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KPA-1500 ATU not working well

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KPA-1500 ATU not working well

I'm wondering if anyone else is having problems with their KPA-1500 ATU on 6-meters? My antenna is cut for 50.100 and has a 2.2:1 SWR at the 50.313 FT-8 frequency. The very best the ATU will do is to lower the SWR from 2.2:1 down to 2.0:1 which is almost no improvement. The 2.0 to 1 is with exciter power, when I switch the KPA-1500 to operate and transmit at 1,200 watts the SWR increases to aprx. 2.2 to 1 and the KPA-1500 will fault and trip off occassionally. Hoping there's a fix for this.

I'm using the latest KPA-1500 firmware.

Thanks,
Dick- K9OM

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tomb18

Re: KPA-1500 ATU not working well

Hi,
I am currently out of the office until July 1, 2018.
If you purchased a license, and have not received it, it is almost 100% sure to be in your spam, junk or other such folder. In Gmail it will be in the web version of gmail. Please check for it there.

All my websites have a section called Documentation. In there you will find video tutorials and lot's of help.
73 Tom

---
This email has been checked for viruses by Avast antivirus software.
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K9MA

Re: KPA-1500 ATU not working well

In reply to this post by Elecraft mailing list

Dick,

Have you tried manually adjusting the ATU? I haven't used mine on 6
meters, but on other bands, no matter what I do, it sometimes doesn't
get a very good match automatically, and I can do better manually. On
the other hand, it may be that the L and C step sizes are just too big
to get a good match on 6. Or there could actually be something wrong. If
you have a good 50 MHz dummy load, try that with the ATU in.

73,
Scott K9MA

On 6/21/2018 22:40, Dick via Elecraft wrote:

> I'm wondering if anyone else is having problems with their KPA-1500 ATU on 6-meters? My antenna is cut for 50.100 and has a 2.2:1 SWR at the 50.313 FT-8 frequency. The very best the ATU will do is to lower the SWR from 2.2:1 down to 2.0:1 which is almost no improvement. The 2.0 to 1 is with exciter power, when I switch the KPA-1500 to operate and transmit at 1,200 watts the SWR increases to aprx. 2.2 to 1 and the KPA-1500 will fault and trip off occassionally. Hoping there's a fix for this.
>
> I'm using the latest KPA-1500 firmware.
>
> Thanks,
> Dick- K9OM
>
>
>
> ______________________________________________________________
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--
Scott K9MA

[hidden email]

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Paul Baldock

Re: KPA-1500 ATU not working well

First let me say that other than some issues with
the ATU, I am after a week of use, very happy with the KPA1500.

So here's the ATU issues:

I find that the ATU very rarely will learn a
setting to get the SWR below 1.2:1 on any band. I
can usually tweak it down to 1.0:1 using the
Utility Program. And yes, before anybody asks, I
have ATU STOP TUNE and the ATU BYPASS set at 1.0:1.

On 6M into a perfect load (laboratory quality to
8GHz) with the ATU bypassed, the internal SWR
meter reads 1.4:1 I would have expected it to be
1.0:1, but Elecraft tell me it is normal. So the
ATU on 6M will have to tune out what is left when
the 1.4:1 internal mismatch sees your external
antenna mismatch. Maybe this is contributing to
your problem. Try adding a quarter wave of coax,
maybe it will achieve a better match. Fortunately
my 6M antenna is flat enough that I can work CW, SSB and FT-8 in BYPASS.

For your interest, on 10M in to perfect load with
ATU bypassed the internal SWR meter reads 1.2:1. Not 1.0:1.

Another issue I have with the ATU is that the
internal frequency counter has 8KHz resolution
which according to one of the Elecraft techs can
lead to a 16KHz error in measurement. It appears
that during "learning" that the ATU is based on
the internal frequency counter measurement, not
the frequency you transceiver sends to the
KPA1500.This means that on the bands that have
10KHz or 20KHz segments, you cannot be sure which
segment you are using, and when you use the tuner
it could be in a different segment. Being off by
a segment could be a problem with a high Q antenna.

Apparently the counter originally had 1KHz
resolution but was changed to fix some other
problem. An Elecraft tech told me they currently
have no plan to change it back to 1KHz. I am not
suggesting that the tuner should change segments
exactly on their edge. Clearly there has to be
some hysteresis to stop hunting. 25% of a segment
width might width be a good number to choose, but
this would require the current frequency counter to have improved resolution.

- Paul KW7Y

At 08:53 PM 6/21/2018, K9MA wrote:

>Dick, Have you tried manually adjusting the
>ATU?Â I haven't used mine on 6 meters, but on
>other bands, no matter what I do, it sometimes
>doesn't get a very good match automatically, and
>I can do better manually.Â On the other hand,
>it may be that the L and C step sizes are just
>too big to get a good match on 6. Or there could
>actually be something wrong. If you have a good
>50 MHz dummy load, try that with the ATU in. 73,
>Scott K9MA On 6/21/2018 22:40, Dick via Elecraft
>wrote: > I'm wondering if anyone else is having
>problems with their KPA-1500 ATU on
>6-meters?Â My antenna is cut for 50.100 and has
>a 2.2:1 SWR at the 50.313 FT-8 frequency.Â The
>very best the ATU will do is to lower the SWR
>from 2.2:1 down to 2.0:1 which is almost no
>improvement.Â The 2.0 to 1 is with exciter
>power, whenÂ I switch the KPA-1500 to operate
>and transmit at 1,200 watts the SWR increases to
>aprx. 2.2 to 1 and the KPA-1500 will fault and
>trip off occassionally.Â Hoping there's a fix
>for this. > > I'm using the latest KPA-1500
>firmware. > > Thanks, > Dick- K9OM > > > >
>______________________________________________________________
> > Elecraft mailing list > Home:
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>Post: mailto:[hidden email] > > This
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>support this email list:
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>delivered to [hidden email] -- Scott K9MA
>[hidden email]
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ANDY DURBIN

KPA-1500 ATU not working well

In reply to this post by Elecraft mailing list

"Clearly there has to be some hysteresis to stop hunting. 25% of a segment width might width be a good number to choose, but this would require the current frequency counter to have improved resolution."

Why wouldn't it be preferable to use the transceiver's exact TX frequency, if available, for learning and selection ? Yes, I understand that Elecraft likes to give the detected RF frequency the highest priority. However, the logic required to allow use of transceiver frequency if difference from RF defected frequency did not exceed a defined limit would not seem to be too complex.

73,

Andy k3wyc

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Wes Stewart-2

Re: KPA-1500 ATU not working well

It might be but the amp is designed to work with radios other than K3s.

On 6/22/2018 5:01 AM, ANDY DURBIN wrote:
> Why wouldn't it be preferable to use the transceiver's exact TX frequency, if available,

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K9MA

Re: KPA-1500 ATU not working well

In reply to this post by Paul Baldock

I wonder why this is so.

Scott K9MA

----------

Scott Ellington

--- via iPad

> On Jun 22, 2018, at 1:17 AM, Paul Baldock <[hidden email]> wrote:
>
> frequency counter measurement, not the frequency you transceiver sends to the KPA1500.

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Paul Baldock

Re: KPA-1500 ATU not working well

In reply to this post by ANDY DURBIN

Andy -

Sounds like a great idea.

- Paul

6/22/2018, ANDY DURBIN wrote:

>"Clearly there has to be some hysteresis to stop hunting. 25% of a
>segment width might width be a good number to choose, but this would
>require the current frequency counter to have improved resolution."
>
>
>Why wouldn't it be preferable to use the transceiver's exact TX
>frequency, if available, for learning and selection ? Yes, I
>understand that Elecraft likes to give the detected RF frequency the
>highest priority. However, the logic required to allow use of
>transceiver frequency if difference from RF defected frequency did
>not exceed a defined limit would not seem to be too complex.
>
>
>73,
>
>Andy k3wyc
>
>
>______________________________________________________________
>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
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Paul Baldock

Re: KPA-1500 ATU not working well

In reply to this post by K9MA

They want to be certain that the amp is on the correct band, should
the data from the radio be incorrect.

- Paul KW7Y

>I wonder why this is so.
>
>Scott K9MA
>
>----------
>
>Scott Ellington
>
> --- via iPad
>
> > On Jun 22, 2018, at 1:17 AM, Paul Baldock <[hidden email]> wrote:
> >
> > frequency counter measurement, not the frequency you transceiver
> sends to the KPA1500.

ANDY DURBIN

Re: KPA-1500 ATU not working well

In reply to this post by ANDY DURBIN

"It might be but the amp is designed to work with radios other than K3s."

The KPA1500 and KPA500 are both capable of receiving frequency from transceivers other than the K3S, so is the KAT500. I don't see how not using a K3S puts any limitation on my proposal.

73,
Andy k3wyc

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K9MA

Re: KPA-1500 ATU not working well

In reply to this post by Paul Baldock

But wait! I know I hear the ATU relays switch when I stop tuning the K3,
before transmitting.

Scott K9MA

On 6/22/2018 10:01, Paul Baldock wrote:

> They want to be certain that the amp is on the correct band, should
> the data from the radio be incorrect.
>
> - Paul KW7Y
>
>> I wonder why this is so.
>>
>> Scott K9MA
>>
>> ----------
>>
>> Scott Ellington
>>
>> --- via iPad
>>
>> > On Jun 22, 2018, at 1:17 AM, Paul Baldock <[hidden email]>
>> wrote:
>> >
>> > frequency counter measurement, not the frequency you transceiver
>> sends to the KPA1500.
>

Paul Baldock

Re: KPA-1500 ATU not working well

True, it then double checks with the internal
frequency counter once rf is applied, and may
choose a different segment if the internal counter disagrees.

- Paul

At 08:48 AM 6/22/2018, K9MA wrote:

>But wait! I know I hear the ATU relays switch
>when I stop tuning the K3, before transmitting.
>
>Scott K9MA
>
>
>On 6/22/2018 10:01, Paul Baldock wrote:
>>They want to be certain that the amp is on the
>>correct band, should the data from the radio be incorrect.
>>
>>- PaulÂ KW7Y
>>
>>>I wonder why this is so.
>>>
>>>Scott K9MA
>>>
>>>----------
>>>
>>>Scott Ellington
>>>
>>>Â --- via iPad
>>>
>>> > On Jun 22, 2018, at 1:17 AM, Paul Baldock <[hidden email]> wrote:
>>> >
>>> > frequency counter measurement, not the
>>> frequency you transceiver sends to the KPA1500.
>
>--
>Scott K9MA
>
>[hidden email]

K9MA

Re: KPA-1500 ATU not working well

That would explain why I sometimes hear the relays click again when I
transmit (I think). Seems that could be fixed by simply requiring that
the difference be more than, say, 20 kHz before the counter takes priority.

Scott K9MA

On 6/22/2018 11:00, Paul Baldock wrote:

> True, it then double checks with the internal frequency counter once
> rf is applied, and may choose a different segment if the internal
> counter disagrees.
>
> - Paul
>
> At 08:48 AM 6/22/2018, K9MA wrote:
>> But wait! I know I hear the ATU relays switch when I stop tuning the
>> K3, before transmitting.
>>
>> Scott K9MA
>>
>>
>> On 6/22/2018 10:01, Paul Baldock wrote:
>>> They want to be certain that the amp is on the correct band, should
>>> the data from the radio be incorrect.
>>>
>>> - PaulÂ KW7Y
>>>
>>>> I wonder why this is so.
>>>>
>>>> Scott K9MA
>>>>
>>>> ----------
>>>>
>>>> Scott Ellington
>>>>
>>>> Â --- via iPad
>>>>
>>>> > On Jun 22, 2018, at 1:17 AM, Paul Baldock <[hidden email]>
>>>> wrote:
>>>> >
>>>> > frequency counter measurement, not the frequency you transceiver
>>>> sends to the KPA1500.
>>
>> --
>> Scott K9MA
>>
>> [hidden email]
>

Paul Baldock

Re: KPA-1500 ATU not working well

At 09:28 AM 6/22/2018, K9MA wrote:
>That would explain why I sometimes hear the
>relays click again when I transmit (I think).
>Seems that could be fixed by simply requiring
>that the difference be more than, say, 20 kHz
>before the counter takes priority.
>
>Scott K9MA

You are not imagining it.

I have EMailed [hidden email] with my
concerns. Maybe if others do also, they will consider a change.

- Paul

>On 6/22/2018 11:00, Paul Baldock wrote:
>>True, it then double checks with the internal
>>frequency counter once rf is applied, and may
>>choose a different segment if the internal counter disagrees.
>>
>>- Paul
>>
>>At 08:48 AM 6/22/2018, K9MA wrote:
>>>But wait! I know I hear the ATU relays switch
>>>when I stop tuning the K3, before transmitting.
>>>
>>>Scott K9MA
>>>
>>>
>>>On 6/22/2018 10:01, Paul Baldock wrote:
>>>>They want to be certain that the amp is on
>>>>the correct band, should the data from the radio be incorrect.
>>>>
>>>>- PaulÃÂ KW7Y
>>>>
>>>>>I wonder why this is so.
>>>>>
>>>>>Scott K9MA
>>>>>
>>>>>----------
>>>>>
>>>>>Scott Ellington
>>>>>
>>>>>Ã --- via iPad
>>>>>
>>>>> > On Jun 22, 2018, at 1:17 AM, Paul Baldock <[hidden email]> wrote:
>>>>> >
>>>>> > frequency counter measurement, not the
>>>>> frequency you transceiver sends to the KPA1500.
>>>
>>>--
>>>ScottÂ K9MA
>>>
>>>[hidden email]
>
>--
>Scott K9MA
>
>[hidden email]

Wes Stewart-2

Re: KPA-1500 ATU not working well

In reply to this post by Paul Baldock

I do not, and probably never will, have a KPA1500. I do have a KPA500 and
KAT500 so I think I can comment. In my opinion, the function of these tuners is
to provide a match into which the amp can deliver full power. If 1.5:1 does
this, then that's good enough in my book. Furthermore, a better match might
entail higher tuner losses. So why worry about it?

Another thing; a 1.0:1 SWR infers infinite return loss. To measure infinite
return loss, you need a directional coupler with infinite directivity or some
mathematical correction derived from very well known calibration standards and
no other errors, So maybe you say, 1.0:1 can't be measured (you would be
correct), let's shoot for 1.22:1. That's a return loss of ~20 dB. Now I have
no idea of what the directivity of the coupler is in the KAT500 or KPA1500 but
considering it has to work from 1.8 to 54 MHz and to keep the numbers easy, 20
dB wouldn't be unreasonable. (Note: I'm only considering the directivity error,
there are several others, internal mismatches, frequency tracking, detector
non-linearities, etc.)

If we measure a load with 20 dB RL using a directional coupler with 20 dB
directivity the answer can be anywhere between infinity to 14 dB. (Full
cancellation of the two reflection coefficients to the sum of the reflection
coefficients) In SWR terms, a 1.22:1 load can measure anywhere between 1.0:1
and 1.5:1. A "perfect" load will measure 1.22:1.

Folks, these things aren't laboratory instruments and until Elecraft builds in
vector network analyzers with full error correction this is what we get.

Wes N7WS

On 6/21/2018 11:17 PM, Paul Baldock wrote:

> First let me say that other than some issues with the ATU, I am after a week
> of use, very happy with the KPA1500.
>
> So here's the ATU issues:
>
> I find that the ATU very rarely will learn a setting to get the SWR below
> 1.2:1 on any band. I can usually tweak it down to 1.0:1 using the Utility
> Program. And yes, before anybody asks, I have ATU STOP TUNE and the ATU
> BYPASS set at 1.0:1.
>
> On 6M into a perfect load (laboratory quality to 8GHz) with the ATU bypassed,
> the internal SWR meter reads 1.4:1 I would have expected it to be 1.0:1, but
> Elecraft tell me it is normal. So the ATU on 6M will have to tune out what is
> left when the 1.4:1 internal mismatch sees your external antenna mismatch.
> Maybe this is contributing to your problem. Try adding a quarter wave of coax,
> maybe it will achieve a better match. Fortunately my 6M antenna is flat enough
> that I can work CW, SSB and FT-8 in BYPASS.
>
> For your interest, on 10M in to perfect load with ATU bypassed the internal
> SWR meter reads 1.2:1. Not 1.0:1.
>
> Another issue I have with the ATU is that the internal frequency counter has
> 8KHz resolution which according to one of the Elecraft techs can lead to a
> 16KHz error in measurement. It appears that during "learning" that the ATU is
> based on the internal frequency counter measurement, not the frequency you
> transceiver sends to the KPA1500.This means that on the bands that have 10KHz
> or 20KHz segments, you cannot be sure which segment you are using, and when
> you use the tuner it could be in a different segment. Being off by a segment
> could be a problem with a high Q antenna.
>
> Apparently the counter originally had 1KHz resolution but was changed to fix
> some other problem. An Elecraft tech told me they currently have no plan to
> change it back to 1KHz. I am not suggesting that the tuner should change
> segments exactly on their edge. Clearly there has to be some hysteresis to
> stop hunting. 25% of a segment width might width be a good number to choose,
> but this would require the current frequency counter to have improved resolution.
>
>
> - Paul KW7Y

Paul Baldock

Re: KPA-1500 ATU not working well

I have found that if the KPA1500 is feeding a
largish SWR (like 1.5:1 as you suggest) then the
drive power required to maintain a constant
output will vary significantly as you tune across
a band. This means you have to keep adjusting the
power control within a single band. This appears
not to occur if the SWR is 1.1:1 or better.

I don't know, but I would guess a solid state
untuned amplifier efficiency is better into a 1:1
SWR than a 1:5:1. This could lead to the dreaded more fan noise.

By the way by suggesting 1.0:1. I did not mean
exactly 1.0000000000000000000:1. I tired to infer 1 digit resolution/accuracy.

- Paul KW7Y

At 11:11 AM 6/22/2018, Wes Stewart wrote:

>I do not, and probably never will, have a
>KPA1500.Â I do have a KPA500 and KAT500 so I
>think I can comment.Â In my opinion, the
>function of these tuners is to provide a match
>into which the amp can deliver full power.Â If
>1.5:1 does this, then that's good enough in my
>book.Â Furthermore, a better match might entail
>higher tuner losses.Â So why worry about it?
>Another thing; a 1.0:1 SWR infers infinite
>return loss.Â To measure infinite return loss,
>you need a directional coupler with infinite
>directivity or some mathematical correction
>derived from very well known calibration
>standards and no other errors,Â So maybe you
>say, 1.0:1 can't be measured (you would be
>correct), let's shoot for 1.22:1.Â Â That's a
>return loss of ~20 dB.Â Now I have no idea of
>what the directivity of the coupler is in the
>KAT500 or KPA1500 but considering it has to work
>from 1.8 to 54 MHz and to keep the numbers easy,
>20 dB wouldn't be unreasonable. (Note: I'm only
>considering the directivity error, there are
>several others, internal mismatches, frequency
>tracking, detector non-linearities, etc.) If we
>measure a load with 20 dB RL using a directional
>coupler with 20 dB directivity the answer can be
>anywhere between infinity to 14 dB.Â (Full
>cancellation of the two reflection coefficients
>to the sum of the reflection coefficients)Â In
>SWR terms, a 1.22:1 load can measure anywhere
>between 1.0:1 and 1.5:1.Â A "perfect" load will
>measure 1.22:1. Folks, these things aren't
>laboratory instruments and until Elecraft builds
>in vector network analyzers with full error
>correction this is what we get. WesÂ N7WS On
>6/21/2018 11:17 PM, Paul Baldock wrote: > First
>let me say that other than some issues with the
>ATU, I am after a week > of use, very happy with
>the KPA1500. > > So here's the ATU issues: > > I
>find that the ATU very rarely will learn a
>setting to get the SWR below > 1.2:1 on any
>band. I can usually tweak it down to 1.0:1 using
>the Utility > Program.Â And yes, before anybody
>asks, I have ATU STOP TUNE and the ATU > BYPASS
>set at 1.0:1. > > On 6M into a perfect load
>(laboratory quality to 8GHz) with the ATU
>bypassed, > the internal SWR meter reads
>1.4:1Â I would have expected it to be 1.0:1,
>but > Elecraft tell me it is normal. So the ATU
>on 6M will have to tune out what is > left when
>the 1.4:1 internal mismatch sees your external
>antenna mismatch. > Maybe this is contributing
>to your problem. Try adding a quarter wave of
>coax, > maybe it will achieve a better match.
>Fortunately my 6M antenna is flat enough > that
>I can work CW, SSB and FT-8 in BYPASS. > > For
>your interest, on 10M in to perfect load with
>ATU bypassed the internal > SWR meter reads
>1.2:1. Not 1.0:1. > > Another issue I have with
>the ATU is that the internal frequency counter
>has > 8KHz resolution which according to one of
>the Elecraft techs can lead to a > 16KHz error
>in measurement. It appears that during
>"learning" that the ATU is > based on the
>internal frequency counter measurement, not the
>frequency you > transceiver sends to the
>KPA1500.This means that on the bands that have
>10KHz > or 20KHz segments, you cannot be sure
>which segment you are using, and when > you use
>the tuner it could be in a different segment.
>Being off by a segment > could be a problem with
>a high Q antenna. > > Apparently the counter
>originally had 1KHz resolution but was changed
>to fix > some other problem. An Elecraft tech
>told me they currently have no plan to > change
>it back to 1KHz. I am not suggesting that the
>tuner should change > segments exactly on their
>edge. Clearly there has to be some hysteresis
>to > stop hunting. 25% of a segment width might
>width be a good number to choose, > but this
>would require the current frequency counter to
>have improved resolution. > > > - PaulÂ KW7Y
>______________________________________________________________
>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]

ANDY DURBIN

KPA-1500 ATU not working well

In reply to this post by ANDY DURBIN

"If 1.5:1 does this, then that's good enough in my book. Furthermore, a better match might entail higher tuner losses. So why worry about it?

My test data for my KPA500 show there is a very significant difference in PA dissipation and also in harmonic output for loads giving indicated 1.4:1 SWR and loads giving 1.0:1 SWR. When I have a more complete data set I'll make it available for peer review. My tentative conclusion is that even a moderate mismatch of KPA500 load is quite detrimental.

73,
Andy k3wyc

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John Oppenheimer

Re: KPA-1500 ATU not working well

In reply to this post by Wes Stewart-2

Putting the Elecraft CP1 through the paces with a 2 port VNA can be
enlightening. The CP1 seems to be representative of Elecraft directional
couplers across the line. There's a picture of the W2 high power HF
coupler in the manual, it's just larger cores.

Sweeping a 20 dB CP1 across the band with a VNWA with a 60 Ohm load,
1.2:1, results with a relative constant -40 dB reflected gain and a -20
forward gain. A closer match to 50 Ohm fall's apart with a wide -40 db
to -70 dB dip at 7 MHz reflected across the band at 50 Ohm.

I can agree, 1.2 : 1 is about the limit.

John KN5L

On 06/22/2018 01:11 PM, Wes Stewart wrote:
> That's a return loss of ~20 dB. Now I have
> no idea of what the directivity of the coupler is in the KAT500 or KPA1500 but
> considering it has to work from 1.8 to 54 MHz and to keep the numbers easy, 20
> dB wouldn't be unreasonable.
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Wes Stewart-2

Re: KPA-1500 ATU not working well

In reply to this post by Paul Baldock

OK, note my qualifier, "If". If there are other detrimental issues with greater
load mismatch then they might need to be addressed. Unfortunately, Elecraft
doesn't specify a load requirement for rated output. Gain ripple that you
observe is possibly a reflection (no pun intended) of the LPFs rather than the
intrinsic performance of the transistors, although as I have reported elsewhere
K3S IMD is frequency sensitive, but not overly so within a band.

One point I would like to make is that guys who wring their hands because the
SWR meters on the K3, KAT500 and KPAs all read differently should lighten up.
There are reasons why this can be without there being product defects.

Wes N7WS

.On 6/22/2018 12:36 PM, Paul Baldock wrote:

> I have found that if the KPA1500 is feeding a largish SWR (like 1.5:1 as you
> suggest) then the drive power required to maintain a constant output will vary
> significantly as you tune across a band. This means you have to keep adjusting
> the power control within a single band. This appears not to occur if the SWR
> is 1.1:1 or better.
>
> I don't know, but I would guess a solid state untuned amplifier efficiency is
> better into a 1:1 SWR than a 1:5:1. This could lead to the dreaded more fan
> noise.
>
> By the way by suggesting 1.0:1. I did not mean exactly
> 1.0000000000000000000:1. I tired to infer 1 digit resolution/accuracy.
>
> - Paul KW7Y
>
>
> At 11:11 AM 6/22/2018, Wes Stewart wrote:
>> I do not, and probably never will, have a KPA1500.Â I do have a KPA500 and
>> KAT500 so I think I can comment.Â In my opinion, the function of these
>> tuners is to provide a match into which the amp can deliver full power.Â If
>> 1.5:1 does this, then that's good enough in my book.Â Furthermore, a better
>> match might entail higher tuner losses.Â So why worry about it? Another
>> thing; a 1.0:1 SWR infers infinite return loss.Â To measure infinite return
>> loss, you need a directional coupler with infinite directivity or some
>> mathematical correction derived from very well known calibration standards
>> and no other errors,Â So maybe you say, 1.0:1 can't be measured (you would
>> be correct), let's shoot for 1.22:1.Â Â That's a return loss of ~20 dB.Â Now
>> I have no idea of what the directivity of the coupler is in the KAT500 or
>> KPA1500 but considering it has to work from 1.8 to 54 MHz and to keep the
>> numbers easy, 20 dB wouldn't be unreasonable. (Note: I'm only considering the
>> directivity error, there are several others, internal mismatches, frequency
>> tracking, detector non-linearities, etc.) If we measure a load with 20 dB RL
>> using a directional coupler with 20 dB directivity the answer can be anywhere
>> between infinity to 14 dB.Â (Full cancellation of the two reflection
>> coefficients to the sum of the reflection coefficients)Â In SWR terms, a
>> 1.22:1 load can measure anywhere between 1.0:1 and 1.5:1.Â A "perfect" load
>> will measure 1.22:1. Folks, these things aren't laboratory instruments and
>> until Elecraft builds in vector network analyzers with full error correction
>> this is what we get. WesÂ N7WS On 6/21/2018 11:17 PM, Paul Baldock wrote: >
>> First let me say that other than some issues with the ATU, I am after a week
>> > of use, very happy with the KPA1500. > > So here's the ATU issues: > > I
>> find that the ATU very rarely will learn a setting to get the SWR below >
>> 1.2:1 on any band. I can usually tweak it down to 1.0:1 using the Utility >
>> Program.Â And yes, before anybody asks, I have ATU STOP TUNE and the ATU >
>> BYPASS set at 1.0:1. > > On 6M into a perfect load (laboratory quality to
>> 8GHz) with the ATU bypassed, > the internal SWR meter reads 1.4:1Â I would
>> have expected it to be 1.0:1, but > Elecraft tell me it is normal. So the ATU
>> on 6M will have to tune out what is > left when the 1.4:1 internal mismatch
>> sees your external antenna mismatch. > Maybe this is contributing to your
>> problem. Try adding a quarter wave of coax, > maybe it will achieve a better
>> match. Fortunately my 6M antenna is flat enough > that I can work CW, SSB and
>> FT-8 in BYPASS. > > For your interest, on 10M in to perfect load with ATU
>> bypassed the internal > SWR meter reads 1.2:1. Not 1.0:1. > > Another issue I
>> have with the ATU is that the internal frequency counter has > 8KHz
>> resolution which according to one of the Elecraft techs can lead to a > 16KHz
>> error in measurement. It appears that during "learning" that the ATU is >
>> based on the internal frequency counter measurement, not the frequency you >
>> transceiver sends to the KPA1500.This means that on the bands that have 10KHz
>> > or 20KHz segments, you cannot be sure which segment you are using, and when
>> > you use the tuner it could be in a different segment. Being off by a
>> segment > could be a problem with a high Q antenna. > > Apparently the
>> counter originally had 1KHz resolution but was changed to fix > some other
>> problem. An Elecraft tech told me they currently have no plan to > change it
>> back to 1KHz. I am not suggesting that the tuner should change > segments
>> exactly on their edge. Clearly there has to be some hysteresis to > stop
>> hunting. 25% of a segment width might width be a good number to choose, > but
>> this would require the current frequency counter to have improved resolution.
>> > > > - PaulÂ KW7Y
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>

Wes Stewart-2

Re: KPA-1500 ATU not working well

In reply to this post by John Oppenheimer

I don't quite understand your methodology but there is one, apparently little
known caveat with the use of the "Elecraft" coupler topology. AFAIK, this was
first used by John Grebenkemper, KI6WX, in his Tandem Match, described in QST,
January 1987.

Paul Kiciak, N2PK, mentions in his paper, "An HF In-Line Return Loss And Power
Meter", that this coupler suffers from poor input match at lower frequencies.
So the SWR meter has high SWR!

If the CP1 wasn't so expensive, I'd buy one just to measure it.

Wes N7WS

On 6/22/2018 1:20 PM, John Oppenheimer wrote:

> Putting the Elecraft CP1 through the paces with a 2 port VNA can be
> enlightening. The CP1 seems to be representative of Elecraft directional
> couplers across the line. There's a picture of the W2 high power HF
> coupler in the manual, it's just larger cores.
>
> Sweeping a 20 dB CP1 across the band with a VNWA with a 60 Ohm load,
> 1.2:1, results with a relative constant -40 dB reflected gain and a -20
> forward gain. A closer match to 50 Ohm fall's apart with a wide -40 db
> to -70 dB dip at 7 MHz reflected across the band at 50 Ohm.
>
> I can agree, 1.2 : 1 is about the limit.
>
> John KN5L
>
> On 06/22/2018 01:11 PM, Wes Stewart wrote:
>> That's a return loss of ~20 dB. Now I have
>> no idea of what the directivity of the coupler is in the KAT500 or KPA1500 but
>> considering it has to work from 1.8 to 54 MHz and to keep the numbers easy, 20
>> dB wouldn't be unreasonable.
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