Re: Diversity Comments

[donovanf]

Hi Dennis,


I don't intend to discourage experimentation, but its useful to be aware
of the underlying science before investing time, money and effort with
low probability of a successful outcome.


The type of diversity we employ -- two receivers feeding two human ears --
isn't likely to improve SNR for signals buried in noise. Its greatest benefit
is in combating fading. Some independence in fading characteristics can
be obtained either with:
- two antennas of the same polarization separated by about
one wavelength or ideally more, or
- two antennas of opposite polarization.


Antennas very close to the ground -- for example, Beverages and BOGs --
are always vertically polarized, NEVER horizontal. Why? The electric
field of the horizontally polarized radiation broadside to a wire close to
the ground -- or laying on the ground -- is effectively "shorted out" by
its proximity to conductive soil.


But a horizontal wire has vertical polarization off the end of the wire.
The electric field off the end of the wire is perpendicular to the ground
and is not "shorted out" but its still lossy when the antenna is very close
or especially when laying directly on conductive ground.


A BOG performs best when its not laid directly on soil, it should be kept
at least supported a few inches above the soil by vegetation or other means.
The only exception is if the BOG is laid on sand having little to no moisture
or organic content.


73
Frank
W3LPL


----- Original Message -----

From: "Dennis W0JX" <[hidden email]>
To: [hidden email]
Sent: Thursday, January 30, 2020 2:00:39 PM
Subject: Diversity Comments

Good Morning Frank,

Thank you for your complete and useful comments regarding diversity reception. I have been operating my K3 in diversity since I purchased it in 2009 without understanding the technical requirements for useful diversity receive.

There is no way that I can achieve a wavelength or even half wavelength separation between my receive antennas! I use a Hi-Z 4 square RX antenna system which I always have connected to the K3 sub RX. That system, of course, is vertically polarized.

I initially began using 450 foot beverages into the Main RX and that seemed to provide some diversity RX benefits. These were separated from the HiZ system by about 100 feet. However, due to growing noise sources surrounding me, I had to abandon these antennas.

Then in 2012, I began to experiment with flag loops connected similar to DHDL's. These have proven to be much lower noise antennas and have been my favorite receiving antennas for some time. Because these are vertically polarized, I assume that diversity reception does not occur because the HiZ system is also vertically polarized.

My main question to you is this: For diversity to work, is it necessary for BOTH antennas to actually hear the DX signal? This seems logical to me but so often on 160 or 80, one antenna system hears the DX station and the other does not depending on angle of arrival of the DX signal.

Perhaps diversity receive is not as useful as it appears to be if your conditions cannot be met. On the other hand, isn't there some added benefit from the combining of signals?

BTW, I am installing two 300 foot phased BOGS aimed north. It will be interesting to see how they will perform in diversity mode since they are horizontally polarized.

161 and hope to work you in the Marathon this weekend.

Dennis W0JX
Milan OH



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