Re: Motorola Quantar & digital modes

Mike Moore
 

I saw a post in the repeater builder group about problems using the Quantar as a digital repeater.  I can't find the link now but will repeat the clipped test of the post.  I can't confirm this problem personally but there is help out there.  Sorry that I don't have the contact information from the post.  73, KC2NM

POST:
Hooking up MMDVM  (I used a ZUMradio Pi Hat v.0.9)to a Quantar was only partially successful.  I have a decent amount of experience with Quantars as well- I run a system which has 7 Quantars which are linked in P25 and analog running mixed mode.  I've also done board level repairs.

It boils down to this:  The Quantar works great in P25 using MMDVM (no big surprise there).  As for DMR, it will transmit DMR no problem, but the receive just WILL NOT WORK.  The furthest it could get was to see the downlink activation request from receive and would key up transmit, but it only intermittently recognizes sync (watching the MMDVM debug output).  I tried it only using P25 and DMR, nothing else.  To get it to this point, I ended up having to tap into the station control board at the most raw audio points I could find that low pass filters were not in the way.  The wireline and MRTI interfaces didn't work at all for me.  I would imagine the other non-TDMA protocols would probably work.

I was really perplexed as to why it would transmit DMR but not receive it.  After doing some analysis with my service monitor and O-scope, it looks like the issue is the phase delay of the RX audio varies wildly as you step up through the audio frequencies.  This is not the case with the transmit side which works nicely.  Keep in mind that all the audio in a Quantar (even analog) is digitized, so you never get to see what would be raw, analog discriminator audio.

As a comparison, I looked at the receive side of a CDM mobile radio which is known to work well with MMDVM DMR and found the phase delay was very consistent, unlike the Quantar receive.  At one point, I had the CDM mobile doing receive and the Quantar transmitting....what a frankenstein.

I had high hopes the Quantar would work with MMDVM because they are EXCELLENT repeaters, but this thing was developed over a couple decades ago and this TDMA wasn't considered in the design process.

I hope that clears this question up.

On Mon, Mar 12, 2018 at 12:37 PM, Steve Stroh <steve.stroh@...> wrote:
To finish John's thought, all digital voice radios that I've ever heard of (D-Star, DMR, P25, even System Fusion) are backwards compatible with FM. With the modification that John describes, you run the radio in FM mode. It's ideal if the radio is flexible about the channel size. For example, D-Star uses a 6.25 kHz channel rather than the (traditional to FM operation) 25 KHz channels, and the more common these days 12.5 kHz channel.

On Sun, Mar 11, 2018 at 3:06 PM, John D Hays - K7VE <john@...> wrote:
Jim,

You don't need an AMBE chip (eg. ThumbDV) at the repeater.  Most digital modes require a modem that is connected to the discriminator and modulator (flat audio, no pre/de-emphasis) and appropriate software to handle the protocol.  The UDRC II was designed to provide the hardware to support software defined modems and PTT  -- see https://nw-digital-radio.groups.io/g/udrc/wiki/UDRC%E2%84%A2-For-Simplex-Hotspots-and-Converted-Analog-Repeaters

On Sun, Mar 11, 2018 at 2:51 PM, jim lang <jimlang@...> wrote:

Does anyone have experience / knowledge of connecting say a Thumb DV or anything digital to a Quantar?  I have recently obtained a UHF Quantar, and was wondering if it is humanly possible to run it both analog (FM) and in digital modes…I know it’s already P25 capable, but thinking more along the lines of D-Star, Fusion, etc., etc.  (whatever the flavor of the month might be!).   Basically, whatever comes in (i.e., analog, Fusion, D-star) goes out.

 

Thanks in advance,

 

Jim / kd9gy




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John D. Hays
Edmonds, WA
K7VE

   




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Steve Stroh (personal / general): stevestroh@...


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