Antennas, Home Brew

Antennas, Home Brew

Postby aa1a » Sat Aug 31, 2002 7:38 am

Antenna designs

IMO antennas are the most interesting aspect of stumbling. Started hamming in the early 50s and probably have used em all by now. For 2.4gc. the spiral helix is great and even a short one is good for illuminating a dish from 1 to 10+ feet as it gets real louder.
Has anyone applied to FCC for certification of their antennas?

The pringles feed or 'polarplexer' as it was known in the 60s is a great portable, directional, easily rotated for V-pol vs. H-pol. and gets real killer if your were to couple into a folded aluminized cardboard box of the right 'horn' dimensions for DX, say out of your van on a high hill...

I am a refugee from 10ghz. ham radio where 300 miles on a 1' dish can be done, unlimited BW, but hams are a dying breed and mostly use cell phones now besides you guys are having more fun.

73s de Dave - AA1A - FN42pb - where wireless really took off in 1906 with the world's first radio voice broadcast and many inventions including antennas...
http://www.radiocom.net/Fessenden



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Postby ted » Sat Aug 31, 2002 8:19 am

Hi, and welcome!

I feel good seeing one with long history of antenna construction! I am myself relatively new here, and I have never been a ham. However, I have had interest in antennas for most of my life, and 2.4GHz has some interesting challences: Wavelength is a bit short/ frequency high to make it trivial to make direct downscalng of many constructs good for RF-VHF. Maybe the antennas like yagi are pretty neat and easy to make, but the matching of feed is more tricky due to tiny dimensions and thus greater accuracy needed. And all the secondary phenomens have bigger impact.

Because you have been on 10GHz you know the "other end" where "real microwaves" exist. I have myself seen and also somewhat tried simple microwave antennas for WiFi -- for example built a waveguide "cantenna" and plan soon to test bi-quad (which is, of course, actually also a typical VHF/UHF construction). But for travelling use, I have been thinking of tiny yagi, which may have easily quite impressive gain, and which would pack flat in a suitcase. Much neater and with better form-factor than a waveguide antenna, or a bi-quad or a dipole array. It would be also be possible to explain to (and be innocent enough for) airport security (no place to hide explosives there). But matching to 50 ohm coax needs a balun, and without instruments it would be hard to verify and tune. So I have not strated the project yet. What is your opinion about the matching issue?
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Postby aa1a » Sat Aug 31, 2002 10:20 am

Hi Ted,

Am new to stumbling and just now received Fed-X from FAB with all the goods to get started...

I have a 'hole' here in the spectrum as far as test gear and sig gen., power meter, etc. but am looking through the surplus houses for some. A simple ham type down converter will do for the AVCOM spectrum analysis, Some reworked sig gen and test gear can be built up as well. I am looking forward to seeing the stumbler program working and to see if a 'signal strength' meter is part of the package to judge relative gain.

Am having many ideas as to innovations and improvements and will post them here as they happen.

As far as the 50 ohm termination goes, at these frequencies you shoot for a target then usually spend some time 'bending' and 'pruning' with the help of a VSWR meter.... A simple low per version should be possible to build for a few bux...

Here are some good sources for learning antenna fundamentals and construction. The 2304mhz. ham band and the 2400mhz AO-40 ( amateur satellite ) band articles are worth a look.
Try http://www.arrl.org to see where they come from...

ARRL Antenna Handbook
RSGB Microwave Handbook series ( Radio Society Great Britain )
ARRL UHF/Microwave Experimenters Manual
ARRL Proceedings of Microwave handbook
ARRL UHF/Microwave Projects Manual

Right now am hoisting a grid antenna up on the tower with bi-directional amp. all store bought and out of the box.

Next antenna to try for getting out of ones back yard is a 5db omni with bi-directional amp all mounted in a PVC cannister and hoisted up into the high pine trees with the aid of a compound bow and counterweight.

This stumbling is getting the juices flowing once again...

73s from Dave

*Here is a thread on a local bbs that shows some basic ham type wireless. One is on 144 mhz. which is too low for us and some laser work which is too high... Now to 'focus' on 2.4 ghz.

http://www.marshfield.net/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=next_topic;f=3;t=000107;go=newer

http://www.radiocom.net/EME.htm
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