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vhf reapter

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#1
Hello my name is Heath. I live in ashdown and have set up my own vhf reapter with 2 62" antanas and I have 2 bafengs radios with a box connecting them. The antanasa are about 12foot in the air and I can only get out about 1500 feet and that's it. From 2 to 3 miles away I can key up the reapter but I can't talk on it. Any idea why?
 
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#2
Most likely answer is what is known as desense. In short the transmit side of the repeater is overloading the receive side. This will happen even if they are set on different frequencies. If you are trying to listen to a conversation across the room from you, someone next to you talking will make it impossible.

A repeater is normally designed to isolate the transmitter form the receiver through various means including shielding the two parts form each other and using a duplexer and a single antenna. The duplexer is tuned so that the transmitters signal is 'notched' out of the receiver. The idea that you can just hook two radios together to make a repeater does not take a lot of things into account. A repeater needs to be designed form the ground up for its job.

You also need a license to transmit using a radio. Repeaters are only allowed to be used by some radio services (i.e. ham radio or GMRS) and there are special rules for repeaters in each service where they allowed if they are allowed at all. Make sure you are authorized before placing a transmitter 'on the air'. It is a simple matter for law enforcement or the FCC to find a transmitter and take enforcement action.
 

902

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#3
Hello my name is Heath. I live in ashdown and have set up my own vhf reapter with 2 62" antanas and I have 2 bafengs radios with a box connecting them. The antanasa are about 12foot in the air and I can only get out about 1500 feet and that's it. From 2 to 3 miles away I can key up the reapter but I can't talk on it. Any idea why?
There are a lot of things you don't mention. Some important things to know:
  • Transmit frequency
  • Receive frequency
  • Type of cable between the radios and antennas
  • How far each of these antennas are away from each other
  • The condition of your antennas

But this is a good start at learning.

First things first: what you're doing requires not only a license, but frequency coordination. If you don't have either, stop and get them. Moving forward, I'll presume you have those.

Vertical spacing is worth more in terms of isolation than horizontal spacing. If you put your receiver antenna 50 feet in the air and had your transmitter antenna at 12 feet, you'd probably do well. That relatively little separation can be worth as much as 400 feet horizontally if the antennas were in the same plane with each other.

Your cable is extremely important. No RG-58 here! In fact, when you're dealing with full-duplex, you don't want any cable that has different metals or potential arc points (like LMR400). You need RG-142 or RG-214 at a minimum depending on how far you run between the antenna and radios. Heliax will do much, much better.

Your transmitter might be "noisy." Transmitters aren't always clean. Sometimes their energy is spread out of where it's intended. That will affect your receiving capability.

Receivers might be wide. They might not have the rejection abilities a "real repeater" would have, especially if they were designed cheaply and to loose specs.

If your antennas are old and corroded internally, you are asking for trouble. And even some new antennas don't duplex well. Hammie antennas that screw together corrode at the junction and create a place where mixing products and desensitization can happen. You need the right stuff.

Finally, frequency separation is critical. If your transmitter is 5 kHz away from your receiver, and your antennas are at the same site, it probably won't work. If it was 5 MHz away, maybe it will. If it was 15 MHz (not likely on VHF), there would be even more isolation.

The name of the game you're playing is called "isolation." Everything you do needs to contribute to the overall electrical separation between the transmitter and receiver.

Once you work your way through these things, you can start looking at duplexers.
 
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#4
There are a lot of things you don't mention. Some important things to know:
  • Transmit frequency
  • Receive frequency
  • Type of cable between the radios and antennas
  • How far each of these antennas are away from each other
  • The condition of your antennas

But this is a good start at learning.

First things first: what you're doing requires not only a license, but frequency coordination. If you don't have either, stop and get them. Moving forward, I'll presume you have those.

Vertical spacing is worth more in terms of isolation than horizontal spacing. If you put your receiver antenna 50 feet in the air and had your transmitter antenna at 12 feet, you'd probably do well. That relatively little separation can be worth as much as 400 feet horizontally if the antennas were in the same plane with each other.

Your cable is extremely important. No RG-58 here! In fact, when you're dealing with full-duplex, you don't want any cable that has different metals or potential arc points (like LMR400). You need RG-142 or RG-214 at a minimum depending on how far you run between the antenna and radios. Heliax will do much, much better.

Your transmitter might be "noisy." Transmitters aren't always clean. Sometimes their energy is spread out of where it's intended. That will affect your receiving capability.

Receivers might be wide. They might not have the rejection abilities a "real repeater" would have, especially if they were designed cheaply and to loose specs.

If your antennas are old and corroded internally, you are asking for trouble. And even some new antennas don't duplex well. Hammie antennas that screw together corrode at the junction and create a place where mixing products and desensitization can happen. You need the right stuff.

Finally, frequency separation is critical. If your transmitter is 5 kHz away from your receiver, and your antennas are at the same site, it probably won't work. If it was 5 MHz away, maybe it will. If it was 15 MHz (not likely on VHF), there would be even more isolation.

The name of the game you're playing is called "isolation." Everything you do needs to contribute to the overall electrical separation between the transmitter and receiver.

Once you work your way through these things, you can start looking at duplexers.
The first step IMHO is like you said, get a license.

The second step should be to throw said Baofeng (portables?) repeater in the trash. If he/she is going to go through all that work as stated to try to set up a basic repeater, the basics should be to get a real FCC type accepted repeater, then proceed with other components.
 

teufler

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#6
If you would setup a crossband operation, vhf-uhf, desense would be reduced, more range. You would have youi radios vhf on the upper side, side A and uhf on the lower, side B. Doesn't matter if you go in on vhf or uhf, you would listen on the non transmit band. The idea, is to increase your range, this would work to the extent your geography limits your signal. Probably about 10 miles, with an antenna about 30 feet above average terrain.. If you are in eastern Arkansas, you have no hills to restrict your signal.Now this all assumes you have a ham license. Business band, not much you can do without FCC authorization.
 
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#7
Also assuming ham use, with appropriate frequency coordination, you could extend the crossband operation into a split-site repeater that would allow you to nearly eliminate the desense issue and may help extend your range even further. At the very least, it would require one more dual-band base radio that has built-in crossband repeat feature (best would be to reduce your existing HT based system and get a second dual band base radio.

Set one at one location receiving on VHF (repeater input frequency) and transmitting on UHF (simplex link frequency) attached to a high gain dual band antenna on a tower or mounting pole. At the second site (at least a half mile away for good separation, closer might be OK, but should be as far apart as practical) set the other radio receiving on the link UHF frequency and transmitting on the VHF repeater output frequency, also using a high gain dual band antenna on a tower or mounting pole. The higher the antenna the better (within reason, of course) and use high quality coax, RG-213 at worse or LDF4-50A (or better) for better signal strength. Avoid LMR-400 or similar LMR type coax since they will not work properly on a full duplex system like a repeater.

For that matter, you could just get two old used single band transceivers (one VHF, one UHF) and a couple of scanners. You'll need some type of controller (probably something like you already have for your HT based solution, but two will be needed in this case). Have the first scanner receiving on your VHF repeater input frequency feeding the UHF transmitter on the link frequency. Have the second scanner receiving on the UHF link frequency and the VHF transmitter on the VHF repeater output frequency. You'll probably need separate VHF and UHF antennas in this case on both ends to prevent blowing up the scanner when the transmitter starts transmitting. Those should be separated vertically by at least a few feet, with the repeater antennas higher than the link antennas (since your link range will be fairly short anyway). Due to the short link distance, you probably could just put the link antennas just above the roof line while the repeater antennas up higher on the towers or poles. Since this approach isn't directly duplex, the LMR coax should be OK here.

Note, if you're planning on a UHF repeater, simply reverse the VHF and UHF notations in either solution above and you should be good.
 
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902

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#8
The first step IMHO is like you said, get a license.

The second step should be to throw said Baofeng (portables?) repeater in the trash. If he/she is going to go through all that work as stated to try to set up a basic repeater, the basics should be to get a real FCC type accepted repeater, then proceed with other components.
I don't disagree. I'm just happy he's interested in building. He'll figure out he needs something better at the point where he gets hands-on with isolation.

Heck, I've been into building repeaters for quite a while and I've still got a desense issue that's just kicking me on 2 meters. Optimizing that 2 meter repeater has been the "boat" I've been building in my spare time. We never stop learning.
 
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#10
I don't disagree. I'm just happy he's interested in building. He'll figure out he needs something better at the point where he gets hands-on with isolation.
I agree, happy he is taking a interest. He did however not state if this is a ham repeater or commercial.

The reason I advocate getting a decent repeater to start is because Baofengs have very very dirty transmitters. Spurs galore, and the Receivers are about as worse as you can get. I'm sure you know. It just compounds the problem when trying to get set up with minimal desence, especially a beginner.
 

902

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#12
The reason I advocate getting a decent repeater to start is because Baofengs have very very dirty transmitters. Spurs galore, and the Receivers are about as worse as you can get. I'm sure you know. It just compounds the problem when trying to get set up with minimal desence, especially a beginner.
Oh, very true!

I've been chasing my tail with implementing a 2 meter ham repeater that's a popular Part 90 type accepted device, but is really nothing more than two mobiles in a rack with a control unit and switching power supply. There's some SP firmware, too. I've been through two duplexers, a number of lengths of RG142, RG214, 1/4" FSJ, and 1/2" FSJ cable between the transmitter and receiver to the duplexer, a few different feedlines, and a new antenna, along with various other things. I've only kept at it because the US marketer has been very nice and supportive. They've made a few changes based on suggestions, like dual-shielded cable and N connectors. So, I haven't given up. But it's been very frustrating to chase. I'm at the point of thinking the transmitter they use is substantially noisier than a Micor/MSF/Quantar or MASTR II/III would be. So far, I can't kill the on-frequency noise into the receiver. It doesn't help that the receiver "brick" doesn't have a mechanical preselector, like the traditional repeater stuff had. He's got those issues and worse.

Now, I might also be fishing for an excuse to buy myself a Siglent SSA3021X with a tracking generator and return loss bridge as soon as I've saved up enough money (Shhh!!! Don't tell my wife!). But I've done this for a while, and this kind of stuff is "fun" for me. This would probably be downright discouraging for a newbie to have to troubleshoot.
 
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#13
Now, I might also be fishing for an excuse to buy myself a Siglent SSA3021X with a tracking generator and return loss bridge as soon as I've saved up enough money (Shhh!!! Don't tell my wife!).
Hey, Santa was good to you this year that's all ;)

Merry Christmas to you.
 
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#14
To the OP:

If you're using Baofengs to make a repeater, it will need to be a cross-band--one channel VHF, and one channel UHF. The receivers do not have the degree of filtering needed to make a single-band repeater work. Instead of having 2 antennas, use a duplexer like this:

https://www.amazon.com/MFJ-Enterprises-Original-MFJ-916B-Duplexer/dp/B00AR0CH54

Connect the UHF radio to the UHF input, and the VHF radio to the VHF input, then connect the common to a dual-band antenna.
 
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Ashdown Arkansas
#15
I got my GMRS license about 2months ago and have changed freqs in my radio to Rx 462.725 TX 467.725 pl tone 151.4. I spaced out the antanas about 30feet and that seemed to work a little better. I don't have the money get to buy a duplexer. I just don't get what Im doing wrong. Im running RG-58 to both antanas. Would it be better to just do simplex? Im 19 and always wanted to build a reapter for along time but just don't understand what is going on.
 
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#16
I got my GMRS license about 2months ago and have changed freqs in my radio to Rx 462.725 TX 467.725 pl tone 151.4. I spaced out the antanas about 30feet and that seemed to work a little better. I don't have the money get to buy a duplexer. I just don't get what Im doing wrong. Im running RG-58 to both antanas. Would it be better to just do simplex? Im 19 and always wanted to build a reapter for along time but just don't understand what is going on.
You're battling desence. (more than likely) Which is the TX radio whipping out the RX radio because of the RF. 30' isn't enough. Vertical separation is what you need, but hard to obtain without a tall tower.

What kind of range are you getting, and what are you using for equipment.
 
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#17
I got my GMRS license about 2months ago and have changed freqs in my radio to Rx 462.725 TX 467.725 pl tone 151.4. I spaced out the antanas about 30feet and that seemed to work a little better. I don't have the money get to buy a duplexer. I just don't get what Im doing wrong.
You didn't buy a duplexer. In order for a repeater to work, the signal from the TX side of the repeater has to be blocked from entering the RX side of the repeater, otherwise it will drown out the incoming signal from the user. Separating the antennas will help a little, but the signal from an antenna 30 feet away is way stronger than one from 30 miles away and you're still going to have desense problems.

There is no cheap way to do what you're trying to do.
 
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#18
He states " spaced out the antennas 30 feet".

He could try spacing the radios out thirty feet from each other. Yes you are going to have to extend the audio cable between the radios.
 

buddrousa

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#19
Plus the duplexers are going to have to be tuned with a service monitor. here is what you are looking for
Celwave 633-6A-9 UHF Mobile Duplexer 50W Tuned 483.25/486.25MHz 6 TEM Cavites | eBay you might get a shop to tune them for another $100 unless they will work with you trying to learn. Next you are going to have to get rid of the mobile coax and antenna get you some LMR400 50 to 60 foot tower and still only going to have limited range due to power and the curvature of the earth for line of site. Here is a ham site that might help you get started. Radio Line of Sight Calculator for use on VHF/UHF Ham Bands
 
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#20
Next you are going to have to get rid of the mobile coax and antenna get you some LMR400 50 to 60 foot tower and still only going to have limited range due to power and the curvature of the earth for line of site.
You do not, I repeat DO NOT want to use LMR400 (or any similar style of coax) for full duplex use (as in a repeater). Due to the braid over foil shielding, you will develop issues with PIM, Passive Intermod Distortion (What is Passive Intermodulation?). It may work fine for a while, but over time you'll start noticing weird issues that will start making your repeater worse and worse and worse until it's basically unusable.
 
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