13dB Fade on 23cms

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G4uvz
Posts: 150
Joined: Sat Dec 09, 2017 10:30 am

13dB Fade on 23cms

Post by G4uvz » Thu May 09, 2019 6:10 pm

I am probably the most distant regular user of GB3ZZ IO80RM

Signals are remarkably stable for 99.99% of the time at my home QTH IO80KX

Since the refit last year at ZZ I can access the repeater with around 500- 1000mW

On a couple the odd occasion the pathloss goes up by up to 13dB, requiring over 10 watts to get in.

Today when this happened, I could see clearly the Mendip hills which are the first obstacle at about 30 miles

The weather in Bristol was not so good with heavy rain .....However viewing the ZZ site webcam I could see that it was not raining.

I checked for the next hour or so and the pathloss was the same ...An hour after that I checked again and I was in with <400mW

I would be interested in any thoughts on the mechanism which might be in operation causing this short term effect.

Adrian

g0mjw
Posts: 868
Joined: Sat Sep 20, 2014 9:15 am

Re: 13dB Fade on 23cms

Post by g0mjw » Fri May 10, 2019 6:55 am

Adrian,

Look at my web pages, http://www.mike-willis.com/Tutorial/propagation.html for a description of potential modes. Sub refraction comes to mind or multipath fading. Also look at ITU-R Recommendation P.452 on the ITU website. It is a free download and has a lot to say about the reliability of point to point microwave links.

Mike

G4uvz
Posts: 150
Joined: Sat Dec 09, 2017 10:30 am

Re: 13dB Fade on 23cms

Post by G4uvz » Sun May 12, 2019 9:59 am

Thanks Mike...interesting stuff!

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