MTR2k+GR500+Digitac CONFIG

[Master Yoda]

My company has 3 MTR2000 VHF,4 GR500 UHF and Digitac comparator.The plan is for MTR's to receive on same freq,and transmit on 3 different freq.GR's are planned to be used as links on 4 different freq's(2 pairs 10M space) between 2 MTR's and Digitac.Digitac would be stationed by the third MTR.Is this configuration possible?Please help,give opinion...

[d119]

If you are going to use the GR500's as links from the MTR2000 receivers back to the DigiTAC, they'll have to be keyed continuously in order to pass status tone, and on a GR500 you'll burn up the PA's post-haste.

You need wirelines or microwave to do what you are trying to do properly.

[Master Yoda]

If the power on the GR's is set to max.5W and the extra cooler fans are installed,is there still a problem of overheat?

[d119]

I don't believe you can safely turn a GM series mobile down to 5 watts... I think regardless of the power setting the things still generate quite a bit of heat, and running the PA that far out of specification is asking for spurious emissions/harmonic issues, etc.

[Master Yoda]

Out of specification?Isn't the power range for GM's 0,8 - 30W?I know the constant transmission will change the conditions,but with GOOD cooling?Please say if I'm wrong...Need to know because I have to test it...

[d119]

It doesn't work that way. Just because you can turn the radio down to 5 watts doesn't mean it will perform properly at that power level. The PA transistors used in that radio are designed to operate at ~30W. While it is possible to turn the radio down (or up), you are running the transistors out of specification, and the results are generally not good.

Other folks on here will most likely say the same thing. There have been issues with the PA's generating spurious emissions, etc. when running at low power levels.

What you may want to do is try to track down some LPI MaxTracs to put in the GR500 housing. The LPI radios are designed to be 2W control stations. I don't know if they'll do 2W continuous duty, but at least you get a lower power level thats within specifications.

What service are these radios being used for? I certainly hope it's not a public safety application, as this is entirely the wrong way to engineer a system like this (not a slam against you).

[Master Yoda]

Thanks a lot!Will look for LPI's...

[JRayfield]

I just joined this site and noticed this thread. Here's a bit of information that I came by recently....

If you're in the U.S., you can't legally run continuous carrier operation (continuous transmit) on 'shared' frequencies - only on 'exclusive' frequencies, or on frequencies that are specifically designated for continuous carrier telemetry operation. This pretty much rules out the use of the 450-470 mhz band for continuous carrier links for voting receivers. You would need to let the VHF voting receivers bring the link transmitters up and down with received signal on the voting receivers.

I just recently ran across a public safety system that is using 450-470 mhz frequencies for continuous carrier links for voting receivers and I double-checked this with my communications attorney....definitely not legal in the U.S.

John Rayfield, Jr.
Rayfield Communications, Inc.
www.rayfield.net

[Rod Farva]

My company has 3 MTR2000 VHF,4 GR500 UHF and Digitac comparator.The plan is for MTR's to receive on same freq,and transmit on 3 different freq.GR's are planned to be used as links on 4 different freq's(2 pairs 10M space) between 2 MTR's and Digitac.Digitac would be stationed by the third MTR.Is this configuration possible?Please help,give opinion...

This is quite confusing! What is it exactly you are trying to accomplish here?


First off, the Digitac has to have a constant status tone (2175) going to each input on the 2 input cards (4 inputs per card) or the input will fail after 30 seconds or so. If the input is not used you can flip the disable switch on that input and it will be ignored. The way the digitac works is like this.


Each voting receiver sends out a constant 2175 status tone down a wire line or microwave link. When the receiver receives a valid signal the 2175 tone drops and the comparator listens and then analyzes the audio quality. This happens in milliseconds, while the comparator analizes the audio quality, the comparator will vote to that particular receiver and keys the transmitter via tone or DC keying. I can go in depths with this but I will not unless you would like me to...



The MTRs can be configured as voting receivers and thus sending a constant 2175 status tone. If your looking at a cheap RF link between the receivers and the comparator and this is on a business band channel you can use Darcom 9000s....