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repeater first time setup questions

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scottp1111

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Carriere Mississippi
Hello,

I need some help from people with more knowledge than I have. My step dad owns a building in our town that was a former cell tower site. The antenna is 180 foot tall and had nothing on it , not even any remaining coax. My whole town is at sea level with the tallest tree or structure around no more than 60 ft or so. The site is in an open clear area. I have plans on putting a VHF repeater at this site. I have constructed the repeater out of 2 GM300 Mobiles. This repeater will use the 154.xxx and the 159.xxx frequencies.

First I need to know what type of coax should be used for optimal performance and the least DB LOSS.
Second , please note the building is directly located below the tower, zero loss between the building and the tower.

I have not put a duplexor on the system as of this time. I will probably purchase one soon. We have been doing some light testing at ground level with two antenna's. All seems to be working well. I need to know what antenna needs to be placed at the top of the tower. I would like to find all items on ebay. The gm300 is turned down to around 25 watts. How far should I expect this unit to talk? We will be using HT1250 portables to talk to the tower and our trucks are equipped with CDM 1250 mobiles.

Please feel free to comment on antenna type, coaxial type recomendations duplex or types and so on. I am looking for the most and the best knowledge for us to build a working system.

Let me answer these questions now!

Yes the frequenices are licensed
Yes this is for a Local Volunteer Fire Department
Yes we have put large cooling fans on the rear of the TX mobile.
Yes the tower is registered and legal.
Yes it is grounded and all equipment connected will be also.
Yes we are aware of the short term GM300 Duty Cycle and have plans to purchase a GR1225 to replace them with as money permits.

I am simply looking for everyones best opionions on how to make this little system a great starting point.

I really appreciate everyone's input,..
 

n5ims

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Licensing questions (you've said the frequencies are legal etc., but there's a bit more to it):
* Does your license cover a repeater on the frequency at the location where that tower is and at the height and power level (or above) where this new repeater will be? Repeaters are licensed for specific locations so if you're currently licensed for your main firehouse location and this tower isn't there (and/or is taller than where it's currently licensed) you need to amend your license to cover this new location (add it as an additional location at least at first!).
* Significant changes in location, power, and/or height may require you to coordinate the frequencies again. They're assigned based on the information provided and attached to the license. Another agency may be fine now, but have significant interference if uncoordinated changes are made and it'll be your responsibility to resolve (and possibly cover the costs of fines, etc.).

Coax question. Pretty simple answer here. You should use a good commercial grade of coax for your install. Repeaters are pretty specialized beasts and you can have serious issues using anything but the right coax. Pick up some Andrew LDF4-50A heliax (Heliax Coax - LDF4-50A) and correct connectors. You'll get proper performance (and very low loss). It's expensive if gotten new, but you can easily find "end of reel" lots on e-bay and other places for not much more than the consumer grade coax would cost. Just make sure that it's long enough to make a single run from your antenna to your building grounding system (you don't want any splices).
 

scottp1111

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Just quick reply, frequencies and tower paperwork was just handled last week by local communications company. Paperwork is all good. I'm looking for Andrew now on eBay...thanks
 

kayn1n32008

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Antenna: Sinclair Radio Labs(Google for more info on their products) model: 210-C4. They are pretty highgain and can have a fairly omni pattern. Mount it at the top of the tower if you can, above the top of the structure.

Duplexer: 6can band pass/band reject. Use proper pass reject cans, stay away from Resloc's if you are going to be in a high RF enviroment. Stay away from mobile duplexers. Also double shielded jumpers from the radios to the duplexer and all jumpers on the duplexer. Double shield is an absolute MUST, RG-214 works well for this.
Again Sinclair Radio Labs makes excellent duplexers.

Coax: HARDLINE, Andrews Heliax
The LDF stuff mentioned above will work fine.
DONOT use LMR-400, rg-58, rg-213, or rg-8.

This is not going to be a cheap endevor, above all else remember that lives are going to depend on this repeater if it is going into fire service. You may want to look at buying a proper 100% duty cycle repeater as well.
 
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ffemt601

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Have you been working with the Pearl River EOC as they have some pretty knowledgeable guys there when it comes to radio systems. Has the SO turned off any of the VHF since moving to MSWIN?

I looked at the FCC ULS and don't see any changes to your license since 05.
 

scottp1111

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Antenna: Sinclair Radio Labs(Google for more info on their products) model: 210-C4. They are pretty highgain and can have a fairly omni pattern. Mount it at the top of the tower if you can, above the top of the structure.

Duplexer: 6can band pass/band reject. Use proper pass reject cans, stay away from Resloc's if you are going to be in a high RF enviroment. Stay away from mobile duplexers. Also double shielded jumpers from the radios to the duplexer and all jumpers on the duplexer. Double shield is an absolute MUST, RG-214 works well for this.
Again Sinclair Radio Labs makes excellent duplexers.

Coax: HARDLINE, Andrews Heliax
The LDF stuff mentioned above will work fine.
DONOT use LMR-400, rg-58, rg-213, or rg-8.

This is not going to be a cheap endevor, above all else remember that lives are going to depend on this repeater if it is going into fire service. You may want to look at buying a proper 100% duty cycle repeater as well.
Thanks again for your advice. ! We plan to upgrade in 4-6 months to a gr1225. This repeater is going to be a backup talk channel or light use fire ground channel. This will not be a primary, this will be for our departments personal use.

Thanks! I will begin to look at some of the products you recommended.
 

scottp1111

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Yes, David and I are very good friends. We actually talk quite a bit. I do some part time communications work for them as well on occasion. ( radio programming ).

The so is using there VHF as a backup system and on occasion revert to it for small talk.
 

scottp1111

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Coax

Guys,


will this cable be acceptable for the long run? we will be using a high gain VHF antenna at the top..



eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices



PS I got more info today, the tower is only 110 feet at the top. It was past used by ALLTELL , and is a guided tower...



PS. I looked at the Andrew , and oh man is it high dollar. We are not saying we want this done for free, but we are working within a small budget. I know that coax may not bee 100% the best , but will the above run work , or is it just a waste of time? I dont want anyone to think that I am being * Quote Hard Headed * , just trying to get a system online with minimal out of pocket and just acceptable quality
 
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ffemt601

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RG-8 would a waste of time for a repeater as well as for that distance. In all honestly anything less than hardline is a waste for a repeater.
 

ffemt601

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Yes, David and I are very good friends. We actually talk quite a bit. I do some part time communications work for them as well on occasion. ( radio programming ).

The so is using there VHF as a backup system and on occasion revert to it for small talk.
Gotcha. I figured that was the case but wasn't sure if you would be lucky enough to be able to acquire their repeaters or coax.
 

stevelton

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I wouldnt say that you couldnt use that coax, but the preformance of the repeater would be severely impaired. Like, having a repeater range of about 5-7 miles to a mobile, where as if you used good 1/2 or 7/8 heliax, from a 110' tower you could be getting 25 miles or better (Im just using those figures to make an example)
Make an investment. Buy the right feedline and antenna the first time. Tower climbers are not cheap (I know, I am one). The repeater and stuff you can mess with yourself, but once that antenna and feedline are up, you dont want to have to mess with it again for a long time!

For a base antenna, also look at Andrews DB-224. I know of those antennas that have been up on a 320' tower for the better part of 20 years.
I hear there are problems with new production ones, But I doubt any worse than any cheap fiberglass antenna
Steven
 

ffemt601

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You may also want to check with Trilogy Communications up in Pearl as they make coax that is comparable to Andrews Hardline.
 

kayn1n32008

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ffemt601 said:
RG-8 would a waste of time for a repeater as well as for that distance. In all honestly anything less than hardline is a waste for a repeater.
Very true, especislly when you are going to have a run of 125' or more. Minimun the op should be using is 1/2" hardline. It is going to cost more, yes but the performance gains over the rg-x that the op posted are going to be big.

Guessing the op is not going to like the cost of the Sinclair equipment, but that is the difference between a repeater that has 10 mile radius verses a 25 mile radius.

Quality materials will result in a quality machine
 

davidgcet

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for 180' VHF go with 7/8" from trilogy if you can, 1/2" hardline(not super flex)if you can't swing the price. anything less will be worthless and too much loss.

for that low power and a 5 meg spread, the regular "mobile" duplexer sold in VHF GR repeaters is fine. 6 cavity hi-Q duplexers are great for higher power and tight spacing, but overkill for a low power wide space repeater. if tuned properly, they will have less than 1 db of loss, which is as good as you can ask.
 

n8emr

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A couple of issues. First are the 2 GM300 Mobiles legal as a repeater on commercial freq, While it common to use them in ham radio applications. Are they narrow band compliant?
 

radioman2001

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Due to the losses of a duplexer and the 100 ft or so run, I would run 7/8 hardline. It costs more but then you don't need a more powerful repeater and or RX preamp. Also with narrow banding coming, my understanding is that mobiles, even narrow-band capable ones don't meet the frequency tolerance required for base and repeater applications. You might want to look into that before putting money down for a GR 1225. A good option is the Icom FR5000 series. 50 watts analog in a single chassis should run you around $700.00. For antenna's I would go with a 3db stick, ASP has one reasonably around $300.00.
From a personal perspective, I've installed a FR5000 on a 3 story building with 12 watts and a 3 db fiberglass stick, and have gotten about 20 mi radius out of the machine. I don't know what you are looking for as coverage, but there is no need to go crazy on power if you intend to cover a small area. High gain antenna's can actually cause dead spots due to their design. Think of antenna signal as a donut, for gain now squish the donut flatter, that's how it gets it's gain at the expense of bandwidth.
 

scottp1111

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Thanks for everyones continued support. As far as the GM300's I do have them setup on the 12.5 split. They will not be around much longer as we plan to upgrade to something better. So far I have gathered a whole lot of great information from everyone. We have contacted Com South out of Hattiesburg to come in and help us get the remaining details sorted out.

Im not sure about the GM300's or the GR1225 meeting the 12.5 narrowbanding requirement. I am sure they will be able to advise us.


Thanks !!
 

R8000

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Easy answer : Contact a reputable two way shop to assist you. Don't cobble job the thing. Your better off hiring a shop that knows radio, then doing it yourself and hosing it all up. Then, having to pay for a shop to come fix your stuff and rework it over. You will save $$ in the long run.

A reputable shop ? A shop that has been around several decades, takes care of county public safety radio systems, etc.

Non reputable shop ? A guy who sells Relm out of his basement on a part time basis.

Sometimes the shop with the uber cool flashy website isn't always the best.
 

kenisned

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Have you considered not going all the way to the top of the tower?

Depending on terrain and how far out you want to go, 50 feet up is pretty darn good, too!
 
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