Solve this technical problem: linked repeaters in a loop.

[Elroy Jetson]

Solve this technical problem in the simplest workable manner:


Four repeaters are arranged in a ring configuration. They form a complete operating link except they obviously can not all be allowed
to operate at the same time or they will form a feedback loop.

We have a north repeater, a south repeater, an east repeater, and a west repeater.

The east and west repeaters are located in the same rack.

Four frequencies are used by all four repeaters. They are assigned as frequencies A, B, C, and D.


The north repeater transmits frequency A to the east repeater's receiver. The east repeater's output is frequency B and
transmits to the receiver of the south repeater. The south repeater's transmit frequency is C, going to the west repeater's
input, and the west repeater's output is frequency D, going to the north repeater's input.

The objective is for ANYONE located in this ring to be able to communicate via these repeaters to anyone else in the area covered
by the system, including right next to him.


This is more challenging than you think. Come up with your answer and walk it out from step to step. See if there are any gaps in
coverage.

Logic control of repeaters is possible. So is creative use of PL tones. Or a combination.


See what you can come up with.


This is a real world scenario. Two of my customers use this type of system. It works.


Elroy

[psapengineer]

Interesting Configuration...........

[ai4ui]

I certainly would not do this the way described. Too much opportunity for a distant station from another system to come into one of the repeaters and tie up the entire system, or a stuck mic. Since you are using the output of one repeater as the input to another, I would imagine that the received signal would be pretty strong, much stronger than any users’ unless they were right on top of the repeater. Also, it doesn’t go backwards. There is no way for you to get signals from repeaters further down the line back to the previous ones without dumping everything back into the first repeater and causing a loop. I don’t think you can do what you are wanting to do as you describe.

“Simple” solution, really.

Add a fifth repeater on a different band. Put it somewhere central to the other four. We’ll call it the hub repeater. The other four we’ll call repeaters “A”, “B”, “C”, & “D”. Configure each repeater to with a half-duplex transceiver connected in as well. The half-duplex transceiver would be tuned to the frequency of the hub repeater.

Repeater “A” would receive it’s users on the input frequency and transmit that on it’s output frequency as normal. It will also transmit the ouput on the input of the hub repeater via the connected in transceiver. Repeaters “B”, “C”, & “D” would receive the output of the hub repeater on their transceiver and transmit that on their regular unique output frequency. Give priority to each repeater to retransmit what is coming in on their regular input so if there is a problem somewhere else in the system they will still be able to communicate amongst themselves. You could also have control stations operating on the hub repeater frequency and be able to monitor & transmit to all.

This set up works. The USFS does this to connect areas together on major wildfires, and I’ve seen ham systems done like this as well.

It is critical that the linking transceiver operate half-duplex otherwise it will lock itself up.

Go here for a pictogram from the NIICD for setting this up:

http://www.fs.fed.us/fire/niicd/docs/sy ... s_v5-0.pdf

Diagram 12 shows exactly what I am talking about and connects four repeaters like you are asking.

Robert

[Jim202]

You didn't say if all 4 repeaters are in the same building or connected via telephone cable.

An option is to make a common audio bridge that ties all 4 receivers together and then you
use that to key up all the other transmitters. In other words, you make a simulcast system.
You did say that all the TX frequencies are different. You didn't say if all the RX frequencies
are different. Hope they are. You end up with 4 ports in and 4 ports out. If it is a full
repeater system, you actually can have multiple RX audio inputs active at the same time.

Any RX will cause all the TX's to come up. When it drops, the next RX input will cause all
the TX's to key up. If you try linking the output directly to the input of the next repeater
in the ring, you will cause a latch-up and then your screwed.

I had to do this for a state police system a number of years ago. Just remember that you
need to keep the audio isolated from each RX and TX. The best way to do this is with some
form of active audio amp that you can adjust the level on. This keeps the audio at the correct
line impedance and also provides isolation between ports.

Jim

[wavetar]

Repeater control aside, I don't see how it could work if the coverage areas of the sites overlap...for instance if a "North" radio keys up on frequency "D", then portables in the "West" site will potentially receive the signal directly from the portable, as well as from their repeater, which will wreak havoc with what the radio will actually be able to recover as intelligible voice. PL's aren't going to help you there. I'm interested to hear how one would get around that.

[d119]

I can't help it. I gotta ask.

Is this the "Do my job for me" forum?

[Jason]

Thinking about this you really only need two repeaters here, a C and an F repeater, for a CF!

Really, if simulcast $$ is really that far out of reach then install 4 stations, 4 seperate RF pairs, with wireline links. Link all the stations fulltime, and the user selects the channel for where they geographically located. (this is unless you can purchase radios with a conventional vote-scan config). For giggles, program the subscribers for BCLO. There going to need it.

You could use another form of non-wireline backhaul, but would have to be hot links. Users in this day and age won't go for the "just keyup and wait 5 seconds for all the links to come up" regardless of it being a taxi, meter reader, or a fire crew responding.

I hope this is not a public safety entity. It is not 1970.