Protecting RSP from nearby transmitter

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franko
Posts: 36
Joined: Mon Aug 28, 2017 9:33 pm

Protecting RSP from nearby transmitter

Postby franko » Sat Aug 25, 2018 6:55 pm

I have several SDRplay RSP's (an RSP2 and several RSPduo's) that I'm setting up for monitoring purposes.

It isn't feasible to run them all through a transmit-receive switch to protect them when I'm doing a transmitting session. However, I'd like to leave the RSP's running rather than powering them down. If I disconnect each RSP from the antenna connected to it and ground that antenna port, is that sufficient? I'd think that is basically what a transmit-receive switch does. But is grounding only one of the antenna ports sufficient? Just wondering if RF from a nearby transmitter could overload any of the other antenna ports on an RSP if that port isn't grounded.

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franko
Posts: 36
Joined: Mon Aug 28, 2017 9:33 pm

Re: Protecting RSP from nearby transmitter

Postby franko » Sat Aug 25, 2018 7:28 pm

BTW I tried to edit the post to add the following information, but was unable to do so because the forum told me I needed to "add at least two poll options" ?):

(Frequency range involved is he HF amateur bands, power =<100w, distance ranges from a few feet (from transmitter and its coax) to tens of feet (to transmitter's antenna).)

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Tech_Support
Posts: 366
Joined: Mon Jun 01, 2015 7:00 pm

Re: Protecting RSP from nearby transmitter

Postby Tech_Support » Sun Aug 26, 2018 12:00 pm

Hello Franko,
Firstly, powering down an RSP will not prevent a RSP from being destroyed by excessive amounts of RF power in its input, so I am glad you do not see this as a preferable solution.

As long as you physically disconnect your receiver antenna from each RSP, that will be sufficient. Actually grounding the antenna port of the RSP is not strictly necessary as long as you have unscrewed the SMA connector or unplugged the green plug from the hi-Z connector. You will probably still see the transmit signal on the receive waterfall as a strong signal, but it will not be sufficient to cause any damage. Any residual pickup of your Tx signal will probably come via the USB cable, but in fact will not be strong enough to damage your RSP.

Protection devices typically use relays to isolate the Tx signal from the receiver on a common antenna, but because of the limited physical separation that can be achieved with a relay, the receiver side is usually also grounded to provide the necessary level of isolation.

Sincerely

Tech_Support

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franko
Posts: 36
Joined: Mon Aug 28, 2017 9:33 pm

Re: Protecting RSP from nearby transmitter

Postby franko » Sun Aug 26, 2018 4:21 pm

Thanks very much for the information. It is interesting to know that an RSP can be damaged from strong, nearby RF energy if it is connected to an antenna, even if it is powered down.

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franko
Posts: 36
Joined: Mon Aug 28, 2017 9:33 pm

Re: Protecting RSP from nearby transmitter

Postby franko » Sun Aug 26, 2018 11:21 pm

I just tried a test transmission to check this out. I had two RSPduo's connected to a Windows 7 PC with a total of six VRX's running to monitor the 80m, 40m, 30m, 20, 17m and 15m FT8 bands, along with an instance of WSJT-X for each one. The RSPduo's shared a 130-foot end-fed antenna through a Mini-Circuits ZFRSC-42 splitter.

When I wanted to transmit, I disconnected each RSPduo from the splitter at the RSPduo's SMA socket, and then disconnected the antenna coax from the splitter and moved it to the transceiver. I sent three 15-second transmissions at ~100 watts on the 40m band (~7.074 MHz).

After this was completed, I checked the instance of WSJT-X set up to monitor the 40m band through one of the RSPduo's. For one of the transmissions, WSJT-X reported a +10 db signal at the frequency I sent at, and also two apparent ghosts. One of these was 120 Hz lower than the main signal, and was reported at -15 db. The other was 180 Hz below the main signal, reported at -20 dB.

Any ideas on the 120/180 Hz spacing between the ghosts and the main signal?

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OH2BUA
Posts: 73
Joined: Mon Aug 29, 2016 8:58 am

Re: Protecting RSP from nearby transmitter

Postby OH2BUA » Sat Sep 01, 2018 7:52 am

Franko,

is Your AC network power frequency 60Hz? If it is, I suspect the ghosts for being hum remainings.

73, Jukka

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franko
Posts: 36
Joined: Mon Aug 28, 2017 9:33 pm

Re: Protecting RSP from nearby transmitter

Postby franko » Sat Sep 01, 2018 1:42 pm

Thanks, Jukka -- that sounds very likely.

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