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Cellular Tower as GMRS Repeater Site


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#1 haneysa



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Posted 03 March 2019 - 12:56 PM

I am sorry if this has been covered previously, but I searched the forums (and the InterWebs) an could not find any information as to interference between GMRS (or even 70cm) and cell tower/WIFI signals.


My reason for asking is this-a mountain that is a few miles from my house has been one of the sites that I was dreaming of putting a repeater on. I have done to rough coverage mapping using the radiomobile app, and this peak looks like it would give excellent coverage in my target area (and about 50 miles to the south and west).


I am trying to find out what the likelihood of intermod is between the bands before I reach out to the tower owner (it is a line of sight wifi internet company). The tower has not gone up yet, they got the AOK from the county last summer. The "cell tower" will be a monopole style one,so I do not know if any other antennas could be attached to it. The site is what I am really interested in, more than the tower itself.


Thanks in advance for any advice.



#2 Radioguy7268


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Posted 03 March 2019 - 01:51 PM

Generally - a well designed (and implemented) system will use proper filtering and isolation, and won't have a problem playing nicely with other nearby transmitters. The farther away (in frequency) the two (three, or four, +) transmitters are, the less chance they'll cause any appreciable amount of intermod.


There are intermod calculators available online - including one thru Radio Mobile. Plug in your frequencies, and they'll run the theoretical results.


Any decent site manager will require that YOU mitigate any interference or intermod problems that your transmitter(s) create. Most operate on a "first in" basis - meaning the guy who was there first doesn't need to fix his system (assuming it was properly built), you need to fix yours so that it doesn't interfere with any other existing user. Once you're in and operating without causing problems, the onus shifts to the next guy coming in.


If the site is owned by a company specializing in Vertical Real Estate, you're going to want to be sitting down before you get the price quote. A smaller company might be more willing to talk, but you're going to need to make a pretty strong case for what you plan to bring to the table that's a benefit to them (rather than just a benefit to you.)

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#3 berkinet


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Posted 05 March 2019 - 10:59 AM

... could not find any information as to interference between GMRS (or even 70cm) and cell tower/WIFI signals.....


If they are using Wi-Fi and not Cellular/PCS, then they will almost certainly be on either or both the 2.4gHz and 5gHz bands. If your repeater is of even only half-decent quality (I.e. not just two CCRs lashed together) the likelihood of interference is nil.  But, as Radioguy7268 noted, you would probably still be held accountable if there was a problem.


BTW, The antenna is just 1/2 the issue. You need rack space as well.  Also, you might ask if remote access (Internet) is available. Virtually any radio that can be programmed via a computer can also be programmed remotely. All it takes is a single board computer (eg Raspberry-Pi), a little know-how, and an Internet connection.

Everything we hear is an opinion, not a fact. Everything we see is a perspective, not the truth.

-- Marcus Aurelius

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