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Author Topic: Building A Repeater  (Read 914 times)
ROBBIE
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« on: February 12, 2005, 05:59:21 PM »

I am in the midst of researching how to build a VHF repeater. I am subscribed to several yahoo groups and in one of those groups I read a post by Richard Galvin of that he had the cable for configuring two Vertex VX-4100 Land Mobiles to repeat. He made it soud very easy. It requires no modification to the radios, and is simply a cable that goes between the two mobiles D-sub connector. I am a little leary of purchasing two mobiles, a duplexer and antenna without knowing without a doubt that I can complete this project. Has anyone ever built anything like this ? If so, what were some of the +'s and -'s of doing this rather than purchasing a regular repeater? Any help would be appreciated.
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W7DJM
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« Reply #1 on: February 13, 2005, 10:11:31 AM »

My first question is, to what purpose?   You didn't post an amateur call, so I don't know if this is for amateur use,  if it's for pirate/unlicensed/illegal use,  for commercial use, or what.

Putting up a proper repeater is no small undertaking, nor is it cheap.   If you are looking at a commercial site, you need a proper duplexer to protect yourself, and others, from interferance, as well as high quality coax (heliax) and other concerns.  

If this is an amateur repeater, then you need an expensive duplexer--because none of the cheaper "notch" duplexers you see on eBay  will work for the close offset needed for amateur work.

None of these radio interface cables, that I'm aware of, offer ANY  sort of "id'er"  "time out timer"   any sort of controls or protection for the radio.

You MUST be under control of your repeater.   If it "locks up" on transmit, due to some failure, interferance, or intentional jamming, you MUST have a control method to shut it down ----3 minutes in US amateur practice.

That means anyway you can "git er done."  

You can stay withing 3 minutes physical time of the repeater whenever it is powered up and receiving.

You can control it through a phone line and probably the internet if you can make it reliable.

You can use a (in amateur service) 222mhz or higher link


In addition to all that blather,  some mobiles make very poor repeaters--they were never designed for extended transmit conditions,  and some have poor front end rejection qualities so far as interferance goes.

There is a reason why "real" commercial repeaters are so expensive.

One excellant place to do some reading is the "repeater builder" site.  There is a LOT of buried information there, including hardware, antennas, and duplexers.


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

(If you haven't spend at least two hours browsing that site, you haven't been there long enough.)
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ROBBIE
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« Reply #2 on: February 13, 2005, 04:36:50 PM »

Im sorry, I am not a ham, so, therefor, I dont have a call sign. There is never a test  in my area to take. I tooke the practice exam on QRZ's website and passed it with an 88.6 % correct.
Anyway, this is for commercial use with one of the local fire departments. I have all of the equipment needed to ensure a clear running repeater with a 2 minute TOT and had planned on hooking a CW ID'er to it for the purpose of station ID. I know how to hook up a repeater, the question is, has anyone ever done this before with two mobiles ?
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AA4PB
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« Reply #3 on: February 13, 2005, 05:47:17 PM »

One additional thing you've got to consider is the duty cycle of the transmitter and power supply. Don't forget that the repeater can be in transmit mode for a considerable amount of time because it must transmit for both sides of the conversation. I have hooked up two transceivers to act as a repeater but experienced reliability problems because of the duty cycle limitations.
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ROBBIE
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« Reply #4 on: February 13, 2005, 07:56:32 PM »

Thanks AA4PB for that tip, I am planning on lowering the wattage output of the transmitter mobile to 25 watts out. In addition, I plan on programming the transmitter mobile to have a TOT set at 2 minutes. Which two mobiles did you use ?
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N3ZKP
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« Reply #5 on: February 13, 2005, 09:15:48 PM »

<< Anyway, this is for commercial use with one of the local fire departments. >>

Just out of curiosity, if this is for a fire department, why isn't the commercial shop that does the rest of their radio work handling this?

Radio equipment used in that service is required to be type-certified by the FCC and I'm not sure a homebrewed repeater, even made with commercial radios qualifies.

Lon
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ROBBIE
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« Reply #6 on: February 13, 2005, 10:02:02 PM »

>>Just out of curiosity, if this is for a fire department, why isn't the commercial shop that does the rest of their radio work handling this?<<

I do most of the radio work at the fire department. There are no other radio dealers close to us. I think people have missed the point of the post. I am not asking how to do this, that is not a question, the question is if anyone has ever hooked up one of these setups, and if so, how did it go.

>>Radio equipment used in that service is required to be type-certified by the FCC and I'm not sure a homebrewed repeater, even made with commercial radios qualifies. <<

I am not using amateur radio equipment to build this repeater, I am using two commercial grade VHF mobile trancievers made by Vertex.
The reason I posted here, is, I have been a member of this website for three or so years, and have read alot of articles on here from alot of hams who know more than I ever will about radios. Taking this into consideration, this seemed the prime place to post the question that I had.
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VA3WXM
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« Reply #7 on: February 14, 2005, 07:09:22 AM »

You may also want to consider signing up to the Repeater Builder's Yahoo group (http://groups.yahoo.com/group/Repeater-Builder/).  TONS of good information there about setting up, running and troubleshooting repeaters from all the major players (Motorola, GE, Vertex, Icom).

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DROLLTROLL
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« Reply #8 on: February 14, 2005, 07:39:39 PM »

Rule Number One. When wiring two mobiles together, you must bypass the pre-emphasis and de-emphasis circuits in the TX and RX stages of the repeater. You don't want your audio to be processed twice or it will sound VERY tinny.
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ROBBIE
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« Reply #9 on: February 15, 2005, 02:42:42 AM »

Thanks very much guys.
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AA4PB
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« Reply #10 on: February 15, 2005, 12:44:18 PM »

I don't remember the exact models. They were two amateur grade 2M mobile radios (not even the same type). We used them in the club repeater for a year or so when we first started.
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WN3R
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« Reply #11 on: April 22, 2005, 12:34:27 PM »

Get a Motorola GR1225 or GR300/GR500 repeater.  Not too expensive on eBay. I have one of each and they work well.

The GR300/GR500 uses GM300 or Maxtrac mobiles with a RICK and duplexer.  THe GR1225 is a single radio unit designed for base and/or repeater use.

Good luck.
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