GMRS Repeater Questions

[Adam76]

--Hi, all. New user here. I am wanting to put up a GMRS repeater and I have no idea where to start. Would it be better to purchase a good used repeater or just assemble my own? This repeater will not be a high profile repeater, but perhaps later, it will be. I have been looking at the GR300 repeater, but have read that the duty cycle is approximately 10%. I would like something with quite a bit more duty cycle (50-100% if possible). What would be a good, med. to high duty repeater that won't break the bank (as cheap as possible without sacrificing quality)? We really prefer something used, and not new, please. I've also seen the GR1225, but not sure on its duty cycle.

--I've heard of people putting together a repeater by using two radio, a controller, duplexer, etc., but I don't know how to do that. Is there an easy to follow, step-by-step "chart" to do that? I am new to repeater assembly and I would appreciate all help/info.

[abrasowski]

Well I won't pretend to be an expert but will offer up my lessons learned putting together one or two budget repeaters and then recently setting up a commercial repeater. A used repeater should work fine assuming it wasn't abused and is still in alignment/specs. USED GR1225 and GR300 repeaters pop up on eBay all the time and are a great solution for a starter GMRS repeater. Also a not well known gold mine is the destrac repeaters which can sometimes be found for $250 or less.

Most importantly, grab a great antenna (NO Antenex FG series please...not a good duplex antenna)-- a more affordable recommendation I have been given is Comtelco. Grab some good coax (you can start with affordable for testing but in the end you will be better of with 1/2" hard line or greater (Andrew Heliax or RFS LDF4/4.5?). Don't use any adapters, try to have the cable cut and connectors installed at the approximate requirements. Above all, get your duplexer professionally tuned after purchasing it, regardless of what any seller on eBay tells you it is already tuned to.

Good luck! You will have a lot of fun with your project and will learn a lot along the way. If you get it right the first time, you are a lucky man

[Bill_G]

--Hi, all. New user here. I am wanting to put up a GMRS repeater and I have no idea where to start. Would it be better to purchase a good used repeater or just assemble my own? This repeater will not be a high profile repeater, but perhaps later, it will be. I have been looking at the GR300 repeater, but have read that the duty cycle is approximately 10%. I would like something with quite a bit more duty cycle (50-100% if possible). What would be a good, med. to high duty repeater that won't break the bank (as cheap as possible without sacrificing quality)? We really prefer something used, and not new, please. I've also seen the GR1225, but not sure on its duty cycle.

--I've heard of people putting together a repeater by using two radio, a controller, duplexer, etc., but I don't know how to do that. Is there an easy to follow, step-by-step "chart" to do that? I am new to repeater assembly and I would appreciate all help/info.

Adam -

Read this GMRS information page - GMRS Information

With GMRS 5 watt limitation, any of the GR series repeaters will be adequate. You won't be as chatty as you think. 10% duty cycle for small repeater will work.

[Adam76]

--Thanks for the replies guys. I'm not sure what the output on the GR300 is for UHF, but if I could turn the output power down at its "bottom end" rating, I guess it would keep it a bit cooler, thus increasing the duty cycle (for instance, assuming this is a 40 watt repeater, I would reduce to 20-25 watts.) Less amperage, less heat, more duty cycle. The local water company actually uses a VHF version of the above repeater, but it is definitely used lightly. Maybe no more than 30 minutes a day total use. Actually, the more I think about it, that's the kind of use my potential upcoming repeater will see during the week. The weekend on Fri. and Sat., probably 4 or 5 hours per day.

--So, assuming the repeater is in good shape, is there one repeater that is better than another? Also, what kind of price range SHOULD these repeaters have? Though not a requirement, do any of these repeaters have DCS? Finally, other than antenna and coax, does the repeater come with everything needed to work? Any other models of repeaters you might recommend?


--Something I have wondered, though I do not plan on doing it, nor would I spend money on it, lol, is it legal for GMRS repeaters to use one of the digital modes like P25 or NXDN, etc.? It's not considered a "scrambled" or "encrypted" technology since anyone can buy the radio to use it (it's no more scrambled or encrypted than using a mode like USB) Maybe I'm wrong, and that's ok. Why would I want to use P25 or other modes? I don't, just curious. Thanks for your help.

[AEC]

Aside from 'amateur' antennas, most of which are not good for use in the commercial/GMRS service, look into anennas that are D.C grounded, such as those available from companies like Telewave.
Look at the specs, what area you need to cover, physical site height(HAAT), and antenna gain.
The more gain, the 'flatter' the vertical plane signal becomes, and this can make certain sites unusable as the gain is too high as a large portion of the signal is causing ground reflections, which causes multi-path.
If your service area is under 20 miles, then a 6 dB antenna would probably be the best choice. Good gain, respectable signal strength for the coverage area.
For feedlines, a good cable to buy as 1/2" Heliax, it has reasonable loss per 100 feet, and is easier to work with and connectors are cheaper as well.
LDF4-50 or FSJ4-50, both are 1/2" cables but require different connector types due to the outer corrugation style.
Do NOT use ANY 'RG' types, such 8213, RG-8, RG-214, Etc...braided cable can not be used due o IMD products, signal attenuation and more.
If you are going to place this machine at a site which has other repeaters co-located, then you should think about an isolator and a low or high pass filter added to the transmit side to minimize IMD, odd and even order products and band specific harmonics. and must be properly tuned to the opeating frequency in order for the isolator to function properly.
If you are the 'new' guy at any site, the duty to prevent interference falls on you if the site has never had issues previously, you will become the bad guy(unfortunately).
But do start with a good quality antenna and cable, you save far more doing things right, right from the start.

[Will]

I think Bill made a typo. GMRS can run up to 50 watts.

Adam -

snip> With GMRS 5 watt limitation, any of the GR series repeaters will be adequate. You won't be as chatty as you think. 10% duty cycle for small repeater will work.

[Bill_G]

I think Bill made a typo. GMRS can run up to 50 watts.

Adam -

snip> With GMRS 5 watt limitation, any of the GR series repeaters will be adequate. You won't be as chatty as you think. 10% duty cycle for small repeater will work.

No. But, the FCC info page may be wrong.

Operating a General Mobile Radio Service (GMRS) System
A GMRS system consists of station operators, a mobile station (often comprised of several mobile units) and sometimes one or more land stations. A small base station is one that has an antenna no more than 20 feet above the ground or above the tree on which it is mounted and transmits with no more than 5 watts ERP.

[PETNRDX]

That FCC page is talking about "a small base station".
I believe the rule for small base stations and 6.1 meter rule control stations are limited to 5 watts.
I also believe that repeaters which are not small bases nor control stations can be 50 watts.
If you were using a small base also as a repeater, that 20 ft / 5 watt limit should
Seems to me that webpage may not give all the info.

[Adam76]

--I've been reading online about the GR300, and assuming it's in good shape, it seems like a pretty good repeater to use for the duty cycle I will probably have. Now, I will have to see what repeaters are in the area so when I have the repeater programmed, it won't be on their frequency. There is a GMRS repeater about 20 miles SW of me, but I cannot remember the frequency of it, but I am pretty sure it's the only repeater within 60 miles of me.

--Thanks for the info. regarding the proper coax to use. Knowing me, I would have just purchased some LMR400 to use. Looks like Andrew LDF4-50A is what I should use.