Re: I want to document some RF techniques, help please
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A bit of topic this, but the general techniques are useful..
The trick with the duplexers is to have a good return loss at the PASS freqy, even at the expense of notch depth.
23db ret loss is a minimum, preferably better at the PASS. it all starts to work far better when there are several cavities connected.
Use a circulator to join Tx and Rx cavities together (assuming single antenna working).
The traditional T-Piece phasing is critical, and will detune the notch cavities.
Also, if this is for a "digital" type of signal like dstar, DMR etc, the group delay distortion caused by notches degrades the decodability.
I have seen undecodable signals though a duplexer which was fine for FM speech.
If you are looking at a wide spaced repeater, say 7MHz split or more, consider bandpass filters so they mutually reject each other (filterplexor) , nice and flat response, so no group delay issues, and cover several channels (maybe all) at once requiring no retuning..
Be wary too of poor local osc's in the Tx and Rx, mostly phase noise. Some are so poor they jam themselves badly.
Even good LO performance requires filtering, that's the point of the filters in the Tx chain, to remove Tx noise power at the Rx freqy.
The microwave connection...
The 10GHz FM repeater diplexer we had here worked perfectly, and fitted in the hand !
On 01/06/2020 10:16, Robin Szemeti - G1YFG wrote:
Try this: http://www.repeater-builder.com/antenna/w6nbc-duplexer-book/ch3.html
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