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

[Wes (N7WS)]

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:

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

[Walter Underwood]

Oops, thanks for the clarification. I should have added “at the antenna”. After 
reading K9YC’s encyclopedic work (http://audiosystemsgroup.com/RFI-Ham.pdf 
) four times, it has seeped into the 
lower neurons.

Maybe I should read it again.

wunder
K6WRU
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Sep 28, 2015, at 6:33 PM, Bob McGraw - K4TAX  wrote:
> 
> 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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Re: [Elecraft] [K1] Question about antenna tuners that I should not have to ask but do.

[Bob McGraw - K4TAX]

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

[John Pierce]

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

[Douglas Hagerman]

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

[Brian Hunt]

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

[Walter Underwood]

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.

This is a good quality balun at a fair price. It says “QRP”, but it will handle 
300W at HF, 200W above 35MHz.

http://www.balundesigns.com/qrp-model-1110-1-1-isolation-choke-balun-1-54-mhz/ 


wunder
K6WRU
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Sep 28, 2015, at 5:24 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  wrote:
>> On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
>>  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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Re: [Elecraft] [K1] Question about antenna tuners that I should not have to ask but do.

[Don Wilhelm]

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

[Doug Person]

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  wrote:

On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
 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.


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

[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  wrote:
> On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
>  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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Re: [Elecraft] [K1] Question about antenna tuners that I should not have to ask but do.

[Don Wilhelm]

On 9/28/2015 8:02 PM, Byron Servies wrote:

On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
 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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Re: [Elecraft] [K1] Question about antenna tuners that I should not have to ask but do.

[Douglas Hagerman]

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  wrote:
> 
> On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
>  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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Re: [Elecraft] [K1] Question about antenna tuners that I should not have to ask but do.

[Byron Servies]

On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
 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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Re: [Elecraft] [K1] Question about antenna tuners that I should not have to ask but do.

[Don Wilhelm]

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

[Douglas Hagerman]

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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