A V/U Handheld Moxon Antenna for Satellites

The Completed MoxonAs per my last post, I have been getting pretty excited about working satellites. However relying on the little ‘rubber duck’ antenna that came with the IC-T90A hand held does limit the range in a way that I could only really work the satellites at high elevation angles. With costs of commercial V/U antennas for satellite work usually over $200 AUD, it was time to build my own.

I did have some constraints around the antenna design:

  • It had to cost under $50 to make.
  • No speciality materials required – I could either readily purchase from a shop, or I already had materials on hand.
  • It had to be made using tools I had on hand.

The last point ruled out making a crossed yagi antenna to my standards as it would require a drill press to successfully fabricate (I am bad at drilling square!)

In the end a quick google found me looking at making a Moxon designed by LY3LP and modified by M1GEO, but I really wanted to get some close ups of some of the more important parts of the build. What follows is an abbreviated build guide with photos. In all, it took less than 2 hours to construct.

Update 22/12/2018 2.15pm – Yep, this antenna is a winner – here is the audio from the AO-91 pass @ 2018-12-22 1342 AEDT. Big improvement – action starts at around 2mins in.

V/U Moxon for Satellite Work

Materials:

  • 4x 3.2mm Aluminium(Tig) Welding Rod – 1 metre lengths
  • 1x 1200x20x12mm dressed pine for boom
  • 8x 4mm irrigation pipe saddle clamps (or get 3mm brass saddle clamps if you can!)
  • 1x 4mm Electrical Termination Block
  • Electrical Tape
  • Hot Glue
  • RG-58C Coax with your favourite connector to favourite length.
  • 2x Dowel or Nylon cylinder 30mm lengths
  • Cable Ties

Costs

Steps

1. Prepare your elements by cutting them to size per the specifications on the M1GEO website. I suggest using George’s modified design. Be sure to round off the ends after you cut to remove sharp edges! I also suggest marking the elements so you know which order to install them later:

Elements marked with a sharpie to identify them

2. Bend the driven element and reflectors at the specified points. I suggest using a vice and hammer to gently tap into a sharp 90 degree angle

Bending the wire in the vice

3. Measure and mark the element locations on your boom per the M1GEO website. With the first element some 30mm from the end, you should have plenty of space for a handle. I have used the ‘flat’ side of the wood, mainly as I will need the extra space later on for 2 clamps for the driven element later on.

4. At this point you may have realised that a 3.2mm rod will not hold in a 4mm saddle clamp. what I have done is measure the centre of each element and then bulk this out with electrical tape as shown below:

Saddle Clamp Spacer

5. Generally you cannot solder to aluminium and this makes connecting a feed line near impossible. You can however solder to brass. Butcher the terminal block with a saw or knife to obtain the brass fittings and then clamp to the driven element before applying the tape spacer at the end of each element. Not only does this assist in fastening but also ensures electrical isolation

Brass Terminal Extracted from plastic bus

Brass Terminals fixed to Driven Element

6. Assemble antenna elements on the boom, using a single clamp for each element, with the exception of the driven element, which will use 2 (see above image).

The Moxon Antenna Assembled awaiting a feedline

7. To provide some mechanical strength between the driven elements and reflector, use a 3mm drill bit to drill out a piece of dowel of nylon to form a spacer. push the ends of the driven elements and reflector firmly into the spacer, but not enough so that they touch.

Drilled Dowel

8. Solder your coax to the brass lugs and use cable ties to fasten to the underside of the antenna boom. When clear of the reflector fasten the coax and wrap a few turns around the boom to act as a balun.

Coax Wrapped around Boom

9. Attach your favourite connector to the other end of the coax. I have used a PL-259 as that gives me some options as I have a variety adaptors, including SMA-SO239 for the handheld.

10. (optional) Use a hot glue to tack the elements in place on the underside of the clip. I thought this is a good idea to give a bit of strength and keep the elements aligned. The strength again is particularly important around the driven element, which is a weak spot in this build.

11. (optional) Use electrical tape to wrap around coax balun the assist in fastening to boom.

Improvements to Build

I am definitely aware that there are some improvements to be made in this design:

  • Replacing the irrigation clips with proper brass clamps would simplify the build requirements and also provide a place to solder feed line to;
  • Alternatively crimp a automotive ring to the end of each driven element and fasten to boom using a screw and washer, which will also give a spot to solder the feed line. This may give better mechanical strength.
  • Or use Nylon tubing to push the driven elements into, clamping to boom.
  • Nylon tube would definitely be the preferred method of attaching between element and reflector.

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