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Conflicting Ground Advice on Loft Antenna!

Discussion in 'Amateur Radio Antennas' started by Defcon1, Mar 25, 2012.

  1. Defcon1

    Defcon1 Member

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    Hi all,

    I've finally purchased my first HF rig but due to conflicting advice on my ground I still haven't worked up the courage to power it up :-(

    Due to space limitations I've installed a 20m long wire in my attic (above 2nd floor) connected to a 9:1 UnUn to bring the high impedance long wire down to about 50ohm to match the unbalanced coaxial input.

    I'm then running 10metres of Mini RG8 Coax down to the ground floor to my HF Transceiver (internal tuner). The Receiver and Power Supply are grounded to a ground rod by 2 metres of copper braid.

    But... I have no ground on the UnUn. The instructions say a ground is not mandatory and the local radio store advised not grounding the UnUn/long wire as it will cause a ground loop with my equipment. As long as the receiver is grounded that's all I need?

    Andy advice would be much appreciated as I don't want to fry my rig which took me a lot of time to save up for. I appreciate that only having an internal Tuner will mean I can't operate on all the bands but money is an issue.

    Many thanks for any advice.

    Cheers,
    Tony


     

  2. Beetle

    Beetle Sr. Member

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    I'd start by making a 1/4 wave "counterpoise" for each band you hope to work. Connect them tightly to the chassis (ground lug) of the radio and run them along the baseboard of the shack. Tape the ends - they will represent a high voltage point on their respective bands.

    I didn't see any mention of what you're using to measure the reflected power; I'd recommend a decent power/SWR meter. The one in the radio (what radio is it?) might be okay but I don't entirely rely on their accuracy.

    Also, the 9:1 UNUN might be needed on some bands and not on others. If you have a very high feedpoint impedance on a given band it will probably help. If you have a very LOW FP impedance, though, your rig may try to put out a lot more current than it's really capable of. Test things with very low power and figure out how the antenna is actually going to operate before going QRO.
     
  3. Dave_W6DPS

    Dave_W6DPS Fount of Occasionally Useful Knowledge

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    Two questions:

    1. Does your internal tuner say it is getting a match?

    2. What do you hear?

    If the match seems okay and you can hear decent signals, then you are probably fine.

    If you can't get a good match then RFgrounding may be one of the issues you have to work through.

    I would suggest coiling up a coax choke where the feedline enters your ground floor. One way this antenna can work is to use the coax shield as the counterpoise. You want to choke off those currents so they don't get back to your tuner.

    Dave_W6DPS
     
  4. Defcon1

    Defcon1 Member

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    Thanks for the replies so far, I'll give the ideas a try.

    I've finished putting in my ground rod for the rig and needed to go down 8 feet in the end to reach good ground (to get passed the stones for drainage).

    I hope to fire up the radio for the first time at the weekend so I'll let you know if it tunes up and on what bands.

    Cheers for now,
    Tony
     

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