Safe distance between RSPduos and a low-power WSPR transmitter?

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franko
Posts: 55
Joined: Mon Aug 28, 2017 9:33 pm

Safe distance between RSPduos and a low-power WSPR transmitter?

Post by franko » Sat Nov 17, 2018 8:36 pm

I have two RSPduo's with several virtual receivers each running 24/7 to monitor a number of HF FT8 bands. One is connected to a Wellbrook ALA1530LNP magnetic loop antenna, the other to a W6LVP magnetic loop antenna.

Later today I'll be receiving one of these WSPR transmitters:

https://www.zachtek.com/product-page/ws ... ransmitter

and plan to use it on the 40m, 30m, 20m and 17m bands. The documentation indicates that it puts out approximately 300 mW of power. I'm not sure yet what antenna I'll usually be using it with, but will test out various wire and vertical antennas.

My question: How far away do I need to keep the WSPR's antenna from the mag loops in order to prevent any possible damage to the RSPduo's? Is there a maximum signal strength I should be looking for in SDRUno if I tune to the WSPR frequency?

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Roger
Posts: 217
Joined: Fri Dec 29, 2017 7:59 pm

Re: Safe distance between RSPduos and a low-power WSPR transmitter?

Post by Roger » Sun Nov 18, 2018 5:10 pm

I did some calculations using 300 mW and typical gains for your transmit antenna (6 dBi) and the magnetic loop antennas (0 dBi). Even at 20m (65 feet) you will have a signal input into the RSP over 0 dBm (which is the safe working level for an RSP). The loop antennas should be OK however because they are usually designed to withstand field strengths at this level.

I suggest you try lowering the signal level 20 dB from the WSPR transmitter by internal adjustment (if possible) or by using a 20 dB attenuator. Then measure the received signal level with your RSP and see if it is below -20 dBm.

One option to consider is to buy or build an RF limiting device to protect the front end of your RSP. Quite a few companies make them (Array Solutions, DX Engineering Cross Country etc.) and they are under $75 US.

For more info on RF limiters and how to build your own check out this post:
https://www.sdrplay.com/community/viewt ... iode#p8937

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franko
Posts: 55
Joined: Mon Aug 28, 2017 9:33 pm

Re: Safe distance between RSPduos and a low-power WSPR transmitter?

Post by franko » Sun Nov 18, 2018 8:05 pm

Thanks, Roger. From the documentation it appears that the WSPR transmitter's power output can be set at custom levels using the configuration software -- I'll check that out further.

Regarding RF limiters, I saw the following item mentioned here or in one of the other SDRplay discussion sites a few months ago, and ordered one of these last spring:

https://www.ebay.com/itm/RF-Limiter-Rec ... F-QRO-use/
rx-protector.jpg
rx-protector.jpg (65.12 KiB) Viewed 2272 times
I haven't been using it regularly, but could. At the outset I'll probably err on the side of caution and leave the RSPduo's off when running the WSPR transmitter.

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