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Posted by: wb8rcr, John Posted On: 08/30/01 Subject: Re: QRP TR Switch Message Posted: In Reply to: Re: QRP TR Switch posted by Ed K2MGM on 08/30/01 The popular T/R switch arrangement for QRP rigs, and the FB-40 is a typical example, only serves to reduce the RF at the receiver input down to the point where it won't damage the receiver. Typically, the signal will still be too loud for comfortable listening. If you are in the 5 watts+ neighborhood, I suspect even with a relay at the antenna there will be enough RF into the receiver to make the signal uncomfortably loud. For a lot of very simple rigs we simply live with this. But as rigs get more complex, there is generally some sort of audio muting circuitry in the receiver to get the audio down to a reasonable level or, sometimes, kill it altogether. These are obviously changes back in the receiver. Look at the schematics for the Norcal-20 or perhaps the updates to the 2N2/40 for an example of how this is handled. So I guess what I'm saying is that with a separate receiver, unless you are willing to go in and do some work on the receiver, you probably going to have an uncomfortably loud sidetone. You can easily, however, prevent front end damage to the receiver. |
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