Bob wrote:
This has been carried to extremes by the OCF dipoles that aren't very good antennas at any frequency, in my opinion
My end-fed half-wave is the off-center-fed-dipole concept taken to the extreme.
Works great, in my opinion.
But it's difficult to get the matching network right, especially if shooting for multiband use.
I simply bought an EFHW-8010 from myantennas.com, though the facebook page
referenced in my previous post tells how to clone it.
The EFHW-8010 matching network is not tuned, so works well across pretty much all
of the HF amateur bands without adjustment and without a tuner at the transmitter.
Some weird tricks were employed to hit desired parts of the bands that are not exact harmonics.
A single band end-fed-half-wave with a tuned matching network is fairly easy to get working right,
plenty of websites describing this.
The common mode choke that Dave recommended is worth trying.
I suspect the primary reason I would use one is to eliminate local noise from getting into the receiver,
since I don't really care about the radiation pattern or a small drop in efficiency due to radiation
from the feedline.
My question to the group is, to best eliminate that local noise in the receiver, shouldn't
that choke be on the receiver end of the coax, not up at the antenna feed point?
I did try one near the receiver here, but being off grid way out in the boonies
there wasn't a noticeable difference.
Bob wrote:
If I want to operate too far from that frequency I might
use a tuner for just that although the efficiency sucks.?
If you have halfway decent coax that's less than 100 yards long, are operating below 30mhz,
the antenna itself is at least as good as 4:1 SWR, and you use the tuner correctly,
efficiency should not suck.
In Maxwell's Reflections III book I referenced yesterday, I said it needed editing.
It needs editing because he keeps hammering away at this point again and again and again and again.
He did so because he kept hearing from the ham community that the antenna itself
had to be in good tune to get a decent signal out.
The power lost in the coax due to reflections between antenna feed point and antenna tuner
can be calculated, and he shows how. And at HF, it usually isn't much of an issue.
Many of the chapters are simply old QST articles from the 1970's, where he felt the need to
recapitulate as readers might not have read the previous articles. But also, the organization
of all the writing is more than a little scattered. On the other hand, it's pretty much all correct.
In my opinion.
Jerry, KE7ER
On Wed, Aug 12, 2020 at 03:37 PM, Bob Albert wrote:
I used to use tuners.? No more.? I cut my antennas so that they are in
resonance or close.? If I want to operate too far from that frequency I might
use a tuner for just that although the efficiency sucks.? And of course the
pi network in my amplifier does the job of a tuner.? If the mismatch is more
than about 2:1 I balk even with a tuner.
So my old MFJ 986 sits in the closet.? Maybe good swap material.
Incidentally I have discovered that if you only trim one end of a dipole, the
resonant frequency changes but the match at resonance deteriorates.? The
upside is that the curve is a bit flatter so it covers a wider band.? This
has been carried to extremes by the OCF dipoles that aren't very good antennas
at any frequency, in my opinion
Bob
