On 7/1/19 8:18 AM, john@kk9a.com wrote:
It needs no tuner or counterpoise and it has great eham reviews! How
does this work?
John KK9A
A 6 dB pad in series with any antenna will need no tuner or counterpoise
to provide a better than 2:1 VSWR.
In general, if there's a skywave path at all, the 6dB probably won't be
noticeable in a casual "can I make a QSO" environment. It's like
working mobile - you just live with what you got.
If you're trying to bust a pileup, or working the marginal ones during
the gray line transition, you'd notice it, but then, you're probably not
using a dipole 10 ft off the ground either.
over the past year, I've been looking at a lot of ionospheric
propagation models for work - My general observation is that for the
most part, either the path is open, or it's not. If the path is open,
it's an SNR thing as to whether you make the Q, and that's more about
path length than anything else - inverse square law is a harsh mistress.
3000km at 10 MHz is 121 dB free space loss, isotrope to isotrope. If
you're radiating 10 Watts (+40dBm), the receiver is seeing -81 dBm - S9
is -73dBm, so that's about S7 or S8, which is a plenty strong signal by
any standards.
So, a 100W nominal transceiver putting out 50Watts, and having 6dB in
the feedline to "improve the match" is still a "work the world" kind of
EIRP.
VOACAP predicts 11,000km, Los Angeles to Athens, with 100W isotrope to
isotrope, at 5UT, puts -117 dBm (S-2?)into the receiver on 20 meters.
(SSN=10)
Looking at it as free space propagation over 11,000 km, which ignores
the hops up to 300km and back down, and the ionospheric absorption,
gives an expected received signal of -95 dBm.
The path length, from VOACAP, using the modeled delay time of 39
milliseconds is about 11,700 km, which is a tiny change. The increased
loss is almost all D layer absorbption, I think.
David Gilbert xdavid at cis-broadband.com
The EFHW-8010 gets rave reviews, but I'm fundamentally suspicious of any
antenna that covers that wide a range without tuning. There have to be
losses somewhere to get that.
Those same reviews also claim similar results for installations 6 feet
off the ground versus 60 feet. That also doesn't make sense given the
effect that ground typically has on the feedpoint of a horizontally
polarized antenna without a lot of loss.
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