Protecting Your RSP from Near-field Coupling

Near-field coupling can cause excessive power coupling from a transmitting antenna into a receiver. This video describes near-field coupling and shows how to calculate its effects. An empirical approach is described to establish whether near-field coupling is a possible issue in your installation. Methods to prevent potential damage, if required, are suggested.
You can download the slides used in this video from: www.sdrplay.com/resources/Nea...
See also this practical demo using an MFJ T/R switch: • Setting up an SDR pana...
Links to sites mentioned:
Wiki: en.wikipedia.org/wiki/Near_an...
Unwanted coupling: www.w8ji.com/antenna_coupling.htm
Everything RF: www.everythingrf.com/rf-calcu...
Rohde-Schwarz: www.rohde-schwarz.com/us/appl...
2 FAQs:
Why is the RSP1A blue and not black? The blue RSP1A used in this video is an RSP1A case with no internal metal coast for RF shielding - it was used to show the worst case scenario. The black cases are coated with a metallic coat which has a small impact particularly at UHF and above.
Why are RSPs more delicate than many other receivers with regards to damage from RF power? Because the RSPs have to cover operation up to 2GHz, it is not possible to use the more rugged protection diodes used in HF rigs for protection - their parasitic properties would degrade performance at UHF and above.
This is one of many video guides from SDRplay - makers of the RSP family of SDR radios. See the full list of SDRplay videos and applications documents on: www.sdrplay.com/apps-catalogue/
The RSP family of SDRs from SDRplay cover 1kHz to 2 GHz with no gaps and give up to 10MHz spectrum visibility.
SDRplay is a UK company. The RSP SDR receivers are made in the UK and can be purchased for worldwide delivery directly from www.sdrplay.com/ (click on purchase and select your country to view shipping costs) or you can buy from any of our worldwide resellers listed here: www.sdrplay.com/distributors/ Many of the resellers offer local free shipping and/or local language technical support.
The SDRplay KZbin Channel is: / sdrplayrsp

[@ralphbeardmore9738]

Superb video Steve. Makes protecting the rsp a total wheeze! Hope the chest gets better soon.

[@davidmartin123]

Good and timely video. The MFJ-1708B-SDRS seemed to be the no-brainer solution for me. But the current price of that item, when I can find it in stock, is higher than what I paid for my RSP1A. This video is spot-on that the first question to ask and evaluate is whether you even need to add any input protection. The video covers this well as it describes the empirical measurements you need to make given your specific rig and antenna configurations to answer that question. For me that would be an ICOM 746 HF transceiver 100W into a G5RV Jr. antenna, and a RSP1A into a MLA-30 loop receive antenna, 40m, 20m, 17m, 15m, 10m, 6m bands, with the antennas about 25 ft. apart. To use a single antenna (G5RV Jr.) for transmit using ICOM 746 and receive on both ICOM 746 and RSP1A would probably require a MFJ-1708B-SDRS.

[@JR-lx8nn]

Nicely done. Well scripted and documented. Other inexpensive protection devices exist, often purchased from online vendors at low cost, but worthwhile even if they die to protect the rig. Thanks for such an efficient treatment of this topic. JR

[@danielwietchy1037]

A well put together video and timely for the upcoming Field Day events where folks (try) to run multiple systems in close proximity. Useful links too, are appreciated. KL1JP (Alaska)

[@saxon12qa]

Great video, now I can confidently run my transmitters near to my rspdx without worrying about smoking the front end.

[@55Ramius]

Good advice. Thanks.

[@capemerlin]

Realy makes sense! 😊 Thanks a LOT!

[@peter360adventures9]

Thank you.

[@lgs6692]

I read that the RF-limiters only work up to 150 MHz, what to use above that frequency ?

[@G0USL]

I use relay switching using the external amplifier tx relay on the back of my TS590SG. This operates an rf relay on the input of my rsp1a, Using a 50ohm resistor to ground to protect the input. RS have ideal rf relays perfect for this as they supply types that are low loss at ghz. 73de GØUSL

[@SDRplayRSP]

Unless you’re using a linear you can set the DRV output on the the TS590SG (not the “S”) to be a protected output to your RSP, no additional protection required.

[@akademic2619]

Im viewing a year later but this advice is timeless and drives away several bad ideas to protect sensitive SDR and other receive equipment. Basically- disconnect and ground the input and casing. In case of direct hit lighting, connect to insurance :)

[@peter360adventures9]

Rspdx metal case is great.

[@anti-corruption-anti-tyranny]

SDRplay Software Defined Radio Receiver Steve I have my sdr play next to my yaesu ft450d. It's rigged upto my pc around 2 Feet away in the same cupboard. The yaesu 450D has a maximum output of 100w but I never use this much power maybe 80w. The yaesu is connected to a sirio 2016 which is mounted around 20FT away from the sdr antenna ( discone) I am absolutely paranoid ill blow my rsp1a. Am I safe to operate at same time? The yaesu has an interface scu17 unit I was going to run the sdr through this too so I get the coverage on screen. I would like your opinion on this. I would never use it in same antenna but the 20-25FT should be enough distance??

[@SDRplayRSP]

You should be ok. If you’re paranoid add a T/R switch, but follow the steps in the video (slowly increment power in the Yaesu while observing the RSP display) to verify.

[@anti-corruption-anti-tyranny]

@@SDRplayRSP OK my friend, thanks very much for the rapid response

[@tealtonerick6345]

If overload has occurred, what kinds of tests can be made to determine the extent of any possible damage to the receiver?

[@SDRplayRSP]

Rick, it tends to be all or nothing - the damage results in deafness across all the bands. Catastrophic fails are often accompanied by a pungent "burnt electronics" smell from the device! In some cases you may deafness at HF and still some semblance of signals at VHF. Or, if you have a multi-input device a large disparity in sensitivity between inputs. Tune to the AM broadcast band and see if ypu still have strong reception. If not, it is probably damaged.

[@tealtonerick6345]

@@SDRplayRSP Got it. Thanks Steve!

[@railgap]

Putting it in an actual metal box could surely help the situation. I've seen first-hand how well metal-coated plastic cases fare in the chamber. I've worked for companies who had to replace coated-plastic enclosures with metal ones when the coated ones could not be made to meet radiation requirements. I've seen spurious signals occasionally which I was able to eliminate by wrapping the RSP1A's chassis with aluminum foil. Tells you how good that sputtered "shielding" is. :(

[@SDRplayRSP]

You may have noticed the blue plastic. It was an early prototype without the spray on coating. I forget to mention this in the video. Fact is unless the frequency is very high (wavelength comparable to size of the box) the shielding does not help much. That’s also why I conducted the various experiments. Bottom line: in the most susceptible state the unshielded RSP1A was not damaged by near-field coupling.

[@MrGohunter]

An interesting video and explanation. However, the suggestion of reducing RF gain to the minimum and reducing the IF gain to the minimum kind of negates the whole point of having an SDR. A deaf SDR is pretty useless if you are trying to use the SDR for receive and your rig to transmit, which I guess is what many people want to do. Same really if you're using it as a panadapter. The whole point is to be able to see what signals are around on the band, both weak and strong. Good info on the fact that removing the USB doesn't protect the SDR. Sounds like the basic issue is that the protection diodes in the RSP input are not able to handle enough power, so why not just replace them with some beefier diodes that can handle enough power to protect it properly? To me, that would seem the obvious and simplest solution, or even add some beefy protection diodes external to the RSP1a at the input connector. Of course you need to be aware of the capacitance of any diodes that you fit, as that capacitance will affect the sensitivity of the SDR.

[@SDRplayRSP]

Hi. The comment re reducing RF gain was only in the context of checking the strength of the local transmit signal. Once you have proved to yourself that the transmitter won't generate more than 0dBm (1mW) RF input power to the SDR then you can use whatever settings you want from then onwards. The damage can occur irrespective of any SDR software settings. As you touched on, the problem with adding "beefy" diodes or protection circuity, is that this hammers the performance as you go up in frequency - this is a wideband SDR designed to work equally well right up to UHF and beyond.

[@MrGohunter]

@@SDRplayRSP Hi and thanks for responding. Ah, it seems that I misunderstood and didn't realise that we could return the RF and IF gain controls to normal after testing. As for the drop off in performance in UHF etc, yes, I did mention that the capacitance of beefier diodes would affect performance. I guess for me, the decrease in performance at higher frequencies wouldn't matter, as I usually only use my RSP1a for HF to see what's around as it is far better than any rig bandscope. One of these days, I will fit some beefy diodes across the input so that I can actually use it without any issues whilst transmitting. 73

[@LionRoars918]

Protection rarely works. Just ask my ICOM receiver.

[@frankENZC]

Excellent video! Thanks, and 73 de WA3RSL.

[@hajekorth]

I am absolute baffled. It seems that the SDRPlay RF limiter solution costs just as much as the cheaper SDR units. There must be a a more cost-effective solution to resolve the issue.

[@hyperionsixzeroeight5064]

NOT as robust as other regular receivers, this is pure malarky. Be prepared to send these off for front end repairs, at your expense. Very disappointed in front end and sdruno software for windows 10, nothing but problems. I own RSP1A and RSPDX, wish I had never purchased them. HOWEVER, when they do work they are good. Front ends are pPOOR design, very fragile compared to any other receiver.

[@user-ot6fk7vs3n]

try using a common mode choke