Batboard

Hi Everyone,

I am looking for some information about renting tower space for a GMRS repeater. I currently have a GR1225 repeater connected to a 6.6 DB gain antenna. The problem is the system does not work very well. I cannot talk to the repeater outside of 1 - 2 mile radius unless I am on top of another hill. This apparently is due to location as we are surrounded by several hills, and also the elevation of the antenna is not very high. I have it about 25 feet in the air but I do not believe that is enough. My question is how I go about finding information about renting tower space on someone else’s tower. Any information or assistance is greatly appreciated! Thank you!

-Bob

if you can find a tower you want to co-locate on, you can get the tower registry number off the placard that is required to be on the out side, plug that ID into the FCC website, and find out who the registered contact is for that facility.

For another thing, a gain antenna when you're in a hilly area is akin to pissing into the wind. Gain antennas merely flatten the RF out, and of course when you're at the bottom of a gulch or a valley you are not doing yourself any favors by flattening the RF right into dirt (RF does not travel well through dirt!).

Getting rid of the gain antenna may help out more than you expect. So might raising your antenna another 25 feet (if possible). Then again, maybe it won't. Without doing a site survey, there is no possible way to know the dynamics of the site, and there are too many variables that affect propagation that you may not even realize exist.

The cost of renting tower space and floor space for your rack will vary. Here in Los Angeles, a rack at a populated mountaintop and a decent spot for your antenna can easily run $1000/month or more. There is no way to say what a "good" price is for your area until you've done some comparison shopping.

I don't know where you live, but like anything else in the world, it's all about supply and demand. If there are many good hilltops in your area with infrastructure ready to go, and not many customers renting space, then you will probably do OK. Few sites and lots of customers can signal a need to get your pocketbook out.

I would still think you would get 1-2 miles of coverage at your current loaction.

What are you using for a duplexer / feedline?

Are you not hearing the repeater at that distance or is the repeater not hearing you?

if the tip of your antennae is 25 feet in the air you should be getting alot more than 2 miles, you can get 2 miles just direct portable to portable. i'd do some looking around and find the problem with what you have now. is it possible the power is turned down on the repeater or as somebody mentioned earlier, is your duplexer tuned right?

Thank you everyone for your input.

I am not sure I want to pay $1000.00/month for a tower :-/ But I will do some looking around. I fear however this might not be a viable option anymore

HLA/VE3NSV,

I asked myself the same questions you are when I started this and found the performance of the system was very lacking. I am using RG8/U feed line traveling approx 30 feet. As far as the duplexer I knew at one time exactly what model it was but I honestly forgot. I believe it is a knotch type duplexer. It is internal to the repeater. I had the repeater looked at by a service tech. and he stated that it was operating fine. He stated it "was more sensitive than he thought it would be with a duplexer." So apparently the repeater is not the problem but I am still not too sure.
So my next question is what options do I have to boost the performance of this system if I can’t find any good sites that I can actually afford? What else can I do to make sure my system isn’t actually the problem? As always I do appreciate your help. It does help me a lot. Thank you. =)

-Bob

put a meter on it and see how much output you are getting.

You're asking the wrong questions... seriously.. a gain antenna at the bottom of a valley?

USSZulu2 wrote:I am using RG8/U feed line traveling approx 30 feet.

There's a major part of your problem. Get rid of that lossy cable and get some 1/2" Heliax. I had a repeater with an antenna at about 25 feet and I got a least a 7 miles away from it before it started crapping out. It would have been even better coverage, but we were using DES on it.

Did the tech do a desens check. Yeah you can still have good sensitivity through a poorly tuned duplexer, and a poorly tuned duplexer can kill coverage. The coax you are using now is not the best, but you stated you were using only 30ft so you have less than 2 db of loss, and thats not too bad, its definitely not your problem. Don't go and spend money on hardline yet. Also have you tried getting another user to sit at the repeater location and see if you can talk mobile to mobile simplex? If you can at ground level then get your repeater double checked. If you can't talk, hook a mobile unit to the repeaters antenna and try that. That will at least point you in a good direction.

agreed. start testing individual parts of the whole, to see what your weak link is.

ard099 says to check your repeater antenna on a separate mobile, i'd also include that to say check your repeater on another antenna, different feed line, check your portables point to point...maybe an alignment....and i would lose the gain antenna in a valley, like escomm said.

I agree that you need to fix your system problems, whatever they are, before you rent some (expensive) site, and find that you STILL need to improve the system.

I formerly had a "quickie" system here locally, an import dual band G6 style monopole 40' up, with about 5 watts output for remote radio control on amateur 440 band. I could easily work it with 5 watts from a handheld 5 miles or so. The tower is in a bit of a depression, too.

You need to actually bribe/hire/get a tech with some test equipment. Measure the loss through your duplexer, your feedline, and the output of the transmitter. Check the SWR into the duplexer, as well as the antenna.

Have someone measure the repeater receiver sensitivity, and check for desense through the duplexer. For all I know the antenna itself may be a stone. Try a different antenna, just for comparison, even if it's a homebrew ground plane 1/4 wave.

USSZulu2 wrote:Hi Everyone,

repeater connected to a 6.6 DB gain antenna.
-Bob

If the antenna is truly 6.6 db gain on UHF it would be 9 to 12 feet long.

What is the model and mfgr. info on your "antenna"?

(I know, here we go on antenna gain ,,AGAIN)

RG8 will probably cause more desense in DB than power it delivers to the antenna. Copper braid and duplex operation do not mix. Get some 1/2 feedline, even a good used piece from the local two way shop will be better than the copper braid noise-maker cable you are using.

Chris
N9LLO

<img src="http://www.la.gg/upl/gain.bmp"></img>

N9LLO meant to say "hardline" or "heliax" instead of "feedline"

Get some 1/2 feedline

I made this picture a while back to demonstrate the effects of high antenna gain when you don't really want it. I realize it is crude and exaggerated, but thats why I'm a dispatcher and not an artist.

That's a nice helpful graphic illustration from nmfire10 . I guess there's greater mystique and hype in antenna marketing than in any other aspect of the profession or hobby so a good illustration is very useful.

One thing I'm not clear on is the relationship of the ground plane surface or the ground plane radials in a base antenna to the overall performance. Does the ground plane figure into the gain formula or the radiation pattern significantly ?

Thank you everyone for your input! It is very useful

I have decided to reevaluate the components of my system. The tech that looked at my system did NOT check the duplexer. He stated that because of how sensitive the receiver was he did not believe it to be needed. He stated that "it was more sensitive than he expected though the duplexer". This duplexer might be a problem though. Anyways I do have a service monitor, however, I never checked a duplexer with it and I am not sure how to go about it. How do you run a desense check on a duplexer? I would be happy to learn!

As far as the antenna, I am using a Decibel DB-408-B. I see what you mean about too much gain for terrain. My question is does that effect received signal or just transmitted signal? I was always under the impression high gain antennas allow to pick up very weak signals. That was what was explained to me by several techs. The problem I am having is mainly the repeater cannot hear me. What would be some good antenna alternatives?

The feed line I agree isn’t the best...however as stated before it is only 30 feet. This probably will be the last component I attempt to repair/replace. From what I understand that type of line can be VERY expensive. I need to verify for sure that is the problem.

I am going to do the recommended checks with simplex and other radios connected to the antenna. If anyone has any other suggestions or if I might have forgotten to comment on your suggestion please tell me. I do appreciate all the assistance everyone is giving me. It’s overwhelming in a good way! =)

-Bob

Well 30ft of 1/2in heliax will only cost you $45, from tessco gold pricing its $1.50 a foot.

If you dont have gold pricing... refer to this post
http://batboard.batlabs.com/viewtopic.php?t=66892

Actually the coax is the thing you should look at first. That
one thing has stopped more repeater systems from working
than almost any other single factor. Phrawg

Ok, for the service monitor, it needs to have a spectrum analyser and tracking generator( their are several posts/threads on this board on how to tune a duplexer, but if you have never tuned one, I dont recomond trying to do it. but I can try to walk you through if need be...) PM me if you need help and we can exchange phone numbers

HW

If all you have is a service monitor,here is a crude test for desense:
Put a telescoping antenna on your generate port of the monitor,generate a signal with no pl/dpl till you hear it on the receiving radio,key up the transmitter with a local mic,if the rec goes deaf,you have desense.
Yes there are many better ways than this,but it will tell you something!
mod

A piece on desense:

http://www.ak2o.org/srg/Desense_testing.html

More light reading from the same page:

http://www.ak2o.org/srg/tech.html


and more yet, an exellant page, by the way:


http://www.repeater-builder.com/rbtip/techindex.html