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Base Station - antenna help needed!

A

aussieausbourne

Member
Nov 6, 2008
2
0
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Hey all

We have a Galaxy DX 2547 base station in our office and a PT99 antenna mounted on the rooftop of our office building. At the moment we have no TX/RX signal except at close range (ie a car parked next to our office block - we have just set up a new taxi service here in Ulaanbaatar, Mongolia).

I was wondering if the main problem might be the fact that we have almost 20 meters of RG58 coax running from the base station, out of the office and up onto the rooftop? Or maybe the PT99 needs to be mounted higher off the rooftop? It is possible to move the location of the antenna closer by around 8 meters or so - we have it where it where it is due to a convenient mounting. There is no coiling of the coax cable.

We are in urgent need of a solution - without it we cant communicate with our drivers.

Any help anyone can provide would be much appreciated!
Cheers
Sam
 

Sam,
That RG-58 might be part of the problem, it is kind of lossy. But I really doubt if it's 'all' of the problem. First question that comes to mind (since I have no idea what a 'PT99' is), is the antenna made for this band, and has it been adjusted/tuned to work there?
A couple of things to try to see if you can localize the 'problem' is to temporarily get the radio and antenna closer together, shorten that feed line by half or more. (checks the feed line)
Another question, can the vehicles talk to each other fairly well when separated sort of widely? (checks the base radio)
Any changes/improvements in either case?
These are just very rough checks to try, certainly doesn't tell you what the exact problem is, just gives you an idea where to look for it.
Have fun...
- 'Doc

(Coiling the coax very seldom does any electrical harm at all. If doing that coiling makes any appreciable difference in things it's because you have a problem with the whole system anyway, or the stuff is being coiled too tightly (mechanical problem).)
 
Okay

The Galaxy base station has a SWR meter built in. Having just had a look at firestik.com I have a hint that the antenna may be 'Short" - chan 1 SWR is 1.4 and chan 40 is 1.2 - I'm no expert at this stuff but I'm assuming that i should raise the height of the antenna and also shorten the length of the coax...

Unfortunately this being Mongolia the chances of locating a proper SWR meter are next to none - it's a challenge trying to find peanut butter here let alone specific test equipment!

One other thing i'm unsure about is this: the Proton PT99 is a 'no ground plane' system? What we have is the base station connected to the PT99 which is mounted on PVC piping on the rooftop with only coax connecting them both. I had the whole package delivered from the United States from a CB equipment dealer so I assume these 2 units should work well together.

Maybe the best solution is to relocate the antenna which will shorten the coax length considerably? The antenna is on top of a 4-storey building. There are some other high rises around but Ulaanbaatar is generally a very low-rise town. I don't really know if that is a contributing factor here.

BTW thanx a million for the fast feedback! I found this site out of desperation and am glad to be a member!

Cheers mates
Sam
 
Sam,
Going only by the SWR you reported, leave the antenna alone, don't try adjusting it's length. Contrary to popular opinion, anything less than about 1.5:1 SWR is just fine.
I think I'd still try getting the feed line a bit shorter (half or less, sort of?). Taking the radio to the roof for a test, if possible, would be a quick-n-dirty way to see if all that coax is a problem.
I think I'd be looking at other things though. Not sure what, but I sort of doubt if the antenna/feed line would be causing all of what's happening.
Sometimes it's the 'little' things. Are you sure everybody is on the correct channel, and that the squelch isn't up too high? Sort of dumb questions, and naturally I've never done that sort of thingy (and promise never to do it again)!
- 'Doc
 
It takes Two to Tango !

So far I have read only about one end of this duo...

Could the problem be on the taxi end ??

Getting a mobil set up without any test equiptment at all seems
to me to be more suspect than the other.

For any distance other than across the street they need to be dead on.

Can two taxis talk to each other miles apart ?


Regards,
John___ KD5WJY
 
Sam - forget the peanut butter, mate. How's the vegemite supply??(y)

Okay - on top of a 4-story building should be good. There will be about 20% of your power lost in the RG-58 (20 meters, assuming 27 MHz and an SWR of 1.3:1) according to my handy online calculator.

Dealer's asked a very good question. How well do the cabs hear each other, and how well do you hear them?

I used to work with some blokes from the RAN. Great group!
 

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