antenna and tone code question!

[brin831]

ok so here is a couple questions i've done some searching for but not sure of the answer ...

1. is there a specific or best tone code to use with a specific frequency? or is it just a random deal ?

2. in the 450-470 range how close or far apart should two antennas be if they are on the same mast run to duplexers ... does it matter

we have basically built this:

http://www.broadcastsportsinc.com/media/6505/wireless communication systems main.jpg

and were wondering about our antenna placement on the same pole as we will have 1 for a repeater on a duplexer combiner and 2 for comms also on duplexer combiners ... all are in repeater pair splits 5 mhz apart.

 

[ramal121]

1. For a tone, roll the dice and hope the one you picked is not duplicated nearby. I would just stay away from 67.0 and 023 as they are the usual defaults in many radio and show up frequently.

2. It all depend on the actual frequencies used. If we are just talking repeaters, you have to look at all TX and RX freqs. If it happens that a RX freq is only 1 or 2 MHz away from a TX freq, then you have to pay attention to separation, as in tens of feet at UHF. If the freqs are all close together you can get by with closer antenna spacing as long as the duplexers are quality BpBr cans. If repeaters number 3 or more, I would toss individual duplexers and invest in a good combiner system engineered for the freqs you need to use. Then there would be 2 (maybe) antennas on the tower to run multiple repeaters.

Now to the picture in your link. Wow! Somebody loves CDM's. If you are using multiple transceivers as a control base radio (as in picture) your only option is to run an antenna for each radio. Putting a pass filter or whatever on one of these is probably out of the question due to the TX RX split. Again, frequency would dictate how much separation is needed between each antenna. The preferred way to run multiple control bases is to have a radio with separate TX and RX antenna ports. This way the control bases could be hooked into a combiner system and then into common antennas.

Last system I put in was 4 repeaters between 461 and 464 MHz. Combiner Engineering required 25 feet minimum separation between TX and RX antennas.

If I get what your post is saying, don't take just a rule of thumb to make this thing fly. Some careful thought needs to be put into this...

Typical receive multicouple:
http://www.telewave.com/pdf/TWDS-2021.pdf

Typical transmit combiner:
http://www.telewave.com/pdf/TWDS-1001.pdf

 

[brin831]

ok thats what i thought about the tones its just a random thing and we do for the most part have a list of whats in the area so we can avoid those ...

well at closest our tx and rx freq's are 4 mhz but could be much farther like 10 to 12 depending on rx freq's used ... our tx ones are set but have a number of simplex freqs avaliable to use for the rx side

so if i'm reading this it wouldn't be too much of an issue to have the antennas fairly close ... like 3 to 5 ft?

what we should really be worried about is the tx of one getting into the rx of another right ?? ... we are talking 15 watts into a 7 db gain yagi

separate radios are being used one for tx and for rx then they would be run into a duplexer bpbr ... we are using xpr digital mobiles so as to eventually upgrade to digital when we get our hand helds upgraded as well for now they are just in analogue.

yes it would be great to use a real combiner setup but the issue is really space and $$ at this point, ha of course ... we have a mobile road case rack that needs to be portable not the luxury of a whole truck ... but we only using 6 radios as well ... 3 for tx 3 for rx with three antennas

 

[ramal121]

OK, I gotcha. If the closest freqs are 4MHz, and there are quality cans on all radios, 3 to 5 feet is better than 1 to 2 wavelengths and I would be comfortable with that. With the proper equipment a desense check could made right when all antennas go up to insure it's all working together. If not, some subjective testing could weed out a prob. Best to know early BEFORE you really need to use the system.

"our tx ones are set but have a number of simplex freqs avaliable to use for the rx side". If you are using split freqs, whether a repeater (full duplex) or a control base with seperate TX RX radios(half duplex), a duplexer is appropriate. If there are simplex freqs being used, you can use just a single radio for these and then run them through a pass can for filtering.

Are you expecting to be frequency agile on these radios (ie ability to change channels)? This presents problems depending on how far you go by the change.

 

[brin831]

well the audio from the rx's needs to repeat on the tx side along with audio from a wired com system, we will simply mix the signals with a little line mixer and then inject that into the tx radio.

yes half duplex.

when you say "3 to 5 feet is better than 1 to 2 wavelengths" what does that mean

and yes it would be great to be frequency agile however i was thinking for this to be the case we could use the duplexer, have the tx side tuned to that freq. and then use a preselector basically a high pass filter on the rx side there for letting the rx freq be any number of freqs above the pass. if not then i guess we use separate antennas which would be possible just not as clean.

 

[ramal121]

A wave length at 460MHz is about 2 feet.

You could use different receive freqs as long as they are close together. If you stray beyond about 200KHz or so your receive will start to suffer through the duplexer as it is getting out of the passband for which the duplexer is tuned for.

Separate antennas would allow more flexability for a receive freq, but the antenna separation (without pass filter) goes up a bunch, as in tens of feet.

 

[zz0468]

Now to the picture in your link. Wow! Somebody loves CDM's. If you are using multiple transceivers as a control base radio (as in picture) your only option is to run an antenna for each radio.

This is no longer true. There are several manufactures offering control station combiners. They're not cheap, however.

 

[ramal121]

This is no longer true. There are several manufactures offering control station combiners. They're not cheap, however.

That is true and we're getting back to my original post. There are several manufactures that can rig up something for you if you just give 'em the freqs. Be prepared to crack the wallet open wider than its ever been before.