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Balun at input or output of tuner

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aandrei

k3 filters and kx3

Can the K3 roofing filters be used in KX3 ?

Adi
2E0TTX

On 12/12/2011 21:22, Jim Miller wrote:

> Poor choice of words: first I fell into the "balun" habit rather than CM
> choke on the first usage. Second: "bifilar wound CM choke" would have been
> a better description for the alternative mentioned.
>
> Jim ab3cv
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Bruce Beford-2

Re: k3 filters and kx3

No, the KX3 roofing filter module is completely different. It works at
"baseband" frequencies, rather than the 8+ MHz IF that the K3 uses. You will
not be able to use K3 filters in the KX3.

Bruce, N1RX

> Can the K3 roofing filters be used in KX3 ?

> Adi
> 2E0TTX

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Terry Posey

Re: k3 filters and kx3

The Elecraft KX3 architects should weigh in on this topic - a simplified
block diagram would be helpful. The KX3 roofing filter is likely a analogue
filter realized with precision op amps and operating at the KX3
low-frequency IF (11 KHz?) - not "baseband". The roofing filter is applied
prior to the ADC and DSP, and not at baseband audio frequencies, else it
would not be roofing filter, but merely a post audio filter.

Terry K4RX

No, the KX3 roofing filter module is completely different. It works at
"baseband" frequencies, rather than the 8+ MHz IF that the K3 uses. You will
not be able to use K3 filters in the KX3.

Bruce, N1RX

> Can the K3 roofing filters be used in KX3 ?

> Adi
> 2E0TTX

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Don Wilhelm-4

Re: Balun at input or output of tuner

In reply to this post by Dean Straw

Dean,

The last two paragraphs of your writeup do not seem relevant to the
discussion of balun (CM choke) at the input or output Those paragraphs
deal with operating coax at a very high 60:1 SWR, and neither support
nor agree with the other points.

Consider the following: A situation where the windowsill connection is
20 feet away from the tuner output. The balun has the same loss no
matter where it is placed, so lets assume it is placed at the output.

Now, consider that the connection between the tuner output and the
windowsill is with 20 feet of RG-213. The balanced line is connected
directly to the coax (no balun). By the analysis presented, the loss
will be exactly the same as with the balun connected at the windowsill
end of the coax.

Both conditions are electrically the same (If that point is arguable,
then the balun at the tuner input is just as arguable).

If we can extend this argument, we would be able to conclude that it
makes no difference on a coax fed antenna whether the balun is placed at
the antenna or at the tuner output - no matter whether the feedline is
coax or balanced line. Oh, yes, both the coax or balanced line must be
isolated and run with the same rules normally applied to balanced line.
The point is that while theory says it makes no difference, it is
impossible to achieve that perfect isolation, so the argument falls apart.

Because most would not consider connecting a balanced line to coax
without an intervening balun because we have been taught that we must
preserve balance in order for things to be correct.
The fallacy I see with the balun at the input vs. balun at the output
argument is that with the balun on the input, everything that follows
must be perfectly isolated from ground - and that is difficult to
achieve when all physical things are considered - if there are *any*
strays, it defeats the principle of perfect isolation. That is also
what makes my example of the 20 feet of coax at the balanced output of a
tuner not a practical consideration - one cannot easily achieve equal
coupling of the center conductor and shield if there are any surrounding
objects. That fact makes the unbalanced tuner with an input balun not
practical because that perfect isolation is just as (or more) difficult
and expensive to achieve than it would be to implement a balanced network.

73,
Don W3FPR

On 12/12/2011 3:38 PM, Dean Straw wrote:

> While we're at it, let's look at the potential loss due to line
> losses at a CM choke balun placed in the wrong place in an antenna system.
> Assume the common scenario where a balanced antenna is fed with open-wire
> transmission line to a 1:1 common-mode choke balun located at the shack
> window. From the balun at the window the ham uses, say, a 20-foot section of
> RG-213 to the antenna tuner (which in this case is an unbalanced tuning
> network). Assume again that the CM choke balun uses three feet of RG-213
> wound on the appropriate ferrite donuts to achieve the target common-mode
> impedance of 5000 ohms so that common-mode currents are choked off properly.
>
> The total length of RG-213 is now 23 feet. Again, we'll present the
> balun at the windowsill with a load of 3000 ohms. The overall
> differential-mode loss in 23 feet of RG-213 is 4.534 dB, nearly 4 dB worse
> than connecting the open-wire line directly to a tuner with a CM choke balun
> at its output! Ouch, that's a lot of wasted power.
>
> 73, Dean, N6BV
>

Jim Brown-10

Re: Balun at input or output of tuner

On 12/14/2011 4:59 PM, Don Wilhelm wrote:
> The balun has the same loss no
> matter where it is placed, so lets assume it is placed at the output.

There we go with that nasty word again (balun) -- we're talking about a
common mode choke, right? :)

The problem is more complex than it looks. Let's say we have a matched
200 ft line with loss of 3dB (to make the arithmetic simple), the choke
is wound with the same Z as the rest of the line, and we drive the line
with 1kW. If we put the choke at the transmitter, the differential loss
in the choke will be half of what it would be at the transmitter end.

Now, let's say we have a mismatched line that we're driving with that
same 1kW, and the Zo of the choke is still the same as the Zo of the
rest of the line, To compute the differential loss in the choke, we
must determine the current distribution along the line so that we know
the current in the choke. Now, the TOTAL differential loss in the line
will be the same no matter where the choke is, but since the coax going
through the choke is coiled up, its dissipation is more concentrated
than the rest of the line, and it's thermally coupled to the core, and
maybe it's also in an enclosure.

The real world may be even more complicated -- perhaps the Zo of the
choke different from the Zo of the rest of the line. Or perhaps there's
some sort of impedance transformer, not a simple common mode choke.
Again, we've got to work through the transmission line problem(s) and
find the current in the choke.

And we haven't even talked about common mode dissipation yet. :)

73, Jim K9YC
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P.B. Christensen

Re: Balun at input or output of tuner

In reply to this post by Don Wilhelm-4

Dean's example is still valid. By placing the CM Choke at the "wrong"
distance of 20 feet from the tuner, the 3,000 ohm Z presented at the balun
in addition to the extra 20 feet of line can create substantial mismatch
loss (i.e., additional loss due to VSWR). The choke simply adds three feet
of coax for a total of 23 feet from the tuner. If the balanced line were
dragged into the shack to reach the tuner output, loss is much less and the
remaining loss is the result of the severe mismatch and heating occurring
over just 3 feet of cable instead of 23 feet. Of course, the tuner will
have some loss of its own that we haven't considered. But the problem is
the extra coax length under a high mismatch conditions -- and not that a CM
choke is present in the line, notwithstanding the three feet of coax used in
its windings.

Prior authors have focused almost entirely on the CM choke's line balance
and common mode reactance attributes and not systematic loss. So, <gulp> if
placement of the CM choke at the tuner input results in no better balance,
but no worse balance, then clearly, system loss in many situations (e.g.,
multi-band dipoles and loops) will be less and that configuration may be
preferred. OTOH, if balance suffers, then one must look at whether loss or
line balance or choke heating is more important, depending on the mismatch
magnitude appearing at a CM choke located at the tuner output -- or at some
"wrong" distance away from the tuner.

Paul, W9AC

----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "Dean Straw" <[hidden email]>
Cc: <[hidden email]>
Sent: Wednesday, December 14, 2011 7:59 PM
Subject: Re: [Elecraft] Balun at input or output of tuner

> Dean,
>
> The last two paragraphs of your writeup do not seem relevant to the
> discussion of balun (CM choke) at the input or output Those paragraphs
> deal with operating coax at a very high 60:1 SWR, and neither support
> nor agree with the other points.
>
> Consider the following: A situation where the windowsill connection is
> 20 feet away from the tuner output. The balun has the same loss no
> matter where it is placed, so lets assume it is placed at the output.
>
> Now, consider that the connection between the tuner output and the
> windowsill is with 20 feet of RG-213. The balanced line is connected
> directly to the coax (no balun). By the analysis presented, the loss
> will be exactly the same as with the balun connected at the windowsill
> end of the coax.
>
> Both conditions are electrically the same (If that point is arguable,
> then the balun at the tuner input is just as arguable).
>
> If we can extend this argument, we would be able to conclude that it
> makes no difference on a coax fed antenna whether the balun is placed at
> the antenna or at the tuner output - no matter whether the feedline is
> coax or balanced line. Oh, yes, both the coax or balanced line must be
> isolated and run with the same rules normally applied to balanced line.
> The point is that while theory says it makes no difference, it is
> impossible to achieve that perfect isolation, so the argument falls apart.
>
> Because most would not consider connecting a balanced line to coax
> without an intervening balun because we have been taught that we must
> preserve balance in order for things to be correct.
> The fallacy I see with the balun at the input vs. balun at the output
> argument is that with the balun on the input, everything that follows
> must be perfectly isolated from ground - and that is difficult to
> achieve when all physical things are considered - if there are *any*
> strays, it defeats the principle of perfect isolation. That is also
> what makes my example of the 20 feet of coax at the balanced output of a
> tuner not a practical consideration - one cannot easily achieve equal
> coupling of the center conductor and shield if there are any surrounding
> objects. That fact makes the unbalanced tuner with an input balun not
> practical because that perfect isolation is just as (or more) difficult
> and expensive to achieve than it would be to implement a balanced network.
>
> 73,
> Don W3FPR
>
>
> On 12/12/2011 3:38 PM, Dean Straw wrote:
>> While we're at it, let's look at the potential loss due to line
>> losses at a CM choke balun placed in the wrong place in an antenna
>> system.
>> Assume the common scenario where a balanced antenna is fed with open-wire
>> transmission line to a 1:1 common-mode choke balun located at the shack
>> window. From the balun at the window the ham uses, say, a 20-foot section
>> of
>> RG-213 to the antenna tuner (which in this case is an unbalanced tuning
>> network). Assume again that the CM choke balun uses three feet of RG-213
>> wound on the appropriate ferrite donuts to achieve the target common-mode
>> impedance of 5000 ohms so that common-mode currents are choked off
>> properly.
>>
>> The total length of RG-213 is now 23 feet. Again, we'll present the
>> balun at the windowsill with a load of 3000 ohms. The overall
>> differential-mode loss in 23 feet of RG-213 is 4.534 dB, nearly 4 dB
>> worse
>> than connecting the open-wire line directly to a tuner with a CM choke
>> balun
>> at its output! Ouch, that's a lot of wasted power.
>>
>> 73, Dean, N6BV
>>
> ______________________________________________________________
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Jim Brown-10

Re: Balun at input or output of tuner

In reply to this post by Jim Brown-10

On 12/14/2011 8:29 PM, Ross Primrose N4RP wrote:
> Is it just me, or does that paragraph have a glaring typo in it????

Yep! Thanks. It should read, "if we put the choke at the antenna, the
differential loss . . . . . "

Jim K9YC
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Cortland Richmond-2

Re: Balun at input or output of tuner

In reply to this post by Dean Straw

I hesitate to step between Dean and anyone else but... it seems to me
that a Balun with good enough common mode choking should fulfill all the
isolation requirements we might have. The isolation any Balun provides
takes place at the point it is inserted, so a Balun built for 50 Ohms
may be used at the input to a (floating) tuner without our necessarily
being worse off than putting it on a tuner output -- if we can tolerate
what imbalance exists on the load side on the load and resulting RF on
the tuner chassis. We must make that RF low enough to live with, for
which we don't need perfect isolation, only _enough_. It may go
without saying that we can put CM chokes anywhere we want -- and as may
times as we want (losses permitting).

This may be moot; in his article/A Better Antenna-Tuner Balun/, QEX,
Sept/Oct 2005, ZS1AN noted the problem with "voltage" Baluns and
inherently unbalanced loads, and proposed a combined voltage and current
balun to gain the advantages of both. excerpt:

/...analyze the performance of the 1:1 current balun and the 4:1 voltage
balun in this application.
The analysis shows that the current balun operates effectively only for
small load impedances,
while the voltage balun is effective only if the load impedance is well
balanced with respect to ground.

I then introduce a new design: the "hybrid" balun, which overcomes these
limitations of the voltage
and current baluns. It can operate with much higher load impedances than
can current baluns and with
unbalanced load impedances that voltage baluns could not drive effectively.
/

Cortland
KA5S

On 12/14/2011 7:56 PM, Don Wilhelm wrote:

Jim Brown-10

Re: Balun at input or output of tuner

In reply to this post by David Herring-3

On 12/13/2011 12:53 PM, David Herring wrote:
> I'd like to ask a few questions.

David,

I hardly know where to begin in responding to your question. First, if
you want a self-supporting vertical antenna for 30-10M, there are some
really good choices that you can buy, that can be easily installed, that
can be fed with 50 ohm coax, that don't require radials, and that don't
require a balanced tuner. Loss in the feedline should be quite small if
you use RG8 (or even RG8X). Look at the Hy-Gain AV-640, which one of my
friends has used to work a lot of DX and do contesting from a small city
lot. You should use one of my chokes at the feedpoint of this antenna.
See my RFI tutorial, previously referenced.

IMO, balanced tuners and so-called balanced line are highly over-rated
solutions to problems that don't exist, or that could be better solved
with other far simpler and less costly means. IMO, the only GOOD use of
high impedance parallel wire feedlines is for very long runs -- 500 ft
or more. Likewise, I am not a fan of all-band non-resonant dipole
antennas, primarily because it is mechanically difficult choke them at
their feedpoint, which makes them noisy and puts RF on the feedline, but
also because their directional patterns vary widely with frequency.
Since you're trying to make a vertical work on all bands, I'm assuming
that horizontal antennas are not practical for you, hence the
recommendation for the AV-640. I'm not a fan of compact, multi-band
verticals below 40M because their efficiency tends to be poor, but at
30M and above they can work quite well.

As to RF in the shack -- nearly all RF in the shack problems are the
result of Pin One Problems in equipment. See the RFI tutorial for an
explanation and solutions. Also see the pdf on Ham Interfacing for
detailed instructions about bonding all of your gear together with short
lengths of copper wire. This kills hum and buzz, and makes a big dent in
the RFI you're experiencing. In extreme cases you may need to add
chokes to individual cables.

http://audiosystemsgroup.com/publish.htm

73, Jim K9YC
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David Herring-3

Re: Balun at input or output of tuner

Hi Jim,

Thanks for the tip on the AV-640...I'll surely look into that. I am looking for a self-supporting solution to minimize my impact upon the XYL's view (to her credit, she's been incredibly patient and understanding about that). The home brew vertical dipole I'm running now requires guys which isn't pretty in her opinion.

You're right about my not having space for horizontal antennas. I had shoe-horned in here an inverted-vee for a while, but that was little more than a cloud warmer -- my vertical dipole out-performs it 10 to 1.

I went with the vertical dipole because I'm leery of verticals without radials...I see the AV-640 has what appears to be a ground plane, so that may work out just fine.

I have been reading your papers and am beginning to have a fair understanding of the pin 1 problem, though I admit I have not gotten very far in physically implementing it. I do notice the amount of RF in the shack varies a lot if I mess around with the position the 450-ohm window line. That's what piqued my interest when I read about the use of a CM choke at the feed point of balanced lines...If that helped to restore balance in the balanced feeder, my thought was that might reduce feed line radiation enough to make my relatively minor RF-in-the-shack problem effectively go away. And if it improved my radiation pattern in the process, so much the better.

But I am seeing now that line of thinking was a bit simplistic and the issue is bigger than that.

Jim, thanks for the response to my post and for sharing your knowledge in general...I for one appreciate it.

73 & Aloha,

David
AH6TD

On Dec 16, 2011, at 9:00 AM, Jim Brown wrote:

> On 12/13/2011 12:53 PM, David Herring wrote:
>> I'd like to ask a few questions.
>
> David,
>
> I hardly know where to begin in responding to your question. First, if
> you want a self-supporting vertical antenna for 30-10M, there are some
> really good choices that you can buy, that can be easily installed, that
> can be fed with 50 ohm coax, that don't require radials, and that don't
> require a balanced tuner. Loss in the feedline should be quite small if
> you use RG8 (or even RG8X). Look at the Hy-Gain AV-640, which one of my
> friends has used to work a lot of DX and do contesting from a small city
> lot. You should use one of my chokes at the feedpoint of this antenna.
> See my RFI tutorial, previously referenced.
>
> IMO, balanced tuners and so-called balanced line are highly over-rated
> solutions to problems that don't exist, or that could be better solved
> with other far simpler and less costly means. IMO, the only GOOD use of
> high impedance parallel wire feedlines is for very long runs -- 500 ft
> or more. Likewise, I am not a fan of all-band non-resonant dipole
> antennas, primarily because it is mechanically difficult choke them at
> their feedpoint, which makes them noisy and puts RF on the feedline, but
> also because their directional patterns vary widely with frequency.
> Since you're trying to make a vertical work on all bands, I'm assuming
> that horizontal antennas are not practical for you, hence the
> recommendation for the AV-640. I'm not a fan of compact, multi-band
> verticals below 40M because their efficiency tends to be poor, but at
> 30M and above they can work quite well.
>
> As to RF in the shack -- nearly all RF in the shack problems are the
> result of Pin One Problems in equipment. See the RFI tutorial for an
> explanation and solutions. Also see the pdf on Ham Interfacing for
> detailed instructions about bonding all of your gear together with short
> lengths of copper wire. This kills hum and buzz, and makes a big dent in
> the RFI you're experiencing. In extreme cases you may need to add
> chokes to individual cables.
>
> http://audiosystemsgroup.com/publish.htm
>
> 73, Jim K9YC
> ______________________________________________________________
> 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