Lapel Speaker/Mic for a Motorola SM50

[WP3WG]

I want to use a Motorola speaker/mic with the SM50 and have the speaker also activated. The reason is that the radio will be inside a case, with only the antenna cable and the mic cable coming out through the water tight Pelican case. How would be the wiring connection? I guess I have to use the accessory connector pins 1 &15 or 16 don't remember. Also, can I get the color wires Id of the speaker/mic. I will get later the model #, but this lapel mic came with a GTX radio.The speaker/mic I am talking about is HMN9030A.

I tried the 4 wires lapel mic without success. I did tried the 9053E which I had as an old mic for a HT750. I wired it using the available BATLABS diagram for RJ45 8 pin mobile connector and the 13 pins lapel mic connector. The match was as follows: SM50 Pin 4 (of the RJ45) to the #7 of the 13 pin connector of the mic, Pin 5 of the mobile to pin 4 of the mic and finally pin 6 of the mobile to pin 5 of the mic. To activate the speaker, I used pin 1 and 16 of the 16 pin accessory connector of the SM50, to pin 1 and 2 respectively of the mic connector. Speaker audio is excellent, clear and high. Mic audio was very low, not acceptable. I opened the mic and found out that threre were several resistance bertween the dynamic (I believe) mic bud and the mic audio wire. I by passed all those resistances with a jumper, and even detached a small one in the mic bud laminated conductors. The audio increased considerably. At least acceptable. I even removed the black foam covering the bud (mistake, I believe). At least I have a functional system that is going into the Pelican case water tight, alomg with the UPS 12V battery. With this battery, the radio is on for a long time, at least 8 hours with low duty use. Only 2 cables (watertight ) will come out from the case. The antenna RG58 and the coiled mic cord.

My only concern is to bag the mic to protect it from the salt water, not only the splash, but sometime it can go into the pooled water that get inside the dinghy. This is mostly for Scuba diving, communication before water entry and after surfacing. If someone can help me increase the Mic audio, I will really appreciate it.

I was even thinking in replacing the bud. In a dynamic mic, does the higher the resistance in ohms the higher the electrical voltage generated for the audio? If that is so, can I get diferent bud with higher ohms, meaning larger coil and increase audio milivoltage? Please reply if you have an answer or a better way to increase the mic audio.

Thanks,

Darrel

[K6LCS]

>> ... I want to use a Motorola speaker/mic with the SM50 and have the speaker also activated. The reason is that the radio will be inside a case, with only the antenna cable and the mic cable coming out through the water tight Pelican case ...

I have read your post several times ... and cannot figure out what you are trying to do.

The standard mike for the SM series is the HMN3174B.

The SM50/SM120 radios use the same microphones and programming cables as for MaxTrac/Radius/GM300 radios. The MIC jack pins are numbered 1-8 from right to left when looking into the front of the radio with the RJ45 tab down.

Pin Function Notes
1 +8V NOT current-limited
2 Clone Used for cloning radios
3 Hook Ground for coded squelch
4 Ground
5 Mic Audio Has +8VDC bias present
6 PTT Ground to activate
7 SCI Bidirectional programming line
8 RX Audio Fixed level, muted, de-emphasized

How about mounting a waterproof speaker to the Pelican case for receive audio?

And see if Otto Engineering has an Evolution H20 immersion-rated speaker mic for your very harsh conditions.

Clint Bradford K6LCS
909-241-7666