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Re: [CQ-Contest] Reciprocity in signal strength

To: cq-contest@contesting.com
Subject: Re: [CQ-Contest] Reciprocity in signal strength
From: David Gilbert <ab7echo@gmail.com>
Date: Sun, 22 Jan 2023 10:53:53 -0700
List-post: <mailto:cq-contest@contesting.com>


The most likely reason for a difference in readability is a difference in local signal strength, but it is also possible that one end of the potential contact has greater QRM ... either from propagation differences (such as if he can hear a multitude of stations near you that you can't because of skip), or if he prefers to listen with a wider bandwidth, or if he has a receiver that pounds the AGC from strong signals 10 KHz away while your receiver has good close in immunity.

In my mind, there is another possible for signals arriving at very low angles and certain QTH's ... although almost nobody agrees with me.  Imagine two terrain features that are relatively close together and higher than the surround terrain, with one of those terrain features being higher than the other.  A signal arriving at a low enough angle would see a different terrain from one direction than the other since the lower terrain feature would be completely shaded by the higher feature from one direction, but not the other.  My personal opinion is that the infamous and debatable "one way skip" could be caused by something like that.  I've tried to figure out a way to use HFTA to demonstrate that, but HFTA ignores takeoff angles below the assumed horizon so it doesn't work to just define an unrealistically high tower.  Maybe somebody else has an idea on how to do it ... maybe with a program like H.O.B.B.I.E.S or FEKO.

73,
Dave   AB7E




On 1/21/2023 11:10 PM, Barry Jacobson wrote:
Hi guys, it seems that in a contest like NAQP where presumably almost
everyone is running the same 100 W power, you should be able to hear the
other guy at the same level he hears you. Even if the other guy has a
$25,000 dollar beam, and you have a simple 10 foot random wire, the
weakness in your transmission ability will also weaken your received signal
just as much in the other direction. So if you can hear him, it guarantees
he can hear you. (Unless one or both of you has separate receive and
transmit antennas, or the receivers you are using are of very different
quality.) Does that make any sense?

Barry WA2VIU

--
Barry Jacobson
WA2VIU
bdj@alum.mit.edu
@bdj_phd
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