There is a slight addendum that I believe should be added to the traditional
belief that antennas need to be physically separated in order to use them for
diversity reception. While I agree with the statement for identical antennas,
it does not necessarily hold for dissimilar antennas. Why? If the two
antennas are identical, then they will be equal in all attributes and unless
they are physically separated, then the signal could be expected to be
identical with either antenna, fading included. But what about dissimilar
antennas? If you have two antennas in close proximity, but they are different,
they can be used to counter the results of some types of fading. For example,
if the two antennas have different radiation/reception patterns, they might
exhibit different characteristics if the fading is along the lines of the
signal arriving from different elevation angles. I've never seen an article
address this phenomenon but based upon empirical data, it does work.
My installation uses two horizontal loop antennas approximately concentric with
each other, that I use on the 40 m band for the Drake Nets and HF swap nets.
The 40 m loop is about 12' high and the 80 m loop is about 25' high. Models
of these antennas show that the radiation/reception patterns are different as
one would expect; a horizontal loop antenna used on frequencies higher than the
fundamental will exhibit more low angle lobes as the frequency is increased.
It is interesting to observe how signals from different directions and
distances are received when using both antennas, one connected to my TR-7A and
one connected to my R-7A. Sometimes one antenna is better than the other, and
sometimes they are the same. What is most interesting is that sometimes a
signal that is Q5 copy on one antenna can't be heard at all on the other. This
results in coverage that would otherwise be impossible had these two, close
proximity antennas not been used.
While many diversity systems use two receivers with various schemes for
connecting the AVC lines etc., you can achieve the same thing functionally by
using the perceptual and cognitive abilities of the human operator. Feed the
signal from one antenna/receiver to one side of your headphones, and feed the
signal from the other antenna/receiver to the other side of your headphones.
While this system isn't supposed to work, I haven't told my antennas that yet
so they just keep on working...
-Original Message-
From: Dennis Monticelli dennis.montice...@gmail.com
To: Nigel A. Gunn, W8IFF/G8IFF ni...@ngunn.net
Cc: Drakelist Drakelist@zerobeat.net
Sent: Sun, Aug 7, 2011 8:29 pm
Subject: Re: [Drakelist] Fading
Yes. Diversity reception is a well known technique, but you need a radio
so-configured or a separate box to process the inputs from the two antennas.
The antennas must be physically separated from each other sufficiently that a
fade on one would not necessarily occur in the other at the same time. The
good news is that the technique really does work.
Dennis AE6C
On Sun, Aug 7, 2011 at 4:27 PM, Nigel A. Gunn, W8IFF/G8IFF ni...@ngunn.net
wrote:
Look up diversity reception
On 08/07/2011 11:22 PM, Neil M Califano wrote:
This is a bit off topic, but how can two receiving antennas be used to reduce
fading?
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