[Elecraft] antenna question

[Ron D'Eau Claire]

>... extended double zepp
> with a transmatch.   My question is, given that I use a
> transmatch anyway, am I better off putting up 137 feet or 142?  I've often
> felt, "get up as much wire as you can."  But being so close to a half wave
> makes me wonder.  Any thoughts?
> dave belsley, w1euy

You are using my favorite wire antenna, Dave!

The issue over the length is strictly what it does to your feedpoint
impedance and that depends upon the electrical length of your feeders of
course.

I'd go for 142 feet and shorten the antenna as needed only if you have
trouble loading on some bands. The difference in the "gain" of the antenna
in its most favored directions is going to be very slight even if you
shorten it by another 10 or 20 feet. You will still get lobes showing gains
over 10 dbi up on the higher bands.

If your transmatch uses a balun at the output to provide balanced feed and
you are concerned about whether it is still providing a balanced feed on
bands where the impedance appears to be very high or very low, I suggest
checking the currents in the lines for balance. Two r-f ammeters with
sufficient accuracy to see a 10% or  20% unbalance can be had very
inexpensively at most stores. They are called "flashlight bulbs", Hi! I have
a couple of little sockets that mount some 12 volt screw in bulbs that I use
for high current feeds. When the impedance is very high, the current will be
very low, and I have a couple of 2.5 volt 25 ma "grain of wheat" bulbs with
clips on the leads that show relative currents there. They are very easy to
"blow" though - especially with the K2 if you forget to turn down the power
THEN transmit so the power control circuits react to the change BEFORE
inserting them in the line. I can get useful indications at only 1 or 2
watts on most bands. I ran a few tests using DC to see how much of a
difference in currents was readily apparent in the bulb brilliance, and I
found that as long as they are only lit dimly it was easy to see a 5% or
less difference.

I've had great success using them down to where they are only 1/4 wavelength
long, provided they are high enough off of the ground. That would suggest
that it would still do an efficient job for you on 160 meters if you like to
operate there.

In my tiny space, I am presently using a shorty 42 -foot center fed doublet
with high quality ladder line. It's just about an "extended double Zepp"
length on 10 meters, but it works FB on 40 through 10 meters.

Ron AC7AC
K2 # 1289