Tuesday, September 27, 2016

Building a 2 Meter Yagi (Version 2)

A while back I built a 2 meter Yagi and had great fun playing around on my local club net with it  attached to a small rotator, but as is the case, I moved on to other things and sold the TV rotator and the Yagi on to a friend.

The original
I noticed in the stats of this blog that one of the most read items is the building of that 2 meter Yagi. It's a very simple design and for its simplicity it works very well especially for my latest project with my newly acquired Trio 700s where I needed a small Yagi antenna. So I read back in the blog and decided to make a mark 2 version.

The first items I required was three aluminium 18mm tubes, two at one metre length and the other at 1500mm and one boom 15mm by 15mm square also at 1 metre in length. I would also require three pieces of wooden curved dowel (12") to support the aluminium tubes when mounted, a small but thick piece of copper wire for the hairgrip 12.5mm in length and 10 plastic tie grips.

The aluminium tubes will be rear element 1020mm, drive element 920mm and front 890mm. The rear and front will remain at their lengths but the drive will need to be cut accurately in half and then two small hole drilled about 2 mm from one end to take a small screw for the coax and hairpin wire.
The hairpin wire should be 5 cm in length bent at right angles 2.2cm width, and bent again at right angles for another 5cm. the width between ground and live should be the 2.2 cm.

A = 5cm B = 2.2cm

The coax should be roughly a metre long, stripped for a PL259 at one end and split for ground and live at the other with two metal eyes soldered on for a screw placement on the drive element. If this antenna was going outside it would then be waterproofed for protection, but in this case it was going in my attic.

You can alter the length of the A  for minor adjustment of SWR.

The elements are fixed by the plastic tie grips going round each of the dowels and the tubes, they are light and hold the tubes in place. The wooden dowels are then screwed in to place in to the boom by a small screw or you could fit a small bolt and nut.

I got a good 1:1 and 1:2 SWR over the upper part of 144MHz  and lower 145 MHz and as soon as I can will be placing it up in my attic to see how it does with a bit of dxing!

Here is the link to the site for further explanation:  Yagi Build

All Mode 2 meter DX and Rotators

I managed to pick up an old Trio 700s all mode transceiver the other day at a fairly cheap price that was just too good to miss, although I already have an Alinco 2 meter rig, but it's purely for local FM traffic. So here was a chance to see what some SSB work on a VHF rig was like as I hadn't done much in all my years in the hobby!

Trio 700s complete with amp and pwr

But the first thing I really needed was a decent antenna, a Yagi or similar and a bit of power as 10 watts from the Trio might not get me too far. My old homebrew Yagi had long gone so I needed to build another and in the meantime my Brother in Law had given me an old 6 element job that needed a bit of a clean up but would certainly do for the moment. I managed to find a small amplifier off the web which gave me 50 watts of power and I began setting things up and experimenting.

It sure is quiet out there, maybe it was conditions but not a lot was happening, but through a bit of perseverance I knew I was receiving and transmitting on the local club net. But that 6 element Yagi was proving very direction and I was getting sick of the arm strong method running downstairs from my shack to where the antenna was placed, a rotator was required.

Have you seen the price of rotators lately?
It was a bit of a shock, I wanted something small and light like a TV rotator, but you try and find a new one in the UK, it seems they are out of favour. plenty of second hand ones on eBay, but going for more than the new ones used to be and they looked pretty worn out anyway!

Still at a loss I kept searching hoping that something would turn up and then out of the blue my brother in law who happened to be doing a deal with mate regarding a radio, was also selling a  Ham IV rotator for £60 and rang to let me know, so I bought it on his word!

The two Rotators and control boxes

I was lucky, it was in reasonable condition, even better it came with a spare that had a cracked collar and two control units, it just need the 8 core cable and it was complete.  The only downsize was I realised it might be a bit heavy for what I wanted, which was to mount on a scaffold pole up 25ft but I could work round that and if necessary place it in the attic with my new home brew smaller Yagi.

Testing the motor on a block of wood it was pretty sturdy and was not going to move all over the place and I decided after a bit of thought I would try it in my attic, height of the antenna might be a problem but I was living in a house at 800 ft above sea level and a 20 foot scaffolding pole might not make a lot of difference.

So I decided to carry on regardless and see what the outcome would be, after all I could always change if needed. I measured the 6 element beam and although at 3 meters it would just fit in the attic at a low position I decided to go ahead and re build a 3 element Yagi and store the 6 ele for another time.

The new 3 element homebrew Yagi has been built copying earlier specifications from my blog and I will do a separate note on how to build it. In the meantime  I've yet to place all the equipment up in the attic, but I intend to do this over the weekend, so updates will follow.

Friday, September 9, 2016

Revamping the Carolina Windom 80 Special

A couple of years ago I had played about with my old Carolina Windom 80 special  by reducing its size to the 40 Windom, but I soon realised when testing that the balun was individually set for a Carolina 80 special and so I had to revert back to its original size to make it work. The problem was I originally reduced the size because I didn’t have the length of land required for it to fit! So the Carolina 40 was put away in the shed until I could find time to re-build and figure out a way for it to fit in my garden!

The 40 I had made from the original Carolina Windom 80 special
The length of antenna issue had been sorted by having the good fortune to purchase a bit more land off the farmer, as it had come up for sale just at the right time, not just for an antenna farm I hasten to add, but for increasing the size of our plot with a mini paddock to do with what we liked and it just happened that a Carolina Windom 80 special happened to fit snugly in the paddock!

The forty being 66 feet in length (41ft and 25ft split), needed to revert back to the original size of 133 feet, 83 feet on one side and 50 feet the other. All I did was increase the length of each side by soldering new pieces of 42 stranded cable wire, nothing else was touched. Now I had to hope that the balun and transformer (1:1 balun) would still be working even though I had been messing about with them and 22 foot coax was now totally new!

I took my old fibre glass 20 foot slotted mast and I increased it in size by 10 feet with some specially strengthened plumbing tubing slotted together so that the 22 foot coax cabling with transformer would hang freely.
I re-measured the actual antenna wire lengths to confirm I now had 83 and 50 feet, did some simple soldering to the 4:1 balun to strengthen and stiffen it and hoisted up to 30 odd feet to do SWR tests, thinking that it probably wouldn’t work but I had some fun doing the build process.

Initial tests were quite good except with the 40 meter band were the average SWR was about 2.0 but even so I could just about use with a tuner.

80 MHz                 1.4 – 1.8 across the band

40 MHz                 1.8 – 2.0 across the band

20 MHz                 1.3 – 1.5 across the band

15 MHz                 1.4 – 1.6 across the band

10 MHz                 1.7 – 1.9 across the band             

Being pleasantly surprised by the outcome and comparing against the Cobweb and Hustler it’s not a bad antenna for a multi bander and of course it does state that you have to use with a good tuner.
Over the next few weeks I will try to make a few improvements here and there. But all things considered I’m quite pleased with my semi homebrew antenna!