Re: T/R Switching
Good question. I do a lot of fooling with different boatanchor matchups. I built this RF sensing antenna switcher from Solid State Design for the Radio Amateur a few years ago that serves me well. It has adjustable drop out, so it's semi-break-in. But no provision for muting so I ride the AF & RF gains.
For little QRP RX and TX boards, I might just use an SPDT toggle switch to swap between TX and RX and maybe get those phones off my ears a bit before transmitting.
But like you said, you'd like to protect a more modern rig. The old BAs were tough. With some kind of SPDT arrangement whether relay or toggle switch, you're never going to have the TX connected directly into the RX input. Worst case, slow switching will have the TX deadheaded for a few ms but I don't know that you'd couple excess RF into the receiver doing that. Maybe if you're on 80 or 40 you can afford to have the preamp off and even a bit of attenuation turned on for an extra measure of protection. A bandaid fix for sure, I admit. However, I have a K3 and if it senses excess RF into the receiver, it will start automatically taking such steps.
If your switch or relay had an extra pole, you could use it to ground the RX antenna input during transmit. That still leaves you with that switching time vulnerability though. The only thing I can think of for that is some kind of sequencer, like a microcontroller. Or as others have said:
Something like the magic box would be the Cadillac solution, of course.
On 2/13/2013 10:06 AM, Jim, ND9M / VQ9JC wrote: