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[K1] Question about antenna tuners that I should not have to ask but do.

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Douglas Hagerman

[K1] Question about antenna tuners that I should not have to ask but do.

Does anybody have a “worked example” of how to use the L and C values reported by the K1 internal antenna tuner to analyze an antenna? I feel pretty guilty asking this, because it’s sort of a “please help me do my homework” question. And I am supposed to know how to do this homework. :-)

I have a space-limited dipole for 20 meters with drooping ends. The KAT-1 tuner will tune it. What I want to know is whether to use a 4:1 or 1:1 balun, or no balun, at the antenna.

If the tuner reports 24 “x10” pF, is that 240 pF or 2.4 pF? A straight reading suggests that it’s 2.4 pF, but I don’t see how the tuner circuit can provide so little capacitance. But C4 (82 pF) plus C5 (150 pF) gives 232 pF which could 240 pF if you include some parasitic capacitance, maybe?

Next, I need to figure out the circuit. If the tuner reports nt 2, I think that means that the coil is next to the tuner’s antenna connector, and the capacitance is in parallel with the radio connector. I guess that is designed to be 50 ohms of pure resistance, so I have a nice little circuit with one of each part. I can figure out the various reactances, etc., and combine them, but am not sure I’m doing it right. That should give me the reactance at the tuner’s antenna connector.

Then I have about 12 feet of RG-8x coax, so I can use a Smith chart to work out how the reactance at the tuners’s antenna connector is transformed to the antenna connection, but there is always the confusion about which way to go around the outside of the chart. And then take into account the 4:1 balun that’s on there. In theory, all of this should tell me the antenna's impedance at the point where the balun connects, which should suggest whether it would be better to use a 1:1 balun instead.

Does anybody have an example of this sort of calculation? I have looked in the Antenna Handbook and other sources and they all dance around it; I’m looking for something practical and cookbook-like.

Or I could spring for a 1:1 balun and try it. :-)

Thanks!

Doug, W0UHU.

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Don Wilhelm-4

Re: [K1] Question about antenna tuners that I should not have to ask but do.

Doug,

I think you are "doing it the hard way", but what you have proposed
along with some math will result in the correct information to give you
the impedance at the shack end of your feedline. That is if and only if
the KAT1 tuner has tuned to an SWR=1.

To figure the impedance at your antenna feedpoint, you will have to know
the type of feedline as well as its length and feed that information
into the formulas or an application such as TLW - (transmission line for
windows).

The easier way is to beg, borrow or steal an antenna analyzer and
measure the impedance at the shack end of the feedline. You will still
need to apply the feedline parameters to determine the antenna
impedance, and the feedline will act as an impedance transformer.

BTW, 24x10 is 240pF.

73,
Don W3FPR

On 9/28/2015 7:37 PM, Douglas Hagerman wrote:

> Does anybody have a “worked example” of how to use the L and C values reported by the K1 internal antenna tuner to analyze an antenna? I feel pretty guilty asking this, because it’s sort of a “please help me do my homework” question. And I am supposed to know how to do this homework. :-)
>
> I have a space-limited dipole for 20 meters with drooping ends. The KAT-1 tuner will tune it. What I want to know is whether to use a 4:1 or 1:1 balun, or no balun, at the antenna.
>
> If the tuner reports 24 “x10” pF, is that 240 pF or 2.4 pF? A straight reading suggests that it’s 2.4 pF, but I don’t see how the tuner circuit can provide so little capacitance. But C4 (82 pF) plus C5 (150 pF) gives 232 pF which could 240 pF if you include some parasitic capacitance, maybe?
>
> Next, I need to figure out the circuit. If the tuner reports nt 2, I think that means that the coil is next to the tuner’s antenna connector, and the capacitance is in parallel with the radio connector. I guess that is designed to be 50 ohms of pure resistance, so I have a nice little circuit with one of each part. I can figure out the various reactances, etc., and combine them, but am not sure I’m doing it right. That should give me the reactance at the tuner’s antenna connector.
>
> Then I have about 12 feet of RG-8x coax, so I can use a Smith chart to work out how the reactance at the tuners’s antenna connector is transformed to the antenna connection, but there is always the confusion about which way to go around the outside of the chart. And then take into account the 4:1 balun that’s on there. In theory, all of this should tell me the antenna's impedance at the point where the balun connects, which should suggest whether it would be better to use a 1:1 balun instead.
>
> Does anybody have an example of this sort of calculation? I have looked in the Antenna Handbook and other sources and they all dance around it; I’m looking for something practical and cookbook-like.
>
> Or I could spring for a 1:1 balun and try it. :-)
>
> Thanks!
>
> Doug, W0UHU.
>
>
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Byron Servies

Re: [K1] Question about antenna tuners that I should not have to ask but do.

In reply to this post by Douglas Hagerman

On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
<[hidden email]> wrote:

>
> I have a space-limited dipole for 20 meters with drooping ends. The KAT-1 tuner
> will tune it. What I want to know is whether to use a 4:1 or 1:1 balun, or no balun,
> at the antenna.
>

Are you feeding the antenna with coax or ladder line?

Even a low dipole will have a feed point impedance of roughly 75 ohm,
so 1:1 would be fine with coax. You may want to consider a current
choke at the feed point, but that's up to you.

With 450 or 300 ohm ladder line, a 4:1 would be more appropriate to
match the feedline to the expected impedance of the K1 input.

> If the tuner reports 24 “x10” pF, is that 240 pF or 2.4 pF? A straight reading
> suggests that it’s 2.4 pF, but I don’t see how the tuner circuit can provide so
> little capacitance. But C4 (82 pF) plus C5 (150 pF) gives 232 pF which could
> 240 pF if you include some parasitic capacitance, maybe?

Xc = 1/(2 * pi * 14 x 10^6 * 240 x 10^-12) ~~ 47.

So, the tuner thinks it is seeing roughly 50 + j47 and needs -47 of
capacitance to balance it out, right? I'd go with the 1:1.

73, Byron N6NUL
--
- Northern California Contest Club
- CU in the Cal QSO Party 3-4 Oct 2015
- www.cqp.org
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Douglas Hagerman

Re: [K1] Question about antenna tuners that I should not have to ask but do.

Unfortunately, the other part of my compromised situation is the shack location, which is at the other end of the apartment from the balcony. So I’m going to need 100 feet of coax to get to the radio. (Wife does not approve of radios in the living room!) That’s why I want to try to get the feedpoint impedance as close to correct as possible.

On the other hand, I’m on the 7th floor, with a reasonably clear view of the Atlantic ocean looking to the south. New Bedford, Massachusetts. :-)

Doug.

> On 28Sep, 2015, at 8:02 PM, Byron Servies <[hidden email]> wrote:
>
> On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
> <[hidden email]> wrote:
>
>>
>> I have a space-limited dipole for 20 meters with drooping ends. The KAT-1 tuner
>> will tune it. What I want to know is whether to use a 4:1 or 1:1 balun, or no balun,
>> at the antenna.
>>
>
> Are you feeding the antenna with coax or ladder line?
>
> Even a low dipole will have a feed point impedance of roughly 75 ohm,
> so 1:1 would be fine with coax. You may want to consider a current
> choke at the feed point, but that's up to you.
>
> With 450 or 300 ohm ladder line, a 4:1 would be more appropriate to
> match the feedline to the expected impedance of the K1 input.
>
>> If the tuner reports 24 “x10” pF, is that 240 pF or 2.4 pF? A straight reading
>> suggests that it’s 2.4 pF, but I don’t see how the tuner circuit can provide so
>> little capacitance. But C4 (82 pF) plus C5 (150 pF) gives 232 pF which could
>> 240 pF if you include some parasitic capacitance, maybe?
>
> Xc = 1/(2 * pi * 14 x 10^6 * 240 x 10^-12) ~~ 47.
>
> So, the tuner thinks it is seeing roughly 50 + j47 and needs -47 of
> capacitance to balance it out, right? I'd go with the 1:1.
>
> 73, Byron N6NUL
> --
> - Northern California Contest Club
> - CU in the Cal QSO Party 3-4 Oct 2015
> - www.cqp.org

Don Wilhelm-4

Re: [K1] Question about antenna tuners that I should not have to ask but do.

In reply to this post by Byron Servies

On 9/28/2015 8:02 PM, Byron Servies wrote:
> On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
> <[hidden email]> wrote:
>
> With 450 or 300 ohm ladder line, a 4:1 would be more appropriate to
> match the feedline to the expected impedance of the K1 input.

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Byron Servies

Re: [K1] Question about antenna tuners that I should not have to ask but do.

In reply to this post by Byron Servies

Sorry, I should have said "none" instead of "1:1". You don't appear to need it.

I also have a very compromised installation, but better now than a
dipole. And, yes, a tidy installation does us a shocking amount of
coax!

Good luck,

73, Byron N6NUL

On Mon, Sep 28, 2015 at 5:02 PM, Byron Servies <[hidden email]> wrote:

> On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
> <[hidden email]> wrote:
>
>>
>> I have a space-limited dipole for 20 meters with drooping ends. The KAT-1 tuner
>> will tune it. What I want to know is whether to use a 4:1 or 1:1 balun, or no balun,
>> at the antenna.
>>
>
> Are you feeding the antenna with coax or ladder line?
>
> Even a low dipole will have a feed point impedance of roughly 75 ohm,
> so 1:1 would be fine with coax. You may want to consider a current
> choke at the feed point, but that's up to you.
>
> With 450 or 300 ohm ladder line, a 4:1 would be more appropriate to
> match the feedline to the expected impedance of the K1 input.
>
>> If the tuner reports 24 “x10” pF, is that 240 pF or 2.4 pF? A straight reading
>> suggests that it’s 2.4 pF, but I don’t see how the tuner circuit can provide so
>> little capacitance. But C4 (82 pF) plus C5 (150 pF) gives 232 pF which could
>> 240 pF if you include some parasitic capacitance, maybe?
>
> Xc = 1/(2 * pi * 14 x 10^6 * 240 x 10^-12) ~~ 47.
>
> So, the tuner thinks it is seeing roughly 50 + j47 and needs -47 of
> capacitance to balance it out, right? I'd go with the 1:1.

--
- Northern California Contest Club
- CU in the Cal QSO Party 3-4 Oct 2015
- www.cqp.org
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Doug Person-3

Re: [K1] Question about antenna tuners that I should not have to ask but do.

Sounds like a great use for a remote tuner. (sure wish Elecraft would
develop one). I have an LDG Remote Tuner for tuning a 44' doublet in
the attic of my town home. Works great. 40 through 10 with acceptable
SWR. (unfortunately for me the noise floor isn't a floor - it's a
skyscraper).

Doug -- K0DXV

On 9/28/2015 6:24 PM, Byron Servies wrote:

> Sorry, I should have said "none" instead of "1:1". You don't appear to need it.
>
> I also have a very compromised installation, but better now than a
> dipole. And, yes, a tidy installation does us a shocking amount of
> coax!
>
> Good luck,
>
> 73, Byron N6NUL
>
> On Mon, Sep 28, 2015 at 5:02 PM, Byron Servies <[hidden email]> wrote:
>> On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
>> <[hidden email]> wrote:
>>
>>> I have a space-limited dipole for 20 meters with drooping ends. The KAT-1 tuner
>>> will tune it. What I want to know is whether to use a 4:1 or 1:1 balun, or no balun,
>>> at the antenna.
>>>
>> Are you feeding the antenna with coax or ladder line?
>>
>> Even a low dipole will have a feed point impedance of roughly 75 ohm,
>> so 1:1 would be fine with coax. You may want to consider a current
>> choke at the feed point, but that's up to you.
>>
>> With 450 or 300 ohm ladder line, a 4:1 would be more appropriate to
>> match the feedline to the expected impedance of the K1 input.
>>
>>> If the tuner reports 24 “x10” pF, is that 240 pF or 2.4 pF? A straight reading
>>> suggests that it’s 2.4 pF, but I don’t see how the tuner circuit can provide so
>>> little capacitance. But C4 (82 pF) plus C5 (150 pF) gives 232 pF which could
>>> 240 pF if you include some parasitic capacitance, maybe?
>> Xc = 1/(2 * pi * 14 x 10^6 * 240 x 10^-12) ~~ 47.
>>
>> So, the tuner thinks it is seeing roughly 50 + j47 and needs -47 of
>> capacitance to balance it out, right? I'd go with the 1:1.

Don Wilhelm-4

Re: [K1] Question about antenna tuners that I should not have to ask but do.

In reply to this post by Byron Servies

Sorry for the blank response. Blame it on late night 'fumble fingers'.

While 'common logic' will say to match the antenna to the line
impedance, that 'common logic' is flawed.

It certainly will be that a good common mode choke is all that is needed
at the antenna feedpoint, and that is a 1:1 impedance transformation.
Its purpose is to keep common mode currents off the feedline and to keep
the real radiation confined to the antenna. That aspect is unchanged no
matter whether the feedline is 50 ohms or 600 ohms.

The feedline will act as an impedance transformer no matter what (unless
the feedline is exactly matched to the antenna feedpoint impedance).
Keep in mind that open wire transmission lines are low loss (that is
important).

If you connect a 600 ohm open wire transmission line to a 'resonant'
dipole having a nominal impedance between 50 and 75 ohms, that
transmission line (even thought it has an SWR between 8 and 12) will
have extremely low loss. 450 ohm ladder line and 300 ohm ladder line
are similar, but will have higher loss than open wire line.

The real problem is to match the impedance of the shack end of the
feedline to 50 ohms. The transmission line will act as an impedance
transformer, and depending on the length of the feedline and the
frequency, the shack end may be vary between a very low impedance and a
very high impedance.

In other words, attempting to use a 4:1 balun or a 1:1 balun (or any
other ratio) at the antenna feedpoint may be an exercise in futility.
It all depends on the feedline impedance transformation at the frequency
of interest. And that depends on the feedline length and the frequency.

One would use a 4:1 balun to match coax to an antenna feedpoint
impedance of 200 to 300 ohms (folded dipole) or to a properly tuned OCF
antenna, but for all other conditions, all bets are off unless you know
the antenna feedpoint impedance of the antenna at all frequencies where
you want to use it.

A study of the ARRL Handbook or ARRL Antenna Book section on
transmission lines should provide you with more information.

73,
Don W3FPR

73,
Don W3FPR

On 9/28/2015 8:02 PM, Byron Servies wrote:
> On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
> <[hidden email]> wrote:
>
> With 450 or 300 ohm ladder line, a 4:1 would be more appropriate to
> match the feedline to the expected impedance of the K1 input.

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Brian Hunt

Re: [K1] Question about antenna tuners that I should not have to ask but do.

In reply to this post by Douglas Hagerman

Another way to approach this problem is from the other end. I've had pretty good success using antenna simulation software, EZNEC, to estimate the feed point impedance of an antenna and then use TLW to simulate the rest of the chain to see what's going on. The key is to do as faithful simulation of the antenna as you can.

EZNEC (a limited version) is on the ARRL Antenna Book CD.

73,
Brian, K0DTJ
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Douglas Hagerman

Re: [K1] Question about antenna tuners that I should not have to ask but do.

In reply to this post by Don Wilhelm-4

Hi Don.

Thanks for the comments!

There is a good article about all this in the June 2015 issue of QST. My problem is that I can’t use open line because I have to go 100 feet, threaded through apartment rooms, to get from the antenna to the radio. So it has to be coax, and as you say, the ideal situation would be to have a balanced signal at 50 ohms at the antenna, connected to the coax, which would not be acting as a transformer because of the good match at the antenna end, and then feeding into the tuner which would say “good, it’s 50 ohms of resistive impedance at this end!” and not do anything.

Or I could throw a piece of wire off the balcony and hope that the pot-smoking hippie downstairs doesn’t freak out when he sees it. :-)

Doug, W0UHU.

> On 28Sep, 2015, at 8:38 PM, Don Wilhelm <[hidden email]> wrote:
>
> Sorry for the blank response. Blame it on late night 'fumble fingers'.
>
> While 'common logic' will say to match the antenna to the line impedance, that 'common logic' is flawed.
>
> It certainly will be that a good common mode choke is all that is needed at the antenna feedpoint, and that is a 1:1 impedance transformation.
> Its purpose is to keep common mode currents off the feedline and to keep the real radiation confined to the antenna. That aspect is unchanged no matter whether the feedline is 50 ohms or 600 ohms.
>
> The feedline will act as an impedance transformer no matter what (unless the feedline is exactly matched to the antenna feedpoint impedance).
> Keep in mind that open wire transmission lines are low loss (that is important).
>
> If you connect a 600 ohm open wire transmission line to a 'resonant' dipole having a nominal impedance between 50 and 75 ohms, that transmission line (even thought it has an SWR between 8 and 12) will have extremely low loss. 450 ohm ladder line and 300 ohm ladder line are similar, but will have higher loss than open wire line.
>
> The real problem is to match the impedance of the shack end of the feedline to 50 ohms. The transmission line will act as an impedance transformer, and depending on the length of the feedline and the frequency, the shack end may be vary between a very low impedance and a very high impedance.
>
> In other words, attempting to use a 4:1 balun or a 1:1 balun (or any other ratio) at the antenna feedpoint may be an exercise in futility. It all depends on the feedline impedance transformation at the frequency of interest. And that depends on the feedline length and the frequency.
>
> One would use a 4:1 balun to match coax to an antenna feedpoint impedance of 200 to 300 ohms (folded dipole) or to a properly tuned OCF antenna, but for all other conditions, all bets are off unless you know the antenna feedpoint impedance of the antenna at all frequencies where you want to use it.
>
> A study of the ARRL Handbook or ARRL Antenna Book section on transmission lines should provide you with more information.
>
> 73,
> Don W3FPR
>
> 73,
> Don W3FPR
>
>
> On 9/28/2015 8:02 PM, Byron Servies wrote:
>> On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
>> <[hidden email]> wrote:
>>
>> With 450 or 300 ohm ladder line, a 4:1 would be more appropriate to match the feedline to the expected impedance of the K1 input.
>

K7KEY

Re: [K1] Question about antenna tuners that I should not have to ask but do.

Doug,

You might consider using a remote antenna tuner, like the SGC-230. I 've
used them for several all band antenna's, horizontal and vertical, and they
have worked quite well for me. Here is a link to some interesting and
thorough explanations and suggestions from SGC about various types and
considerations regarding all band antenna's incorporating a remote tuner at
the antenna feed point.

http://www.sgcworld.com/technicalInfoPage.html

A somewhat less expensive remote tuner is the GC-3000. (I read somewhere
that this is the same as the MFJ remote tuner, but I'm not sure about
that.) I own one of those and it works almost as well as the SGC tuner.
It just doesn't seem to have quite the matching range as the SGC tuner.
This means you might have more band segments with a 1.5:1 or 1.7:1 match
instead of a 1.1:1.

John K7KEY

On Mon, Sep 28, 2015 at 6:14 PM, Douglas Hagerman <[hidden email]>
wrote:

> Hi Don.
>
> Thanks for the comments!
>
> There is a good article about all this in the June 2015 issue of QST. My
> problem is that I can’t use open line because I have to go 100 feet,
> threaded through apartment rooms, to get from the antenna to the radio. So
> it has to be coax, and as you say, the ideal situation would be to have a
> balanced signal at 50 ohms at the antenna, connected to the coax, which
> would not be acting as a transformer because of the good match at the
> antenna end, and then feeding into the tuner which would say “good, it’s 50
> ohms of resistive impedance at this end!” and not do anything.
>
> Or I could throw a piece of wire off the balcony and hope that the
> pot-smoking hippie downstairs doesn’t freak out when he sees it. :-)
>
> Doug, W0UHU.
>
>
>
>
> > On 28Sep, 2015, at 8:38 PM, Don Wilhelm <[hidden email]> wrote:
> >
> > Sorry for the blank response. Blame it on late night 'fumble fingers'.
> >
> > While 'common logic' will say to match the antenna to the line
> impedance, that 'common logic' is flawed.
> >
> > It certainly will be that a good common mode choke is all that is needed
> at the antenna feedpoint, and that is a 1:1 impedance transformation.
> > Its purpose is to keep common mode currents off the feedline and to keep
> the real radiation confined to the antenna. That aspect is unchanged no
> matter whether the feedline is 50 ohms or 600 ohms.
> >
> > The feedline will act as an impedance transformer no matter what (unless
> the feedline is exactly matched to the antenna feedpoint impedance).
> > Keep in mind that open wire transmission lines are low loss (that is
> important).
> >
> > If you connect a 600 ohm open wire transmission line to a 'resonant'
> dipole having a nominal impedance between 50 and 75 ohms, that transmission
> line (even thought it has an SWR between 8 and 12) will have extremely low
> loss. 450 ohm ladder line and 300 ohm ladder line are similar, but will
> have higher loss than open wire line.
> >
> > The real problem is to match the impedance of the shack end of the
> feedline to 50 ohms. The transmission line will act as an impedance
> transformer, and depending on the length of the feedline and the frequency,
> the shack end may be vary between a very low impedance and a very high
> impedance.
> >
> > In other words, attempting to use a 4:1 balun or a 1:1 balun (or any
> other ratio) at the antenna feedpoint may be an exercise in futility. It
> all depends on the feedline impedance transformation at the frequency of
> interest. And that depends on the feedline length and the frequency.
> >
> > One would use a 4:1 balun to match coax to an antenna feedpoint
> impedance of 200 to 300 ohms (folded dipole) or to a properly tuned OCF
> antenna, but for all other conditions, all bets are off unless you know the
> antenna feedpoint impedance of the antenna at all frequencies where you
> want to use it.
> >
> > A study of the ARRL Handbook or ARRL Antenna Book section on
> transmission lines should provide you with more information.
> >
> > 73,
> > Don W3FPR
> >
> > 73,
> > Don W3FPR
> >
> >
> > On 9/28/2015 8:02 PM, Byron Servies wrote:
> >> On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
> >> <[hidden email]> wrote:
> >>
> >> With 450 or 300 ohm ladder line, a 4:1 would be more appropriate to
> match the feedline to the expected impedance of the K1 input.
> >
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> 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]
>

Bob McGraw - K4TAX

Re: [K1] Question about antenna tuners that I should not have to ask but do.

In reply to this post by Byron Servies

I would agree that a 1:1 balun is preferable in as much as a center fed
dipole appears to have a balanced feed point while a coax feed line is
unbalanced. In addition, a common mode choke at the feed point is
suggested. For 100 ft of RG-8x at 14 MHz the loss is ~ 1.25 dB when
matched. Other than using a balanced feed system, which will much more
complex to install, RG-8x is about the best way to go. You may also
find that a 2nd common mode choke at the radio will also be helpful as
well.

The Balun Designs products work very well in this regard. For Common
Mode Chokes, in several applications I use a product from The Wireman
being model #8232. This is a 3' coax jumper with beads and is good for
160M - 10M at near legal limit power.

73
Bob, K4TAX
K3S s/n 10,163

On 9/28/2015 7:40 PM, Walter Underwood wrote:
> A 1:1 current balun could be very useful at rejecting nearby common-mode interference. At my house, that dropped the noise floor by about 6dB.

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Wes (N7WS)

Re: [K1] Question about antenna tuners that I should not have to ask but do.

In reply to this post by Douglas Hagerman

Looking at the KAT-1 manual, it appears that NT 2 has the capacitor on the
antenna side of the tuner. I'm guessing that X10 means just that; whatever
value displayed x10. If you can do the parallel/series math to derived the Z
looking back into the tuner then go here: http://ac6la.com/tldetails1.html and
down load the program. This will do the transformation for you for the coax
cable. Just be sure to get the direction correct. (R & X at the input) Once
you have the antenna Z determined, you can use these values for the load and
change the length of coax and see what you get. Remember that the first answer
is the conjugate of the antenna Z.

Regardless, use a 1:1 current balun.

Wes N7WS

On 9/28/2015 4:37 PM, Douglas Hagerman wrote: