Repeater Box Build: Attempt 1

[WRDJ205]

I did a lot of reading on the forum from different posters and watched all the YouTube vids that I could find.  And despite most people saying it wasn't worth the effort, I was still hoping that this would be a good project to work on with my kids-get them off the screens and find more interest in something tangible-ish.  I know that the choice in budget HT's is not ideal, but this would be used only for family communications at a rural property very intermittently.  We don't quite get full coverage so the idea would be to take this suitcase repeater out to a hill, hook up an antenna and use it while we're out and about.  

However, it didn't take long before I hit a roadblock.  I wanted to test out the new 50W duplexer tuned for the 462.725/467.725 pair with a couple of HTs that I originally planned to use in the build.  The first issue I had was the mic jack on one of the radios is damaged and wouldn't transmit to the receiving radio on the mic to speaker cord.  So that radio will be moved to the handheld function and not connected to the duplexer.  

The input / output tones and frequencies were all checked, and everything worked well without using the duplexer (see pic "Function w-o Duplexer").  Yes, there was a significant amount of desense as expected.  I turned the power to low on the receiving radio.  I tried the vox at 1 and a 9 without noticing much difference.  I did have to put the volume down very low on the receiving radio to minimize feedback.  

Next, I hooked both radios to the duplexer and immediately, the transmit radio (on right) began transmitting as shown with the red light (pic "Connection Transmit").  Initially, I thought it was caused by something in the duplexer recognizing that there was something to transmit.  The indicator light was on for several seconds, then flashes a couple of times and then the radio goes into normal standby.  With same two radios used on the non-duplexer test, one set to 467.725 and the other to 462.725, I tried to transmit.  I get the green receiving light on the left side receive radio (467.725) but nothing coming out of the transmit radio on the right side (see pic "No go w Duplexer").  

The radios are the GMR-5RH which seem to be a re-badged UV-5G.  The menu is almost identical to the AR-5RM (that's the one with the broken mic jack).  I've gone through the menu's multiple times on the transmit radio and while there are a couple of different settings that seem to relate to the repeater function, they seem to be related to squelch tail.  I did try changing some of the settings but I'm hoping someone can point me in the right direction. 

Is the issue radio setting related - receive or transmit?  Duplexer related?  Radio function in general related?

Thanks in advance.  

[SteveShannon]

The duplexer is passive. It can’t command a transmission. Presumably you powered off the radio before connecting to the duplexer because the noise generated while connecting it to the antenna port could cause VOX to activate. 
Second, although the duplexer might filter it all out, I recommend turning off your B channel. You almost have the national calling frequency (146.520 MHz) tuned for both radios. 
I’ve not built a repeater using two handhelds so I can’t answer your other questions, sorry. But you make me want to try just to learn.

[WRUE951]

I would implement a controller, Surecomm will have something that works with HT's   

[WRDJ205]

Tried it again with another set of radios.  Works ok enough without the duplexer (less desense).  

But, it still doesn’t transmit from the speaker of the receive to the mic of the transmit.  

[marcspaz]

I need to ask some questions...   You are using a cable to go from the receiver audio out to the mic audio in, and set to vox?  Correct?

If you simply remove the antenna cables from the duplexer, everything works (as well as to be expected without a duplexer, anyway)?

When you hook up the duplexer, the receiver receives a signal, gets a green light, but the transmit radio doesn't go into transmit mode, even though vox works fine without the duplexer?  Or does the transmit light/display indicate that the transmitter is actually transmitting, but there is just no output from the duplexer?

[WRDJ205]

@marcspaz

Yes, using cable exactly as you describe with Vox.  

Yes, it seems to work without going to the duplexer using whip antennas.   There’s some background noise but I figure that’s due to the proximity of the antennas.   
 

1 hour ago, marcspaz said:

the receiver receives a signal, gets a green light, but the transmit radio doesn't go into transmit mode, even though vox works fine without the duplexer

This is what happens. 
 

As a separate troubleshooting effort, I moved the common antenna away when the HTs were connected at one point.  Still nothing.  
 

It seems to be on the receiving radios output or the transmitting radios input.  But the connection cable works fine without the duplexer so I’m leaning more to duplexer issue.  
 

I’m open to suggestions.   

[LeoG]

So this is a full spectrum tuned duplexer.  Says 550-725 on the label.

 

So have you tried this on other frequencies?

How about separating the RX and TX HTs.  Put on of them in a metal box to try to isolate it.

Maybe the common antenna is desensing the HTs

[WRDJ205]

2 minutes ago, LeoG said:

So have you tried this on other frequencies?

I haven’t tried it.   Won’t be able to test it til Friday but definitely worth the attempt.  Thanks for the tip.  

[marcspaz]

I am thinking you need to swap radios on the duplexer ports.  Like, I think they are labeled backwards.  It would make sense that the case of the HT is letting enough RF leak in to trigger a receive light, but there is not enough of a signal to create usable audio output to trigger the vox operation.

 

If its not labeled wrong and it is wired correctly, you could just be washing out the systems due to being to close to each other and too close with the test handheld.  I have seen some HTs so sensitive to RFI from other HTs, that we had to separate them by 75 to 100 yards before the RFI and desense was small enough for the radios to work correctly.

[WSIK532]

12 hours ago, WRDJ205 said:

I did a lot of reading on the forum from different posters and watched all the YouTube vids that I could find.  And despite most people saying it wasn't worth the effort, I was still hoping that this would be a good project to work on with my kids-get them off the screens and find more interest in something tangible-ish.  I know that the choice in budget HT's is not ideal, but this would be used only for family communications at a rural property very intermittently.  We don't quite get full coverage so the idea would be to take this suitcase repeater out to a hill, hook up an antenna and use it while we're out and about.  

However, it didn't take long before I hit a roadblock.  I wanted to test out the new 50W duplexer tuned for the 462.725/467.725 pair with a couple of HTs that I originally planned to use in the build.  The first issue I had was the mic jack on one of the radios is damaged and wouldn't transmit to the receiving radio on the mic to speaker cord.  So that radio will be moved to the handheld function and not connected to the duplexer.  

The input / output tones and frequencies were all checked, and everything worked well without using the duplexer (see pic "Function w-o Duplexer").  Yes, there was a significant amount of desense as expected.  I turned the power to low on the receiving radio.  I tried the vox at 1 and a 9 without noticing much difference.  I did have to put the volume down very low on the receiving radio to minimize feedback.  

Next, I hooked both radios to the duplexer and immediately, the transmit radio (on right) began transmitting as shown with the red light (pic "Connection Transmit").  Initially, I thought it was caused by something in the duplexer recognizing that there was something to transmit.  The indicator light was on for several seconds, then flashes a couple of times and then the radio goes into normal standby.  With same two radios used on the non-duplexer test, one set to 467.725 and the other to 462.725, I tried to transmit.  I get the green receiving light on the left side receive radio (467.725) but nothing coming out of the transmit radio on the right side (see pic "No go w Duplexer").  

The radios are the GMR-5RH which seem to be a re-badged UV-5G.  The menu is almost identical to the AR-5RM (that's the one with the broken mic jack).  I've gone through the menu's multiple times on the transmit radio and while there are a couple of different settings that seem to relate to the repeater function, they seem to be related to squelch tail.  I did try changing some of the settings but I'm hoping someone can point me in the right direction. 

Is the issue radio setting related - receive or transmit?  Duplexer related?  Radio function in general related?

Thanks in advance.  

Hello,

 

this is whats missing Amazon.com: ZEZEFUFU Two-Way Relay Walkie Talkie Repeater Box RX/TX for Baofeng UV-5R Accessories 5MHz U-V V-U Cross Band Walkie Talkie Repeater : Electronics

[WRUE951]

7 hours ago, WSIK532 said:

Hello,

 

this is whats missing Amazon.com: ZEZEFUFU Two-Way Relay Walkie Talkie Repeater Box RX/TX for Baofeng UV-5R Accessories 5MHz U-V V-U Cross Band Walkie Talkie Repeater : Electronics

Yup..

[marcspaz]

Just added that to my cart. I'm gonna test it next week.

[WRUE951]

17 minutes ago, marcspaz said:

Just added that to my cart. I'm gonna test it next week.

Make sure to fill us in..  

[WSIK532]

1 hour ago, marcspaz said:

Just added that to my cart. I'm gonna test it next week.

Im ordering it over the weekend. i really thing that's the missing part to the setup.

[WRDJ205]

I did try one like it but the one I had did not work.  It may be a bad one but I had better results with just the wire with the appropriate jacks on either end.   

[WSIK532]

1 minute ago, WRDJ205 said:

I did try one like it but the one I had did not work.  It may be a bad one but I had better results with just the wire with the appropriate jacks on either end.   

Maybe,  but there are a few different ones to try.

[WRDJ205]

On 6/18/2025 at 8:41 PM, marcspaz said:

I am thinking you need to swap radios on the duplexer ports.  Like, I think they are labeled backwards.  It would make sense that the case of the HT is letting enough RF leak in to trigger a receive light, but there is not enough of a signal to create usable audio output to trigger the vox operation.

I'm now leaning more to a connector problem (either the direct wire or the connector box (shown in a prev post)) coupled with a possible duplexer problem. I've swapped btwn 2 cords and the connector box, all combinations of 6 different radios (from 2 different man'f), high side/low side connections on the duplexer, antenna combinations, frequency pairs, etc.   I can still get a receive and transmit using either the cords or the connector box (this box only works with H3's) when not connected to the duplexer.  

Using the connector box, the transmit radio does key up on today's trials but it doesn't stay in transmit long enough to actually say anything.  

I am still open to new thoughts or ideas and will give it some more thought over the weekend.  I don't have an issue hooking things up and doing some basic troubleshooting, but I'm out of my element and don't have the tools to troubleshoot much further.   

 

[marcspaz]

1 minute ago, WRDJ205 said:

I'm now leaning more to a connector problem (either the direct wire or the connector box (shown in a prev post)) coupled with a possible duplexer problem. I've swapped btwn 2 cords and the connector box, all combinations of 6 different radios (from 2 different man'f), high side/low side connections on the duplexer, antenna combinations, frequency pairs, etc.   I can still get a receive and transmit using either the cords or the connector box (this box only works with H3's) when not connected to the duplexer.  

Using the connector box, the transmit radio does key up on today's trials but it doesn't stay in transmit long enough to actually say anything.  

I am still open to new thoughts or ideas and will give it some more thought over the weekend.  I don't have an issue hooking things up and doing some basic troubleshooting, but I'm out of my element and don't have the tools to troubleshoot much further.   

 

 

The only other thing I can think of is the duplexer is not tuned correctly on either side and the protective limiter circuit and the transmit radio is stopping it from transmitting so it doesn't break. You are going to need a VNA at a minimum to test. At this point I don't trust the duplexer.

 

I'll kick some thoughts around, but without being right in front of it it's going to be hard to troubleshoot from this point.

[WRDJ205]

Found a combination that works using the Tidradios.  I’m not sure what was done differently other than using the H3 radios and trying a different frequency and the connection box.   Even with the duplexer they’re putting out about 3W out of the duplexer to the mag base antenna. 
 

As a test I put the Boafeng in the exact same configuration.  I could only get them to work on the .600 pair.  But they were pushing closer to 5W out. 
 

 

[WRDJ205]

5 hours ago, WRDJ205 said:

I’m not sure what was done differently other than using the H3 radios and trying a different frequency and the connection box.  

I realize that’s several things different.  
 

To make sure it wasn’t an anomaly I took it all apart and reassembled and it worked again.   There is an appreciable delay in the transmit (a couple of seconds) but if you wait it out it does work.  
 

Another change was in the transmission time.  With the connector box cable there must be something that recognizes transmission.  If you aren’t talking it stops transmission.  Almost like a VOX on the radio would work.  I think that was also throwing me off before.  
 

So for now, I have all the working components with the main parts being the duplexer (tuned for multiple pairs) and the two H3 radios connected using the connector box cable. 

 

I was hoping to get closer to the RT97S power >5W but with the H3 HTs it seems like 3W is going to be the top end.