Batboard

I'm trying to find which Motorola mobile radios would use the same audio PA and similar flat/de-emphasised audio output as the XTL-series radios for testing purposes. I've got several CDM, CMxxx, etc. radios on the shelf, and I'm wondering if any of those would have similar enough audio characteristics to substitute for an XTL-series and set audio levels on an interface box before I ship it across the country.
Any recommended radio models that are less expensive than an XTL?

Did it ever occur to you that you might get an answer faster if you explain just what it is that your trying to do.
We can guess and suggest all day long, but not knowing just what it is that your trying to interface with or
how is just spinning the wheels.

Detailed information will always provide some suggestions. Veiled questions and hints of your intentions only brings
more questions and few solid workable solutions.

Jim

Copperlion wrote:I'm trying to find which Motorola mobile radios would use the same audio PA and similar flat/de-emphasised audio output as the XTL-series radios for testing purposes. I've got several CDM, CMxxx, etc. radios on the shelf, and I'm wondering if any of those would have similar enough audio characteristics to substitute for an XTL-series and set audio levels on an interface box before I ship it across the country.
Any recommended radio models that are less expensive than an XTL?

One scenario I'm trying to work with is connecting to an IP-223 from Telex, using filtered audio (non volume controlled at the radio) into the IP-223 box, and leaving the sp+/- for a (locally volume controlled) local speaker. I will be using an XTL5000 radio when it gets on-site, but the radio is currently in use, so I don't get to set levels and such with it until the IP-223 and associated equipment is actually connected on-site. I'm wondering if I can set audio levels with a CDM or other series radio. I need to know if the audio output is going to be a similar format (impedance matching, similar audio PA, or any other necessary characteristics) so I can at least get close to plug-and-play, rather than have to set levels from scratch while I have a dispatcher standing over my shoulder.
Also, I see the RX_FILT_AUDIO on pin21 of the XTL accessory connector. What should I use as a reference for that audio? If I use that as my Rx-audio-high, what should I use for Rx-audio-low?

Another application I'm working on is connecting the flat audio to a 4-wire E&M circuit. I don't want the volume control on the radio to adjust the audio going to the remote dispatch through the 4-wire circuit, but I need 2 wires for Rx and 2 wires for Tx in order to make this work. Which pins would be appropriate for the use? The E and the M get split off to their own separate wires for PTT and COR, which I'm assuming would be pins 16 and 13 respectively.

One of the concerns that I would have is to try and match the impedance of your E & M system. Normally these
are in the order of 600 Ohms. Just pulling wires from the radio and connecting the audio to what ever your calling
a 4 wire E & M circuit is not good practice. The best way would be the use of some audio transformers.

In connecting to the XTL, bear in mind that the TX audio line input will have a DC bias on it to make an external
mic function. You will not need the bias and should put a series coupling cap inline to prevent shorting the bias
voltage to ground.

On the RX audio side you will find that there is also some DC bias, depending on just where you pull the audio
from. I have been in the practice of also placing a coupling cap in series to keep the radio happy.

The radio service manual will provide you with the correct pins to use for your audio connections.

You may have to make some software changes in the radio settings to get your audio to play correctly.

Jim

Copperlion wrote:Another application I'm working on is connecting the flat audio to a 4-wire E&M circuit. I don't want the volume control on the radio to adjust the audio going to the remote dispatch through the 4-wire circuit, but I need 2 wires for Rx and 2 wires for Tx in order to make this work. Which pins would be appropriate for the use? The E and the M get split off to their own separate wires for PTT and COR, which I'm assuming would be pins 16 and 13 respectively.

Unfortunately, I can't find anything in the service manual about how to use the RX_FILT_AUDIO pin in a 2-wire Rx audio setting. What should I use as the audio reference? In a single-wire audio system, that pin would be fine. I need to use it in a 2-wire system.
The bias voltages are listed in the manual, as is the isolation coupling recommendation. Thank you for adding emphasis to that, though.

Any ideas on the audio reference for that pin?

I have been out of town for a while. It might be to your advantage to look again in the XTL service manual.
The manual will give you schematic information on some of the pin configurations and pin out information for the
accessory connector on the XTL mobile.

I will tell you that your probably going to have to go into the XTL software and set the external mic gain higher
than the default 0 db it is set to. I normally set the gain to a +9 or +12 depending on just what is being connected.
Shut off the AGC.

As for your question about the second wire connection, I would say that common sense prevails here. If you don't
know what to use, then that indicates that you shouldn't be messing with the radio connections. Maybe you should
find a radio technician to do the work, before you damage a $4000 to $5000 radio.

Don't get me wrong here, I am not trying to give you a hard time. It's just that messing around here with a very
expensive radio can have things go wrong in a flash if you make a wrong connection. There are digital and analog
grounds. Using the wrong one might cause noise or other problems. Tread cautiously here. If the device your
trying to interface with is 600 ohms, then you should use a transformer to match the impedance.

Jim

Copperlion wrote:Unfortunately, I can't find anything in the service manual about how to use the RX_FILT_AUDIO pin in a 2-wire Rx audio setting. What should I use as the audio reference? In a single-wire audio system, that pin would be fine. I need to use it in a 2-wire system.
The bias voltages are listed in the manual, as is the isolation coupling recommendation. Thank you for adding emphasis to that, though.

Any ideas on the audio reference for that pin?

As a matter of fact, I am a technician with 4 years of experience- just not so much with this model radio. I was hoping to get some advice from someone who does have the hands-on experience with this model, to avoid doing the damage you mention.
Motorola is a very different beast when compared to Icom or Kenwood, all of which I have experience with. The APB radios (Above Price Book: XTL, XTS, etc.) are also quite different from the conventional/commercial models.
The schematics in the manual are somewhat convoluted- spread across several pages without any clear reference to pair with the flat/filtered audio pin. On the VHF Main Board pages (Controller Audio), it shows the RX_FILT_AUDIO coming off pin 5 of U0200, but that's about the only reference I see to that pin- with no corresponding match to make it a pair. SP+ and SP- come off a different component- after the volume controls.
There is no direct reference in the "Theory of Operation" section, either. That is why I posted my question here.
The "Technician" at Motorola tech support read the manual to me, which is about as useful as a mechanic telling you the headlight is busted after you tell him the headlight isn't working. What ever happened to the technicians that know more about the equipment than what the book or computer software tells them? --that's really a separate issue for another time and place, so don't bother actually answering that question. I put it here to illustrate my position: I would like to get the assistance I'm not getting directly from Motorola, regarding some expensive Motorola equipment.