GMRS Repeaters - What do they get you?

[Blaise]

Hi folks,

I'm new, so bear with my stupid newb questions, but I'm having trouble getting my head around repeaters!

So I understand the basic idea: If two radios are in range of a repeater, but not each other, the repeater allows them to talk.  My major questions center around range, though.  I get that a repeater can be relatively high-powered, compared to say a handset, so they can reach out significantly farther, but since the handset can only manage it's own meager range, how does the repeater hear *them*?

 

I guess what I'm asking is, does a repeater ever get you more than at most the sum of the effective ranges of the communicating radios?  It seems an awfully expensive move to set one up if all it does is extend a transmitter's range by  maybe a factor of 2, if you're lucky, so I feel like I must be missing a piece of the puzzle.

 

Thanks!

[tweiss3]

GMRS is largely a "line of site" service. In other words, hills, buildings, and even the curvature of the earth are what cause the real limitations for a radio. Keep in mind, in the amateur radio service, many people can communicate with satellites at only 1-5Watts. What a repeater does is create a vantage point way above normal ground level, which lets you overcome the hills and curve of the earth.

 

This article very briefly explain how the "line of site" concept works relative to height: https://www.hamuniverse.com/lineofsightcalculator.html

 

[Blaise]

I see, so you're saying that the altitude creates added range for the transmitter too, because the signal has less in its way... 

So if I grok that right, it would also imply that if you got two low-powered gmrs radios and put them on mountaintops twenty miles apart on a clear day, they could feasibly communicate with each other.  Or am I just not getting it?

[tweiss3]

4 minutes ago, Blaise said:

I see, so you're saying that the altitude creates added range for the transmitter too, because the signal has less in its way... 

So if I grok that right, it would also imply that if you got two low-powered gmrs radios and put them on mountaintops twenty miles apart on a clear day, they could feasibly communicate with each other.  Or am I just not getting it?

And there are many people that do this. In fact, there was a thread on here not long ago about a 10W repeater on a mountain in Alaska that has incredible range.

[axorlov]

1 hour ago, Blaise said:

it would also imply that if you got two low-powered gmrs radios and put them on mountaintops twenty miles apart on a clear day, they could feasibly communicate with each other

Yes, indeed. On a foggy and rainy day too. Not just feasibly, but reliably.

[WyoJoe]

3 hours ago, Blaise said:

I see, so you're saying that the altitude creates added range for the transmitter too, because the signal has less in its way... 

So if I grok that right, it would also imply that if you got two low-powered gmrs radios and put them on mountaintops twenty miles apart on a clear day, they could feasibly communicate with each other.  Or am I just not getting it?

You've got it. The primary advantage to most repeaters is the elevation. In general, they are placed on mountaintops, tall buildings, radio towers, etc. and have significant advantage due to their position. If you were to stand where the antenna is placed, you could expect to reasonably transmit to the places you could see from there provided you have adequate power to do so. In theory, any handheld radio in any of those same places should be able to reach the repeater, too. In reality, there are some real world obstructions that lessen the range or interfere with transmissions from some radios, but in general, the communication will be line of sight.

When you transmit to a repeater from a handheld radio, the repeater in turn re-transmits your signal to everywhere within its range. Any other radio within that range should be able to receive that signal, and provided conditions are right, should be able to transmit back to the repeater, to have its signal re-transmitted.

[Blaise]

Thanks folks, that really helps!  

Now for my second question.  I've scanned these fora and watched some videos, and I think I have a handle on programming repeater channels, offsets, ctcss/dcs codes, and the like, but assuming I get all that right, how do I test that my radio is connecting properly?  I suppose I can get my wife on my second unit to verify when it *is* working, but won't really help troubleshoot when it isn't.  Is there a method for connecting to a repeater with just one radio where the repeater itself confirms that your connection is working?

[wayoverthere]

1 hour ago, Blaise said:

Thanks folks, that really helps!  

Now for my second question.  I've scanned these fora and watched some videos, and I think I have a handle on programming repeater channels, offsets, ctcss/dcs codes, and the like, but assuming I get all that right, how do I test that my radio is connecting properly?  I suppose I can get my wife on my second unit to verify when it *is* working, but won't really help troubleshoot when it isn't.  Is there a method for connecting to a repeater with just one radio where the repeater itself confirms that your connection is working?

It's not a 100% confirmation that you're getting in clearly, but you can transmit, and listen for what's called a "squelch tail", which sounds like a short pop or burst of static. This will let you know you at least opened the repeater.  Some repeaters will also come back with a courtesy tone or beep when you unkey.

Most current radios come programmed with all the frequencies you need, and from there it's just being in range and having the right tones. You can hedge your bets on range by getting closer in to the presumed location of the repeater.

[BoxCar]

Another test would be to program the second radio to receive on the uplink frequency and transmit on the downlink, if you can't trigger the repeater.

[AdmiralCochrane]

Its called "kerchunking" the repeater.  Technically its not legal, but people do it all the time. 

[Blaise]

Thanks for all the advice!