sábado, 10 de octubre de 2009

Some GP antenna and Pictures

Hi Harry¡¡¡

This is Pedro again...

Let's see if this way is a good one to keep in touch, I will send to you and e-mail when i have any comment. You only have to put on web browser http://antennacourse.blogspot.com and you will see the blog. Please answer yes when you receive an invitation to join, so, you can answer here.That way we can have several posts on several topics.I hope this solves the problem with e-mail and windows version. :-)

I enclose to you some pictures from Gp antennas, i have built.

This one shows a gp antenna for uhf i built several years ago, this time it has a classical approach, I mean element and radials are made from copper wire, soldered with solder wire and flux. Performance is below 1.3:1 for entire band (430 - 440 MHz), as you can see, central element is over tinned (that time i was not very good on solder skills) hi hi

As good points on this approach I would underline that it is robust, perfect electrical union, very good performance, and very simple, on the bad side I would say that it is difficult to store, and that if you want to experiment you have to build another one.

This pictures shows the new approach I have used for this antenna, (i have built it for the course), I also used an so239, but no tin, no solder for this antenna. Metallic pieces were cannibalized from a electrical connections clamps, I ripped off the insulating plastic and got the metallic parts and screws. It is perfect as the screws fit perfect on the so239's holes, as you can see on the picture.

This image shows the so-234 ready to accept the wires, just need to put the wires and screw it.

A close view of a 4 radials version, wires are aluminum recovered from some retail electrical works close to my house... it is good and cheap (the hardest is to separate the wires from the jacket, as far as the cable was 2,5 inch size).

A view of four radials version finished on the firs picture (second plane), you can see another view of this antenna.

Why I did this?, just because i like to experiment, so with just a so239, i can built many antennas, the other point is for better transportation, my idea is to create 2 sets of wires (vhf and uhf), and to store them inside a pvc pipe, with 2 m. of rg50 coaxial, and a
screwdriver, so in less a minute i can have a good antenna for sporadic operation.

On the good side: simple, extremely simple, just an screwdriver, a wire cutter and a metric tape, to have an almost free but good performance antenna. As mentioned before, transportation is also a good point, and that is easy to have several for several bands.

On the cons: I think that this antenna should be just for occasional use as far as elements are not soldered, so, may be, corrosion could affect on a long time exposed to elements. I would use this antenna, as said, to have it on the trunk, just for light use.

In the building of this antenna i took an experiment, I wanted to compare a 4 radial with 2 radials as the book suggest.

This is the result:

Freque. 2 rad 4 radials swr
430,000 1.2:1 1.1:1
431,000 1.2:1 1.1:1
432,000 1.2:1 1.1:1
433,000 1.1:1 1.1:1
434,000 1.1:1 1.1:1
435,000 1.1:1 1.1:1
436,000 1.1:1 1.1:1
437,000 1.1:1 1.1:1
438,000 1.1:1 1.1:1
439,000 1.1:1 1.0:1
439,975 1.1:1 1.0:1

So conclusion is that, concerning to swr, it does not affect, to use 2 or 4 radials, so a 2 radials could be simpler, you can see a very small difference in favor of 4 radials antenna, but it is so small, that i would consider it not significant.

This is on the swr point of view, but what about radiation plot?

Could be that 2 radials would show some kind of lobe just like a dipole?

If you think i should take any other activity relating to this lesson,just let me know.

Thanks in advance.