Batboard

This is more a question out of academic curiosity, so don't think I'm going to go try setting this up tomorrow on a public safety system or anything...

Cell towers typically have three "sides," each with a fairly directional antenna, presumably nice and high-gain. By comparison, almost every repeater I've ever seen uses a single omni.

Has anyone ever set a system up "cell-style," with a few fairly wide beams spread out to cover 360 degrees? Does it work as well as it seems like it could, or does the gain end up not being much better than a high-gain omni? And how would receive be implemented -- do you end up running a voter for each antenna?

Besides the chance of great range, I think the neat thing here is the potential for triangulation--if I can figure out what side of the tower you're coming in on, and you're detected at multiple sites, I should be able to triangulate where you're transmitting from.

Does this sort of thing actually work?

fogster wrote:Besides the chance of great range, I think the neat thing here is the potential for triangulation--if I can figure out what side of the tower you're coming in on, and you're detected at multiple sites, I should be able to triangulate where you're transmitting from.

Does this sort of thing actually work?

Of course that would work...

Can you actually deal with the interference and gain of the necessary directional antennas though.

It wouldn't be worth the effort. Would it?

Actually, one of the repeaters I maintain W0SOE/82 uses a dual antenna setup.

Let's address the issues in order.

First, you either have to have a separate receiver for each antenna (like a cell tower) or a power combiner, which is a narrow-band device (it's a quarter wavelength stub transforming 50 ohms to (25|16.7) ohms, which then feeds the (2|3) 50 ohm antennas in parallel).

If you are running multiple receivers, then, well, you have to have multiple receivers, a voter, multiple feed lines, multiple grounding devices - in other words, more to go wrong.

If you are running one receiver and a power combiner, you can save on the feed lines, but you now have one more thing up on the tower to go wrong (we've lost 2 combiners because the tower climbers didn't properly secure them to the tower and they were destroyed by ice falling on them.)

Second of all, you won't be able to do triangulation unless you are feeding each antenna into its own receiver.

Yes, you will pick up gain relative to one antenna. You will also help reduce the null caused by the tower itself.

Cell sites run multiple antennas not so much for sensitivity but for capacity: each sector of a tower can, to an extent, reuse the same frequencies as other sectors.

Terry_Glover wrote:Can you actually deal with the interference and gain of the necessary directional antennas though.

It wouldn't be worth the effort. Would it?

I guess I didn't phrase my question that well... Your question is more what I was getting at -- I had the idea kicking around in my head, but wondered whether anyone actually did this for one reason or another, and whether it was worth the trouble, or whether it was just putting up lots of antennas for no real benefit.

An added problem, I suppose, is that high-gain beams tend to have narrow beam widths... 60 degrees is common, meaning that, rather than my mental image of mounting three corner reflectors or the like on a tower, we'd need six antennas... And now it's sounding like an awful hassle.

I guess what I really meant to ask: does anyone actually do this? Is it ever worthwhile?

Having spent almost 20 years in the cellular field, I can understand where your trying to go with this. The problem
is that public safety trunking systems or plain conventional systems are not set up for sector operation. Without
this feature, it is almost impossible to be able to obtain any directional information without adding very expensive
equipment to the site. It also requires that multiple antennas, feedlines and receivers be installed.

In cellular systems, many sites put the control channel onto the sectored antennas also. This needs to be done
carefully as the signal phase becomes important. I have seen one engineer try doing this with total disregard
to the coax cable lengths going to the sectored TX control channel antennas. If all the control channel coax cables
are not the exactly the same length, you end up with phasing differences between the sectors that can cause all
sorts of strange problems. This is of course dependent on your having a single source and split the feed to the
different sector TX antennas the same. In the installs I am talking about, the techs used what ever cable length
that fit the need. No attempt was made to make the total feedlines electrically the same.

Anyway, you should be seeing the light of this type of antenna system and how it will or will not work in a
public safety system. Cost is the big factor and generally no one will want to spend the funds required to
make a system like this play. It seems that the normal choice would be to just go with a high gain or medium
gain omni antenna and be done.

Jim

fogster wrote:

Terry_Glover wrote:Can you actually deal with the interference and gain of the necessary directional antennas though.

It wouldn't be worth the effort. Would it?

I guess I didn't phrase my question that well... Your question is more what I was getting at -- I had the idea kicking around in my head, but wondered whether anyone actually did this for one reason or another, and whether it was worth the trouble, or whether it was just putting up lots of antennas for no real benefit.

An added problem, I suppose, is that high-gain beams tend to have narrow beam widths... 60 degrees is common, meaning that, rather than my mental image of mounting three corner reflectors or the like on a tower, we'd need six antennas... And now it's sounding like an awful hassle.

I guess what I really meant to ask: does anyone actually do this? Is it ever worthwhile?

We did this on the clock tower of a hundred year old courthouse because we had to use the windows on three sides.

We had been on the roof with an omni but when the roof was redone they had us take it down and didnt want it back up there.

We used 3 element yagis out the windows and a power divider. Not my first choice but it seems to work.

Not panel antennas but could have been.

In the picture you can barely see the windows below the clock...

That's quite a scenic place!

Has it given you an improvement over the omni at all, or is it about the same (or worse due to the power division)?

Its about the same This site is at the north end of the county so no north facing antenna was needed. Power is directed in three directions now.

We took out probably 50 feet of 1/2 inch heliax and the antenna was probably 35 years old or so.

We took a lot of loss out of the system but lost a little elevation and have a few more connectors.

Its working for them though.

Just to add- although we're not set up to triangulate, one could go to the power splitter and look at each of the antenna's manually and look at the signal strength of an interfering signal if it hung around long enough...