Ground ruminations

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  • #237
    Paul47
    Participant

    I’m a newbie at this game, just bought an RSPduo to replace my old hardly-used RSP1. I have read and listened to a lot of (often conflicting) discussions about grounds, including this interesting one: https://www.youtube.com/watch?v=qvbeip0JFqo&feature=youtu.be

    And I still have some questions…

    I have an 83′ length of wire across my back yard, plugged into a piece of coax about a meter long, in turn plugged into a 50 ohm port of the RSPduo. That in turn is connected to my laptop via a 32′ active USB cable and a shorter type B cable. The laptop is powered by a double-insulated (2-prong) plug. At the moment, the only ground in this system at all, is the connection between the wire and a ground braid of an external house lamp, through a 1 M-ohm resistor, in place to drain off any static electricity when the RSPduo is not connected.

    I notice (with an ohmmeter) that the USB, 50-ohm port and High-z port grounds of the RSPduo are all tied together, or at least they seem to be.

    This thing seems to work even though I don’t quite understand how it can. After all, when the antenna develops a voltage, doesn’t the duo need to detect that voltage with respect to a reference, which is ground? But the system ground here is just floating, not bonded to anything. It leaves me with a queasy feeling.

    I seem to have 5 options: 1) install a counterpoise (the ground will still be floating, and how will I mow my lawn?); 2) get a ground rod and drive it in like the video says, then run ground strap upstairs (it will pick up noise); 3) run a much longer wire around to the other side of the house to connect to the existing house ground rod, or at least to the cable coming from it since the rod itself is under concrete (it will pick up even more noise); 4) ground the duo to my existing house wiring (it already has noise); 5) leave the thing as it is.

    I’m having a hard time deciding which.

     

    #313
    Roger
    Participant

    While a ground is recommended for many reasons you don’t always need one to receive signals. For example you can use a dipole antenna and feed it into the RSP with a battery powered laptop and get great results. An automobile transceiver (CB or ham radio) does not have a connection to earth because it is on rubber tires and they work very well. The issue of grounding or not depends on your requirements for lightning protection, electrical safety and if you are using certain types of antennas like a vertical.

    In your case you are feeding a long wire directly into the RSP input via one meter of coax. So what is the other half of the antenna? It is the shield on the 1 meter length of coax and the shield of the 32 feet of the active USB cable. This will be a very noisy arrangement and you will have a very poor impedance match to the input of your RSP. The end result is low signal levels with lots of local noise pickup from all the digital devices (washing machines, heat pumps, appliances) in the vicinity.

    If you are into serious listening you will require a better antenna setup. End fed or random wire antennas can work well but you generally need an impedance transformer and some current baluns (RF chokes or line isolators) in order to get the noise floor down to an acceptable level. The subject of antennas is a broad topic and there are many resources and sites on the Internet devoted to short wave listening antennas.

    #534
    diysdr
    Participant

    Depending on your lot/geography but I’d suggest just running another length of wire similar to 83′ length in the opposite direction and connect that to the shield of your coax so you will in effect have a dipole. If distance is a problem then I’d split that 83 ft lenght in half. yes, it may be resonant at some odd frequency and not carefully balanced but for receiving its definitely good enough, you won’t be picking up so much EMI from the house. If you become a ham and want to xmit then you’d want to do better. I was able to locate a g5rv 120 ft away from house strung between some trees and it works amazingly well on receive and xmit on 80, 40, 20, 17M without a tuner and definitely good enough for receiving everything in between.

    #536
    merlinmaxwell
    Participant

    I have been playing radio for many years (50+) and in all that time the very best receive antenna I have is a Wellbrook loop, they are expensive (as much as an RSPDuo, if not more). Someone reverse engineered one (look up Wellgood loop) definitely worth a project. I live in an urban setting and the difference is astonishing, just like it was before all the SMPS/PLT/PLASMA crap we put up with these days.

    With a good aerial the RSPs show off their amazing performance (not just value for money but sheer performance).

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