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. WJ4U

    WJ4U 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.
     
    KK5JY and KD9PAI like this.
  7. W6OLY

    W6OLY Premium Subscriber QRZ Page

    Hi All,

    I installed a 15' square LoG about 80' from my shack (metal building). I wrapped a 5:2 isolation transformer using magnet wire and a type 73 binocular core. Soldered wire to a SO-239 and used a F-to-PL=259 adapter to connect the coax to the transformer.

    Connected the wire to plugs which were connected to the other magnet wires.

    Pulled the antenna into a IC-7300 with the RDX-7300 modification that adds a receive only SMA connection. I used a F-to PF-259 connector which I connected to a pig-tail that converted it to a SMA connection which I connected to the radio.

    The performance was terrible.

    I monitored FT-8 and got 1 signal on 40m over the course of 30 min. When I switched back to the Hustler 6-BTV I found a band alive and busy. Back to the LoG and nothing...

    I had pre-amp 2 engaged but it didn't seem to make a difference.

    Any advice? I used a nanoVNA and it shows dips on the logmag and swr. It appears to be working. I could try to reduce the adapters in the coax, but I cant' see that being the difference between it working or not.

    I'd be grateful for any help you can give me.
     
  8. NQ8J

    NQ8J Ham Member QRZ Page

    Is the transformer backwards? 5 side should go towards antenna.

    As you may know LoG has very low gain, so depending on your waterfall display settings, it could look like there are no signals present if they are below the minimum. Do you see the noise floor?
     
    Last edited: Jul 7, 2020
  9. W6OLY

    W6OLY Premium Subscriber QRZ Page

    I double checked the transformer, it was 5 to the antenna 2 to the radio. I didn’t see the noise floor but I didn’t hear anything in the headphones either.

    I was wondering if maybe it needs to be moved? I was considering maybe moving the antenna to a different part of the property but don’t know if that would make much difference.

    is there a “cut-off” on the radio that would make it ignore signals below a certain dB?
     
  10. NQ8J

    NQ8J Ham Member QRZ Page

    I built two of these. The second one was inside an area surrounded by chain link fence and blocked by a house with aluminum siding on one side. It still worked, but seemed like it was down in performance compared to the one I placed in a more positive open area.

    I've never used a 7300, but I have used some dsp, and some dsp noise reduction algorithms will remove weak signals as well as noise.
     

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