Feeding amplified audio into a PM400

[Pyrojim]

Hi all,
I’m connecting a PM400 to an alternative audio source. I have a need to transmit some recorded SMPTE Time Code audio to a client and it will feed the PM400 via an iPod, an iPad, or some other amplified audio source. I’m working on an interface to connect the two.

This is what I know from the Motorola documentation:
The PM400 accessory plug has two inputs:
Pin 2 is listed as “Input impedance: 500 Ohms. 80mV rms at 1 kHz for 60% deviation. This path is enabled when external mic PTT (pin 3 ) is keyed.
Pin 5 is listed as Flat TX Audio Input: Input impedance greater than 35K ohms. The nominal input level is 150 mV rms for 50% deviation.
Here are my questions:
1) Can anyone suggest a schematic for an interface to connect an amplified audio source to the PM400? I believe it will require an audio matching transformer and an audio taper potentiometer at the least? I could really use some component values.
2) Which of the above two pins is the proper pin to feed this through?
3) Does anyone make such a thing that I can just buy off the shelf? As much fun as it would be to build this, I’m short on time right now and I need to have this working.
Thanks,

JIM

[FMROB]

Unless someone else has some advice on this, and this is just a thought (again a thought), I would use the pin 2 input and I would put a line matching transformer between the ipad and the rear of the radio. You could whip this up with a trip to radio shack and setting two pins into the accessory plug of the radio. You would of course have to install a switch between the PTT pin 3 and ground pin of the radio to activate when the radio should transmit. The ipad should have an audio output volume adjustment and your off to the races.

http://www.bogen.com/products/pdfs/spec ... WMT1Am.pdf

Rob

[Will]

We use a 2.2 K resistor and a 2.2 uF capacitor in series with the mic input. The + side of the capacitor towards the radio's mic input, blocks the DC on the mic line.

Use the mic input either on the mic jack or the accy jack.

[Jim202]

We use a 2.2 K resistor and a 2.2 uF capacitor in series with the mic input. The + side of the capacitor towards the radio's mic input, blocks the DC on the mic line.

Use the mic input either on the mic jack or the accy jack.

As Will has mentioned, there is a DC bias voltage on the mic input line. You also need to drop down the audio level going into the radio. Too high of a level will cause distorted transmit audio. You might have to add an adjustment potentiometer to be able to adjust the level. The series resistor may also be required to be able to get the audio level into a range you can use. Some experimenting may be required to obtain the correct level.

Jim

[ve3nsv]

The PM400 will do VOX so no PTT switch should be required.

Unless someone else has some advice on this, and this is just a thought (again a thought), I would use the pin 2 input and I would put a line matching transformer between the ipad and the rear of the radio. You could whip this up with a trip to radio shack and setting two pins into the accessory plug of the radio. You would of course have to install a switch between the PTT pin 3 and ground pin of the radio to activate when the radio should transmit. The ipad should have an audio output volume adjustment and your off to the races.

http://www.bogen.com/products/pdfs/spec ... WMT1Am.pdf

Rob