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switching 2m between yagi and downconverter



James Hall wrote: 

I will have two 2M runs - one for transmit and one for receive (IF). Anybody using, say, Daiwa coax switches for this - or what is the recommendation ? Also, I seem to remember an item from my reading on this BB that would protect the downconverter from accidental RF transmission.

Wayne replies:

For this application I have a strong preference for a coaxial relay instead of a coaxial switch.  With a coaxial relay you have a control signal that can also disable the 2m transmitter when the downconverter is selected.  That's what I do, and my "automatic 2m TX disable" circuit has on SEVERAL occasions prevented me from accidentally transmitting into my downconverter.

There are other ways to protect your downconverter.  "Protector" gizmos from DEM or SSB that go on the coax cable.  The one from DEM shunts accidental TX power to a dummy load.  The one from SSB presents a high SWR and depends on the transmitter to fold back the power.  I think the DEM design is more elegant, and it also costs less.  If you want to be cheap, an attenuator on the coax cable might be sufficient to protect the downconverter from accidental RF power.  A 6 dB attenuator with F-connectors is very cheap at Radio Shack.  I don't know if that's enough attenuation to really protect the downconverter.  High TX power may blow the attenuator like a fuse, protecting the downconverter.

Wayne Estes W9AE
Mundelein, IL, USA
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