Repeater with Dual receivers

[JD]

I am trying to design a switching circuit for the receive side of a repeater that will lock onto one of the 2 receivers for the duratiion of the audio path. I need a switch that will hold the signal from the first receiver audio that appears until the carrier is dropped. No priority of either receiver is needed.
Any suggestions?
Thanks

[gdsteele]

I thought about doing the same thing for my GR300. I thought I could just OR the two COR signals from the two receivers and take that to the tx radio PTT. I think you have to do something with the two audios, though. I was going to use an analog switch and the COR signals to route the rx audio to the tx radio.

I know that some logic will need to be included to handle signals on both rx radios, but except for that, would that work?

Jerry

[JD]

I have a DPDT relay wired and the audio and PTT pass fine. I just need to figure out how to make it operate as stated above. I can hook the relay to one of the COR's , but then it will always have command. I want it so that if a signal is received, the message will complete nad not be over ridden by the receiver that has the COR connected to the relays coil.

[RKG]

What is the purpose?

Usually, when an Aux Receiver is used, it listens to the repeater output frequency so that the console operator to be able to hear "direct" traffic whenever the repeater is not transmitting, and the Aux Receiver is switched out if the repeater is keyed either by the input receiver or the wireline. Obviously, the input receiver should and will have priority, and high end stations (like the Quantar) can be programmed to do this out of the box. However, it does not sound like that is your purpose.

It sounds to me more like you want to have two input channels, to either of which the repeater will respond, with the other channel inactive while the repeater is responding to the one that keyed it (and no wireline). If the channels use the same RF but different input tones, wouldn't a community repeater panel do a better job? If they are different RF channels, how about having a single receiver that scans?

If you want to do this with two separate receivers and relays, how about using two 3PDT relays? Whichever relay is pulled in first will gate audio and key as you wish, with the third pole interrupting the coil circuit of the other relay so long as the first one is pulled in.

In theory, whichever receiver unsquelches first takes control of the transmitter, which cannot be grabbed by the other receiver so long as unsquelched. The only problem I see is that if two units key more or less at the same time on the separate channels and the second guy is still keyed when the first guy drops. If this happens, the first receiver will lose control to the other as soon as it unsquelches and may not be able to get it back until the second guy drops.

[JD]

This sounds just what I needed. I will use a hang time on the receivers so this should work just fine. Not too worried about the 2cd repeater keying up. The company using this understands that this is quite simple and basic.

Thanks.

[RKG]

Take a look at Mouser sku 655-KUMP-14D18-12. http://www.mouser.com/catalog/626/1357.pdf We have used these for audio switching and they work just fine.

[JD]

Thanks to all, I just ordered a couple of the relays from Mouser. The manufacturer of the one repeater panel I am using, highly recommended to use relays and not IC's or transistors,( fat chance of me figuring that switching circuit out), said that a relay is more reliable. Why would that be ?

[Dan562]

Hello JD,

This Relay Logic that you're using seems okay but you haven't mentioned what type of a /\/\ Base Station you're using. If you're using either a Quantar or a MTR2000. this has been accomplished many times before as a T1-2R repeater configuration. The configuration consist of a Standard Repeater Pair and the Second RX Frequency is on the Repeater's TX Frequency Output. For the MTR2000 there's a SP QLN Field Modification Kit available through the /\/\ factory with all of the necessary hardware and software to accomplish this configuration.

Example:

T1 = 454.400 MHz R2 = 459.400 MHz Repeat Path Priority
T1 = 454.400 MHz R1 = 454.400 MHz Talk Around / Simplex

Any time the transmitter is Keyed Up Wire Line # 2 is Muted to prevent an Audio feedback loop to the Dispatch Console. With the FMK there's a Coaxial T/R Relay and additional cables included to route the T1/R1 RF through the same RF Cavity Filters providing minimal insertion losses on Simplex TX and RX.

Note: A WORD OF WARNING, Try to stay away from using the RX SCANNING feature in PUBLIC SAFETY USE. As the Receiver Scans terrible mistakes can happen in a Crisis Situation such as "Don't Shoot" with the Scan freature is Enabled, might cut-off or muting the word "Don't" creating a bigger catastrophy by having the Officiers "Shooting" their weapons.

[JD]

I am using a Mortorola CDR repeater setup with 2 receivers . I just need for whicever receiver is receiving, not to get interrupted by the other.

Thanks for the information.

[jackhackett]

Thanks to all, I just ordered a couple of the relays from Mouser. The manufacturer of the one repeater panel I am using, highly recommended to use relays and not IC's or transistors,( fat chance of me figuring that switching circuit out), said that a relay is more reliable. Why would that be ?

Well, since the radios aren't made out of relays, I'd say that a properly designed transistor/ic circuit wouldn't be any less reliable than the radio itself.
Figuring out the logic probably wouldn't be that hard, maybe use a Karnaugh map. The relays will be the simplest and easiest way though.

[MassFD]

Why not use 1 receiver and set it to scan both channels, seems like it would work if the frequencys are close. The scan hang time would allow time to respond to the trannsmission. If you are cross banding this would not work, is that why you are using 2 receivers ?

[JD]

That's what I was considering at first. However read the above thread by DAN562, he makes a very good point.

[MassFD]

That's what I was considering at first. However read the above thread by DAN562, he makes a very good point.

But even with relay or solid state logic you will have problems, what happens when the "dont shoot" comes over receiver 1. When the mobile unit unkeys both receivers are now avaiable. Receiver 2 receives a signal and locks out receiver 1, the officers are now unable to continue the conversation that started on receiver 1 because receiver 2 now has the transmitter.

If the mobile units have MDC PRE enabled the scan should stop long before the first word is spoken as long as the officer waits till the side tone stops.

I agree with DAN562 in that I would not do either of these schemes in a public safety system.

[JD]

This will be used by a small town volunteer fire department. It has to be set up for paging due to the fact the dispatch center will not use the phone system for paging. THey are dispatched from 2 different counties.

Thanks to all for their inputs, great discussion !!!!

[thebigphish]

So two different dispatch centers will be paging you out, and you don't want one to have the priority on the RX side of things? What happens when 1 accidentally opens the mic on the console, and the other is paging out for a involved structure with people trapped? Granted in a minute or two the call will go out again, but do you want that minute to be brought up in court? If it's for the same dept in the same area with two dispatch centers, why are they on different frequencies? Does one know when the other goes and requests services? I would be careful when you say "no priority of either reciever is needed" in your summary, because i think what you are doing is really downplaying the situation!

You really need to get this situation to change. Propose both centers going to a mutual frequency for this dept...because this sounds shaky at best, in terms of public safety work.

[JD]

Good point, however neither dispatch center will go to the others paging frequency or will not go to a mutual . They said they do not have the funds to do this. One dispatch center in the main county cannot reach the pagers, they are paging through the repeater.
Thanks

[thebigphish]

they don't have the funds for a mobile radio and an encoder? There has to be another reason for that...that sounds weak. There must be another reason that they won't reprogram their existing system to your frequency or someone elses and use one...get to the nitty-gritty of this problem, before it bites you in the ass.

worst case scenario is you do a rebroadcast of each system - 1 RX & 1 TX for each system on the same frequency, and if they both go off at the same time you get mush...You gotta do something about the 2 ins and 1 out setup you have now.

[JD]

The one county said there equipment is old and will not interface, they are getting a grant and will have more options in 12 to 24 months. Definitely more involved but you can not alienate them or they will not cooperate at all !!!!

[thebigphish]

Their old paging equipment cannot be reprogrammed?

[Dan562]

JD,

There may be another solution to the Multiple Fire Dept Dispatch Paging Points. A similar system was developed for a Fire Dept out in Kansas. They did not have Land Lines to the Base Station / Repeater so a separate receiver was integrated into system with a DTMF Decoder using a Set Up of a 3 digit sequence code 1-2-3 to Latch the "Priority" Paging Audio Sequential Tones routed through the repeater's Transmitter.

Once the Priority Paging was completed, the Dispatch Console was required to send the Knock Down DTMF 3 digit sequence code 3-2-1 to revert the system back to the normal repeater mode. This particular customer needed this function since they were located in Tornado Alley and the remote Paging Decoders activated Warning Sirens.

Dan

[JD]

We will use QCII tones to open up the receiver. Once the first set is sent, then the page will be sent again. The receiver then automatically resets to the QCII operation. This receiver will only be used for one way paging and this will be very few times.
Thanks.