Monday, December 12, 2016

Results From 20M The Delta Loop & Learning About 4:1 Baluns

I completed the building of the 20m Delta Loop antenna over the weekend. The components I needed arrived on the Friday, so it was just a case of picking out some time Friday afternoon and Saturday morning to complete.

In the end I used 42 stranded speaker cable for the wire, the 4:1 balun is a temporary one I purchased off eBay for the princely sum of £19. I put it on the MFJ 259 to test and it was OK and it's recommended maximum power is 200w coverage. (I come back to that later in the post).

A bit of a mess of wires, but you can make out the basic triangle with my 6 meter experiment and the hustler in the background!

Measuring off 71.4 ft (for 14.060 the cw portion) of wire, the raised triangle was smaller than I had originally thought. The 4:1 balun was fed at the bottom left corner as recommended for DX. The only tricky bit was actually the raising of the antenna, but that was quickly sorted.

The commercial balun which I will replace with my homebrew at a later stage

Testing and reports so far has been good. Measuring the SWR I get a good 1:1 through to 14.200 where it rises to 1:2 up to 14.300. Only a few contacts so far but they have been good with 5/7 and 5/9 reports and the background noise is so quiet compared to my cobweb.

Coming back to the 4:1 Balun, I'm not too happy with buying one. I'd rather learn about them and build my own, simply because it's a big part of the hobby if your building antennas, obviously it's cheaper to build your own and you have peace of mind that it has been tested and built by you!

Having never built one before I've been looking at the Web to see what designs  are about and I have ordered the parts to have a go at building a high powered Guanella Balun. These are x2 FT 240-31 toroids and some 15 A automotive /speaker wire and a small box to house. I have all other bits in my junk box so that shouldn't be a problem. This should be enough for a reasonable power and should cover more than the UK legal limit.

A typical example of a Guanella balun

The interesting thing when you start learning about Baluns is that you are opening up a wealth of different information which can be quite tricky to understand. To this end I'm actually feeling good about learning a new part of the hobby!

As an update I completed the 4:1 balun. The Toroid's were bigger than I had expected but the actual winding was fairly easy and my impatience got the better of me as my box for containing the balun hadn't arrived due, no doubt to Xmas post, so I used an old butter dish as a container instead which worked reasonable well but was slightly too big!

Anyhow, I did some testing and the SWR was slightly low peaking at 1:2 at 13.600 Mhz. This after research was because my toroid leads were too long (the size of the butter dish). So waiting for the proper container to arrive I trimmed the wires and all seemed much better.

Morale of the story don't be so impatient!!

Finally the container arrived and I fitted the balun. Did some more testing and the SWR looked good , 1:2 spot on the QRP at 14.060. Later that day I did a test transmission on 14.060 and I got a Spanish station who gave me a 589 at 5 watts.

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