distribution on antenna signals

[brin831]

looking for a couple suggestions from some more knowledgeable people than me ...

we are setting up a comm system through radio tx/rx interface for what amounts to a eng truck that can be used in a number of applications ...

using 2 radios as constant tx which injected audio tied through a rts com system so we can have a director cue tallent, cam, etc from inside the truck then use another 3 to 4 radios for separate rx of the hand held radios to inject back into the com system so the field can talk back ...

my question comes in the antenna distribution of these signals ... the rx side is fine i understand how to split one antenna across a couple radios and deal with the db loss splitting the signals oh and everything is operating in the 450-470 mhz range ... the issue comes in with the tx side of things i'd like to be able to use 1 or 2 antennas at most for the tx with a total of up to 4 tx signals, all would be running same watt tx which we are licensed for up to 11 frequencies ... here is where i run into a concern i would like to have the flexibility to field program the radios (moto cdm's) to any of the various frequencies depending upon local frequencies and other systems in use we may need to change frequencies ... we have a nation wide temporary use license but others don't always adhere to the rules of the road so to speak ...

is there a way to combine tx signals without having to adjust filters etc all the time ... we are talking 10 watts tx here

at the least i could use 4 duplexers to combine all tx rx signals but that still limits to a specific set of freq's. without having to re-tune

thanks any ideas would be a great help ... just trying to cut down on number of antennas we would have to set up as well as feed lines etc.

thanks!

[wavetar]

You can do what you want, but not cheaply, and not without significant insertion loss. What you seem to need is known as a base station combiner. You can get info & specs here:

http://www.dbspectra.com/WebSite/Produc ... 0&sIdCat=2

[brin831]

well yeah that seems to be what i've been looking for all ive been able to find was similar products but in the 800 mhz range that looks to be what i need i'll have to make a few calls and see what the damage would be ??

thanks

[Bill_G]

I've played with those wavetar, and they are a great product.

Brin - The dbSpectra is an excellent suggestion. I've used them on surveillance vans, and remote production trucks like you seem to be asking for. The inserion loss is huge, they are HEAVY, but they work as advertised. No tuning required. Just plug your radios in and away you go with one caveat - keep all your t & r freqs separated by at least the standard 5M split, AND throw a broadly tuned pass/reject filter in on both sides if it will be used as a continous duty rtu. Otherwise desense will kill you. All your connections better be well made, dry, and tight, or you will have a noise maker as the generator vibrates the vehicle, and the antennas, along with every loose piece of metal on the truck. Range will be measured in hundreds of feet. that is generally enough for the director to be in the van, the producer off to one side, while the grips, camera crew, and talent are working the shot. You will also have to factor in your STL freqs if they are UHF as well. Try to keep your RTU and STL freqs as far apart as possible, and do not run your STL through this combiner.

The poor mans version of this is to run each xmitter into an isolator terminated to a dummy load with an iso-tee set for -10db out into a multiport block and cavity. I've done four rtu's this way, and it worked fine.

[Jim202]

Not trying to throw you off track, but have you looked into the "National Interoperability" channels that are
available for use at incidents to allow multiple agencies to communicate with each other? There is the restriction
that you can't use them on a daily basis for normal communications. Unless you plan on using base stations
on these channels, you don't even need to modify any existing public safety license.

On UHF, these provide an additional 3 channels plus the call channel.

Jim

looking for a couple suggestions from some more knowledgeable people than me ...

we are setting up a comm system through radio tx/rx interface for what amounts to a eng truck that can be used in a number of applications ...

using 2 radios as constant tx which injected audio tied through a rts com system so we can have a director cue tallent, cam, etc from inside the truck then use another 3 to 4 radios for separate rx of the hand held radios to inject back into the com system so the field can talk back ...

my question comes in the antenna distribution of these signals ... the rx side is fine i understand how to split one antenna across a couple radios and deal with the db loss splitting the signals oh and everything is operating in the 450-470 mhz range ... the issue comes in with the tx side of things i'd like to be able to use 1 or 2 antennas at most for the tx with a total of up to 4 tx signals, all would be running same watt tx which we are licensed for up to 11 frequencies ... here is where i run into a concern i would like to have the flexibility to field program the radios (moto cdm's) to any of the various frequencies depending upon local frequencies and other systems in use we may need to change frequencies ... we have a nation wide temporary use license but others don't always adhere to the rules of the road so to speak ...

is there a way to combine tx signals without having to adjust filters etc all the time ... we are talking 10 watts tx here

at the least i could use 4 duplexers to combine all tx rx signals but that still limits to a specific set of freq's. without having to re-tune

thanks any ideas would be a great help ... just trying to cut down on number of antennas we would have to set up as well as feed lines etc.

thanks!

[jackhackett]

Not trying to throw you off track, but have you looked into the "National Interoperability" channels that are
available for use at incidents to allow multiple agencies to communicate with each other?

using 2 radios as constant tx which injected audio tied through a rts com system so we can have a director cue tallent, cam, etc from inside the truck

I'm guessing that wouldn't be an approved use of the NI channels.

[brin831]

Bill ...

As i said we have 11 freq's to choose from and we are easily able to keep pairs at 5 mhzsplits

I followed you until you get to the "poor mans version" not sure exactly what your saying do with an isolator and a T sorry if this seems elementary my expertise is definitely on the com side the rf stuff is a bit new to me and i've learned a lot from reading online and trial and error ha ...

Jim ...

no we haven't looked into any other freq's because we have rights to more than we need and have spares to use so i guess it comes down to running up multiple antenna for tx

so this brings another question in without any kind of isolator/filters on our tx radios if we are running 3 separate tx signals do i need to worry about separating the antenna by a specific amount what kind of issues would this cause if not done and obviously get the rx antenna as far away from the tx as possible
thinking about using small yagi's for everything ... as most times we are looking in a specific direction

[Bill_G]

I'm guessing that wouldn't be an approved use of the NI channels.

But, it would be fun for a little while. Everybody loves a fox hunt.