Multiple negative ground radios on a single power supply

Discussion in 'General Technical Questions and Answers' started by NQ8J, Sep 10, 2020.

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  1. KI7TGX

    KI7TGX Ham Member QRZ Page

    OK, so what power supply do you recommend? And if I was to tamper with my Astron, which I did measure has continuity between the ground in the AC-plug and the negative DC terminal (if I remember correctly), how do I (safely) remedy the situation?
     
  2. KB0MNM

    KB0MNM Ham Member QRZ Page

    For the issue of two radios on one power supply, maybe a dual-output isolated power supply or two isolated output power supplies. If you look closely at photos of 'lab grade' equipment, almost all of the power supplies have the customary red and black for D.C. outputs, yet also include a green-colored 5-way binding post ( includes banana jack- some are extra large jacks ) and a separate ground stud on the case. If you break that 'straight short' from the power supply output negative ( black lead ) to chassis/case that has been connected to the A.C. input 'ground', you make the power supply capable of being used like a 'battery' in most instances. That chassis connection might also be in the secondary of the main power transformer, and needed for a rectifier bridge reference. Yet on the better ( higher current ) Astron(TM/R/Etc.) Power supplies, some Motorola(TM/R/etc.) power supplies, some B & K ( Dynascan Corp. ) (TM/R/Etc.) power supplies, and many more- you should find a 'floating' output possible. Generally, the maker will tell you in the instruction manual how to remove a jumper or 'shunt bar' ( these usually are on the front, connecting the green 5-way post to the black one ) so that you could put supplies in 'series for greater voltages'. This only eliminates the longer ground loop which goes through the panelboard ( circuit breaker panel ) back to the service entrance. It does not affect the 'single-point-ground' which many amateur radio operators are supposed to connect to antenna coaxial cables. To break that loop, one would need a transceiver with chassis isolation for the circuit boards. Some currents can be isolated, others ( R.F. currents ) can be suppressed. That is why 'chokes' and baluns are so highly prized. See post #61 about Astron supplies, and #68 for a QST magazine article on what is 'required'.
     
  3. N3HGB

    N3HGB Ham Member QRZ Page

    I'll make it more complicated - say I add a 12 volt rig to my home shack along side my TS-940. The radios will be grounded together by coax shields at the least and also probably ground wires to the chassis and one is 120 volts and one is 12 volts. Seems like the 12 volt negative is getting connected to ground one way or another!
     
    N0TZU likes this.
  4. KB0MNM

    KB0MNM Ham Member QRZ Page

    Yes, the original post was a push to recognize that the radio coax connection does form a ground loop with respect to the power supply. Yet the coax to single-point ground connection is shared, as is the power supply green conductor in input cord ( which is for safety only ) when plugged in. That green wire finds it's way back from an outlet ( receptacle ), to the panelboard ( also known as 'circuit breaker box' ), and then to the service entrance ( in the area of the meter ) where it is connected to 'neutral' of the A.C. Folks will tell you that it is a bad idea to use a 'ground lifter' adapter on a A.C. to D.C. power supply. The answer sometimes is the same as an adult hygiene paper and chemical product- that "Depends(TM/R/etc)" on what you intend. You violate code with that little block. The jumper, not so much.
     
  5. N3HGB

    N3HGB Ham Member QRZ Page

    A heavy gauge wire between each radio ground and station ground would make any coax ground loop current minimal and probably is a good idea anyway.
     
    W9WQA likes this.
  6. KB0MNM

    KB0MNM Ham Member QRZ Page

    Right, but if you pull the power supply jumper ( in those low current Astron(TM/R.Etc) power supplies that have it installed and directions to remove it ), you take the A.C. power line loop away from the one that was described in post #1. That stray current is likely unavoidable, because the boards within the radios are tied to the radio cases(es). The heavy gauge wire is for the case(es) to 'single-point' ground, which gets added near the meter. Chasis /Chassis/ Chasiss is a fancy word for cases which include the frame.
     

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