Some really casual antenna building observations

[Pro-95]

First off I don't have any measurement equipment for antennas. But I've built a few antennas with the last two being directional and built from perfect free space designs. Which doesn't necessarily transfer well into the real world.

Now the J-poles I am still very happy with and they are mounted on the roof and connected via my homebuilt antenna switch, which also works to my satisfaction. When I built the J-poles I really knew nothing about antenna designs and charectoristics, now I'm much more dangerous.

So I tackled a Yagi-Uda and by luck (really) matched the antenna and coax to a pretty good match. I felt so confident in my building skills that I built a really long beam Yagi-Uda. I wasn't as "lucky" on the match with this one and still am adjusting the match via capacitors. It has however taught me a lot regarding tuning and hte critical nature of antennas.

I built a heliax antenna to suffice while I re-work the long beam antenna with a more solid mount and durable design. The heliax antenna was built after receiveing my antennas book from ARRL which has progressed my knowledge imensly. The results are a much better (apparent) match with some knowledge as opposed to just luck thrown in.

I get a charge out of seeing math in action. Trimming the overall lenght of the antenna changes the match point and with incremental trimming you can "watch" the match move up and back down the conductor. I know that with varying elements (length in a heliax) I am altering match but without measurement devices I can't see if it's true match or an inverse.

But nonetheless, it's pretty cool as you fine tune the match you can see a directional antenna become more true in direction, meaning that it will be more specific (directional variance from the beam) and point to the true location of the antenna it is receiving. When the match is out you can see a broader area of reception but also an apparent (again no measuring tools) loss in strength of the signal. What this means is that I can "see" the lobes as defined on the charts that describe antennas. And I just think that is so cool.

Just had to share.

If I get any free time tomorrow I'll snap some shots of the ray gun as Debbie calls it.

 

[N_Jay]

You next step is to buy a spectrum analyser with a tracking generator and a return loss bridge.

Then you will be able to both tune and match!

 

[loumaag]

You next step is to buy a spectrum analyser with a tracking generator and a return loss bridge.

Then you will be able to both tune and match!

In the spirit of Mike would rather build than buy, check out this site.

 

[Pro-95]

Where is the drooling smiley when you need it! You got that right on the build it over buy it, especially when my backside hurts near the wallet when looking at the pre-built units.

 

[BJ_NORTON]

Just a few thoughts on matching here.

I felt so confident in my building skills that I built a really long beam Yagi-Uda. I wasn't as "lucky" on the match with this one and still am adjusting the match via capacitors. It has however taught me a lot regarding tuning and the critical nature of antennas.

When I was working on a portable quad a year or so ago, I had somequestions about matching, and about spacing the elements.I was told the only element that had to be exact is the driven element, or the element you are connecting the coax to. The other elements just direct were the signal goes, but are not as critical to get right. If they get messed up, you may have a funky radiation pattern, but no harm to the radio.

Also, if I remember right, I think there is a section in the antenna book about Quagis. The guy who "invented" the Quagi had trouble tuning the antenna, but found that by using a loop (or in this case a square) for the reflector and the driven element,that it was easier to tune the antenna. The rest of the antenna has the regular elements. I think they also mentioned that at the higher frequencies (900mhz ham band) that the connectors they used had to be taken into account. Tolerences were mentioned in 1/8 inch increments too. Anyway, its something you might look into. The tuning problems may be why you see so many of the VHF/UHF guys and rover stations using loop antennas instead of the little stubs.