Re: T/R Switching

Wayne Dillon

Hi Jim,
One of the solutions which springs to mind is the "Magic Box" an excellent example of one of the 4SQRP kits, check it out on the website. One other solution I have used in the past is a single transistor driven C/O driving a relay, don't forget to put a couple of back-to-back diodes across the RX input to help limit what the RX sees. I can't guarantee it's safety with the good ole '857 though. There will be others on here who will no doubt offer more accurate and up-to date advice. Do ckeck out the "Magic Box" though, as a standalone solution to T/R switching it's neat.
72/3 es God Bless de Wayne - KC0PMH

On Wed, Feb 13, 2013 at 10:06 AM, Jim, ND9M / VQ9JC <Claryco@...> 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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