Connecting David Clark to CDM1550

LCFD1 · Post by **LCFD1** » Fri Sep 03, 2004 10:27 am

Hello All-
I have been asked to connect a DC 3800 series system to a CDM 1550. At this point, I have the 6 conductor cable coming from the DC radio interface box hanging out by the radio.

Does anybody have any pointers on getting these two interfaced? I want to interface it to the accessory connector, and not the microphone connector. I immagine that the pins have to all be programmed for the correct function as well. Does anybody have a documented setup thet they know works?

Thanks a lot!
-Sonny

Post by **wavetar** » Fri Sep 03, 2004 11:34 am

It shouldn't be too hard. I don't know what wire is what for the David Clark unit, but the CDM1550 accessory pins are as follows:

Pin 7 - GND/TX-/RX-
Pin 2 - Mic audio (TX+)
Pin 3 - PTT (grounding pin causes radio to TX)
Pin 11 - RX audio - set in the programming for 'filtered'. If set for 'flat', it will always be unsquelched.

That should be all the connections you require for the hook-up.

Todd

thebigphish · Post by **thebigphish** » Fri Sep 03, 2004 2:20 pm

we've been wondering the same for a good six months now

kmoose · Post by **kmoose** » Fri Sep 03, 2004 2:36 pm

Do you know which DC radio interface module you have? I show three different models for the 3800 system: a U3810, a U3811, and a U3812. I don't have schematics for any of these boxes, but I can probably get them. Let me know if you can figure out which module you have.

BDB · Post by **BDB** » Fri Sep 03, 2004 7:23 pm

On the C3821 cable

Red is mic high
Wht is mic low
Grn is audio high
Blk is audio low
Blue is PTT low
Yellow is PTT High

Bret

jim · Post by **jim** » Fri Sep 03, 2004 8:30 pm

Also, set your accessory microphone gain to approximately 36 dB in CPS.

thebigphish · Post by **thebigphish** » Fri Sep 03, 2004 9:57 pm

BDB wrote: Red is mic high
Wht is mic low
Grn is audio high
Blk is audio low
Blue is PTT low
Yellow is PTT High

So, am i correct in assuming that in
Pin 7 - GND/TX-/RX- = mic lo / audio lo / ptt low?
Pin 2 - Mic audio (TX+) = mic hi
Pin 3 - PTT (grounding pin causes radio to TX) = ptt hi
Pin 11 - RX audio = audio hi?

because that seems WAY too easy. and are the trigger voltages ( hi / lo vals) close? because that makes WAY too easy....incase i haven't said that. i gotta be missing something.

Post by **wavetar** » Sat Sep 04, 2004 5:13 am

thebigphish wrote:
BDB wrote: Red is mic high
Wht is mic low
Grn is audio high
Blk is audio low
Blue is PTT low
Yellow is PTT High
So, am i correct in assuming that in
Pin 7 - GND/TX-/RX- = mic lo / audio lo / ptt low?
Pin 2 - Mic audio (TX+) = mic hi
Pin 3 - PTT (grounding pin causes radio to TX) = ptt hi
Pin 11 - RX audio = audio hi?

because that seems WAY too easy. and are the trigger voltages ( hi / lo vals) close? because that makes WAY too easy....incase i haven't said that. i gotta be missing something.

Why does it have to be complicated? You're simply keying the radio & routing audio to/from it. I'm not sure what you mean by 'trigger voltages'. The only voltage involved is 8.75Vdc mic biasing voltage on pin 2. You may need to put a capacitor in-line with it to block the DC voltage if the David Clark unit doesn't need it. I interfaced an ICOM & MCS2000 into a 3810 series (I believe) a couple of years ago, those pins are all you need.

Todd

jim · Post by **jim** » Sat Sep 04, 2004 6:47 am

DC mic high - to- pin 2
DC PTT high - to - pin 3 (or whatever is programmed for PTT)
DC mic low and PTT low to pin 7
DC speaker hi to pin 1
DC speaker lo to pin 16

No cap is needed. Nothing else is needed. Don't worry about voltages or anything.
Make sure that "external mic" is selected in CPS.

Post by **wavetar** » Sat Sep 04, 2004 8:36 am

Jim is correct that you can also use the speaker outputs (pins 1 & 16) for RX lo & hi. Just be aware the volume control of the radio is going to affect the overall RX audio level coming out of the David Clark box. If the David Clark unit has any sort of audio amplification, you'll probably want to use the lower level pin 11, which isn't affected by the radio's volume control.

Todd

jim · Post by **jim** » Sat Sep 04, 2004 4:22 pm

Unfortunately, the DC has no amplification. If you use a simple audio amplifer driven by pin 11, you can drive the DC system.

Note that the DC system has an isolated audio input that doesn't connect to ground so that you don't have to use an isolation transformer on certain "non-floating ground" Motorola radios that can suffer from audio PA failure. Just go straight in.