Thursday, December 29, 2016

17M Moxon Antenna

Over the Christmas break I had another go at building a Moxon antenna. This time not the 10m but a 17m which is a little bit bigger!
I'd had wanted the 20m but I felt it was going to be too big even in the new paddock so I settled on the 17.

Details of the build can be seen on my Moxon page, but below is a taste of the completed build on the twenty foot fibre glass mast, I've just got to mount it on the 35ft aluminium mast with a rotator at some stage. But all the testing is pretty well complete.

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.

Wednesday, December 7, 2016

Building a Delta Loop for 20 Meters

So far within my new paddock  I have installed my top band antenna, (which seems to work very well). However, I'm getting itchy feet to try another antenna. The one I've always wanted to try is a Delta Loop antenna, specifically for 20 meters.

The one advantage I have here is that my take off points around the house are pretty good especially towards Australia and opposite towards the Americas. I'm fairly high up at about 700 feet above sea level with no major obstacles apart from the odd tree dotted around the garden and they say from the Cotswolds east towards Russia the next high ground you hit are the Urals which are well over a thousand miles away, so you can see my take off points are pretty exceptional.

Reading the reports about the Delta Loop, they are a quiet on receive and with vertically polarized loops good on low angle radiation so I reckon they would work well around here for some serious dxing. I thought about which band I would set it up for and came to the decision of 20 meters simple because there would be a high amount of activity both in the Americas and Australia so I should have no problem with contacts especially in the part of the low activity cycle.

I'd like to use Plan D with the apex at the corner, to maximise a good low angle of take off. I have a spare 30 foot telescopic mast which I can lengthen a further 10 feet should I require it and tying off the bottom corners should not be a problem

Calculations for the antenna are fairly simple, to determine the length of wire needed for the desired band you simply divide the resonant frequency in Mhz into 1005 and because the impedance is normally 90 to 120 Ohms you can either use a quarter wave length of 75 ohm coax to match or a 4:1 balun (which I will be using). You need to have a triangular shape (or near as) for it to work properly and of course an ATU will be required. Better to cut slightly longer and use a good SWR analyser to tune the wire to your desired frequency.

I've had to order some more wire , but so far that's been the only expense. So hopefully this will work out as a fairly cheap project. More updates to follow!

Friday, December 2, 2016

Learning/Practising Morse Code

I received an interesting email the other day from a CW fan called Gerry. Back in the 60s he'd been in the Royal Navy serving as a Leading Radio Operator so was obviously proficient in the use of CW. His last live transmission on air was back in 1968 , he didn't become an amateur radio operator and stayed fairly quiet until about four years ago where he came across MorsePower/CW.Com.

He now uses it daily and has become very proficient at CW once again. He wrote to me to advertise and to say even if you are not licenced you can still chat in CW via the internet and of course it's an excellent way to learn Morse Code without the pressure of being on air so to speak!

You can send and receive  at your pace and have fun in the process. For my particular CW it's excellent because I can go at my speed and I can practise receiving without any pressure I always feel when transmitting on air (this is entirely down to my head and the stroke I had back in 2015!)
If you need to practise why not give it a try and see what you think .