A couple of days ago, Thom, W8TAM e-mailed me:
http://www.ad5x.com/images/Articles/FrontEndProt.pdf
That’s pretty compelling, and not a long parts list for the first circuit. Thoughts?
He was looking for a way to protect the front end of his SDR receiver when he was transmitting. I replied:
This circuit was designed to be used in a contest station, and actually switches out the receiver protection while you’re transmitting. Not only that, it seems way too complicated for your application. Here are some other ideas:
AY Technologies RIP-1 Receiver Isolator/Protector. This device simply switches out the antenna and shorts the receiver antenna when you transmit. I don’t know what the price is as the website says, “At this time, we are not manufacturing products on a regular basis, but we continue to provide them according to customer requests and our available time. Please contact me by e-mail to inquire about pricing and availability of our products Our “Products” listing shows what types of products may be available.” AY Technologies is, apparently, a one-man operation run by Gary, K9AY, who I think has some good technical chops.
OK1RR’s Yet Another Front End Saver. This does basically the same thing but uses three relays and a couple of transistors. The extra relays disconnect the antenna and connect the AMP KEY output. (The AY Technologies device uses a DPDT relay to switch the antenna in and out and does not have a relay for the AMP KEY output.) OK1RR also has some good technical chops.
Array Solutions AS-RXFEP Receiver Front End Protector. I kind of like this one, as it doesn’t appear to need any control signal. It costs $55, though. The schematic is at https://www.arraysolutions.com/images/AS-RXFEPdatasheet.pdf. The white packages contain transformers. It looks like they are Mini-Circuits transformers, and you can probably get them for $5 or less.
Thom replied that the AD5X circuit could, of course, be built without the relay, something I hadn’t thought of. That makes the circuit much simpler:
He’s going to go ahead with the AD5X circuit. Anyone else have some other thoughts about this?