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Overloading RF Input Protection?

Posted: Sat May 25, 2019 10:42 am
by Trevor
I'd been having fun with an RSP1A for a while (listing to various things via a wire antenna looped around my attic) and I thought I'd like to get a bit more into the hobby, so I got my amateur license and a Baofeng UV-5R and whip (1W). I setup the Baofeng to transmit to a local repeater's input and the RSP1A to listen to the repeater's output (so I could test I was being received). The problem I'm having is that I *think* transmitting with the Boafeng near the RSP1A's antenna (in my front room directly below the attic) is overloading the RSP1A. What happens is that when I press the PTT button on the Baofeng and the RSP1A seems to shutdown (waterfall hangs) and I need to reboot the PC to get the RSP1A working again.
I guess my questions are:
1) Is 1W output from the Baofeng likely to actually damage the RSP1A?
2) This article ( ... onRev2.pdf) seems to suggest I'm suffering from "near field coupling" and I could use a MFJ-1708 to protect my RSP1A... by detecting when my Baofeng is transmitting and disconnecting the antenna from the RSP1A... am I reading that right? The PTT isn't connected to the MFJ-1708 so I'd be relying on it detecting the transmit automatically.
Any help advice much appreciated! :)
Many thanks, -Trevor.

Re: Overloading RF Input Protection?

Posted: Sun Jun 09, 2019 2:47 pm
by Trevor
Answering my own post... if there are any others with similar concerns, I recommend reading the packaging!
info.jpg (76.41 KiB) Viewed 2012 times

Re: Overloading RF Input Protection?

Posted: Fri Aug 02, 2019 2:48 pm
Hello Trevor,

Hum... The MFJ-1708SDR is said to be an automatic RF sensing switch, to protect your SDR, but... it his made to be used with a transmitter and an SDR receiver, sharing the same antenna. So, it detects (or sense) the power present on the antenna connection, from the transmitter, and then automatically switch the antenna connection going to the receiver, to ground, so that the RF (radio) enegy coming from the transmitter is then going to the physical antenna.

And so... my understanding, is that this MFJ switch, only detects the RF energy present on the antenna connector from the transmitter, and not the RF energy "floating" in the air around the switch. If nothing is connected to the antenna connectior from the receiver, will it be able to detect anything ? That is the question. Maybe in your case, where you are not transmitting thru the transceiver antenna connection of that switch, maybe you could try with connecting a coax jumper, acting as a small antenna, would be enough to allow that RF energy to be sensed by the switch.

Another possibility, with that MFJ switch, is that you can also operate it manually. Well, the MFJ manual says that by connecting the PTT switch to ground, it will flip the switch to protect the receiver. The same thing happend if you are turning off the switch. So every time you want to use your handheld baoffeng transmitter, you can activate manually that switch to protect your SDR receiver.

Let me know how it turns out. ;-)

Chris, from montreal area.