Multi-Band 4 Foot Magnetic Loop with Gamma Match

 

4 Foot Diameter Magnetic Loop In Operation

 

4 Foot Diameter Magnetic Loop In Operation

As my mag loop projects progress, I’m learning a lot about building them and using them. This antenna works on 17, 20, and 30 meters, with the best bandwidth on 20 meters. The bandwidth on 17 and 30 is quite small but usable. There is a 20 KHz bandwidth on 20 meters. I used a vacuum capacitor to build this particular loop for 100 watt operation. The air capacitors are good for QRP but will arc over using much power over QRP levels.

4 Foot Magnetic Loop Antenna with Gamma Match

4 Foot Magnetic Loop Antenna with Gamma Match

This photo was taken before I trimmed the Gamma Match.

I didn’t know how long the Gamma Match should be, so I made it long enough to allow for trimming after the match to 50 Ohms was made.

This is the first mag loop that I made with a Gamma match. I like this match better than the usual Faraday feed loop that is featured in my previous mag loop antennas. Matching is easy and building the Gamma match is not difficult. I’m planning to build other smaller loops that will also feature the Gamma match. The smaller loops will target 10, 12, and 15 meters. Loop size determines which band its best suited too. Although it is possible to get more bands on one loop, the bandwidth is small and the tuning ‘dip’ is very sharp. I found it better to limit the number of bands in favor of wider bandwidth and antenna efficiency.

Please look up my previous posts for more details on parts and plans.

 

 

 

Clamp Connects Gamma Match To Main Loop

Here is a good close up of the clamp.

(Before Trimming)

 

Gamma Match After Trimming

Gamma Match After Trimming. This enables a 50 Ohm Match for all three bands.

 

 

 

 

Gamma Match Clamp, PL 259 Coax Connctor, and PVC 'Tuning Aid Pipe

 

Gamma Match on the left, PL 259 in the center and, Tuning Aid Stick (PVC) pipe , on the right.

The vacuum capacitor is ‘tuned’ by twisting the PVC pipe that is attacked to it with a cotter pin.

Tuning the cap to the ‘loudest noise’ on the air will put you in the ball park for operating.

You can also use an antenna analyzer if you want to know the exact SWR, and RR of the antenna.

Tuning with a radio attached is fast and easy.

 

Making a Gamma Match 2

Making the clamp for the Gamma Match

 

Making a Gamma Match

Soldering The Back Plate and PL 259

 

 

Removing Oxidation

Removing The Oxidation Before Soldering

The main loop is 5/8 inch, soft copper tubing.

 

 

 

Soldering The Gamma Match to the PL 259 Connector

Close Up of PL 259 to Gamma Match Joint

The center of the PL 259 had a #10 solid copper wire inserted and soldered in place.

The Gamma match is 3/8 inch soft copper tubing.

This part of the job was done with a soldering iron, the rest was done with a plumbers torch.

 

 

Third Hand, Helper Clamp

 

Handy ‘third hand’. A clamp to hold the Gamma match in place while I soldered it.

My town was going to hire a ‘Mad Scientist’ but it couldn’t afford one, so they settled for a ham radio operator instead. Me!

73 de AA1IK

Ernest Gregoire

Ernest Gregoire, AA1IK, is a regular contributor to AmateurRadio.com and writes from Florida, USA. Contact him at [email protected]mail.com.

15 Responses to “Multi-Band 4 Foot Magnetic Loop with Gamma Match”

  • Wa6njv/4:

    Great job on building that antenna. Tom

  • ac7af:

    the perfect portable antenna for hf tell us how it worked on the air especially 20m

  • Jason KE7TDY:

    all i can saw is AWESOME!

  • alexander - yo2ldk:

    very nice job,
    thank you for sharing!

    73!

  • Peter Cook g0peq:

    Hi iam interested in building this may loop as I have a postage stamp for my back yard can u tell me what size was the variable vacuum capacitor was … it looks great can not wait to build one .thank you for any info on the capacitor ..

  • John MW1CFN:

    Nice loop! Wider copper aids efficiency, but loops are anyway much more efficient than models compute; maybe 30dB more (see Sutherland, etc.)

    A twisted gamma match is even easier!

    Loop lovers may like to examine G3JKF’s three element array, also built by MW1CFN, both on QRZ.com

  • p v Veldhoven:

    Beste Amateur Radio .com
    ZOU U MIJ KUNNEN VERTELLEN.
    Ik heefd eenloop voor 27.555 gemaakt ,maarik krijg er geen signaal op .
    loop is 2.60 mtr dia mtr 0.82 1.2 mm koper , met gamma krijg wel 1-1 swr
    maar hoord geen stations. wat is er fout ?
    hoort wel 1400mhz beetje.
    Ps welke condensator is nodig .

    Met vriendelijke groet p.v Veldhoven

  • Ernest AA1IK:

    PV Veldhoven,

    27.555 is not a ham radio frequency. 10 meters begins at 28.000 and goes up from there.

  • Colin - G1IVG:

    Looks great, I also use a similar look and it works great. My gamma match is not so tidy so I’m going to copy your idea on my loop.

  • Lin M0TCF:

    Nice work and a good lot of information to follow up on! I used a Mag Loop on a field day last Saturday and was really rather surprised how well it actually worked considering it was sitting on the table next to my FT817! Thanks for putting the page(s) up. 73’s Lin. Exeter. UK

  • VE6RJD Robert Ditchfield:

    Good article. The only question I have is how long was your gamma match. I will be using aluminum pipe at about 1 1/4 inch at about 7 foot diameter. Should the gamma match be made from the same matterial. Thanks Robert

  • Bert Somera/KB 446-24:

    Great job doing antenna like these. i want also to build one.

  • Derrick/W4DEY:

    Very nice! Am interested in building one for 80 meter cw (QRP). Any thoughts as to the dimensions needed?

  • John M Cliff G0WXU:

    Thank you for the very detailed close-up photo’s of the loop build. 73 de G0WXU

  • Beppe IU2MKE:

    Great work!
    I agree with you about a match instead of ring….I tried to tune it but I cutted a lot of copper wires and always had a too high swr….
    So I write you because I’m looking for suggestions about magnetic loops with aluminium. I’ve seen some people using flat bar (1 mm thick X 25mm large).
    Have you any experience about ?
    73 de IU2MKE. Beppe.

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