4 replies to this topic

[dalbert02]

At work we have a 'junk box' of what most people consider useless parts. I went rummaging through it today and found a Peak Antennas CO-1925-4.5 antenna. A quick look on thier website reveals it is an older version of the CO-225-4.5 with a reported bandwidth of 1.98GHz to 2.5Ghz. http://www.peakantennas.com/ I thought that must be some pretty exagerated specs as that is over 500Mhz of bandwidth and most of the antennas I make are only good for a few tens of megahertz. Well, it just so happens we have a new toy at work, an Anritsu Site Master Antenna Analyzer http://www.us.anrits...r...spx?&ID=595. I hooked it up and did a sweep from 2.0Ghz to 2.5Ghz and guess what? The SWR went from a low of 1.0 to max of 1.4! I thought for sure Peak was exagerating but it looks like this antenna is pretty wide band after all. I decided to take my new found 'junk' antenna apart and see what voodoo magic was inside. It certainly is not just a length of wire, that is for sure! The base is machined aluminum with an Amphenol 'N' connector. The radome is good quality fiber glass with an aluminum top. Attached are pics of the inside. Very unusual in my opinion. A series of cones and cylinders where the ground and conductor alternate. Very interesting.
-dave

[Mr.RC-Cam]

That must be "fun" to manufacture.

If the signal and grounds are alternating on each element, then it's a collinear or variant of that theme. Is it sort of arranged like this? http://www.rason.org...ant/collant.htm

Don't get too excited by the flat SWR. Sometimes such things yield a wide variance of RF gain and a beam pattern that depends on the operating frequency being used. Ultra wide bandwidth is convenient when you need it though.

[dalbert02]

That must be "fun" to manufacture.

If the signal and grounds are alternating on each element, then it's a collinear or variant of that theme. Is it sort of arranged like this? http://www.rason.org...ant/collant.htm

Don't get too excited by the flat SWR. Sometimes such things yield a wide variance of RF gain and a beam pattern that depends on the operating frequency being used. Ultra wide bandwidth is convenient when you need it though.

Yes, it is very similar to the link you have. So would this be a bad choice for recieve only purposes such as FPV? I have taken some HyperLink antennas apart and they are basically just a straight wire for a few cm then coiled like a spring for a few cm and then back to just being a straight wire.

-dave

[Mr.RC-Cam]

The ideal way to know for sure would be to get a data sheet for the antenna and look at the RF pattern and gain for your exact operating frequency. Then decide if you like what they claim. Next best is to just try it.

[W3FJW-Ron]

We use Collinears like these at 2 meters and 70 cm. for base and repeater antennas. they work very well giving good gain figures. However at 2.4gc it is very critical on matching each section to the other and RG58 just won't cut it. Too lossy and too unwieldy at SHF (?) frequencies. At 2.4gc a half wavelength is ~ 2 inches long and 1/32" can make a large difference in mismatch and skewing the radiation pattern, neither of which is good.
The most economical commercial (or homebuilt) antenna for receivers that I've been able to ascertain is still a patch antenna(s) even with their directional properties, and a 1/4 wave vertical for the TXs and/or airborne receivers. Personally (so far) I wouldn't consider wasting my money on unknown (to me or my circle of friends), antennas no matter what the mfgr claims. After over 50 years being a ham and home brewing all kinds of antennas. I feel I have some knowlege on the subject.
If you're determined to achieve long range with minimal wifi interference, use an auto-tracking dish. With good weather and a good dish you'll reach out to 30 miles or better with at least a 100mw TX on the plane.

Now there's a good project. Design and build an auto tracking system which would even work with patch antennas.

On another note, Wide bandwidth is a characteristic of antennas (except for the most part, dishes) used at 144mc and above. The higher the frequency, for all practical purposes, the wider the bandwidth.

Edited by W3FJW-Ron, 18 August 2008 - 04:20 PM.