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First GMRS Repeater build


Ronster
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I''m trying to put together a repeater using the CDM750 radios I have. My plan is to use the 25 watt for RX and the 40 watt for TX. The duplexer I'm looking at is the EMR 653160 MC.

The frequency I'm thinking is Rx at 462.550 and Tx 467.550. My antenna is a Diamond X700 dual band mounted on my 43' tower with a 380' asl.

I actually never planned to use this antenna but it is almost flat across the 462-470 Mhz range. with a forward loss of almost nothing.

Since this is my first GMRS repeater, I plan the range to be around 25 miles hopefully.

I would like opinions of experience GMRS repeater builders on this arrangement.

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Good radio choice, just make sure you get decent cable (heliax 1/2). Use N connectors if possible. I personally would chose a 2-bay or 4-bay dipole over anything Diamond made.... 

There are places like radiomobile.com that will do a crude site analysis for you. You punch the gain, the location, etc, and you get a coverage map. 25 miles in UHF is hard to achieve, especially in rough terrain.

G.

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Sounds like a good setup -  try it and see how it works!  I'm using an old/used VXR-7000 repeater with LMR400 coax, PL259 connectors, and a Tram 1486 antenna - I have a good/high location and I get a range of about 55 miles - it would be further but I'm surrounded my mountains..  Location more than anything else will determine your range but that tower should help.

Be wary of "some people" that will leave comments and try to drastically over-complicate everything trying to impress us.

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Turn that 40 watt transmit radio down to 25 watts if you want it to live. And blow some cooling air on it with a muffin fan. CDM's are good radios for the price, but they're not designed for even a 25% duty cycle at high power. The difference in total coverage area will be small, your transmitter will thank you, and your receiver will probably work better. 

 

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So far so good, recommend running the 40 watt radio at 25w and blowing some cold air on it if you're going to turn the keys over to the public or use it for a good rag-chewing session; if you need a simple repeater controller to handle time-out and ID consider the ID-O-Matic IV - it has a built in fan controller too.

If you have other transmitters with decent power output at your house in the 70cm or other UHF bands that will key up while the repeater is in use, you need to be aware of and understand mixing products, how they work, and how they can be mitigated. Mixing products can and regularly do wreak havoc throughout the radio spectrum and cause all kinds of problems not just with your own gear, but other licensed uses as well. I can elaborate if this will be your setup, they're one of the reasons why commercial sites are more complicated to install at properly.

What feedline are you planning on running? Good grade cable is tantamount to having a good set of ears as the cheaper stuff will cause noise to the point where it deafens your receiver, since your transmitter is sharing the same cable as the receiver. RG-58 or RG8x isn't going to cut it; good quality LMR400 is fine for backyard or other 'short-run' installs, hardline is better but will probably not pay back in your application - save that for a site you don't want to have to yourself drive back to. Don't forget grounding, weatherproofing, and surge arrestors, but that's kind of a given...

Edited by JeepCrawler98
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2 hours ago, JeepCrawler98 said:

So far so good, recommend running the 40 watt radio at 25w and blowing some cold air on it if you're going to turn the keys over to the public or use it for a good rag-chewing session; if you need a simple repeater controller to handle time-out and ID consider the ID-O-Matic IV - it has a built in fan controller too.

If you have other transmitters with decent power output at your house in the 70cm or other UHF bands that will key up while the repeater is in use, you need to be aware of and understand mixing products, how they work, and how they can be mitigated - they can wreak havoc throughout the radio spectrum and cause all kinds of problems not just with your own gear, but other licensed uses as well. I can elaborate if this will be your setup, they're one of the reasons why commercial sites are more complicated to install at properly.

What feedline are you planning on running? Good grade cable is tantamount to having a good set of ears as the cheaper stuff will cause noise to the point where it deafens your receiver since your transmitter is sharing the same cable as the receiver. RG-58 or RG8x isn't going to cut it; good quality LMR400 is fine for backyard or other 'short-run' installs, hardline is better but will probably not pay back in your application - save that for a site you don't want to have to yourself drive back to. Don't forget grounding, weatherproofing, and surge arrestors, but that's kind of a given...

Yes, I have fans on all my radios and yes, running 25w on a 40w capable would definitely help. My present feedline is RG-213U. I may replace it later if it doesn’t work well, but my tower climber won’t be available until the end of April. My climbing days are over even at 43’. I run a couple 0.5w Shari’s behind Pi’s, but that’s about it. I was looking at the Openrepeater Pi based controller, but I haven’t ordered it yet.

Thank you for your insight!

Ron

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2 hours ago, Radioguy7268 said:

Turn that 40 watt transmit radio down to 25 watts if you want it to live. And blow some cooling air on it with a muffin fan. CDM's are good radios for the price, but they're not designed for even a 25% duty cycle at high power. The difference in total coverage area will be small, your transmitter will thank you, and your receiver will probably work better. 

 

Thank you!

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19 hours ago, Ronster said:

Yes, I have fans on all my radios and yes, running 25w on a 40w capable would definitely help. My present feedline is RG-213U. I may replace it later if it doesn’t work well, but my tower climber won’t be available until the end of April. My climbing days are over even at 43’. I run a couple 0.5w Shari’s behind Pi’s, but that’s about it. I was looking at the Openrepeater Pi based controller, but I haven’t ordered it yet.

Thank you for your insight!

Ron

I wouldn't expect the Shari's to cause you any problems; but since you're probably familiar with AllStar - using that package as a repeater controller is perfectly feasible as well; it's the same back end that the myGMRS network uses should you be interested in linking at some point (or not)

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