Making a "repeater" with two HTs?

[WRTC928]

I've seen a number of videos demonstrating how to make an impromptu repeater using two HTs and a connector box. One guy even demonstrated it using a simple audio cable, which begs the question, what does the commercial connector box do? Has anyone here done this? If so, how well did it work? TBH, I can't think of very many situations where I would find it useful, but if it's as easy as throwing an audio cable in my bag, I'll probably do it. Any personal experience?

[WRUE951]

Amazon and Ebay are loaded with HT repeater controllers, just make sure you get a controller that supports the two specific HT's you plan to use. Most Baufangs will be supported.. And you'll need a low power duplexer..  Probably not worth the trouble with HT's though. The same concept will work with most mobil transceivers and would be a better way to go.  Some mobil transceivers, like the Wouxun KG-1000 and Maxon's won't need a controller as it is part of the radio but rather a jumper cable between the two.    

[SteveShannon]

Mobile radios can sometimes be paired to create a decent repeater.  But many of them are just not shielded well enough and so the transmitter desenses the receiver. 

[WRTC928]

1 hour ago, WRUE951 said:

Amazon and Ebay are loaded with HT repeater controllers, just make sure you get a controller that supports the two specific HT's you plan to use. Most Baufangs will be supported.. And you'll need a low power duplexer..  

What, exactly, does the controller box do? One guy demonstrated it without the controller box; instead he just used an audio cable from the speaker output of one to the mic input of the other. What additional functionality does the controller box add? And I'm certainly not going to go out and buy a duplexer on the off chance that I may want to set up a quick repeater for the grandkids to run around on the farm. That's why I'm asking for personal experiences. 

[WRTC928]

33 minutes ago, SteveShannon said:

Mobile radios can sometimes be paired to create a decent repeater.  But many of them are just not shielded well enough and so the transmitter desenses the receiver. 

I understand about the possibility of desensing, which is why I'm trying to find out if anyone has actually tried it and whether that was a problem. I suppose if you separated the antennas enough, it wouldn't be an issue, but then you're back to having to carry extra crap around. I'll go as far as an audio cable and maybe even a $30 connector box, but that's about it. 

[WRQC527]

1 hour ago, WRTC928 said:

I've seen a number of videos demonstrating how to make an impromptu repeater using two HTs and a connector box. One guy even demonstrated it using a simple audio cable, which begs the question, what does the commercial connector box do? Has anyone here done this? If so, how well did it work? TBH, I can't think of very many situations where I would find it useful, but if it's as easy as throwing an audio cable in my bag, I'll probably do it. Any personal experience?

I tried to make it work with a pair of Baofeng UV5Rs set up in cross-band fashion, which is the simplest way to do it. I found that it's not as simple as connecting one cable between the radios. I ran into an issue where just connecting the radios with a standard 3-conductor audio cable put the transmit radio into perpetual transmit mode. I had to modify the cable. There are interfaces available, but honestly, out of all the videos of folks putting these setups together and bench testing them, I couldn't find even one video that showed the setup being successfully used in the field. If you can come up with a use case and you can get it set up and working, then by all means give it a try. I found it frustrating and ultimately not useful... for me anyway. Also, a duplexer is only needed if you're using the setup on a single band, like 2 meters. If you're cross-banding, no need for a duplexer. Duplexers also eat up RF power, something that you can't afford when you only have 5 watts to start with.

[WRTC928]

5 minutes ago, WRQC527 said:

There are interfaces available, but honestly, out of all the videos of folks putting these setups together and bench testing them, I couldn't find even one video that showed the setup being successfully used in the field. 

That's exactly why I'm asking. I've seen videos where it seemed to work on the bench but I haven't seen it done "in real life".

[WRQC527]

25 minutes ago, WRTC928 said:

That's exactly why I'm asking. I've seen videos where it seemed to work on the bench but I haven't seen it done "in real life".

I still have the goal of making it work and posting a video. The interfaces on Ebay employ an audio isolation transformer that among other things, breaks the electrical connection between the radios while still allowing the receive radio to trigger the VOX on the transmit radio. Some of them don't use VOX, they have some other voodoo circuitry. An additional power source like a solar panel charging an AGM or LiFePO4 also helps, because the duty cycle of an active repeater powered by only the radio batteries would substantially reduce run time. The list of parts needed to go from experimental bench testing to practical real-world use gets long and a bit costly. At some point, a radio with built-in cross-band repeat functionality is probably a better option. I have a ham friend who successfully uses a Yaesu FT8800 mobile for cross-banding. I think there are HTs available as well, but don't quote me.

[WRUE951]

1 hour ago, SteveShannon said:

Mobile radios can sometimes be paired to create a decent repeater.  But many of them are just not shielded well enough and so the transmitter desenses the receiver. 

Pretty easy to mitigate if two radios have that problem.  I had it with my KG1000 repeater and a simple piece if sheet metal cured it.   I have two Maxon’s in an ammo Box serving as a portable repeater and no issues with desenses without adding shielding.   I think if you use decent radio’s,  you’ll be o.k.  

[WRYZ926]

The easiest solution for a low power GMRS repeater is the Retevis RT97. Yes it will cost more that two HT's and some cables, but it will work as intended and will be a lot easier to setup with just one antenna. 

[SteveShannon]

9 hours ago, WRTC928 said:

I understand about the possibility of desensing, which is why I'm trying to find out if anyone has actually tried it and whether that was a problem. I suppose if you separated the antennas enough, it wouldn't be an issue, but then you're back to having to carry extra crap around. I'll go as far as an audio cable and maybe even a $30 connector box, but that's about it. 

The YouTube channel Notarubicon tried it using two Wouxun KG1000 radios.  These radios were built with this capability as part of the design. He has two or three videos describing what he did honestly.  Randy, the social media influencer who produces and performs in the Notarubicon videos, is @OffRoaderX on this forum.  It wasn’t a failure, but I don’t think he would describe it as ideal either. If using two antennas you need a lot of vertical separation or much much more horizontal separation; a duplexer really is the way to go.  Even considering the loss of power through a duplexer it is worth it.  
Randy ended up using a dedicated repeater and duplexer.

Here’s the first in his series of videos on building a repeater: 

 

If I wanted to set up a quick GMRS repeater for my family I would use the Retevis RT97S.  

[SteveShannon]

9 hours ago, WRTC928 said:

What, exactly, does the controller box do? One guy demonstrated it without the controller box; instead he just used an audio cable from the speaker output of one to the mic input of the other. What additional functionality does the controller box add? And I'm certainly not going to go out and buy a duplexer on the off chance that I may want to set up a quick repeater for the grandkids to run around on the farm. That's why I'm asking for personal experiences. 

The controller provides the necessary switching and provides level matching as well as sometimes providing the ability to identify the repeater at various intervals as required by regulations.

The speaker of a radio is probably between 4-16 ohms.  The microphone is a higher impedance than that. For best results the impedance should be matched.

[SteveShannon]

9 hours ago, WRTC928 said:

I understand about the possibility of desensing, which is why I'm trying to find out if anyone has actually tried it and whether that was a problem. I suppose if you separated the antennas enough, it wouldn't be an issue, but then you're back to having to carry extra crap around. I'll go as far as an audio cable and maybe even a $30 connector box, but that's about it. 

Notarubicon separated the antennas but having the two radio boxes near each other still caused desense. He ended up solving that by placing them in separate metal compartments as I recall. They just weren’t shielded enough.  Commercial Motorola radios are capable of being used clamped together because of their superior shielding, but the price difference is significant.

[WRTC928]

8 hours ago, WRYZ926 said:

The easiest solution for a low power GMRS repeater is the Retevis RT97. Yes it will cost more that two HT's and some cables, but it will work as intended and will be a lot easier to setup with just one antenna. 

That is true, but that won't satisfy my curiosity. This isn't really about having a repeater. As I said, I actually have little use for a repeater. It's more about knowing if it can actually be made to work easily and cheaply. My curiosity often sends me down rabbit holes. If it can work, it's worth knowing how in case it someday becomes useful.

[WRQC527]

3 minutes ago, WRTC928 said:

My curiosity often sends me down rabbit holes. 

You've hit on one of the things that sort of "differentiates", if you will, GMRS from amateur radio. GMRS is a "buy it and use it" endeavor. Amateur radio is an experimenter's paradise.

[SteveShannon]

6 minutes ago, WRQC527 said:

You've hit on one of the things that sort of "differentiates", if you will, GMRS from amateur radio. GMRS is a "buy it and use it" endeavor. Amateur radio is an experimenter's paradise.

This is exactly right.  Developing the skills needed to build various radio systems doesn’t require a person to become a ham, but it’s often easier if a person has engaged in studying the basics in preparation for the ham tests or has worked in commercial or military communications.