PCB to 2 CDM750's on different freqs

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PCB to 2 CDM750's on different freqs

Postby wndmlr » Sun Apr 15, 2012 3:03 pm

I have a computer that sends commands and receives confirmations over a CDM750. I will be changing the frequency on the system and want to broadcast and receive on both the new and old frequencies for the period of time it will take to program the radios in the field. The system currently uses an interface cable between the computer and the radio. Can an interface cable be built to transmit and receive on 2 radios on different frequencies. I do control wiring for this notification system but it seems I'm learning more and more about radios.

Any assistance is appreciated.......THANKS IN ADVANCE!!!!!
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Re: PCB to 2 CDM750's on different freqs

Postby HLA » Mon Apr 16, 2012 8:41 am

the tx part should be easy, it's the recieve part that's gonna mess you up. splitting an output is one thing, combinding two outputs is another. you're probablly best with two different computers and interfaces. how many radios are you talking about in the fleet that need reprogramming and are they all the same models?
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Re: PCB to 2 CDM750's on different freqs

Postby wndmlr » Mon Apr 16, 2012 3:56 pm

the tx part should be easy, it's the recieve part that's gonna mess you up. splitting an output is one thing, combinding two outputs is another. you're probablly best with two different computers and interfaces. how many radios are you talking about in the fleet that need reprogramming and are they all the same models

This system is a mass notification system with the control center manned 24/7.

Two computers and interfaces is not an option.

Remote unites are stationary and total over 100.

All radios are CDM750's.

What if I set up 2 radios next to the controller that are connected together with a duplex repeater cable? The controller would transmit on freq A and activate all remote units still on freq A. One of the radios in the repeater pair would be also be on freq A and would then repeat the activation on freq B. I have never worked with radios connectors as a repeater. Will I have to do something special in radios' programing?
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Re: PCB to 2 CDM750's on different freqs

Postby Jim202 » Tue Apr 17, 2012 4:13 am

wndmlr wrote:the tx part should be easy, it's the recieve part that's gonna mess you up. splitting an output is one thing, combinding two outputs is another. you're probablly best with two different computers and interfaces. how many radios are you talking about in the fleet that need reprogramming and are they all the same models

This system is a mass notification system with the control center manned 24/7.

Two computers and interfaces is not an option.

Remote unites are stationary and total over 100.

All radios are CDM750's.

What if I set up 2 radios next to the controller that are connected together with a duplex repeater cable? The controller would transmit on freq A and activate all remote units still on freq A. One of the radios in the repeater pair would be also be on freq A and would then repeat the activation on freq B. I have never worked with radios connectors as a repeater. Will I have to do something special in radios' programing?



Making a repeater out of two radios can be both simple and hard. The first question that comes up is you need to know the exact frequencies that you need to work with. The separation between them is where the rub will come in. If they are close to each other, then using a repeater setup may or may not work. A repeater uses a duplexer to isolate the TX and RX antenna path so they don't cause problems between the two frequencies. It also has some sort of audio control and timing control between the RX and TX. You might be better off just keying up the two radios on the different frequencies at the same time with some sort of a console patch.

You need to spit out more details of what your trying to do. I am not understanding about the receiving of the two channels at this point.

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Re: PCB to 2 CDM750's on different freqs

Postby wd9cms » Tue Apr 17, 2012 6:08 am

What software are you running ? Can you run two different copies of the software on the same computer with two radios on separate serial ports. As others have indicated you may run into problems with frequency separation issues.

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Re: PCB to 2 CDM750's on different freqs

Postby HLA » Tue Apr 17, 2012 7:10 am

100 radios can easily be altered in a weekend, I think you are trying to make it more difficult than it is. What is the data, what do you do, why does this have to take so long? Since all are 750's the info will write to all the radios the same, shouldn't be any more difficult than reading one radio, making the alterations, and writing that codeplug back to all of the radios? You're gonna spend more time trying to trick your computer into tx & rx on two different radios
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I never check PM's so don't bother, just email me.
I won't reply to a hotmail, gmail, aol or any other generic free address, if you want me to reply use a real address.
STOP ASKING ME FOR SOFTWARE OR FIRMWARE, I JUST FORWARD ALL OF THE REQUESTS TO THE MODERATORS
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Re: PCB to 2 CDM750's on different freqs

Postby wd9cms » Tue Apr 17, 2012 8:50 am

This is another possibility. Since you have to reprogram all of the field radios and the CDM750 have multi-channel and scan capability, you can program the new frequency in channel 1 and the old frequency in channel 2. Then you can set the radio up in talk-back scan mode, the radio will receive signals on either channel and transmit on the channel a signal was received on. In this configuration the base can continue to operate on the old channel until you have all the field radios programmed and then you simply switch the base radio to the new frequency. Then you can go back to the field radios at you leisure and eliminate the old channel and the scan feature. Its a simple fix but will require going to all the field radios and reprogramming twice. This would not require any special software or base station configuration while keeping the full system operating during the transition.

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