Batboard

Someone who'd know, please answer this:

If you were to set out to build the absolute simplest, most basic Astro trunked radio system imaginable, (from a hardware
standpoint), what would be on the equipment list to make it happen?

This is only a thought experiment. I'm not REALLY planning to build the first-ever VHF Astro trunking system in the 2-meter band. But If I DID...and had access to the equipment that was needed, what would I need?

Presume that I already have an adequate quantity of Astro-capable VHF repeaters. MSF5000s, or something suitable.

Figure the minimal number of channels. Two, three, five, whatever...

No need for logging of any kind. Local site control only. No interconnection to any other site. A controller, a few
repeaters, and of course, antennas. What else?


Elroy

Two IntelliRepeater Quantars back to back, though you'd have no ID validation, and they'd run in Site Trunking all the time, unless there's a way to turn that off. You can turn that alert off in your radios though.

You can also set up conventional Astro to have seperate talk-groups in the radio that emulates "trunking" and would remove the need
to have a constantly transmitting control channel, which has become a very debated topic as to its legality in ham radio .

Mark

Well, here's a quick cure...MAYBE...

Put the control channel in the commercial section of the band, properly licensed, of course.

If it's low power (short range, obviously) you could even put the CC on an itinerant channel at least for testing purposes.

I can't see how that would be a problem. But I haven't deeply investigated the FCC's rules on things like that, either.


Elroy

Elroy Jetson wrote:Well, here's a quick cure...MAYBE...

Put the control channel in the commercial section of the band, properly licensed, of course.

If it's low power (short range, obviously) you could even put the CC on an itinerant channel at least for testing purposes.

I can't see how that would be a problem. But I haven't deeply investigated the FCC's rules on things like that, either

You can't do that - simply because of the fact that you can't use ham as a back haul for commercial, or vice versa. Granted, if your on a microwave link or something like that, i don't think anyone would really care, but I don't think your supposed to use the ham/commercial channels in that way - there should be enough "ham" bandwidth to reasonably allow for one to take on such experiments.

-Alex

KS4VT wrote:You can also set up conventional Astro to have seperate talk-groups in the radio that emulates "trunking" and would remove the need
to have a constantly transmitting control channel, which has become a very debated topic as to its legality in ham radio .

Mark

FWIW, I personally wouldn't put much weight in the debates without hearing the FCC's position on the matter directly, when deciding whether to do something like this for real.

Yep...I guess no one out there really want to make the time investment and request the FCC to clarify or modify the rules.
I was just making the comment being the OP brought up Amateur Radio deployment.

Not to mention the fact that the firmware for these trunking controllers does not support the amateur band, and that ordering one in the amateur frequencies is likely impossible, as is modification of the actual firmware for the controller.

Though if you really wanted to do it up right, you'd need a quantar for each channel, and an MTC3600 controller.

I was under the impression that you only had to program the individual repeaters to their frequencies and the trunking controller didn't necessarily have to know what
those frequencies are? Or at least, shouldn't you be able to fake it by playing games with the offset? Say, program the controller to think the channels are 5 MHz away
from where they really are?

Elroy

When you program a subscriber, you only program the control channels, the controller tells the subscriber what frequency to go to. In 800 it uses the assigned channel numbers, there is another protocol for vhf and uhf, but I don't remember it at the moment. As for intellirepeaters, do they exist for p25? The p25 system I work on goes into failsoft when the controller is gone. I think for site trunking, you would need a controller also.

The key to supporting an arbitrary frequency in APCO-25 is in the IDEN_UP messages on the control channel.

The IDEN_UP message describes how to map an APCO-25 Channel ID/Number pair to a frequency. The mobile radio is supposed to listen to the set of frequencies it has been given as control channel frequencies: when it finds a control channel with an acceptable network ID, it listens for the IDEN_UP messages, which tell it that for a given channel ID (think bank of channels) the base frequency is $FREQ, the bandwidth of the channels is $BW, the channel spacing is $CHAN, and the TX offset is $OFFSET (from TIA/EIA-102.AABC, page 101).

Given that information, the radio can calculate the frequency for any given channel ID and number by looking up the ID in its internal table, then computing the offset for the given channel number within that ID.

So if your repeater is sending an IDEN_UP saying "ID 0, base freq is 144.0MHz, bandwidth is 12.5kHz, spacing 12.5kHz, TX offset 0.600kHz" then the only question is "can the radio tune to those frequencies".

d119 wrote:Though if you really wanted to do it up right, you'd need a quantar for each channel, and an MTC3600 controller.

Or for ASTRO SmartNet 3.0, an appropriate 6809 controller.