Antenna questions

Thread Starter

qbert55ca

Joined Aug 19, 2008
11
Well, for such a contraption to work decently, the base station (your control box) would not only have to know it's GPS position, but also it's orientation (which direction it is facing) fairly accurately; within a few degrees.

If the A/C were within a certain distance (say, 100 yards) you'd want to switch to an omnidirectional antenna, as otherwise the antenna may lag behind the A/C's current position.

Sure would be easier to just have the antenna mounted on your control box :D
OK, on start up just point the GPS antenna that is sitting beside the plane to due North. That way it now has a directional refeerance and a gps pin point ont the ground.

Ya, I was actually thinking about switvching to the omni about 2 or 3 Km out the Omni is good for more than that.

About one of your other posts. I am well aware that there is a high load of 900mhz traffic aound my area but for some reason I have not had any problem. One the plane and the base station get a lock on each other I have had it out to 5 km with out lose of signal.

The IP guys around here use 911 and 915 for the tower transmitters and North of me the oil companies go nutz with 900mhz transmitters from the oil and gas wells back to the control station. The only thing that I can think of is that we use a Spread Spectrum 1 watt modem and these other guys are using less than 1 watt ISM radios on specific channels. We do know that if I get to close to houses with wireless internet we can interupt their signals.

Robert
 

Thread Starter

qbert55ca

Joined Aug 19, 2008
11
But, such a thing would be rather difficult for a hobbyist to put together, even if they were pretty well-versed in electronics - and our OP has stated that they have neither the experience nor the focus to acquire the knowledge necessary. So, it's rather pointless to persue such an avenue.
Your right there Sarge. But just the info that you guys have passed on is giving me ideas like this one.

I may not have the technical ability to put this together but I'll be I can find some one who could if it's feasible.

You said sarge that you could tie antennas together. OK, what about this.

Since I only need about a 120 degree sweep at over 5km and I can use the omni close in, what about just tying two or three directional antenna's together at an offset angle to encompass that 120 degrees. Ya I know I need to get the antennas to play nice with each other but I'll leave that to the techs. Would something like this work. I've see this with omni's on some of the newer modems but not with directionals.
 

SgtWookie

Joined Jul 17, 2007
22,230
No, I didn't say that you could tie antennas together.
I basically said switch between a directional antenna and an omnidirectional antenna.

Well, it's zero-dark-thirty, and I'm on the trailing edge of a hurricane, so I'm signing off for the evening. Basically looked in here to see if the computer still works after we lost power for a bit.
 

SgtWookie

Joined Jul 17, 2007
22,230
Since I only need about a 120 degree sweep at over 5km and I can use the omni close in, what about just tying two or three directional antenna's together at an offset angle to encompass that 120 degrees. Ya I know I need to get the antennas to play nice with each other but I'll leave that to the techs. Would something like this work. I've see this with omni's on some of the newer modems but not with directionals.
OK, if you did couple several directional antennas together, you would divide the power between them. It's not quite that simple though.

With an omnidirectional antenna, the radiation/reception pattern looks pretty much like a circle; it's pretty even all around.

With a simple directional antenna, the radiation pattern looks more like a skinny '8', with the antenna at the center. The main lobe extends on both sides of the antenna. The more directional the antenna is, the more narrow and tall the '8' is.

A simple example of a moderately directional antenna would be a matched pair of vertical antennas that were 1/4 wavelength of the transmitted frequency. You may have noticed this kind of antenna configuration on 18-wheel trucks roaming the highways. The length of coaxial cable from the tranceiver to the base of each antenna is identical in order to obtain the most centered lobe. This configuration gives the truck driver considerably more range to the front and rear than those using single antennas.

Basically (and within limits) the closer together the antennas are, the more omnidirectional the antenna array becomes (the '8' gets shorter and fatter until it becomes a circle); the further apart, the more directional. However, the longer a coaxial cable is, the more power is lost.
 

Thread Starter

qbert55ca

Joined Aug 19, 2008
11
You may have noticed this kind of antenna configuration on 18-wheel trucks roaming the highways. The length of coaxial cable from the tranceiver to the base of each antenna is identical in order to obtain the most centered lobe. This configuration gives the truck driver considerably more range to the front and rear than those using single antennas.
Hey Sarge..

Although you did not come up with the answer, you sure gave me information that although it will not do exactly as I wanted it will be close enough. We are going to use the Omni close in, say within 2 or 3 Km and switch a directional antenna. We won't get quite the distance of the Roo but we get a full 120 degrree signal sweep. which is 3 times the Roo. There is no way that the 120 degrees will not cover the down range area we need to.

Additionaly, we are going to set the antenna up on a pan and tilt system with an SWR meter and if we need to fine tune it to get a better signal, we can do it that way.

Thanks for all you help and ideas.

I'll send you a PM with how it turns out.

Robert
 
Last edited:

RAH1379

Joined Dec 13, 2005
69
SgtWookie [URL said:
http://www.tpub.com/content/neets/index.htm[/URL]



It's a very good series, and you can't beat the price.
Thanks SgtWookie for the cool site, it looks very interesting so i saved it for future study.
 
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