[App_rpt-users] Motorola CDM1250 JU551 position B

[Bryan Fields]

On 1/7/19 9:39 PM, Bryan D. Boyle wrote:
> DMs are stupid simple to connect to a URI.  Just need discriminator rx
> audio, ground, xmit flat audio, and ptt.  IIRC, rear connector pins 3, 5,
> 7, 11 (check the multitude of online sites for the specifics, but this is
> what I recall)
> 
> set up radio in CPS to send the right signals to the right pins, turn off
> pre/deemphasis in radio, do all the rest (COS, pl decode/encode,
> de/preemphasis, etc) in asterisk.

I have some example codeplugs for transmit and receive radios.  I built a test
node a couple months back for dev use and used CDMs.  I will put them up on
the wiki <https://wiki.allstarlink.org> once I get the uploader working for
cpg files.

Some pics of the repeater:
https://imgur.com/a/NXIlQ45

Note, I put in two DE-9's for connecting to the audio interface, one is simple
usb, the other is usbradio.

I did run into one issue on the CDM, as the transmit CDM was a UHF 2 that I
brought down to cover 440-517 MHz (from 450-527).  The deviation response vs
modulation frequency (modulation balance) was way off, even after aligning to
the Motorola standard.

What I found was motorola says to use a 80 Hz and a 3000 Hz at the same level
to align the balance in tuner.  The issue is by 3000 Hz the radio is already
rolling off, and this distorts the modulation balance.  The solution i found
was to align it using 80 and 2500 Hz.  This makes the radio look like a known
good radio.

Made a little graph of it here if anyone is interested.
> https://docs.google.com/spreadsheets/d/17_wWe14px_-2LUHl6XJN6EMRTjYnuYQXnqUBVkd49vY/edit?usp=sharing

Again, OT here and likely not applicable unless you're needing to completely
re-align the radio due to moving the frequency.

> Take longer to wire the cable up than to get the sw working, in my
> experience.

Verification of perfection is what takes the longest.

73's
-- 
Bryan Fields

727-409-1194 - Voice
http://bryanfields.net