Re: Passive Relay's

Phil Guttridge G3TCU


So why does Airscout suggest the optimum place for a plane is mid way on the path then? And that seems to work in practice, if you're ever lucky enough to have a plane flying exactly along the path.

I'm aware there are special cases, like when one station is in a valley and can only 'see' the plane when it's pretty close.

I assume an aircraft must be a form of passive reflector or is there a difference between aircraft *scatter* and a passive repeater that is a deliberate reflector?

Thanks & 73, Phil G3TCU

On 19/05/2020 12:11, Andy G4JNT via wrote:
If the repeater is exactly on the direct line from Tx to Rx,  MAXIMUM loss occurs if it is placed mid way
Better to have it close to one end or the other

Spreadsheet for a simplistic view will follow shortly

On Tue, 19 May 2020 at 11:29, Andy Talbot <andy.g4jnt@...> wrote:
I feel a spreadsheet coming on ..
Seem to recall doing this calculation back in the dim and distant past for work, and IIRC the mid point gave furthest range extension.   But that would have been for a naval scenario and no hills !

On Tue, 19 May 2020 at 10:58, Iain Young <g7iii@...> wrote:
Hi Nick,

On 19/05/20 10:24, Nick Gregory G0HIK via wrote:

> I have been told that you cant have the passive repeater anywhere near
> the middle of the link and has to be right at one end of it. Not sure
> how the logic works, as several of the communities fed by these are not
> that close to them, say up to 2 to 5 miles away.

I beg to differ. While this was done on 144MHz, and 433MHz, last time I
checked the rules of physics don't change at 1.2GHz and up,so here are
a couple of links tto a presentation that I did based on an experiment a
couple of years ago:

Personally, I think it's all about overcoming the extra path loss, so
you need gain in the antennas. I must try it on 23cms and up sometime...




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