[CQ-Contest] Reciprocity in signal strength

[David Gilbert]

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 at alum.mit.edu
> @bdj_phd
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