MORE ON 2 ELEMENT VERTICAL BEAMS

A few months ago, I decided to try out using a parasitic element on a tripod to convert the vertical on my car into a 2 element vertical beam (see http://www.ea5on.com/2012/05/welcome-back-after-6-year-delay-to-see.html)

The more recent tests have been using the vertical dipole, 2 element yagis, and 4 element yagis, also reported on this blog.

At my current location in the port, it seems like development is afoot and shortly I may have to find myself a new spot to operate from since they are planning to build a boatyard where I usually operate from. So. before that happens, I wanted to try to operate a contest from there to see how I got on with the beams. I had thought about CQWW CW but my CW is still quite poor, so, since all the antenna trials are on 10m, why not the ARRL 10m contest?

The recent tests indicated that perhaps on some paths, propagation might not always be coming in on the expected path, and that either an omnidirectional, or perhaps better, a rotatable antenna, would be desirable in order to both check the differences, and of course work more stations in the contest! My idea is to try QRP, so every little extra dB counts.

One idea which is under way is to build a simple rotary 2 element yagi using the 6m mast I used for the quad in CQWPX, and making the vertical elements out of telescoping whips. Watch this space!

In the meantime I decided to take a leaf out of the CBers books and try to make a beam on top of the car. If it was to work, it might be a cheap and cheerful way to get some gain and easy directivity without a complicated setup.

I measured the distance from the back ball mount to a point on the roof where I could mount another vertical reasonably straight, it measures just short of a metre and a half, acceptable for 10m. I put the magmount on, measured another vertical a few inches shorter (this time using a 3 foot mast and a 4 and a half foot telescopic whip) and installed this director element on the magmount. SWR was lowered a bit, as expected.

On-the-air tests yesterday with stations in Ukraine, Canada, and the USA, indicated a more or less expected front to side pattern of between one and 4 s units, depending on the station. However since this depends on propagation and QSB (fading), and there was no reference antenna, plus I wasn't in a great place for 360º testing, I wanted to do more on-air tests.

Here's what it looks like set up:

When is an omnidirectional not an omnidirectional?

The answer is, when it's on a car.

This afternoon I made a sked with Victor EA5KV to do a local test with no QSB. Before doing anything else, I wanted to test the single vertical I normally use, to see if it made any difference depending on where the car was looking. I went to a location close by to my normal spot but where I was able to drive around in circles without any problems.

Conventional wisdom says that the best place to put an antenna on your car is in the centre of the roof. If you put it at the back or front, it will radiate better over the area of metal. That is to say, in my case where the antenna is mounted in the centre of the rear, there should be a stronger signal forward over the car roof.

The first noticeable thing was that there was a big difference while driving around in a 360º cicle, including a big null where Vic lost me completely, we hadn't expected there to be a big difference.

The second thing, which we noticed after getting the compass out to confirm, is that the antenna radiated the strongest signal at approx 70º left of forward, and the null was 180º from that. We checked this three times to make sure it was correct. I can think of no reason why it should be that way. Strongest signal was S7.

Having done the single element test we tried the 2 element, and this gave more of a text book result. About 1 S unit of gain above the single element at its strongest, but the direction was correct. Front to side and back were quite noticeable. I wanted to try FM for better S unit reading but Vic has a fixed roofing filter in his FT-1000 which is too narrow for FM use.

I wanted to continue tests against the 2 element vertical yagi on the fishing rods but the rain started getting very heavy and we had to abandon for today.

More crazyness will follow when the sun comes out!