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Author Topic: GM 380 roip PTT  (Read 3681 times)
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m3odq
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« on: December 09, 2010, 08:39:19 PM »

Ive started to get interested in roip again and im trying to interface my GM380 to my PC.

I've built a vox circuit which provides closure to ground when it is hit with audio.

I just cant get the 380 to TX from the accessory connector on the back. Angry

I've looked at all the guides and I've wasted a whole weekend google searching for any info. It seems simple enough but just wont work for me!

I've got pin 3 (ptt) and 7 (gnd) shorting them does nothing. I've been into the codeplug and tried all kinds of settings for pin 3 i/o settings.

Can anyone help? Im just about flumoxed here! LOL!

Dave
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m3odq
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« Reply #1 on: December 09, 2010, 11:21:45 PM »

By the way, I have now shorted pin 3 to 7 on a VHF GM340 and an MTM700 tetra set...  Works just fine on those!!

Any ideas why it wouldn't be working on a GM380?
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shedcreations
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« Reply #2 on: May 01, 2018, 10:25:49 AM »

hi there,

I think you and I have gone round the same block?  I have been trying to interface my GM340 VHF to my PC too.  I all depends on how you want the PTT to energise?

Pin 3 can be set to "Voice PTT" & "High" in the software if set like this the PTT expects to see 5 volts to energise.  If set to "Voice PTT" & "Low" is expects to go to ground.

My PC interface is using a COM port voltage via the DTR pin of +6 volts to allow the PTT to energise.  My GM340 did not energise if I set it to"Voice PTT"  "Low" in the software and tried to ground it.

I have another problem? My PTT now works (giving it +6v), but I'm not getting any audio into the external mic pin (pin 2)?  The external mic has an impedance of 600 ohms and I think the PC soundcard is 8 ohms?  Have you had this problem?

Hope to hear from you soon

Jon
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m3odq
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« Reply #3 on: July 02, 2018, 11:32:58 AM »

Hi Jon,

Wow, this was a long time ago. The original post was almost a decade ago!
I can't remember what happened with my problem in the end, but I've run a number of GM series radios in the meantime, so I must have sorted it at some point.

As for your problem..
I strongly recommend using line in audio rather than microphone audio. I avoid any amplification if possible to try and keep the noise down.
Try using Pin 5 (Flat TX audio). Input needs to be about 150mV for 60% deviation (from Moto datasheet).

Also, I refuse, point blank, to short ground connections between devices after killing a really nice MP3 player during testing.
After the above happened, I put 1:1 600ohm transformers between everything, and use either opto-isolators or relays for the PTT. This means that the radio has absolutely NO electrical connection to the "other" device (PC etc).
The transformers also alleviate impedance issues.

I'll keep an eye out here, but if problems persist, contact me on any of the details below and I'll have a closer look.

I've been building interfaces for people on an ad-hoc basis for somewhere in the region of 15 years. This has started to wear thin, due to the problems inherent with veroboard designs.
I'm moving to a more reliable design with the build process documented here: https://www.facebook.com/voxlinkroip/
The above is a work in process!!

I can be contacted at admin@digitalradiohacker
Website: www.digitalradiohacker.co.uk
Facebook Page: https://www.facebook.com/DigitalradiohackerUK/
« Last Edit: July 02, 2018, 11:50:26 AM by m3odq » Logged

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