How well does the MMDVM really work?

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tbiggums
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How well does the MMDVM really work?

Postby tbiggums » Mon Mar 06, 2017 4:52 am

I've tried searching around for info on some real repeaters using the MMDVM, but really haven't found what I'm looking for. I'm primarily interested in DMR and P25, and would like to build a repeater that supports both. Whatever radio I use it with needs to be a real repeater--100% duty cycle, 100 watts, and a professional grade receiver that performs well at high RF sites. I really didn't find much info online with details of people using a MMDVM with a MTR2000, MASTR II or III, or similar. I was hoping to find a lot of performance test data of the MMDVM paired with a variety of repeaters, where someone actually measured the transmitted modulation fidelity in P25 or DMR, and performed BER test on the receiver with a weak signal.

I guess a lot of people using the MMDVM don't have access to digital LMR test equipment, as about all I can ever find about how well the MMDVM works is "works pretty good" or something along those lines. It's kinda like that Tytera MD-380 radio that can't keep it's RF in it's own timeslot--seems all the hams with one of those radios just say "it sounds fine to me!"

Has anyone actually measured the transmitted modulation fidelity of the MMDVM on any radio? If it was above 5%, did they try any modifications to get it lower? For the receiver in DMR mode, how well does a typical analog repeater receiver handle both timeslots being used simultaneously with one signal significantly stronger than the one in the other timeslot?

I guess I'm just skeptical when I see people say "pretty much any wideband analog radio that has flat audio in and out can work with the MMDVM". I'd want whatever I build to be on par performance wise with a MTR3000 for DMR, or a Quantar for P25. Is this realistic?

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Project25
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Re: How well does the MMDVM really work?

Postby Project25 » Mon Mar 06, 2017 2:10 pm

There are some emails going around the Yahoo group right now concerning interfacing to a MTR2000.

In testing the (analog) sensitivity of various repeaters I've found Quatar receivers to hit 12 dB SINAD around -124 dBm, MTR2000's around -123 dBm, MTR3000's around -123 dBm and SLR5700's to -124 dBm. Only third party receiver I've seen to even be close in spec is the Hamtronics receivers (mainly due to the adjacent channel rejection).

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Re: How well does the MMDVM really work?

Postby DC5AJ » Fri Mar 10, 2017 10:40 am

I guess a lot of people using the MMDVM don't have access to digital LMR test equipment, as about all I can ever find about how well the MMDVM works is "works pretty good" or something along those lines


You are right, I would say most of the people have no test equipment at all, not even deviation is measured. I'm following the project pretty close and I would say most of the time people wiring it all together then turn the potentiometers until something happens, then using the BER reading that MMDVM gives you to tweak it to the lowest possible value. TX deviation is found by try and error most of the time.

I guess I'm just skeptical when I see people say "pretty much any wideband analog radio that has flat audio in and out can work with the MMDVM"


"Can work" is a broad definition, many analog radios can be used and it works as a bench top repeater or hotspot, but a bad receiver is just that and isn't magically super hot just because it's MMDVM now, seems that some people a bit over enthusiastic there.

I have no digital test equipment either nor do I know a person in my area that does, so I set the deviation using my analog gear, compared the output with spectrum analyzer and reality is, it is working ok, but in the fringe zone I can work a Quantar just fine and MMDVM regardless of what radios I use for RX/TX doesn't work from the same spot. My personal opinion is it is a great project, the performance depends highly on the used radios and available test equipment. Have no digital test set, so I did real world tests and compared MMDVM against a Quantar for P25 and Hytera RD985 for DMR, at the time I did this test, it was not on par. We should keep in mind the there is very active and fast development on the software side and also on the hardware, improved filters and so on, if you find test data or measurements that is half a year old, it may not be valid at present.

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tbiggums
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Re: How well does the MMDVM really work?

Postby tbiggums » Tue Mar 14, 2017 1:37 am

Thanks for the replies. That is pretty much what I was thinking. I browsed around the MMDVM yahoo groups posts some, and was hoping to find "here's exactly what I did to get a MASTR III repeater to have less than 2% modulation fidelity error on transmit and receive a P25 signal down -120 dBm with less than 5% BER", but didn't really find anything like that.

I guess one other question that I never really found the answer to was can the MMDVM be used to make a stand-alone repeater? The site I'd be using doesn't have any network connectivity at the moment.

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DC5AJ
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Re: How well does the MMDVM really work?

Postby DC5AJ » Tue Mar 14, 2017 7:01 am

Yes, stand-alone operation without network works without any problems.

Code: Select all

[P25 Network]
Enable=0
GatewayAddress=127.0.0.1
GatewayPort=42020
LocalPort=32010
Debug=0


Just set Enable=0 in the MMDVM.ini, you can disable / enable all modes and linking there. If you want to configure P25 linking you have to install and configure the P25Gateway also.

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crazyboy
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Re: How well does the MMDVM really work?

Postby crazyboy » Thu Aug 24, 2017 4:24 pm

Well I've been farting around with getting it running on a GR1225 and have been having a nightmare of a time getting audio levels set to a point where the digital will reliably pass through. All audio levels set to "spec" using the tuning apps, the answer turn the dials until audio passes through. Dohhh, Well then wouldn't that defeat the purpose of tuning it and it doesn't seem to be helping anyway. So I am currently contemplating getting an MTR2000 and trying the MMDVM with that, perhaps it just did not want to play well with the 1225. The other option is give up on the MMDVM and hope for a good deal on a quantar and go on the p25.nx network.

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MOTechGuy
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Re: How well does the MMDVM really work?

Postby MOTechGuy » Fri Aug 25, 2017 11:22 pm

crazyboy wrote:Well I've been farting around with getting it running on a GR1225 and have been having a nightmare of a time getting audio levels set to a point where the digital will reliably pass through. All audio levels set to "spec" using the tuning apps, the answer turn the dials until audio passes through. Dohhh, Well then wouldn't that defeat the purpose of tuning it and it doesn't seem to be helping anyway. So I am currently contemplating getting an MTR2000 and trying the MMDVM with that, perhaps it just did not want to play well with the 1225. The other option is give up on the MMDVM and hope for a good deal on a quantar and go on the p25.nx network.


I followed the directions here on tuning it and it works great:
https://www.f5uii.net/en/installation-c ... a-gm360/5/

However the MMDVM doesn't work good at all with some radios. The 1225 series might be one that it doesn't work with. I've had good luck with using Maxtrac series radios for RX and MCS2000 radios for TX. However the MCS2000 and VRM650/860 are terrible receive radios at least for DMR.
Make Amateur Radio Great Again! Use P25 and DMR on the ham bands.

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crazyboy
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Re: How well does the MMDVM really work?

Postby crazyboy » Fri Aug 25, 2017 11:26 pm

MOTechGuy wrote:
crazyboy wrote:Well I've been farting around with getting it running on a GR1225 and have been having a nightmare of a time getting audio levels set to a point where the digital will reliably pass through. All audio levels set to "spec" using the tuning apps, the answer turn the dials until audio passes through. Dohhh, Well then wouldn't that defeat the purpose of tuning it and it doesn't seem to be helping anyway. So I am currently contemplating getting an MTR2000 and trying the MMDVM with that, perhaps it just did not want to play well with the 1225. The other option is give up on the MMDVM and hope for a good deal on a quantar and go on the p25.nx network.


I followed the directions here on tuning it and it works great:
https://www.f5uii.net/en/installation-c ... a-gm360/5/

However the MMDVM doesn't work good at all with some radios. The 1225 series might be one that it doesn't work with. I've had good luck with using Maxtrac series radios for RX and MCS2000 radios for TX. However the MCS2000 and VRM650/860 are terrible receive radios at least for DMR.


Yup, that's the process I followed. Then after posting on somy hammy mmdvm group the answer was turn the pots until you get intelligible audio. :headbang: I'm thinking it just doesn't like the 1225.

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MOTechGuy
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Re: How well does the MMDVM really work?

Postby MOTechGuy » Sat Aug 26, 2017 2:38 am

https://wiki.brandmeister.network/index ... brew/MMDVM

This is a good reference. It says the M1225 has an unstable BER on receive. Then again someone claims the GR1225 is works?

I'm guessing you're having the issues with receive BER so I'd say a GR1225 doesn't work for RX.

I can personally confirm a GM300, Radius, Maxtrac, or Waris CDM series radio would work great for receive. That's what I'd recommend. I'm also re-capping a "Digital" MSF5000 and will see how that works for some VHF 25 and DMR.
Make Amateur Radio Great Again! Use P25 and DMR on the ham bands.

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crazyboy
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Re: How well does the MMDVM really work?

Postby crazyboy » Sat Aug 26, 2017 6:36 pm

MOTechGuy wrote:https://wiki.brandmeister.network/index.php/Homebrew/MMDVM

This is a good reference. It says the M1225 has an unstable BER on receive. Then again someone claims the GR1225 is works?

I'm guessing you're having the issues with receive BER so I'd say a GR1225 doesn't work for RX.

I can personally confirm a GM300, Radius, Maxtrac, or Waris CDM series radio would work great for receive. That's what I'd recommend. I'm also re-capping a "Digital" MSF5000 and will see how that works for some VHF 25 and DMR.


Yea, pretty much gave up hope on the 1225. It will either be sold or find its way onto gmrs. The ultimate goal is to have an actual repeater as there is no p25 machines here, so I'm leary on going the waris or maxtrac route since we all know how much hams like to chat. Then again the 1225 wouldn't last those rag chews either I'm sure. Will have to come up with plan B.


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