Does anyone here have experience with mag Loops?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by G4SEB, Sep 6, 2020.

ad: L-HROutlet
ad: l-rl
ad: L-MFJ
ad: abrind-2
ad: L-Geochron
ad: HRDLLC-2
ad: Left-2
ad: MessiPaoloni-1
ad: Left-3
  1. K6CLS

    K6CLS Ham Member QRZ Page

    Bob, excellent! I too use NCDXF beacons extensively.

    http://www.ncdxf.org/pages/beacons.html

    (Sadly, we've had times when even W6WX, 50 miles away, didn't come in. Wow, tough conditions!)
     
  2. AI5DH

    AI5DH Ham Member QRZ Page

    OK that is not a antenna or even a good cloud warmer. You have an earth worm sauna and spa heating up dirt.
    You have me confused. You said you cannot get your dipole any higher than 2 meters or about 6 feet. A vertical 20 meter will be 5 meters tall and requires a counterpoise.

    Back to the point I was making, a mag loop will outperform a compromised dipole. If you cannot erect an antenna higher than 2 or 3 meters above dirt, then you are an excellent mag loop candidate. I know a few hams who live in HOA's and had attic dipoles roughly about 15 to 20 feet above finished grade. Their world was mostly NVIS local stuff, DX was rare. Mag loops opened the world more frequently to them.

    Put it to you this way. The USN has mag loops on just about every ship in the fleet. Would love to get my hands on salvaged units. The melt value of the silver would make it worth it. Once in a while you see them come up for sale. Made a bid on one, but got out bidded.
     
    KK4NSF and AK5B like this.
  3. K6CLS

    K6CLS Ham Member QRZ Page

    I bet those are LF MF RDF antennas, not general HF antennas. Entirely different.
     
    PU2OZT likes this.
  4. AI3V

    AI3V Ham Member QRZ Page

    No, the navy does not "have mag loops on every ship in the fleet"

    Because they are exceptionally lousy transmit antennas.

    On a us navy ship the usual hf transmitter antenna is a 33 foot whip with a base mounted impedance matching unit.

    Sometimes, there are 2 whips, about 3 feet apart and fed in parallel.

    Decades ago the navy experimented with a antenna called a DDRR :

    https://duckduckgo.com/?q=ddrr+antenna&t=fpas&ia=web

    They work almost as good as the 33 ft whip, if,

    1- you make the loop almost a wavlength in diameter.

    2- you make the loop out of 4 or 6 inch diameter tubing.

    3- you bring the loop into resonance with a ginormus vacuum capacitor.

    And 4- you have a few thousand tonns of steel or aluminum underneath it, preferably floating on salt water.

    [​IMG]

    Image from:
    http://navy-radio.com/ant-ship.htm

    The idea behind the ddrr was it could be installed aft on the helicopter deck, and avoid the bother of having to tilt the aft antenna for flight ops.

    Most ships just relocated the whips up onto the superstructure.

    [​IMG]

    About the closest thing to a "magnetic loop" would be the an/ssr-1 uhf satellite receiving antennas, they are full wavelength "eggbeater" receiving antennas:

    [​IMG]
    Rege
     
  5. WA4SIX

    WA4SIX Ham Member QRZ Page

    Really???? Never knew that....

    Ed
     
  6. AI3V

    AI3V Ham Member QRZ Page

    While I was stationed on Diego Garcia one showed up in a giant box at the receiving site.

    So we dug a 800 ft ditch for the 8 coax runs and put the thing up.

    The loops were around 1 meter in diameter, and about 5cm thick, each individual loop had a amplifier built in it.

    The array was a 8 direction "end fire" set up.

    It was ok, more or less equal s/n as the big full sized antennas, but with the bother of testing 32 preamps every month.

    There was a test port on the bottom of each loop, and a hand held signal generator/detector unit that I would hold in the middle of each loop and observe the reading on a meter.

    The whole affair used the fact that qrn at hf is much louder than KTB noise, so the "small" loop, while being 20 or so db weaker absolute than the big antennas still had the same s/n

    Rege
     
  7. G0VKT

    G0VKT Ham Member QRZ Page

    For a first antenna try something that works and is simple. Once you know that works you will gain experience and confidence.

    Why not try a 10m telescoping flagpole. Strap it to a wooden post in the ground. Could be removed in seconds and is not very visible. Make a simple quarter wave vertical using just wire attached to it and three or four radials sloping down at about 45 degrees. These could be detached at the ends when not in use and left to hang down.

    Or use it as an EFHW with a suitable coupler at the base. I can dig out a good link for a link coupler if you are interested.

    Paul G0VKT
     
    N8TGQ likes this.
  8. AF7ON

    AF7ON Ham Member QRZ Page

    I second trying a vertical. My own favorite for 20 meters is a 3/8 wave vertical with 1/8 long radials. It's about 22 feet high and the 8' radials are easy to deploy. Even better, it is a good match for 50 ohms. An inexpensive telescopic fibreglass pole would be a good investment.

    Mike
     
    WA7ARK and AK5B like this.
  9. WA4SIX

    WA4SIX Ham Member QRZ Page

    I was being sarcastic...

    Ed
     
  10. AI3V

    AI3V Ham Member QRZ Page

    That's ok.

    There is a lot of misinformation about "magnetic loops", and I am privileged to have installed and used what is possibly one of the biggest arrays of them on the planet.

    If a station wanted to build, say, a 160 meter directional receiving antenna small loops have a lot of advantages.

    To tramsmit 20m signals not so much.

    Rege
     
    AK5B likes this.

Share This Page