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Repeaters are confusing.


Elkhunter521
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Hi, I have been looking into putting a repeater on my hunting trailer. Most all of the guys i hunt with carry gmrs-v1 radios from Btech. We hunt western Washington state,and these hand helds work ok. We have had concerns about losing someone (out of radio contact). My truck has a midland 40 watt, two other trucks have the 15 watt midland. The repeater in the trailer would be parked as high as possible plus a 20 foot mast. Electric pallet jack batteries ( 4 x 6 volt set up paralel over series, 12 volt ) power the trailer with a 3500 watt generator and 100 watt solar panels. Here is the question, remember i am new to this.

 

What is necessary to build a repeater system.

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Two radios, some kind of control circuitry (a repeater controller) to have the transmitter start sending audio from the receiver when the receiver hears something, and enough isolation between the transmitter and the receiver to prevent the repeater from interfering with itself, intermod/desensitization or otherwise. The transmitter can't just be anything lying around, it has to be able to handle the duty cycle of a repeater's potentially continuous transmissions. There's some build threads around here on the forums, and I've got a personal project of one based on CDM750s in the drafting stages. For a portable repeater in a low-RF environment, a mobile duplexer is inexpensive and gets the job done, but it has to be properly tuned and the seller doesn't always do that correctly.

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If you don't mind spending the money, don't want to mess around trying to build something, and just want to buy an "out-of-the-box" GMRS repeater system ready to go, call the folks at Bridgecom Systems.

 

https://www.bridgecomsystems.com/

 

Ask them about a BCR-40U analog repeater with a BCD-440 duplexer, and their recommended antenna and coaxial cable, all pre-tuned and set up for you...

-- plug and play --

 

Again, as I have said in previous posts, I do not work for or represent Bridgecom in any way, but I do use their equipment at 5 of my sites, and I'm happy with it.  ...and it will run on 12 Volts DC, or 120 VAC.

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Kevin Custer W3KKC at repeater-builder.com does a pretty good job of explaining everything that one would need to build a repeater:

 

http://www.repeater-builder.com/rbtip/repeater101.html

 

eBay also has pre-assemebled repeaters like this:

 

https://www.ebay.com/itm/GMRS-Ham-prepper-30w-CDR700-UHF-16ch-Repeater-S-split-450-512mHZ-free-prog/283041647587

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I also have a Bridgecom, but for a trailer with 12v power,  a repeater made of two mobile is a better choice. Yes the bridgecom can be run from 12v but it is made to run on AC power and 12v as a backup. You should be able to find a nice repeater made of two Motorola's on E-bay, that can be run full power from your trailers house batteries. Also depending on the length of your trailer, you may be able to forgo the duplexor and run two antennas. Not to mention a new Bridgecom is expensive.

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The MTR2K is a VERY nice repeater package. Built as a giant aluminum heat sink, it will handle 100% duty cycle at 40+ watts of power all day long 24/7.  It will run on standard AC power from the built in power supply - or you can run DC power directly using the power pole connectors on the back.

 

You would (normally) need to provide a duplexer. (Unless you're running a split antenna system - one antenna for transmit, a second antenna for receive). Many MTR2000's would come with a built in high performance preselector to help filter out receive side noise or interference.

 

Repeater-builder.com has a complete and well written breakdown on the MTR2000.  

 

I've had quite a few of them running in commercial service 24/7 for nearly 20 years. I did have to replace one of the power supplies a few months back, as it finally gave up the ghost. 30 minutes later, it was back up and running without missing a beat.

 

IMHO, it's the best repeater package Motorola ever built - a compact performer that will run up to 100 watts all day long. 

 

Software is getting old & is totally unsupported anymore. Make sure you can source the software (or find someone locally to program/test it) before you take the plunge.

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Have you ever opened up your BCR-40U? It is in fact nothing more nor less than "two mobiles in a box". There is of course a custom controller, front panel controls, display, and a 30 amp power supply. ;)

Correct, have you ever run it full power direct from battery? I was afraid to change the setting. either way if you did 40 or 50 watts and moderate use would likely require a larger house battery, maybe two 6 volts in series. Don't get me wrong, I love the BCR repeater, I just immediately thought of the low voltage.

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If I understand correctly, a duplexer is not necessary with two antennas. This trailer is 16 ft in length. Aantennas would bebon 20 ft masts (from ground).

Isolation between transmit and receive can be achieved if you have enough spacing between the 2 antennas. The trouble is, horizontal spacing requires about 300 ft to get 60dB of isolation in UHF, which isn't really enough. Vertical spacing only requires about 25 ft height difference for decent theoretical isolation in the UHF GMRS band. But, I'd still run a bandpass can on the receive side.

 

http://www.repeater-builder.com/antenna/images/vertsep.jpg

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I user the Motorola MTR2000 at every one of my sites, a 40W can be picked up on ebay for 600 or less. These machines are bullet proof.

 

 

The MTR2K is a VERY nice repeater package. Built as a giant aluminum heat sink, it will handle 100% duty cycle at 40+ watts of power all day long 24/7... ...Many MTR2000's would come with a built in high performance preselector...

 

Repeater-builder.com has a complete and well written breakdown on the MTR2000.  

We are looking to replace our GR1225 with something a little more robust and the MTR2000 is at the top of our list. I have a couple of questions:

  1. For GMRS use in a fairly RF intensive area (SF Bay) how important is the pre-selector?
  2. Are there any gotchas or beware-ofs I should know about while shopping?
  3. Any other hints, helps, or tips?

BTW, I looked at repeater-builder and found a lot of info there (as usual, maybe even too much info, it is hard to know where to start.) I know Mike, wa6ilq from way back.

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We are looking to replace our GR1225 with something a little more robust and the MTR2000 is at the top of our list. I have a couple of questions:

  1. For GMRS use in a fairly RF intensive area (SF Bay) how important is the pre-selector?
  2. Are there any gotchas or beware-ofs I should know about while shopping?
  3. Any other hints, helps, or tips?

BTW, I looked at repeater-builder and found a lot of info there (as usual, maybe even too much info, it is hard to know where to start.) I know Mike, wa6ilq from way back.

 

Depending on the exact location and situation - as well as the type of Duplexer you might be using, a Preselector is probably more of a Nice to have, as compared to a Need to have. But, if you're buying a used repeater, get one with a Preselector if you can - especially if the price is within $50 or so.  Buying a Preselector after the fact would probably run you @ $200 + tuning. 

 

If you have a really good duplexer (meaning a properly tuned 6 cavity bandpass/bandreject) the benefit you would get from a Preselector is minimal. If you were running a typical compact flatpack notch duplexer - the benefit would be amazing.

 

The front end (receiver) of an MTR2000 is worlds better than most any '2 mobile radio based' duplex repeater package out there. The MTR2K converts received signal into PCM (Pulse coded modulation) digital signal for all it's internal processing, and the internal noise level introduced by the machine is nearly non-existent. You get a clearly reproduced voice -- even with a weak input signal from a distant mobile. 

 

Trouble areas are minimal - but if you're getting one off eBay, be super careful. If you can wait on them, you will often find people selling off a batch of them as they part out an old UHF trunking system - recent pricing between $450 and $650. The power supplies can be troublesome on the 100 watt units - but I've picked some up for a few hundred dollars that had known power supply issues, and then turned around & grabbed a huge 26 volt DC rack mount power supply for $100 or less (plus the $50+ for shipping the beast). Nice way to eliminate a known problem spot & put a 100 watt repeater on the air for less than $500.

 

Motorola doesn't support them anymore, and many of the components are designed as "bricks" - so you can swap around a receiver, a power amp, a power supply module, but each component is sealed up & considered non-serviceable by Mother M. I don't think I've ever seen any schematics or break downs to component level. Software is a little old & cludgy, but I've still got a winXP machine that runs it well enough. The last time I programmed one - I realized it had been nearly 5 years since I'd touched one for a customer. A testament to the "set it and forget it" nature of those machines.

 

Basic single user repeater mode is pretty straightforward. If you try to run a multi-tone panel things get a little more complicated, but the method to do it has been well documented and doped out. 

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