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Old 29-07-2010, 07:42   #1
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Command Mic Transmit Audio

I was wondering if anyone with a remote microphone could answer a simple question for me. If the radio is transmitting on the main microphone, does the transmitted audio come back over the remote microphone? Could the person at the helm hear what the person below deck was saying through the command mic?
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Old 29-07-2010, 16:16   #2
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I was wondering if anyone with a remote microphone could answer a simple question for me. If the radio is transmitting on the main microphone, does the transmitted audio come back over the remote microphone? Could the person at the helm hear what the person below deck was saying through the command mic?
G'Day mate,

For an Icom command mike/M-422 combo the answer is no.

Cheers,

Jim
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Old 29-07-2010, 17:02   #3
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ditto with our raymarine vhf
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Old 29-07-2010, 17:16   #4
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You could though have two radios, one on transmit and one on receive on the same channel and that would work...although probably illegal for marine band VHF. It would be an abuse of the purpose of a VHF, plus you would be transmitting your one-way conversation all over the harbor, even on one watt. If you want to do this then FRS walkie-talkies work well onboard and they are more certainly more private.
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Old 30-07-2010, 02:13   #5
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I was wondering if anyone with a remote microphone could answer a simple question for me. If the radio is transmitting on the main microphone, does the transmitted audio come back over the remote microphone? Could the person at the helm hear what the person below deck was saying through the command mic?
Most have an intercom mode between base set & remote command mike. You are not going to get this option when transmitting using either mike though.
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Old 30-07-2010, 09:24   #6
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I figured it wouldn't have the transmitted audio, but it was worth a shot. I certainly wouldn't have a way of testing that on my own without buying a new radio. I appreciate the quick replies.

The goal with this project is to interface a licensed shore VHF marine station to a recording system. This is used for SAR operations, and there are many situations where we would like to go back after an incident and review how communications were handled. If the command mic would output the transmit audio too, I could just take it apart and tap the speaker connection in there. I've called and emailed several companies, and everyone has told me this was impossible to do for less than $2,000 per radio for a class A DSC radio that interfaces with a VDR. I just found a company that markets a "Marine DVR" that interfaces with most VHF marine radios, but they don't seem to sell the interface cables - only the entire DVR. I know that what I'm trying to do is possible now, but I just need to figure out how to do it.

Thanks for the help!
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Old 30-07-2010, 11:18   #7
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Why not just use another cheap VHF or scanner with it's audio output to the DVR which would then record both sides of the communications?

Eric
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Old 30-07-2010, 12:33   #8
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That was my first thought too, but VHF communications are simplex and the radio's antenna is at about 200 ft AGL. It would be prohibitively expensive to put another antenna on the tower that would have equal receive capabilities, and having a dedicated radio for the recorder would require us to change the channel in two places instead of one.

The direction I'm heading right now is to find a VHF with a removable microphone (like the IC-M60) and get in touch with the DVR company and pray that they will sell just the interface cable. I'd appreciate any other suggestions this forum might have for me.

Thanks!
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Old 30-07-2010, 18:58   #9
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The Icom M-604 has a pigtail microphone jack on the back of the unit that is electrically in parallel with the microphone jack on the front of the unit so all you need to do is connect this to the DVR assuming the MIC level is enough to drive the DVR for recording of the transmit audio. Do you have a link for the marine DVR?

Eric
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Old 31-07-2010, 14:01   #10
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OK, you want to record audio on a particular channel, for some defined period...for training during SAR ops?

I don't understand your comment about the scanner....just put it on the simplex/output freq and record on a DVR or whatever. If it's recording the output of the repeater it doesn't matter that your antenna is lower - unless you're outside the antenna aperture. Thats why repeater outputs are on high antennas: For big coverage.

If you want to record local simplex chatter on handhelds, a similar receive-only device will work, at the scene. You can put it in an otterbox or something for waterproofing. There are very inexpensive VOX (voice activated switching) switches available as well, to save tape/space.

You could also use a PC with mic in to record.

What am I missing here?
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Old 31-07-2010, 16:27   #11
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If it's recording the output of the repeater it doesn't matter that your antenna is lower - unless you're outside the antenna aperture. Thats why repeater outputs are on high antennas: For big coverage.
I didn't see any mention of a repeater.

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Old 31-07-2010, 17:25   #12
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Given your requirements re antenna, channel tracking, recording it looks like your only option is to swap in a VHF with a recording option built in (probably some expensive police basestation), OR have an engineer modify your existing radio. The modification would seem to be straightforeward and $2000 sounds about right.
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Old 03-08-2010, 06:49   #13
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The Icom M-604 has a pigtail microphone jack on the back of the unit that is electrically in parallel with the microphone jack on the front of the unit so all you need to do is connect this to the DVR assuming the MIC level is enough to drive the DVR for recording of the transmit audio. Do you have a link for the marine DVR?
That's what I was leaning towards right now. (I made a typo in my previous post and said IC-M60 instead.) There don't seem to be many VHF's with removable microphones, and that one has the best receive capabilities I can find for under $2000. If the microphone level is not high enough, is there a way to amplify it from the radio side? Also, I don't see any pinouts in the manual. Do these radios usually have a service manual available?

The marine DVR can be found at this url. I was told that the VHF interface would only work with their DVR and wouldn't be compatible with our PC-based recording system. From a technical standpoint, I don't understand how that would work - audio is audio, right? The only thing I can think of is that maybe they have figured out a way to crack into the command mic interface, and it requires some processing with their proprietary computer software to convert into an audio stream.

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I don't understand your comment about the scanner....just put it on the simplex/output freq and record on a DVR or whatever. If it's recording the output of the repeater it doesn't matter that your antenna is lower - unless you're outside the antenna aperture. Thats why repeater outputs are on high antennas: For big coverage.
We don't have a repeater. As much as I'd like for us to have one, we just use standard VHF marine radios for all of our communications. There is only one high antenna for us to use, and it would be difficult and cost prohibitive to add another antenna to our shared tower.

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If you want to record local simplex chatter on handhelds, a similar receive-only device will work, at the scene. You can put it in an otterbox or something for waterproofing. There are very inexpensive VOX (voice activated switching) switches available as well, to save tape/space.
If two boats are out of range of each other, the one radio that can hear both of them is at our communications center. It would be possible to record audio at the scene, but it would ideal to keep recording centralized in our communications center. The existing system also runs in the background with no human input required. If the equipment were carried on the boats, it might get turned off accidentally, or the files might not be transferred back to the communications center.

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Given your requirements re antenna, channel tracking, recording it looks like your only option is to swap in a VHF with a recording option built in (probably some expensive police basestation), OR have an engineer modify your existing radio. The modification would seem to be straightforeward and $2000 sounds about right.
A regular land mobile base station like most public safety agencies use would not be type accepted to operate on the VHF marine band. I have had trouble getting this clarified, but the consensus from the radio shops that I have contact is that even with our FCC license, we still need to use type accepted VHF radios - they can't just program a land mobile radio to work on VHF marine frequencies. As much as I'd love to get a Spectra or a shiny new XTL-5000, they just can't be legally programmed.

If it costs $2,000 to modify an existing VHF radio, I'm better off buying a class A DSC radio with a dedicated output to a VDR and a superior receiver. I'm hoping that there is a way to just tap the microphone cable and mix it with the receive audio, since we don't have that kind of budget.
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Old 03-08-2010, 10:49   #14
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If the microphone level is not high enough, is there a way to amplify it from the radio side? Also, I don't see any pinouts in the manual. Do these radios usually have a service manual available?
You could tap off of the Mic amplifier, IC6a on the AF board. I do have a service manual for this radio. Here's the mic pinout.
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