[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/ <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 <byron at n6nul.org> 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 <byron at n6nul.org> wrote:
>> On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
>> <douglas.hagerman at me.com> 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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