VHF Audio override

[dolabriform]

Hi all

I'm thinking about adding cockpit speakers and a radio, but I also want to be able to hear the VHF. Back when I used to work in the music industry, we would rig up a keyed gate, so that when audio arrived on the key, it would dim / cut the main audio so that the key could be heard.

With this kind of setup any audio emanating from the VHF would cut the audio from the radio, and the audio from the VHF would be heard on the cockpit speakers.

Pretty easy in theory, however this will be with amplified signals rather than line level signals, and there will need to be a way to set the voltage from the key that triggers the changeover.

Any ideas folks? Have you come across something that will do this?

Thanks

David

 

[KenMcCulloch]

There’s a gadget that bikers use to integrate audio entertainment, voice prompts from a satnav and a short range two way radio for talking to your mate. The name escapes me for the moment but I am pretty sure it would do what you want.
(Edit) it’s called Autocom.

 

[William_H]

Simplistically you take a sample of the VHF audio rectify it and use that to operate a relay to switch speakers off music to VHF audio. You might need an amplifier to amplify VHF audio level to that which will operate the relay (or a DC amp to operatre relay from low level signal) and need to build in a time delay to keep on VHF for say 2 seconds to allow for breaks in message. olewill

 

[BelleSerene]

Part of the problem is fixed for you (depending on the hifi unit you use) by an 'ATT' (attenuate) input on the entertainment system. On Sony units it's a light blue wire. It's designed for a car telephone's 'I am operating' line to mute its audio. I think you'll still need to rig up a circuit from the audio output of the ship's VHF radio to amplify it, rectify it and low-pass filter it so you get a basically digital signal that will power this line. I have no idea what the impedance of that ATT input is. You could also rig the PTT line of the radio mic to control the same thing, so the entertainment system also mutes when you are transmitting. A bit messy, I grant, but at least you don't need to mess with relays and your speaker circuits. Would be nice if the VHF provided a 'mute' output to interface with such things. Perhaps some do.

[Edit:] Here's where the other part of the problem is pretty much solved. If you get the service manual of your marine VHF radio (search online), you can look up where the device's internal receiver-muting signal is. Mine is an Icom M601. There's an 'Rx mute' pin on the CPU and presented to an internal connector, which is taken high (+5V) to mute the audio. From the service manual, which provides the circuit diagram and PCB layout diagrams:

The main CPU compares “SQL” voltage with “SQLV” voltage from the SQL board, and outputs the “MICM” and “RMUTE” signals to toggle the AF mute switches (Q7, Q13).​

You could drive a transistor circuit from this to the 'ATT' input of your hifi unit. Depending on the impedance of the latter, you may not even need one.

 

[rogerthebodger]

Hi all

I'm thinking about adding cockpit speakers and a radio, but I also want to be able to hear the VHF. Back when I used to work in the music industry, we would rig up a keyed gate, so that when audio arrived on the key, it would dim / cut the main audio so that the key could be heard.

With this kind of setup any audio emanating from the VHF would cut the audio from the radio, and the audio from the VHF would be heard on the cockpit speakers.

Pretty easy in theory, however this will be with amplified signals rather than line level signals, and there will need to be a way to set the voltage from the key that triggers the changeover.

Any ideas folks? Have you come across something that will do this?

Thanks

David

I tried this some years ago in the same way as Willam_Hposted and it worked but there was as loss of the start of the VHF message due to the time delay in the circuit.

I also found the same problem with a VOX setup on a HH simplex radio setup I had at one time.

 

[BelleSerene]

I just returned to this, having installed a new stereo in the boat. It has a ‘mute’ wire which you can take +ve to mute the sound.

The ICOM M601 VHF has no such output, however. Well ours does after an evening’s work, but it was damn fiddly. I identified the ‘RMUTE’ (Receive Mute) line (active low) on its logic circuit board and contrived a three-transistor low-side driver circuit to drive the stereo’s mute line. The driver transistor is PNP, which would have done the job alone had both boxes run off the same voltage; the (NPN) transistor before it was necessary to protect the output line of the ICOM’s 5V chip from the stereo’s 12V supply. I then needed a third transistor before that one, to invert the signal. Probably someone smarter than me could have done it with only two transistors, but it works. My circuit happily available FWIW; I’d doubtless learn something from a real electronics expert. It’s not for the unsteady of hand, as the soldering to pick up the right line on an SMD was minute.

There’s a good amount of spare space inside the ICOM to mount a small circuit board (using a 3M picture-hanging tab!), and I passed two wires out of a hole I drilled in the back, resealed (not that it needs to be, below decks) with superglue.

 

[[70521]]

If anybody wants to listen to music onboard they can do so wearing headphones.

 

[dolabriform]

I just returned to this, having installed a new stereo in the boat. It has a ‘mute’ wire which you can take +ve to mute the sound.

The ICOM M601 VHF has no such output, however. Well ours does after an evening’s work, but it was damn fiddly. I identified the ‘RMUTE’ (Receive Mute) line (active low) on its logic circuit board and contrived a three-transistor low-side driver circuit to drive the stereo’s mute line. The driver transistor is PNP, which would have done the job alone had both boxes run off the same voltage; the (NPN) transistor before it was necessary to protect the output line of the ICOM’s 5V chip from the stereo’s 12V supply. I then needed a third transistor before that one, to invert the signal. Probably someone smarter than me could have done it with only two transistors, but it works. My circuit happily available FWIW; I’d doubtless learn something from a real electronics expert. It’s not for the unsteady of hand, as the soldering to pick up the right line on an SMD was minute.

There’s a good amount of spare space inside the ICOM to mount a small circuit board (using a 3M picture-hanging tab!), and I passed two wires out of a hole I drilled in the back, resealed (not that it needs to be, below decks) with superglue.

THat is genius Sir :encouragement: