Batboard

Ok, I have a question for the installers out there......

Looking to put together a heavy salvage / fire rescue type apparatus in the near future. Will be a custom 8 person cab. Rear seating area will have a small desk for a command type area. At the command desk i am looking to place several mobile radios. VHF Hi, VHF Low, UHF, 800, and a scanner. This will be only if it is needed in a command setting. There will also be a need for a VHF Hi mobile on the dash area up front for our main communicating with dispatch.

My dilemma is this.... how to make the two VHF Hi radios work alright without interfering with one another with feedback etc. I considered a remote head setup with dual heads. Drawback is the driver/operator has an outside external speaker that would be tied into the dash unit for his use of listening to dispatch/operations. And the unit in back would always have to follow the front etc. It doesnt seem like that setup is advantageous as they could need to be on different channels at times. So i am looking at two different mobile VHF Hi units. What sugestions do you have, so that these units - should they be on the same channel at the same time dont interfere with one another?

I am sure this situation has come up before elsewhere and i am interested in the possible solutions availible to make this all work.

Thanks.

Quote: "...should they be on the same channel at the same time don't interfere with one another?"

It is not possible to operate two radios simultaneously on the same frequency (channel). If you're asking about operating the two radios on the same band simultaneously that's another matter and can be done with proper engineering work, antennas, etc.

I'm guessing, based on your description, that the seating areas are physically separated from each other, so you wouldn't have to worry about audio feedback between front and rear. I'm also assuming since you mention a heavy rescue rig that you've got quite a bit more roof real estate than a normal line engine or truck.

The one benefit a dual head single drawer radio has for you is the possibility of using it for intercom functions. However, if you're already looking at a separate intercom solution, then it's a moot point.

Your main concern with that many radios is desense, especially with multiple radios on the same band. If you're not putting out more than 50w or so (e.g. no 110w high power drawers), and presuming sufficient real estate as above, I would tend to think you could get enough horizontal separation between the front VHF-Hi and rear VHF-Hi to eliminate desense from being an issue. Providing sufficient horizontal separation between *all* the antennas and any surrounding obstructions is obviously an important factor in how well your radios will perform.

Any further specific descriptions or pictures could help us advise you further.

The fire truck/ command vehicle is nearing delivery. and i am still undecided on the two vhf hi radio issue.
What if they were high powered units? How far away would they need to be with antennas to not blow out the front end etc of each other?
I realize i may have some feedback and i can turn the speaker down etc. But what if the radios are on the same channel and one of them transmits? do you forseee any major issues with the radios?
I am putting a hi power up front for the driver/ officer. and would like to put one in back in the command area (still in same cab but to the rear). The one in the command area will have a interoperablity box added to it that will basically make that unit unusable if its connected and being used to talk to disalike bands. so i was thinking a radio up front would be good so the officer or driver would be still free to transmit if needed on there own etc.
i've seen these huge command trailers with multiple work stations and multiple radios so i figure there has to be a way to make it work.
Truck will be a Pierce Velocity. non walk in heavy rescue.

If your concern is too much rf hitting the front end of another radio, keep all your power down below 30w, and separate the antennas as much as possible. If your concern is acoustic feedback, put in crossmute relays tied to ptt.

Thankyou.

I will have to see about lowering the power it seems.

Using one antenna in a raised position with the other antenna a low profile or sometimes called undercover antenna will help from frying the front end of one of the radios. Rod