My experience is similar to Don's outlined below. Both gain and noise
figure are important in very low noise environments. In my own case, I have
a noise floor from my TX array in the high -120s or -130s assuming a quiet
atmosphere. A high RDF performance RX array often brings virtually no
improvement. In my case, since the RX arrays lack gain, they often don't
have the horsepower (gain) to reach down and hear the super low level
signals picked up by the TX array. Switching from the TX antenna to the
high RDF receive array not only fails to make the signal "jump out of the
noise" (what noise?) but fails to hear the signal at all. In these
circumstance both gain and noise figure become very important factors.
73. . .Dave, W0FLS
----- Original Message -----
From: "Don Moman VE6JY" <ve6jy.1@gmail.com>
To: "Topband@Contesting. Com" <topband@contesting.com>
Sent: Wednesday, December 17, 2014 10:53 PM
Subject: Re: Topband: 8 circle: DXE vs Hi-Z
Well I disagree that gain isn't important. Maybe you topbanders in the
better areas of propagation can afford to throw away many db to get a
better rdf, but that sure isn't the case up here in mid-northern VE6 land.
I have numerous receive antennas including many beverages and Wellbrook
loops (large area) and the Hi-Z 4-8PRO 8 element circle. They all work
more or less as expected on the "easy" stuff and show reasonable
directivity but when I need help for the weaker dx, there just isn't any
signal there to work with. The beverages do the best of the bunch, they
aren't anything special - typically in the 700-1100 foot range. With the
many vertical structures I have there is no doubt their patterns are
somewhat affected but they seem to work fine for Eu and JA bcb dx vs the
loops and the 8 verticals. Not that this has been a good year for much of
anything on the low bands in this area.
The HI-Z was erected quite aways from anything else which involved
bushwhacking and clearing the entire circle, trenching almost 1200 feet of
feedline etc so there was a lot of sweat work done on that project. But
on 160 and 80 where I have the tx antennas to use as a comparison, the
specialized rx stuff just doesn't hear the weaker stuff. And it's not
that
I have a pristine "can hear a pin drop low noise qth", esp on 160 - plenty
of flare stack ingitors plus the usual powerline and smps junk. It's
especially frustrating to hear all the glowing success stories of these rx
arrays and how they make the dx just jump out of the noise and into your
log...
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|