Re: T/R Switching

w5jhjerry <jerry@...>

Hi Jim,
Phil Salas, AD5X, wrote a QST article about a boat anchor T/R switch. He has a copy on his web site. It is here:

One of the problems I see with his design is that he uses 2 relays. The first relay follows your keying or keyer. He uses this relay to mute the receiver and key the transmitter. A problem may occur because the relay will switch with the keyer and the relay will unmute the receiver before the transmitter signal has decayed. If you added a second relay to his design one which would be in parallel with the antenna relay, it would probably work fine. The additional relay would be used to mute the receiver. His design will handle up to 100 watts or so.
Jerry W5JH
"building something without experimenting is just solder practice"

--- In 4sqrp@..., "Jim, ND9M / VQ9JC" wrote:

As a recent joiner of 4SQRP, I'm looking forward to getting back into building my own stuff. The NS-40 seems to be a popular and well designed rig, and my plan is to use my FT-857 for the RX side. Otherwise, the 857 is my day-to-day rig, and I have to protect it. (For QRP use, I drop the drive down and measure the output on an external wattmeter.)

So here's a newbie query from an old time ham (me!) who should know the answer but doesn't: What is everyone else who uses separate TX and RX units doing to mute their RXs when the TXs are doing their thing? A rule of thumb was given me a few days ago that there must be at least 40 dB attenuation to protect the RX front end, but that's also going to depend on what the TX power is to start with.

My old Hallicrafters RXs could handle a bit of a pop at QRP levels when I did manual switching. I'm a bit leery however about subjecting the "newfangled" 857 to similar treatment. I never had a Dow key which would've done nicely for the boat anchors, but - assuming I could put my hands on one - would a Dow key with its mechanical relay have fast enough response time to protect the 857's front end?

What other alternatives are currently in play?


Jim, ND9M / VQ9JC

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