crossband repeater help

[fire_master_21]

As part of a joint set up with my fd and the highway patrol. I have been givin the task of setting up a portable cross band repeater. We are on vhf and they are on uhf. We already have the radios cdm 1250's in both bands. How do I input the freq into the radios? our tx is 150.xxx rx is 154.xxx and they are tx 465.xxx and rx 460.xxx. I hope I explained this right. I have everything for the set up but just don't know how to configure this with the cps. TIA for any help.

[Jim202]

[quote="fire_master_21"]As part of a joint set up with my fd and the highway patrol. I have been givin the task of setting up a portable cross band repeater. We are on vhf and they are on uhf. We already have the radios cdm 1250's in both bands. How do I input the freq into the radios? our tx is 150.xxx rx is 154.xxx and they are tx 465.xxx and rx 460.xxx. I hope I explained this right. I have everything for the set up but just don't know how to configure this with the cps. TIA for any help.[/quote]

I am not trying to pop your baloon, but before you go trying to gluge up a cross band repeater this way on a highway patrol frequency, I would have a letter from the highway patrol communications officer in charge stating clearly that you will be allowed to do this.

Second, in the 35 years involved with the fire departments I would never recomend that the fire service be allowed to control and have free access to a police frequency without some strict guidelines and wriiten agreement. In trying to read between the lines here I don't even see the hint that this is your case.

Now to flip the coin and answer your questions. First, you will need some form of interface to tie the two radios together. This normally is done with a cable that connects to the external mic connector. In between the radios is a control board with timers and audio circuits to set the levels. It also needs a keying line to go between the 2 radios.

To program the radios you will need a RIB, the RSS and a slow computer.

Have fun and stay out of the way of the FCC.

Jim

[nmfire10]

CDM1250's use the CPS and run under windows on fast computers. You need the software, a RIB and cables.

The accessory connector of the CDM1250 has all you need. Audio in, audio out, PTT, and COR. You don't need to plug anything into the front panel mic jack which leaves it free for a local mic.

In fact, you can even get away without even using a board to control the link. You can link PTT to COR both ways, and audio out to audio in both ways. The software has adjustable microphone gain so you can set it that way. It doesn't get any simpler that that.

Now, here's the problem. If either agency's repeater has a hang-time with PL, it is going to drive you insane. In fact, it will end up ping-ponging itself until someone pulls the plug. You need either NO hang time, or a hang time with no PL on the repeaters. Only then, will a cross-link with two mobiles tied together work. Of course, this is no concern if you are trying to link simplex channels together.

[fire_master_21]

I guess I should have said this is not on any repeater system now these are both tac channels that would be used to make this repeater in the event the something major should happen that we would all need to talk to each other. Both side have all ready agreed to this. I will be making this into a suitcase and it will sit on a shelf and most likely will never see any action ( I hope not ) but at least we will all have comms if we should need it. Like I said I should have said all of this in my first post be I didn't think of it as it was 1 am.

[nmfire10]

OK. Well if this is the case, you should just be able to connect the CDM's back to back as described, set the audio levels, and your done. The harder part will probably be mounting and making it look nice rather than hooking it all up.

[KB2ZTX]

If the last thing you described is it, You should use simplex channels. A local deparment had a similar unit to what you described and the only issue was "fire" portables on vhf could not hear each other. It worked fine to talk to the mutual aid on lowband, but if FF1 called for a mayday, only the lowband people heard it. Since we have switched to simplex on both sides.

Just my thoughts...

jas

[n5tbu]

our tx is 150.xxx rx is 154.xxx and they are tx 465.xxx and rx 460.xxx.

You are describing repeater split freqs,and as Matt said,if you have a tail with pl,it will go into a circle jerk scenario.
If you have a good high location you could program the repeaters input freqs into both vhf and uhf radios,this works well if your site can hear all the mobiles.
mod

[1motoman]

This might be what you are looking for.

http://www.linkcomm.com/security.html

[thebigphish]

this is for scene ops, right?
as long as it's simplex....OR single channel in (PL / Hangtime is a nonfactor) to a repeated out...take your radios (attach them with what ever controller you want, Will will gladly sell you an extender module, and NHRC or Link Comms system, or Nand's direct wire) and do what n5tbyu says (and what we did with Matt's lovely NHRC board they didn't want)...catch the repeater in freq and have the other side of the system to TX on the repeater out freq...

as such;
Highway Patrol
tx 465 rx 460

your agency
tx 150 rx 154

all you'd do is program one mobile for each system backwards...put the tx freq where the rx should be (for normal ops) and connect them to the controller (or a extender module) if you use a half duplex system (that won't allow the other radio to tx) your crosspatch won't cause the proverbial circle jerk that is so much a nightmare of a system like this...somewhere i have the single wire setup schematic that nand put up here, which works really well...and is minimalistic in parts....or if you wanna rack it up and put it in an ammo-can and throw it in the back of the rescue, talk to will...have him build you one and you will be kosher.


btw...don't worry, most of the batlabs work here is done at 1am anyways, we work better at night.

[Will]

The Link or Extender Module is what is used by most FD' and a good explanation is here:

http://www.webimaging.com/echocomm/


You can also use Nands wire interconnection, but it is missing the ground, and has no protection if one radio fails or locks up.

With the Extender Module a switch disables the two radios and the radios then can be used normally from the mic. without unpluging the Extender Module.

There is also a Repeater/Link Module that does repeater and a link at the same time.

[Nand]

You can also use Nands wire interconnection, but it is missing the ground, and has no protection if one radio fails or locks up.

Ground loop problems??? Nonsense!

The additional ground wire between the two connectors (pin-7) is intentionally not there. Since the two radios both have their power wiring connected to the same source with fairly heavy wire that has a low resistance and low impedance for the audio signals involved, the two radios can be considered as sitting on the same chassis even though they are not. To be really safe, both radio frames can be bonded together, either with a strap or through a metal cabinet with the proper mounting hardware.

Using a ground wire between the two accessory connector grounds (pin-7) actually could cause damage if the TX radio ever lost it’s main power ground and started drawing current through this signaling ground wire from the RX radio instead. This wire would likely melt its insulation if subjected to several amps.

As for the TX radio staying keyed when the RX radio fails or is turned off, that is what the timeout timer in the TX radio programming is for. The time out timer in the TX radio prevents the radio from staying keyed under all conditions, including a RX radio failure.
The likelihood of the RX radio failing is the same as the likelihood that an external module or controller fails. The built in time out timer prevents all the above problems and is required by regulation.

http://www.storm.ca/~nand/990/RICK/rptr.pdf

NMFIRE10 mentioned using CDM radios, allowing a xband repeater without any components and making the audio level adjustments with the CPS. This will work fine, but a small capacitor (1uF or 2 uF non polarized) should be added in the mic line to prevent reverse voltage on one of the internal capacitors in the radio. Other than that, 4 wires and no ground wire is all that is needed for really the simplest and likely most reliable bi-directional xband repeater using mobiles.

Nand.

[nmfire10]

Thanks Nand! One question regarding the who "failing radio" thing. Why would one radio crapping out cause the other to lock into transmit? If you PTT control is active high, it is not going to go into transmit unless something applies voltage to it.

[Nand]

The PTT line is active low, and the COR is programmed active low when receiving a signal. In most radios, the COR pin is pulled high to the 5 volt bus through a pull-up resistor when no signal is received. When the radio is turned off, the 5 volt bus drops to ground causing the COR line to look like a ground, causing the TX radio to go into transmit.
In the not fully implemented 16-pin connector as on some GM300 radios, The COR transistor does not use a pull-up resistor (called open collector). With these models, turning off the RX radio will not key up the TX radio.
A simple way to eliminate this possibility altogether is to program the TX radio for ignition control and feed the ignition control line from the RX radio’s switched B+ at its 16-pin connector.
The time out timer takes care of this as well.

Nand.

[nmfire10]

Ah, I can see how this would be a problem using the older radios.

However, since we are talking CDM's here, the pins are all programable active high or low. You can make the PTT and COR be active high and eliminate this problem all together.

[Nand]

Not really, you will introduce a new problem because when you program the external PTT pin in the CDM as active high, the radio will key up when the cable is disconnected. The reason for this is that all programmable inputs are pulled high in the radio already.
So again, the time out timer is still the best option in this case.

The only time that you would not want to use the radio’s time out timer is when using an external controller like Will’s module when it provides hang time. In that case the external controller needs to take care of the timeout timer as well. I believe Will’s module does provide both these functions. But for a cross band repeater or extender, you don’t want any hang time at all.

Also, the only failures that I have seen where a Maxtrac type radio stayed keyed up by itself was because the protection diode across the PTT line internal to the radio was shorted. Most diodes fail in the shorted mode and my burn open only if enough current is present.

Nand

[Nand]

Something I didn’t mention. For someone who isn’t familiar with the technical side of things or doesn’t trust their own workmanship, I definitely suggest using Will’s module. You can’t beat the price considering the parts and work that goes into it.

Nand.