The Radio Information Board

Our Fire Engine has an external speaker hooked up near the pump panel but we wanted to add the ability to transmit from that location. I was thinking of addding another speaker/mic to the through some sort of switch (or manually plugging each one in) to determine where the Engineer would transmit from (the cab or the panel)

Any thoughts? or other ideas how to achieve this (cheaply)

Brian

is this a dual bander? if not then I think you can connect a mic to the 15 pin connector on the back of the radio deck.

It is not dual band. So I can have two mics hooked to it if I can wire it to the back? I'll think people have posted the pin outs on the back before, so I'll try that. Thanks

Brian

After I posted that I had second thoughts. It was posted by N5TBU awhile back that if you use the 15 pin for a second mic then both elements will be hot on transmit. The other mic would pick up lots of noise and might not work out. Imagine driving down the road and the outside mic is picking up road noise. Another thought and also pretty easy would be to make a small switchbox by the radio head to select the front or rear mic. You can get a 6 pin RJ plug to connect to the radio and 2 RJ sockets on your box, run an extension to the rear preferably with a shielded cable then it would be pretty much a plugin without any internal radio mods. But the best solution would be to convert the radio to a dual head. That would cost the most but it would work great. Peter.

This problem is overcome with the x90 series by using a noise cancelling mic. The noise cancelling mic has two elements one in the front you yak into and one in the back that picks up noise. They are fed into an op amp on opposite sides so most of the noise gets cancelled. Originally they were always hot but because of this problem they came out with a solution which is simply to put a PNP in series with the voltage supplying the electronics and ground the base to the PTT switch through a resistor. This way when the PTT on the mic is not closed to ground the mic is effectively dead.

I also made this work on a retrofit by using the Midland mic that was already there. It had two sets of contacts in the PTT so I made one set the PTT switch and the other set the mic element contacts. In addition to modifying the inside mic as described.

I have heard that Kenwood has changed so that the mics come from the factory like this but I have not seen any, yet. The last batch of 90s we ordered was quite a few months ago and we had to mod all of them.

Birken

The 90 series can be ordered with that mic modification.
The black 6 pin kenwood mic can be modified in the same way that the 90 mics are modified.
mod

The best way is a dual head setup using the krk-3dh. this allow two separate mic and speakers. I lets you adjust the volume independtly and can be used as a intercom. I do have two of these, but no cables or heads extra.

Terry

How far apart can you set up the seperate heads? What type of wiring would you use? I would be interested in getting one of the krk-3dh.

Brian

one more thought, would you recommend putting a remote head outside the truck? I'm thinking exposure to the elements and such...

Brian

The noise cancelling mic for the 30 series radios had a double pole PTT switch. You can run the mic hot through it to have it only be open when you PTT.

I saw one cable on ebay that was 50 feet, generally most of them are 17 feet long. The Heads are rated for harsh weather, I woudl feel confident to use them outsite of a fire truck ( I did one on a fire truck eight years ago, still going strong.) one cable part number I found is E30-3060-15, best bet is to watch ebay if you are going the low ball route.

terry

Many years ago,my employer tried two 400 foot extensions for an offshore platform....it worked flawlessly! However we never sold the idea,so I have no long term results.
mod