setup is :
>
> K3 (or any radio) - bandpass filter - External Antenna Tuner - Antenna
>
> So the antenna was tuned via the external tuner, but saw a guy then
> using the K3 ant tuner to touch up the SWR between the radio and the
> bandpass filter. Is that an acceptable practice?
>
> I would think not?
>
> Rich
>
> K3RWN
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Joe Subich, W4TV-4

Re: OT a bit: K3 Ant Tuner

In reply to this post by Elecraft mailing list

On 2019-07-05 1:55 PM, Jack Brindle via Elecraft wrote:

> The external ATU takes care of the antenna matching, and should
> present a 50 ohm load to the BPF.

This only hold true for the *single frequency* on which the external
antenna tuner is "tuned". Typically (depending on the tuner Q and
losses), the SWR seen by the BPF will be *HIGHER* away from the one
"matched" frequency (e.g., the other end of the band) than it would
be without the external tuner in place.

As such, the tuner in/tuner out will increase losses and heating in
the BPF. If the BPF is a marginal design, the added loss/heat could
be fatal to the BPF.

The proper way to handle a rig with built-in tuner is to bypass the
internal tuner (or tune it into a 50 Ohm load in the middle of the
band) and do *all tuning with the external tuner* which assures the
BPF always sees a 50 OHM load.

73,

... Joe, W4TV

On 2019-07-05 1:55 PM, Jack Brindle via Elecraft wrote:

> Lets step back a bit and look at the system here. The K3, with ATU, drives into the BPF, when then drives into the external ATU and finally the antenna.
> The external ATU takes care of the antenna matching, and should present a 50 ohm load to the BPF. The BPF, because of its design, should present a 50 ohm load to the ATU as well, so everything is matched there.
> Before anyone jumps on this, remember the signals go both ways, outbound for transmit, inbound for receive. Also, we have a fundamental principal thrown at every EE student, that for best transmission of signal, the source and load impedances should match.
>
> OK, so let’s look at the K3 side. The K3 antenna port connects directly to the BPF’s radio port. Again, we are presuming the BPF is designed for 50 ohms resistive source/load. The K3 is designed to transmit into a 50 ohm load, but it may not itself be a 50 ohm source. And, the receiver input may not be 50 ohms as well. Adding a tuned ATU does bring this to 50 ohms, providing a proper match into the BPF, so that optimum signal flows both ways. So it could actually be beneficial for the ATU to be in-line and properly tuned. The best way to perform the tune would be to tune the ATU into a 50 ohm dummy load, but tuning into the BPF at low power should work also. The exception to this would be if the BPF changes impedance when power is applied, but then if this happens the best place for that BPF is the trash can.
>
> Now having said this, the ATU can also be bypassed in the K3, and that circuit may provide a proper 50 ohm source/load for the BPF. I would probably take this approach myself (and in fact do so in my station). The reason I take this approach is to avoid the small loss that the internal ATU presents. In contesting, every db matters.
>
> Note that we are talking nits at this point. Unless the ATU was tuned for a load quite a bit off 50 ohms resistive, (quite possible), then retuning won’t make much difference. Perhaps the op had this situation, and thought it better to return the ATU than to bypass it, or he didn’t even think to bypass it. The point is, both methods will work, and I doubt he did anything wrong it performing the tune.
>
> 73!
> Jack, W6FB
>
>
>> On Jul 5, 2019, at 10:18 AM, Mark Goldberg <[hidden email]> wrote:
>>
>> I could not let this go. I've done a lot of work with bandpass filters. The
>> mismatch will degrade the filter.
>>
>> For an example, I used Elsie, which is a filter calculator. Using the
>> example 20 Meter bandpass filter, the passband loss is about .25 dB with
>> matched 50 ohms in and out. Changing the output impedance to 38+j12 (38
>> ohms plus 135 nH inductor at 14.15 MHz, about 1.5:1 SWR), the passband
>> losses increase to about 0.4 - .44 dB and vary more over the band.
>>
>> Here are the schematics and plots, anyone is welcome to check my
>> calculations, as I do make mistakes!
>>
>> https://drive.google.com/file/d/1kj31IL_px6nVyRadW4nOi_c6FLgyaRyk/view?usp=sharing
>>
>> The loss in the filter will almost double. For 100W in, the loss goes from
>> about 6W to about 10W. So, it is not a good idea. A worse match will result
>> in even more losses, perhaps overheating and destroying the filter.
>>
>> 73,
>>
>> Mark
>> W7MLG
>>
>> On Fri, Jul 5, 2019 at 8:32 AM Don Wilhelm <[hidden email]> wrote:
>>
>>> Rich,
>>>
>>> Yes and no. With 2 antenna tuners in-line, there will be a bit more
>>> loss due to inductor winding resistance, but other than that, it should
>>> do harm.
>>>
>>> Several bandpass filters indicate that they should be between the rig
>>> and the tuner (so the bandpass filters are not run at a high SWR).
>>> If the power rating of the bandpass filter is marginal with respect to
>>> the rig power, then I would observe that caution. Refer to the bandpass
>>> filter specs.
>>>
>>> 73,
>>> Don W3FPR
>>>
>>> On 7/5/2019 10:57 AM, Rich wrote:
>>>> To minimize emails direct replies would be nice. I searched the web and
>>>> could not find an answer. I know there are a ton of smart folks on
>>>> this list so I thought I would ask.
>>>>
>>>> On Field Day at typical setup is :
>>>>
>>>> K3 (or any radio) - bandpass filter - External Antenna Tuner - Antenna
>>>>
>>>> So the antenna was tuned via the external tuner, but saw a guy then
>>>> using the K3 ant tuner to touch up the SWR between the radio and the
>>>> bandpass filter. Is that an acceptable practice?
>>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> Message delivered to [hidden email]
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>
> ______________________________________________________________
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> Post: mailto:[hidden email]
>
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> Message delivered to [hidden email]
>

Elecraft mailing list

Re: OT a bit: K3 Ant Tuner

As commonly used, bandpass filters have one main use - to protect receivers. That may be the local receiver, protecting it from sting out of band signals, or a neighbor receiver, gain protecting it from strong out of band signals.
This quite well describes SO2R stations, where we are very concerned about receiver damage. The BPF is commonly placed between the transceiver and antenna, which for a multiple of reasons needs to be 50 ohms impedance.
One of the major jobs given to the BPF is to suppress harmonic content of the transmitted signal, for which the antenna load will most certainly NOT present a 50 ohm load to the BPF. There are many references for this, I would refer to W2VJN’s publication “Managing Interstaion Interference” and the excellent articles by K9YC (who will most likely join into the discussion shortly). Jim has done a lot of testing with BPFs, and has some very interesting articles comparing and discussing their use, as well as other articles about how to avoid damaging receivers in SO2R stations with their use, as well as the use of stubs for harmonic suppression.

The point is, BPFs are designed for both scenarios, to pass signals in-band, where the load impedance is 50 ohms, and reject out of band signals, where the impedance is almost never50 ohms. Note that most BPFs do not do much for in-band signal rejection (by design). Using them to protect a receiver in the same band is a recipe for disaster.

There is another point being missed. The K3 design, like most transceivers, contains a Low Pass filter (LPF) after the PA (used for both the low power output and the KPA3 if installed), followed by a directional coupler. The directional coupler needs to see 50 ohms at both the input and output for it to measure signals accurately. It can pretty well be assumed that when the internal ATU is in bypass, the K3 is close to 50 ohms at the antenna port. Thus, in bypass, the BPF should see the load it needs at its output.

Again, the purpose of the BPF is to protect receivers, so the load we generally discuss is the K3 receiver, which will be 50 ohms due to the directional coupler input, But we also need for it to see an in-band 50 ohm load at its other end so that it can properly do its job. Note that BPFs are bidirectional - it really doesn’t matter how you connect them they do the same job both ways. They will generally see higher signal levels when in the active TX path (and thus dissipate more heat), but they are active in both directions, and for passing signals with very little loss, need to see a proper load.

73!
Jack, W6FB

> On Jul 5, 2019, at 12:27 PM, Joe Subich, W4TV <[hidden email]> wrote:
>
> On 2019-07-05 1:55 PM, Jack Brindle via Elecraft wrote:
>
>> The external ATU takes care of the antenna matching, and should
> > present a 50 ohm load to the BPF.
>
> This only hold true for the *single frequency* on which the external
> antenna tuner is "tuned". Typically (depending on the tuner Q and
> losses), the SWR seen by the BPF will be *HIGHER* away from the one
> "matched" frequency (e.g., the other end of the band) than it would
> be without the external tuner in place.
>
> As such, the tuner in/tuner out will increase losses and heating in
> the BPF. If the BPF is a marginal design, the added loss/heat could
> be fatal to the BPF.
>
> The proper way to handle a rig with built-in tuner is to bypass the
> internal tuner (or tune it into a 50 Ohm load in the middle of the
> band) and do *all tuning with the external tuner* which assures the
> BPF always sees a 50 OHM load.
>
> 73,
>
> ... Joe, W4TV
>
>
> On 2019-07-05 1:55 PM, Jack Brindle via Elecraft wrote:
>> Lets step back a bit and look at the system here. The K3, with ATU, drives into the BPF, when then drives into the external ATU and finally the antenna.
>> The external ATU takes care of the antenna matching, and should present a 50 ohm load to the BPF. The BPF, because of its design, should present a 50 ohm load to the ATU as well, so everything is matched there.
>> Before anyone jumps on this, remember the signals go both ways, outbound for transmit, inbound for receive. Also, we have a fundamental principal thrown at every EE student, that for best transmission of signal, the source and load impedances should match.
>> OK, so let’s look at the K3 side. The K3 antenna port connects directly to the BPF’s radio port. Again, we are presuming the BPF is designed for 50 ohms resistive source/load. The K3 is designed to transmit into a 50 ohm load, but it may not itself be a 50 ohm source. And, the receiver input may not be 50 ohms as well. Adding a tuned ATU does bring this to 50 ohms, providing a proper match into the BPF, so that optimum signal flows both ways. So it could actually be beneficial for the ATU to be in-line and properly tuned. The best way to perform the tune would be to tune the ATU into a 50 ohm dummy load, but tuning into the BPF at low power should work also. The exception to this would be if the BPF changes impedance when power is applied, but then if this happens the best place for that BPF is the trash can.
>> Now having said this, the ATU can also be bypassed in the K3, and that circuit may provide a proper 50 ohm source/load for the BPF. I would probably take this approach myself (and in fact do so in my station). The reason I take this approach is to avoid the small loss that the internal ATU presents. In contesting, every db matters.
>> Note that we are talking nits at this point. Unless the ATU was tuned for a load quite a bit off 50 ohms resistive, (quite possible), then retuning won’t make much difference. Perhaps the op had this situation, and thought it better to return the ATU than to bypass it, or he didn’t even think to bypass it. The point is, both methods will work, and I doubt he did anything wrong it performing the tune.
>> 73!
>> Jack, W6FB
>>> On Jul 5, 2019, at 10:18 AM, Mark Goldberg <[hidden email]> wrote:
>>>
>>> I could not let this go. I've done a lot of work with bandpass filters. The
>>> mismatch will degrade the filter.
>>>
>>> For an example, I used Elsie, which is a filter calculator. Using the
>>> example 20 Meter bandpass filter, the passband loss is about .25 dB with
>>> matched 50 ohms in and out. Changing the output impedance to 38+j12 (38
>>> ohms plus 135 nH inductor at 14.15 MHz, about 1.5:1 SWR), the passband
>>> losses increase to about 0.4 - .44 dB and vary more over the band.
>>>
>>> Here are the schematics and plots, anyone is welcome to check my
>>> calculations, as I do make mistakes!
>>>
>>> https://drive.google.com/file/d/1kj31IL_px6nVyRadW4nOi_c6FLgyaRyk/view?usp=sharing
>>>
>>> The loss in the filter will almost double. For 100W in, the loss goes from
>>> about 6W to about 10W. So, it is not a good idea. A worse match will result
>>> in even more losses, perhaps overheating and destroying the filter.
>>>
>>> 73,
>>>
>>> Mark
>>> W7MLG
>>>
>>> On Fri, Jul 5, 2019 at 8:32 AM Don Wilhelm <[hidden email]> wrote:
>>>
>>>> Rich,
>>>>
>>>> Yes and no. With 2 antenna tuners in-line, there will be a bit more
>>>> loss due to inductor winding resistance, but other than that, it should
>>>> do harm.
>>>>
>>>> Several bandpass filters indicate that they should be between the rig
>>>> and the tuner (so the bandpass filters are not run at a high SWR).
>>>> If the power rating of the bandpass filter is marginal with respect to
>>>> the rig power, then I would observe that caution. Refer to the bandpass
>>>> filter specs.
>>>>
>>>> 73,
>>>> Don W3FPR
>>>>
>>>> On 7/5/2019 10:57 AM, Rich wrote:
>>>>> To minimize emails direct replies would be nice. I searched the web and
>>>>> could not find an answer. I know there are a ton of smart folks on
>>>>> this list so I thought I would ask.
>>>>>
>>>>> On Field Day at typical setup is :
>>>>>
>>>>> K3 (or any radio) - bandpass filter - External Antenna Tuner - Antenna
>>>>>
>>>>> So the antenna was tuned via the external tuner, but saw a guy then
>>>>> using the K3 ant tuner to touch up the SWR between the radio and the
>>>>> bandpass filter. Is that an acceptable practice?
>>>>>
>>>> ______________________________________________________________
>>>> Elecraft mailing list
>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>> Post: mailto:[hidden email]
>>>>
>>>> This list hosted by: http://www.qsl.net
>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>> Message delivered to [hidden email]
>>> ______________________________________________________________
>>> Elecraft mailing list
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>>>
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>> ______________________________________________________________
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Jim Brown-10

Re: OT a bit: K3 Ant Tuner

In reply to this post by K9MA

Actually, I suspect that they're designed for 50 ohms at least in part,
because that's how they will be measured! We try hard to present a
matched load in the passband, but, as others observed, output stages are
usually lower than 50 ohms and few antennas, even when matched by a
tuner, look anything like 50 ohms away from resonance. So all we can
really hope to gain by matching is to minimize loss in the passband.
AND -- any performance specs and/or measurements at 50 ohms in and out
are a fiction away from resonance, and with other than a 50 ohm source.

73, Jim K9YC

On 7/5/2019 11:37 AM, K9MA wrote:
> Bandpass filters are generally designed for 50 Ohm source and load
> resistances, mainly because the actual source and load impedances are
> usually unknown. These filters will only perform as advertised with a
> 50 Ohm source and load. With real world impedances, you just have to
> hope for the best.

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George Danner-2

Re: OT a bit: K3 Ant Tuner

In reply to this post by Elecraft mailing list

-----Original Message-----
From: Jack Brindle via Elecraft

...

Now having said this, the ATU can also be bypassed in the K3, and that circuit may provide a proper 50 ohm source/load for the BPF. I would probably take this approach myself (and in fact do so in my station). The reason I take this approach is to avoid the small loss that the internal ATU presents. In contesting, every db matters.

Note that we are talking nits at this point. Unless the ATU was tuned for a load quite a bit off 50 ohms resistive, (quite possible), then retuning won’t make much difference. Perhaps the op had this situation, and thought it better to return the ATU than to bypass it, or he didn’t even think to bypass it. The point is, both methods will work, and I doubt he did anything wrong it performing the tune.

Jack,
If I'm not mistaken - the KAT3 is not able to be physically bypassed in a K3 - don't know in a K3S; but I thought the KAT3A did a physical bypass.
My understanding is that when you bypass the ATU (KAT3), it is merely being set to a value that cancels the internal L & C of the board.
I would think a tune would not actually actually change much of anything; but leave it to someone to actually test the true output impedance in both.

73
George AI4VZ

---
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David Woolley (E.L)

Re: OT a bit: K3 Ant Tuner

In reply to this post by Elecraft mailing list

I think we have the maximum power transfer theorem fallacy again here.
The maximum power transfer theorem does not give the right result when
you want to maximise efficiency, which is what you generally want to do
in a transmitter, as it always results in worse than 50% efficiency.

One would expect the output impedance of transmitter to not only differ
from 50 ohms but to radically differ from it. If I remember correctly
for a simple transconductance device, the resistive component will be
many times 50 ohms. If heavy negative feedback is used, I think it may
actually be much lower than the "matched" value. See
<https://www.edn.com/Pdf/ViewPdf?contentItemId=4124437> for typical real
reverse termination impedances.

Unless you put a (ferrite) isolator between transmitter and filter your
filter design needs to assume far from 50 ohm reverse termination.

Putting a matching network in will simply destroy the PA efficiency, or
even destroy the PA, through overheating. If one really wanted to do
it, you would have to adjust the SWR based on a received signal.

That matching network, will, itself, have a frequency response, as will
the one leading to antenna.

Another reason for not operating anywhere near 50 ohm reverse terminated
is that the dynamic resistance of output devices is far from linear, and
a close match could produce a lot of distortion.

--
David Woolley
Owner K2 06123

On 05/07/2019 18:55, Jack Brindle wrote:
> Lets step back a bit and look at the system here. The K3, with ATU, drives into the BPF, when then drives into the external ATU and finally the antenna.
> The external ATU takes care of the antenna matching, and should present a 50 ohm load to the BPF. The BPF, because of its design, should present a 50 ohm load to the ATU as well, so everything is matched there.
> Before anyone jumps on this, remember the signals go both ways, outbound for transmit, inbound for receive. Also, we have a fundamental principal thrown at every EE student, that for best transmission of signal, the source and load impedances should match.

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Mark Goldberg

Re: OT a bit: K3 Ant Tuner

In reply to this post by Elecraft mailing list

On Fri, Jul 5, 2019 at 12:54 PM Jack Brindle via Elecraft <
[hidden email]> wrote:

> As commonly used, bandpass filters have one main use - to protect
> receivers. That may be the local receiver, protecting it from sting out of
> band signals, or a neighbor receiver, gain protecting it from strong out of
> band signals.
>

You are only thinking of good Elecraft radios. There are plenty of crap
radios that transmit harmonics or even wideband noise.

> This quite well describes SO2R stations, where we are very concerned about
> receiver damage. The BPF is commonly placed between the transceiver and
> antenna, which for a multiple of reasons needs to be 50 ohms impedance.
> One of the major jobs given to the BPF is to suppress harmonic content of
> the transmitted signal, for which the antenna load will most certainly NOT
> present a 50 ohm load to the BPF. There are many references for this, I
> would refer to W2VJN’s publication “Managing Interstaion Interference” and
> the excellent articles by K9YC (who will most likely join into the
> discussion shortly). Jim has done a lot of testing with BPFs, and has some
> very interesting articles comparing and discussing their use, as well as
> other articles about how to avoid damaging receivers in SO2R stations with
> their use, as well as the use of stubs for harmonic suppression.
>
> The point is, BPFs are designed for both scenarios, to pass signals
> in-band, where the load impedance is 50 ohms, and reject out of band
> signals, where the impedance is almost never50 ohms. Note that most BPFs do
> not do much for in-band signal rejection (by design). Using them to protect
> a receiver in the same band is a recipe for disaster.
>
>

In general a BPF will present a low impedance shunt load and a high
impedance series load. Even into an unmatched load, it is likely that the
BPF will still have a much lower shunt impedance and a much higher series
impedance than what it is working into. In the example I showed, the change
out of the passband was much less than the change in the passband. Out of
the passband, it still works pretty well to reject signals. The unmatched
load affects the in band performance a lot.

I found Elsie to be really useful to get an understanding of what filters
do under various conditions.

73,

Mark
W7MLG
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Re: OT a bit: K3 Ant Tuner

In reply to this post by George Danner-2

Good observation, George. The KAT3A indeed does have a bypass relay, while the KAT3 (in the original K3) does not. As I recall, the KAT3 switches the inductors and capacitors out in bypass mode, but does not necessarily provide the best 50 match. This is due to variances in the components and placement from unit to unit. Tuning into a good 50 ohm dummy load can provide a better 50 ohm match, but it has the slight down side of adding a slight amount of loss to the path. In the end they do pretty much the same thing, but if someone wanted to be a real perfectionist (and I’ll admit to that with many things), then tuning into a dummy load will provide an oh-so slightly better match.

The important point here is that it really needs to tune into a known-good 50 ohm resistive load to get what you want. Tuning into the BPF might get you there depending on the output of the BPF.

As I stated earlier, I set my K3s to bypass mode for driving either my BPFs or my KPA500s.

73!
Jack, W6FB

> On Jul 5, 2019, at 12:56 PM, Gmail - George <[hidden email]> wrote:
>
>
>
> -----Original Message-----
> From: Jack Brindle via Elecraft
>
> ...
>
> Now having said this, the ATU can also be bypassed in the K3, and that circuit may provide a proper 50 ohm source/load for the BPF. I would probably take this approach myself (and in fact do so in my station). The reason I take this approach is to avoid the small loss that the internal ATU presents. In contesting, every db matters.
>
> Note that we are talking nits at this point. Unless the ATU was tuned for a load quite a bit off 50 ohms resistive, (quite possible), then retuning won’t make much difference. Perhaps the op had this situation, and thought it better to return the ATU than to bypass it, or he didn’t even think to bypass it. The point is, both methods will work, and I doubt he did anything wrong it performing the tune.
>
>
> Jack,
> If I'm not mistaken - the KAT3 is not able to be physically bypassed in a K3 - don't know in a K3S; but I thought the KAT3A did a physical bypass.
> My understanding is that when you bypass the ATU (KAT3), it is merely being set to a value that cancels the internal L & C of the board.
> I would think a tune would not actually actually change much of anything; but leave it to someone to actually test the true output impedance in both.
>
> 73
> George AI4VZ
>
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Frank Krozel

Re: OT a bit: K3 Ant Tuner

I have a plain K3 that I bypass the built-in tuner on 80 all the time.
On 20 and 40 it is in-line all the time.
de Frank KG9H

> On Jul 5, 2019, at 4:42 PM, Jack Brindle via Elecraft <[hidden email]> wrote:
>
> Good observation, George. The KAT3A indeed does have a bypass relay, while the KAT3 (in the original K3) does not. As I recall, the KAT3 switches the inductors and capacitors out in bypass mode, but does not necessarily provide the best 50 match. This is due to variances in the components and placement from unit to unit. Tuning into a good 50 ohm dummy load can provide a better 50 ohm match, but it has the slight down side of adding a slight amount of loss to the path. In the end they do pretty much the same thing, but if someone wanted to be a real perfectionist (and I’ll admit to that with many things), then tuning into a dummy load will provide an oh-so slightly better match.
>
> The important point here is that it really needs to tune into a known-good 50 ohm resistive load to get what you want. Tuning into the BPF might get you there depending on the output of the BPF.
>
> As I stated earlier, I set my K3s to bypass mode for driving either my BPFs or my KPA500s.
>
> 73!
> Jack, W6FB
>
>> On Jul 5, 2019, at 12:56 PM, Gmail - George <[hidden email]> wrote:
>>
>>
>>
>> -----Original Message-----
>> From: Jack Brindle via Elecraft
>>
>> ...
>>
>> Now having said this, the ATU can also be bypassed in the K3, and that circuit may provide a proper 50 ohm source/load for the BPF. I would probably take this approach myself (and in fact do so in my station). The reason I take this approach is to avoid the small loss that the internal ATU presents. In contesting, every db matters.
>>
>> Note that we are talking nits at this point. Unless the ATU was tuned for a load quite a bit off 50 ohms resistive, (quite possible), then retuning won’t make much difference. Perhaps the op had this situation, and thought it better to return the ATU than to bypass it, or he didn’t even think to bypass it. The point is, both methods will work, and I doubt he did anything wrong it performing the tune.
>>
>>
>> Jack,
>> If I'm not mistaken - the KAT3 is not able to be physically bypassed in a K3 - don't know in a K3S; but I thought the KAT3A did a physical bypass.
>> My understanding is that when you bypass the ATU (KAT3), it is merely being set to a value that cancels the internal L & C of the board.
>> I would think a tune would not actually actually change much of anything; but leave it to someone to actually test the true output impedance in both.
>>
>> 73
>> George AI4VZ
>>
>> ---
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>> https://www.avast.com/antivirus
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>
> ______________________________________________________________
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