How NOT to blow up my RSP1A...?

Discussion in 'Software Defined Radio (SDR)' started by WQ4G, Sep 18, 2020.

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  1. WQ4G

    WQ4G Ham Member QRZ Page


    I tried to ask this question in a different thread and did not seem to get a satisfactory answer. It was probably because my question was not clear. So I figured I would reword the question and try again...

    I am new to SDR. I have an RSP1A receiver. I do NOT have my RSP1A connected to my Transmitter in any way. I am not trying to use my RSP1A with my Transmitter.

    When NOT using my RSP1A, how do I protect it from stray RF? Like when it is NOT connected to an antenna and when it is just laying around the shack, how do I keep the RF from destroying the front end of the RSP1A?

    I have been doing some very brief testing with the center conductor of the SMA connector of the RSP1A shorted to ground through the shield. I am doing this with an adapter cable (SMA to SO-239) and a PL-259 with a wire connected between the center pin and the outer shell. I then transmit with 10 watts into an outdoor antenna and watch for the size of the spike in the RSP1A receiver. Even with the antenna connector of the RSP1A shorted to ground and only using 10 watts transmit power the spike reaches just under +0 dBm. If I were to transmit at a 100 watt level, the spike in RSP1A receiver will most likely exceed the +10 dBm short duration maximum input power level specified by the manufacturer and destroy the front end of the receiver (so I'm afraid to try it). And, if the +10 dBm short duration maximum is not exceeded when I use 100 watts, I'm sure it will be exceeded when I switch on my amp...

    Oh, I also tried removing the adapter coax cable completely - so that there was nothing connected to the antenna jack of the RSP1A. The spike in the receiver was still there...

    Anyway, I'm afraid to use my transceiver and amp now because I'm concerned it's going to inadvertently burn out the front end of my RSP1A when it's not even hooked up to an antenna (and not being used). Is this an unfounded conclusion? Do I need to build a Faraday Cage to keep my RSP1A in when it's not in use? Does the RSP1A need additional shielding? Is this even necessary? Do other SDR users/owners take special precautions to protect their receivers when not in use?

    Any help and advice would be greatly appreciated....


    Dan WQ4G
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I have one also and nothing has ever destroyed it. I run a kilowatt on several bands and just use a simple coax switch (Alpha-Delta) to switch "away" from the RSP1A when I'm not actually using it, even though the common port of that switch goes to my main station antenna switch which is carrying a kW of RF.

    Do you have a big static electricity (ESD) problem in your shack or something?
  3. WQ4G

    WQ4G Ham Member QRZ Page

    Well, I don't think I do. I have not noticed any thing out of the ordinary - no sparking going on, no 'static' sounds in my radio (other than the usual atmospheric static), and nothing 'hot' with RF.

    The USB cable I am using is a USB 2.0 cable made without Ferrites. I have installed a 'snap on' Ferrite on the computer end of the cable... Do you think maybe the RF is getting in through the USB cable?

    Also, when ever I have the receiver disconnected from the antennas (and not in use), the only ground path is through the USB cable and computer. Perhaps I should ground out the receiver's antenna jack to an Earth ground (rod), while not in use, instead of relying on the ground coming through the computer and USB cable?

    I'm curious about your set up... Is your RSP1A located in close proximity to your rig and amp? And, does your coax switch connect the unused connections to ground when you 'switch away' to a different rig or antenna?


    Dan WQ4G
    Last edited: Sep 19, 2020
  4. DK7OB

    DK7OB Ham Member QRZ Page

    I am running a RSP1A as my second receiver. With nothing connected to the RSP1A antenna input, I receive my own 500W TX signal with about S6 to S9. I think most of it comes over the RSP1A USB connection.

    You are safe with nothing connected to the RSP1A.

    Just in case you want to use the RSP1A as a second RX: I disconnect the RSP1A during transmit with a small RF relay with good RF isolation. Signal levels are the same.
    WQ4G likes this.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The A-D coax switches all ground the unused ports and only activate the selected one, by design.

    The RSP1A is plugged into a laptop (Macbook Pro) on the second "operating desk" here in the shack, about four feet from my kW HF amp and closer than that to my rigs. I had a "receiver select switch" patched to my main "HF antenna select switch" anyway, as I sometimes use an old 75A-4 for receiving only (it's only a receiver), so another port on that switch can select the SDR dongle. My antennas aren't very close to the shack; closest is "one end" of my 80/160m inverted vee which terminates about 40' behind the house and about 20' above ground where a rope ties it off to a low tree limb. The other antennas are much farther away. I never disconnect or unplug anything.

    Never had any kind of problem.

    The reason I asked about ESD is I usually don't have any particular problem, either, but sometimes can, especially on the coldest winter days when we run the heating and the humidity level drops to nearly zero. Walking across the carpeting in my hamshack with shoes on, one day I came in and touched a small Radio Shack VHF-UHF "scanner" receiver and could feel a small spark. Oops. That took out the scanner! It was not grounded in any way (plastic case, powered by a "wall wart" power supply that is ungrounded, cabled back to the scanner with 12Vdc or whatever it was, and using an indoor whip antenna -- everything totally "floating") and the small spark made it back into circuitry somehow and really killed it.

    I didn't bother repairing a 10 year-old scanner that cost about $79 when it was new, so it's happily residing in a landfill somewhere.:p
    WQ4G likes this.
  6. W1PDZ

    W1PDZ Ham Member QRZ Page

    It's a good thing you brought this up. I am waiting on a RSP1A that should be here tomorrow and didn't even think of that issue. I'm going to double check all my grounding as well which is what I do about every 6 months and is about due anyway.
    Keeping the SDR unit and a dedicated computer isolated away and all by themselves on the 2nd desk I have in the shack is probably a good idea. It is the perfect size for them, and now this gives me a very good excuse to buy a much bigger work bench for my projects. I think 8 feet should be sufficient :D
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    If you blow up your RSP1A when it is disconnected, You should be wearing a metal hat.

    Don't cheap out using a aluminum hat, Get a good thick metal hat with a ground strap.

    A Lead Apron may be a good idea also.
    K4RGN, HA3FLT and N0SYA like this.
  8. KC2RGW

    KC2RGW Premium Subscriber QRZ Page

    I leave my RSPs connected to a 4 port antenna switch all the time and have done so with them and other SDR receivers for a long while without any trouble. They are in an environment where I get a good S9+20 signal into them through leakage and I use that to monitor myself when setting TX params regularly. No problems.

    Just don't TX directly into them and you should be fine.
  9. W6UV

    W6UV Premium Subscriber QRZ Page

    Don't worry about it if you don't have a direct connection between your transmitter and RSP1A.

    I have several SDR receivers here in the shack, including an RSP1A, and have never had an issue with any of them being affected by my transmitters, despite running 1500 watts. Some SDR manufacturers say that damage is possible if the receiving antenna is in the near field of the transmitting antenna, but I've never had an issue with that myself (I don't disconnect the SDR receivers from the receive antennas while transmitting 1500 watts on my main antennas).

    And even if you do blow up your RSP1A, they're cheap enough that it's not going to hurt too much.
    W9WQA likes this.
  10. 2E0CIT

    2E0CIT Ham Member QRZ Page

    Input to my RSP1a is usually from one of my small active antennas, -coax heavily choked so that any signal pickup by the coax shield is minimised and the SDR operates perfectly well even when I'm txing but if I connect it to a wire antenna I fit a receiver protection unit in line :

    (It's reassuring for me to read that WB2WIK and other very experienced operators find the SDR quite bombproof but I've had expensive disasters in the past that cause me to act cautiously! :eek:)

    I've found that the protection unit, whilst passing HF signals with no problem, totally attenuates VHF -UHF. Not a problem for me as I'm either working on VHF-UHF or HF, but not simultaneously.

    Incidentally, when using efficient wire antennas where I've encountered very strong incoming signals that have overloaded the SDR (despite reducing the gain) I made a 1:1 ferrite transformer with just one turn of wire on input and 1 turn on output.(The turns spaced an inch or so apart)
    From my junkbox I chose a piece of a cheap ungraded ferrite rod that would likely be inefficent at HF. It successfully attenuated incoming signals to bring them within an acceptable dynamic range and cost far less than any commercial attenuator units.
    73 Jeff
    Last edited: Oct 4, 2020

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