Posted by
Bob McGraw - K4TAX on
Oct 11, 2019; 2:20am
URL: http://elecraft.85.s1.nabble.com/KX2-Antenna-Curiosity-tp7655612p7655645.html
The only issue I've encountered with single band antennas, to staff a
Field Day site to operate 2 or 3 stations per band, and 5 bands, there
needs to be some 10 to 15 antennas erected. Where as a single 135 ft
wire with a balanced feed system, a good 1:1 balun, and a good tuner
{not one of those internal radio 3:1 tuners} will allow each station to
operate 5 bands with one antenna. Thus 3 stations = 3 antennas. That
greatly simplifies operation and installation.
After all Field Day was conceived to allow hams to operate under less
than ideal conditions and to commence operation as expediently as
possible. I don't think installing 10 to 15 antennas for 2 or 3
stations falls under the definition of expediently.
I totally agree with Joe, W4TV where he says "The one "multiband"
antenna one can use in a multi-transmitter
configuration is the flat-top with open wire feeders and a *Link
coupled* tuner. The link coupled tuner is a bandpass filter
that significantly reduces harmonic/broadband noise just like the "Q" of
a single band antenna."
The optimum end result of any multi transmitter site is to have clean
transmitters. We've been begging for better receivers, now it is time
to beg for cleaner transmitters.
73
Bob, K4TAX
On 10/10/2019 1:59 PM, Tim N9PUZ wrote:
> If you are talking about a single band dipole then any half wave dipole cut
> to the standard formula and fed with good quality coax should work well. If
> you want a "multi band" dipole then I would recommend cutting it for the
> lowest frequency you plan to operate and feeding it with balanced line.
> Even the best coax can have a lot of loss under high SWR conditions
> (between your tuner and the antenna feedpoint) whereas even at 1 10:1 SWR
> balanced line does not have much loss. The radiation pattern of a multi
> band configuration can vary a lot from band to band.
>
> The end fed wire you describe is not specific to the KX2. You typically
> want the longest wire possible that is NOT a half wavelength or even
> multiple on any band you want to operate. The main reason for this is when
> a wire is a half wave or an even multiple the impedance at the end of the
> wire can be very high and it is more difficult for most tuners to obtain a
> match there. By it NOT being a half wave, the impedance is lower and a wide
> range tuner like the one in your KX2 can match it more easily and present
> the proper impedance to the radio.
>
> Here is an article that suggests good lengths for a "random wire" antenna.
> The lengths aren't really very random, they are specifically chosen to be
> easier to match. At 58.5 feet you arrived at one of the good lengths.
>
> <
https://udel.edu/~mm/ham/randomWire/>
>
> Tim N9PUZ
>
> On Thu, Oct 10, 2019 at 11:03 AM Joseph Shuman via Elecraft <
>
[hidden email]> wrote:
>
>> I have had my KX2 with the ATU for about 10 months and operate on 40m QRP
>> SSB from various locations. Experimenting with different antennas I have
>> experienced best results with a 58.5’ wire tossed about 25’ up a tree with
>> a 16.5’ counterpoise. I ran the same length wire from my house to the
>> workshop, grounded the shield side of the cable, and have seen similar
>> results to the field setup.
>>
>> Is there some engineering/design factor of the KX2 for this type of
>> antenna setup? I am planning to setup a Dipole at home, but as a newbie am
>> wondering if the “ideal” Ham Dipole can be expected to improve performance.
>>
>> Keeping Watch-
>> shu
>>
>> Joe Shuman
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