2M Portable YAGI experiment

2M Portable YAGI experiment

August 6, 2018 0 By Andrew

So I have been wanting to pay around with other antennas for Portable work.

I came across lots of information on people who had built a 2M YAGI using scraps of PVC pipe and an old steel tape measure.

Well, being one to jump on the bandwagon, I thought I would give it a go.

SO digging around the garage I found a old piece of pipe, and old 3M cheap tape measure and a lump of coax. This has to be a zero cost experiment, If it works then I may build a more sturdy version. (as you will see this one doesn't do well in the wind!)

 

There are many many sources of information, most will be more useful than this blog!

Frequency Selection

Design frequency was 145.000 MHz the centre of the band. This means the lengths are as follows:

  • Reflector length 1007mm tip to tip, solid, at the start of the boom position (the start position)
  • Driven length 973mm tip to tip, with a 10mm gap, at 414mm boom position
  • Director length 905mm tip to tip, solid, at 569mm boom position

Note: The driven is tip to tip measurement, this includes the 10mm gap at the centre. The boom positions should be marked on the boom from one end, starting at 0mm then 414mm and finally 569mm.

A hair pin match was made from some 2.5mm bare copper wire (from twin and earth mains). The dimensions for this 85mm long and 25mm wide

3D Printing Brackets

For the brackets I decided I should fire up the 3d Printer and make a few little brackets. Again zero cost to me (other than the PLA and electric, but we will discount that)

Using Autodesk Fusion 360 (free for hobby use) I made the bracket to mount on the pipe and 2 4mm holes to bolt the tape on with.

Printing these off took about 20 mins, and they were simply glued onto the pipe at the right measurements along.

Feeder Cable

The feeder is RG58 and should be cut to an odd half wave length of the design frequency.  This is also used to build an RF Choke by 8-9 wraps of the coax around the pipe. 

Have a read of this if you are interested in why this is done.

Length = 150/Mhz * Velocity Factor * Odd number of meters of cable

feeder length (meters) = ( (150 / 145.000) * 0.66 ) * 7

HairPin 

A hair pin match was made from some 2.5mm bare copper wire (from twin and earth mains). The dimensions for this 85mm long and 25mm wide. The paint/covering on the tape measure was scratched off/filed and tinned. Then each side of the coax is soldered, trying to keep it balanced length of the inner and shield and as short as possible.

Mounting Ideas.

As this is really just a prototype to see how well it works before I build something more permanent, I decided the easiest way would be just to drill a hole in the plastic so it can be screwed onto a spare photography tripod I have laying around.

Two holes were drilled so that I can mount it Horizontally for FM and Vertically for SSB.

 

Trial Run - 1

The first outing was at the Essex Ham Galley wood day, but it was raining and windy, which proved to be the biggest issue as the tape measure just folded over in the wind.

 

But holding it above my head I was able to make contact using cheapy Baofeng handheld with M1ECC from Galleywood to Basildon. So I would say that was good start.

I did try rotating through 90 degrees and the report was that signal completely went. So it is directional.. that's another tick...

Photos courtesy of Pete - M0PSX from Essex Ham

Trial Run - 2

The second attempt was done the weekend 4th August. Much sunnier and very hot, but no wind...

Using the tripod means the Yagi is at about 2.5 meters up, vertical polarised and using 2m SSB for the competition that was on.

Put out some CQ calls and was able to work about 8 or 9 stations from Kent up to Colchester way.  This time with 23watts off the FT857D.

Conclusion

It was a worth well couple of hours to build, learnt some new things and has definitely prompted me to want to build another more robust version for future use. 

 

As always, comments, suggest and general feedback welcomed.