RF Grounding

Discussion in 'General Technical Questions and Answers' started by NL0H, Apr 15, 2019.

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  1. KF5LJW

    KF5LJW Ham Member QRZ Page

    Sounds like you are ghost hunting looking for a Ground issue. Unlikely you have a ground issue. My educated guess is an Antenna problem like a missing choke on a dipole.
     
  2. W9WQA

    W9WQA Ham Member QRZ Page

    ? lets say you have the "perfect ground" system. you are radiating 100 pure watts into a nearby ,big antenna and inside wires .
    do you think that could be a problem.
    ground wont stop your 100 watts,huh?
    rf is rf...
     
  3. NL0H

    NL0H Ham Member QRZ Page

    My temporary vertical was using the metal roof for the ground. I think that a RF ground on my station is necessary... but not necessarily the problem. Of course installing a RF station ground is nearly impossible for awhile yet. The antenna/feed seems to be the issue. I do not have a choke on my antenna. A mfj dipole causes the same issues. Also my transmissions must be bleeding in to the studio audio cables, eh?
     
  4. W9WQA

    W9WQA Ham Member QRZ Page

    replace the antenna with a dummy load,see if its the coax.

    ". Also my transmissions must be bleeding in to the studio audio cables, eh?"
    yeah, from the antenna...
     
    Last edited: Apr 16, 2019
  5. K4SAV

    K4SAV Ham Member QRZ Page

    If a dipole causes the same problem as the vertical, that is a good clue and casts a vote for grounding as not being a solution. Dipoles and verticals without chokes can have some common mode currents on the feedline but when your antenna is very close to something (as in your case) it's likely that the RF radiated by the antenna will couple a lot more signal into things than the feedline will. If you had been running a vertical with only a few wire radials and no choke on the feedline, that may not be true. The effect of using the roof as the counterpoise, which also goes over the commercial station is a total unknown. The dipole having the same problem kinda says that the metal roof is not the problem. That dipole isn't hanging off the station tower is it?

    Sounds to me like the problem is in the commercial station's cabling. Just another typical RFI problem, however in this case the equipment being affected belongs to someone else. Sounds like you are going to have to get the station engineer involved, or possibly consider moving your antenna further away from the station.

    Grounding should be a problem if you are concerned about lightning protection, but that is a different discussion. For most people it is very difficult to provide lightning protection when the antenna is on a roof. You have to treat it like a lightning rod, but unlike a lightning rod it has a feedline, which extremely complicates the solution. Although you may be lucky and be under the cone of protection from the commercial station's tower. A metal roof can also help, or it can be liability if AC wiring runs next to it, although a commercial station should have already taken care of that problem. Not easy to do when the building belongs to someone else.

    Just for reference purposes, there is no such thing as a practical RF ground. Once I figured out what it would take to implement a "good enough" RF ground and it was a totally ridiculous configuration. No one could implement it.

    Jerry, K4SAV
     
  6. NL0H

    NL0H Ham Member QRZ Page

    The dipole is suspended off the tower.... About 20’ of rope though between tower and antenna. Another problem here is there are no trees. The tower is my only option for horizontal antennas.
     
  7. NL0H

    NL0H Ham Member QRZ Page

    It seems I have a very non-ideal situation.

    Henry
    N1HEN/KL7
     
  8. NL0H

    NL0H Ham Member QRZ Page

    I am not concerned about lightning here as it is very uncommon here.

    Henry
    N1HEN/KL7
     
  9. KF5LJW

    KF5LJW Ham Member QRZ Page

    Ditto. I concur as I said before you are most likely Barking Up the Wrong Tree looking for a ground issue. After reading all your comments, strongly suggest it is BRUTE FORCE RFI getting into Station Cables.

    The first logical thing to try based on symptoms is install a RF Choke. Inexpensive with a decent chance to fix the problem. But to answer your question the best place to obtain a ground is to find the building steal and bond to to it. There is no better way than using Building Structural Steel, and no cable you could run to improve it.
     
  10. W9WQA

    W9WQA Ham Member QRZ Page

    its sounding like there is "good" rf and "bad" rf !! good comes off the antenna, bad off the feed line ! all from the same source huh??
     

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