[Elecraft] KX3 with BL2 Question

[rich hurd WC3T]

Thanks for the feedback.

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72,
Rich Hurd / WC3T / DMR: 3142737
PA Army MARS, Northampton County RACES, EPA-ARRL Public Information Officer
for Scouting
Latitude: 40.761621 Longitude: -75.288988  (40°45.68' N 75°17.33' W) Grid:
*FN20is*


On Wed, Oct 4, 2017 at 11:50 AM, Don Wilhelm <donwilh at embarqmail.com> wrote:

> Rich,
>
> It is a common misconception that the characteristic impedance of the
> feedline is what you will have to match.  That is only true for resonant
> antennas.  The feedpoint impedance of a dipole in free space is 72 ohms,
> but when mounted at practical heights above ground, the feedpoint impedance
> will drop.  For most HF antennas, 50 ohms is a better choice.
>
> The other point is - yes, a balun is a good thing.  For parallel feedline,
> the balun should be at the junction of the coax and the parallel feedline
> to keep the antenna and feedline currents opposite and equal (the required
> condition for balanced), and to keep common mode current to a minimum.
>
> For non-resonant antennas, the feedpoint impedance of the line at the
> transmitter can vary from very low to very high.  It all depends on the
> length of the feedline, the length of the radiator and the frequency.
> In many cases, feeding an antenna with 450 ohm feedline, a 1:1 balun will
> work better than a 4:1 balun.
> You must match the feedpoint impedance, and that is not the characteristic
> impedance of the line.
>
> BTW, zip cord is quite lossy at RF, and should only be used in situations
> where nothing else is available.
> Your example will work, but it is a one band antenna.  The main reason for
> using parallel feedline is to be able to use the antenna on multiple bands.
>
> 73,
> Don W3FPR
>
>
> On 10/4/2017 10:35 AM, rich hurd WC3T wrote:
>
>> Would not a bnc-to-banana plug adapter hooked to a doublet made from 100'
>> of zip cord be equally useful?   Is there even a reason to have a balun
>> in-circuit?   I've read the characteristic impedance of the zip cord (or
>> speaker wire, etc.) is about 75 ohms.  If you "unzipped" 67 feet or so and
>> put on a tie wrap (to avoid further unzipping), you'd have a quite
>> serviceable 40 meter dipole with an SWR of 1.5:1 or so.
>>
>>
>