Kind of interesting.
https://www.retevis.com/repeater/

A friend of mine bought the RT97 GMRS repeater.  I'm going to help him set it up Saturday.  

It would be neat to get one and re tune it for the 70 cm band, but after watching some videos, it looks like the nano VNA isn't quite up to the task.

If you mean using it to tune the notch duplexer, I have used a NanoVNA to do that.  I hooked it up to a PC and used the software to get better resolution, and it's not great due to the slower sampling rate, but it can be done with patience.

I'll stick with SLR5700's.  50W 100%DC analog/dmr/mixed repeater.


SLR, IPDU, flat-pack duplexer, and a router on the back... apply power and the repeater's up.  Connect ether to whatever, and with the router you can do all kinds of neat stuff.

$3000 vs. $300: apples and oranges.

After fooling with the retevis, I don't know what's going on with it and how it achieves filtering.  It uses a single antenna, but the enclosure is pretty small.  I don't know if a set of cavity filters would fit inside.

It has like 10 different "channels" you configure in software.  But when it coles out of the box, they are all set to the same frequency.  The instructions make no mention of re tuning filters.  And it has a pair front panel buttons for cycling through the channels.

How can they achieve full duplex operation through a single antenna and be able to operate on multiple frequency pairs at the press of a button?

They have one of those tiny duplexers in there.  You'd have to retune that if you wanted to reprogram from the original frequency pair.

Hmm...  

After doing some reading it looks like if you order the GMRS version it comes tuned for 462.625 and 467.625, (which would be the middle of the GMRS frequencies allocated for repeater use) and supposedly can be changed on the front panel to the other GMRS repeater pairs and still function.

Knowing this though, I advised my friend to open it up and read the frequencies off the label on the duplexer.  If it's not the pair I posted above, he will need his duplexer tuned.

That said, it just so happens that by a stroke of luck, we programmed those exact frequencies in the software that came with the repeater, and it does function as expected using a mobile GMRS radio and two different handheld radios.

If the duplexer center frequency was off by a full 1 MHz, would it still appear to function?

5meg split, it'd ""probably"" work, but poorly.  Probably 20dB loss just through the filter being that far off.

Also, with that tiny duplexer, it's probably only going to work well with large offsets, such as the 5MHz used in GMRS.

A late ham friend used to work with the "flat pack" duplexers quite a bit. He said careful tuning could get the ones with six inch cavities to 2.2 dB of loss. He said on GMRS, tuning the recieve notch edge at 462.725mhz and the transmit edge to 467.550 would allow it to work on all 8 frequency pairs. I can't speak for the mini-duplexers.

UHF uses a 5 MHz offset everywhere but T-Band. VHF can really vary...500 kHz to 5.25 MHz.

Neat.
I don't think I would strap that to a tree for a few days with a battery to use at a hunting camp once or twice a year.
The positives for the tiny repeaters to me is it can be strapped to a tree on a ridgeline with a 12ah battery and be as hidden as a game cam.
It would be easy to carry in a canoe to the boundary waters for group comms.
I don't think rack mounted equipment is suited for those applications.

Turns out my friend's is set with a 10MHz split in the 70cm ham band.

When we tested it with GMRS frequencies, it appeared to work, but it was just outside the house maybe 75 feet away at best.

He's returning it and ordering the GMRS version.

Yeah, I could play with trying to re-tune the duplexer with my nano VNA but I'd rather experiment on my own stuff instead of someone else's.

DMR can repeat on a single frequency by using the opposite timeslot.


Transmit on timeslot 1, receive on timeslot 2.



The manual strongly implies you must select the specific (one of the eight) frequencies to operate on. (As opposed to repeating any one of the 8 at any time).  But as you have one to play with, I’m guessing you’ve experimented with that?

Single frequency repeating isn't part of the DMR specification. It's available from several manufacturers but should not be expected to interop across the manufacturers. Similarly, dynamic dual slot operation is available from multiple vendors and isn't part of the spec either.

The little Retivis repeater has a micro-duplexer in it. Another repeater which uses a similar (but differently sized) duplexer is the Motorola SLR1000. It's just a standard nochplexer but doesn't provide the isolation to handle more than about 5 or 10 W.

The AnyTone AT-D578UVIIIPRO cross time slot repeat does not work at all, at least when we tried to do it, even though they advertise the function.

My friend bought one, thinking to use it for GMRS, so his version was not the DMR version.  I had him open up the case and take a pic of the duplexer label and text it to me.  The duplexer is tuned in the 70cm ham band.  

The radio can be programmed anywhere from like 439 to 470 MHz.  He's returning it for the GMRS version.

Funny thing is it worked when programmed for a GMRS repeater pair, but we were only 100 feet away when we function tested it.  

They are advertised as being able to operate on 8 different channels.  But I think the best course would be to simply program 8 different CTCSS tones and use the same frequency pair that the duplexer is tuned to.

Then you can use the front panel buttons to choose different tones.

He will still need to rig a way to cut power remotely to block access.

In the mean time, I ordered a surecom repeater controller and I am probably going to get a cheap UHF duplexer to play with at home, just to see if I can really tune one with a nano vna.

The cool thing about the repeater controller is you can use any combination of 2 radios, and the cables use TRRS plugs so you can easily make your own radio cables.

Get one with a very good receiver with good rejection for the receive side, and a mobile radio for the transmit side.

The good thing about the surecom controller is it will take DTMF codes to shut it down remotely.

I definitely like the convenience of these "repeater in a box" things from retevis but they lack the ability to shut them down.

I think they are great for temporary use in a remote location, not sure I would rely on it for heavy use. Hell, the kit version gives you and your hunting buddy comms in one neat package.