OK, I can buy that ... except that the term "ground reference" as used
by you and Don doesn't really apply. The counterpoise is simply
providing some minimal balance to the high impedance at the end of the
EFHW, and it doesn't need to have anything to do with "ground".
If the counterpoise is located at the rig (as I inadvertently thought
Don was suggesting) instead of at the end of the antenna then indeed the
feedline would radiate, and if located at the rig the impedance
transformation effect of the transmission line (depending upon it's
length) could easily put a low impedance there ... rendering a short
counterpoise essentially ineffective.
For the record, I know how electricity works.
Dave AB7E
On 7/14/2016 3:42 PM, Walter Underwood wrote:
The transmitter needs to drive into two terminals. That is how electricity
works. If you do not provide a ground or a capacitive RF ground (counterpoise),
the ground is the chassis of the transmitter. In a big grounded shack, that
might be a stable reference. Otherwise, you need to provide a ground reference.
Without that, the feed impedance changes every time you touch the rig.
The ground reference does not need to handle much RF current, because of the
high impedance feed (around 10 kOhms). Even a little capacitance to ground will
stabilize the feedpoint impedance.
A minimum length of coax feedline would reduce the SWR due to losses, but it
would also provide an RF ground reference with currents on the outside of the
shield. Currents on the inside of the shield are balanced, of course.
Walter Underwood
[email protected]
http://observer.wunderwood.org/ (my blog)
On Jul 14, 2016, at 2:40 PM, David Gilbert <[email protected]> wrote:
I'm confused why an EFHW should need a counterpoise. If it needs a
counterpoise it isn't actually acting like an EFHW. If it needs a counterpoise
that means there isn't enough choking impedance at the feedpoint, and it means
that the feedline is radiating with the counterpoise acting as ... well, a
counterpoise.
Manufacturers state a minimum length feedline simply to have the feedline
losses help swamp out SWR variations along the line, and of course to
marginally lower the SWR.
Dave
AB7E
On 7/14/2016 1:03 PM, Don Wilhelm wrote:
Andy,
What happens if you connect to a dummy load? Does the KX2 tune it properly?
If so, then you know the KX2 is operating into a 50 ohm load OK.
Do you have an antenna analyzer? If so, then connect it to the antenna
feedline and look at the impedance - both real and reactive - as well as the
SWR.
That will tell you whether the antenna is troublesome.
You specifically said an EFHW - that should be a resonant antenna. If instead
you have a random length wire (not a halfwave), and what is the matching device?
Many EFHW antennas need a counterpoise to work - that is why many manufacturers
state a *minimum* length feedline.
If the problem is *not* the antenna, contact Elecraft support.
73,
Don W3FPR
On 7/14/2016 2:40 PM, Andy Clift wrote:
Just received my KX2, but unable to get it to tune an EFHW wire. I’ve tried a
home made one and then tried a SOTABEAMS MultiBander that I’ve used
successfully with an FT-857. I’ve checked the continuity in the wire and also
the continuity in the KX2 between the BNC connector and where the wire connects
inside the KX2 (as I removed this to fit the end panels). Battery is at over
11v. Any ideas please?
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