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Loop-On-Ground Antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF5LJW, Aug 1, 2018.

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  1. WN6F

    WN6F Ham Member QRZ Page

    Whoa - I'm definitely going to check out that software!

    Jerry - unfortunately I don't have room for a bog, and my vertical loops are useless against neighboring noise sources that travel along wires and have no point-source anymore. Thus the log and dog are my last hopes. I think this is the "niche" that some of us are in. Otherwise, sure - I'd use a directional antenna.

    Update: more open wire testing inspired by W6NBC - but taken even further:

    Previously the transition from outside to inside the shack was via a Comet "through the window" slim little coaxial jumper. I mean really thin. Yeah, it works.

    I replaced that with nothing more than say 24-gauge zip line - the type that you see with some wall warts, and ran that in and around my 12x6 foot aluminum window frame's u-channel and close it gently. Success - no new noises or increase in noise. There seems to be no coupling to the window frame. Of course both ends of the zip-line from rig to antenna are choked.

    Passes my drill-test!

    1) Get a battery powered drill from the garage. No bit needed.
    2) Put on headphones.
    3) Fire up the drill-motor and wave it around the operating position looking for hot-spots of noise. Other than what is picked up directly by the antenna, I love to walk my lines with helpers with the drill-motor running looking for hot spots.

    Stoked - running tiny zip-cord through the u-channel of my aluminum framed window would seem to be an obvious no-no. Well, what do you know? One has to try it to believe it.
     
  2. KJ4VTH

    KJ4VTH Ham Member QRZ Page

    If I have a LOG and my DOG pees on it does that create a BOG? Asking for a friend. ;)
     
  3. WN6F

    WN6F Ham Member QRZ Page

    Your friend is on the right track - some new BOG installations wait for the rainy-season, cut it in half and tune it up as a DOG and reconnect. Then just before a contest, they water down the BOG. Seriously.

    Not a contester here, but seriously happy to have JA's on 40m cw chasing dx making my wires warm with consistent S6-S7 sigs at 1:30 am pacific with my 36 foot "dirty dog". :)

    Just as a point of interest - unlike my LOG which I made with some nice radial wire, for the temporary DOG I'm NOT using speaker wire - running 18/2 SPT-1 (spt-1 has less insulation than spt-2) colored brown for both dipole and now 50 feet of transmission line. And still have *plenty* of signal to work with, even up at 20 meters... I guess I should measure this stuff....
     
  4. WN6F

    WN6F Ham Member QRZ Page

    Some operational notes to buddies hesitant to unroll even a foot of wire ... :)

    Sky-noise:
    Yes, any small length of wire on the ground has a high component to it. Compared to say their verticals, there *is* a tiny amount of additional skynoise, but not enough for a lot of arm-waiving.

    I'm sensitive to long-term listening noise, but it is not as bad as one might think and is easily controlled. And I don't like using heavy dsp unless I have to.

    1) Rigs with no dsp: you might move the if-shift as a faux tone control (not it's purpose but many use it like that) just a hair more than usual. Or use an external speaker with just one more step for high-freq slope.

    Older rigs like an Icom 718: The dsp set to it's lowest value of "1" just mellows out that very slight ragged edge.

    Kenwood 520s and Yaesu FTdx 1200: instead of dsp, the noise-blankers also set to their lowest (or default) value do a nice job of just barely slicing off the top without disturbing the signals. No need for heavy dsp - the noise blankers seem to catch that very slight edge.

    I spend a lot of time inside headphones, and am sensitive to long-term noise and these simple fixes made the concerns about overhead skynoise really not much worrying about.
     
  5. WN6F

    WN6F Ham Member QRZ Page

    I think I'm finally satisfied with my slight alterations to the great project by KK5JY.

    1) Both the log and dog are basically balanced antennas, with the log even moreso.

    2) I use balanced transmission line directly connected to the antenna with no isolation, nor impedance transformer there. I view the receiver to be the "load" for the antenna.

    450-ohm ladder line works, but needs a 9:1 transformer in the shack. 110-ohm zip-cord works fine too, and is close enough not to be a problem at either the rig, or the antenna. I have *plenty* of signal well above the noise floor so I don't need any impedance transformation at either end.

    110-ohm zip cord for the low bands (20m and below), seems to be a reasonable compromise despite its dielectric loss characteristics which rise sharply on the high bands. But I'm not using anything above 20m anyway, nor is my run longer than say 50 feet. It is certainly more practical for winding ferrite chokes around. And, I have suspicions that the extreme close-coupling as compared to window-line helps here. Seems like just the pvc covering thickness itself is enough - at least in an rx-only application, so I run it where most say you can't - on metal / ground etc. Think W6NBC open wire testing (he didn't test zipcord!)

    3) ISOLATION
    When viewing the receiver as the load for the antenna, THIS is where I placed my 1:1 galvanic isolation transformer - at the shack end. Even this wasn't absolutely necessary, but without it, I could hear some issues below 1.9 mhz. Since I like 160m cw down near 1.8mhz, I needed it. Note that instead of a physical galvanic isolator, a few commercial heavy duty ferrite commercial chokes also worked here instead. 160m really puts these to the test. Do what you like.

    Anyway, I think I've finally found *my* preferred configuration, which is basically the isolation transformer in the shack, and a compromise impedance balanced transmission line. (110 ohm lamp cord)

    It's been a blast. Do what works for *you*.
     
  6. NQ8J

    NQ8J Ham Member QRZ Page

    I'm in a noisy environment, a 20 meter dipole in an attic was about the best I could do, but a 15' square outside next to the garage is not a problem, so I gave the LoG a try. With the dipole I barely had any SNR. With the LoG, the waterfall on my SDR is full of very listenable signals! I had a lot fun listening to 160, 80, and 40 meters as well as some SWL last night. It will nicely compliment the narrow tuning of the transmitting mag loop I'm building.
     
    KD9PAI likes this.

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