UHF Trunking On Trunker

[JohnnyGalaga]

I am completely new to UHF trunking and figuring out the offset and base frequencies. What's the difference between this and 800 MHz trunking ? Here's a trunker file I've been trying to work with:

DISPOSITION=ascsdsesfulxnspssn
v0x000 ,0,ffff,b
v0x010 ,10,ffff,9
v0x17c ,17c,ffff,ea
v0x18c ,18c,ffff,fd
d 407.7625,1dc,ffff,0

How do I figure out how to put which frequencies where ? Are there any online documants explaining how UHF trunking works in the first place?

Thanks !

 

[mam1081]

If I was to do it, I would find at least one other freq and note which channel code it was using (run trunker on the UHF system and search on another scanner). Look at the freq for your control channel and look at the freq for your other found channel. The channel codes are in Hex. Convert them into decimal. Your step size will be something like 12.5, 25 or 50 probably. The difference in your two channel codes and the actual frequencies can be compared to get the step channel (like you posted 407.7625 - say that is channel code 19c = 412 in decimal. Find the other channel - like 18c = 396. If your freq was 407.5625, your step would be 12.5 - if it was 407.3625, it would be a 25k offset).

The third set of hex numbers (ffff) in your sys file are the inputs. If you have not changed or deleted any of the channels, you actually have twice as many channels than are used. If you notice, two channels highlight up when a transmission happens. One of those is the input. You will need to put the channel code hex (like 18c) in the place of the "ffff" on each of the channels to eliminate this "doubling" while the program is running.

I can't remember exactly, but you do something with the number 380 with your base. I'm sure there are lots of other forums on this. I'm sure I just mudded up the waters for you anyhow....


Good luck,
Mark

 

[ericcarlson]

I am completely new to UHF trunking and figuring out the offset and base frequencies. What's the difference between this and 800 MHz trunking ?

The 800 and 900 MHz bands have predefined channel plans for each band, so 800 and 900 MHz radios know where to go for a given channel X. For other bands, the radio has to be told how to map a channel number X to a corresponding frequency.

Here's a trunker file I've been trying to work with:

DISPOSITION=ascsdsesfulxnspssn
v0x000 ,0,ffff,b
v0x010 ,10,ffff,9
v0x17c ,17c,ffff,ea
v0x18c ,18c,ffff,fd
d 407.7625,1dc,ffff,0

How do I figure out how to put which frequencies where ?

Repeater outputs start at 17C hexadecimal (380 decimal). You can ignore the repeater inputs below 17C unless you are specifically interested in them. To convert hex to decimal, you can use the Windows calculator in scientific mode, or use your favorite search engine to find a web site that will do the conversion. You really need at least two channels in the system to determine the base and spacing; you have one already: channel 1DC is 407.7625.

Assuming a 12.5 kHz spacing (probably safe in this case), the base should be 406.5625 MHz.
How do you determine that?
1DC hex is 476 decimal
476 - 380 = 96 (subtract the repeater output offset from the channel number)
96 * 0.0125 = 1.2 MHz (multiply the channel offset [from 380] by the spacing in MHz)
407.7625 - 1.2 = 406.5625 MHz

The formula in general (when the base/spacing are known) is:
frequency in MHz = ( ( channel number in decimal - 380 ) * spacing in MHz ) + base in MHz

So, for your channels from Trunker:
17C = 406.5625 MHz
18C = 406.7625 MHz
1DC = 407.7625 MHz

Are there any online documants explaining how UHF trunking works in the first place?

http://www.radioreference.com/apps/...Base/Step/Offset_for_VHF/UHF_Motorola_Systems

-Eric

 

[JohnnyGalaga]

Thanks for the replies. I think I got it working. Here is my new file:

MAP=22222222
OPTIONS=nVDF
PLAN=0
DESCR=Type II 138.46 Hz
THRESHOLD=99
DISPOSITION=ascsdsesfulxnspssn
dv406.5625,17c,0,7f7
dv406.7625,18c,10,0
v406.9625,19c,20,39
dv407.7625,1dc,60,738
v408.1625,1fc,80,85

What confuses me is that I though UHF had a standard positive 5 MHz offset, so the words "offset" and "input" were throwing me.

 

[mam1081]

No, even on conventional stuff, the feds don't usually use 5 MHz offsets. I've never seen a 5 MHz offset. I have seen a 6 MHz though...

If you were to program the trunked radios for that system, you would need a base, step and all that for the transmit as well as the RX. You an set them up independently. It could make for some interesting combinations - never the same. Also, I have heard of some systems using different bases and offsets on the same system. I know you can program several per system in the radios, but have never experienced one to listen to.

 

[loumaag]

What confuses me is that I though UHF had a standard positive 5 MHz offset, so the words "offset" and "input" were throwing me.

Well, in addition to what mam1081 said, the frequencies associated with the channels 0-379 (0x000 - 0x17b) do not have to be lower than then frequencies associated with the outputs (380-759).

 

[ericcarlson]

MAP=22222222
OPTIONS=nVDF
PLAN=0
DESCR=Type II 138.46 Hz
THRESHOLD=99
DISPOSITION=ascsdsesfulxnspssn
dv406.5625,17c,0,7f7
dv406.7625,18c,10,0
v406.9625,19c,20,39
dv407.7625,1dc,60,738
v408.1625,1fc,80,85

Is this system already in the RR Database?

-Eric

 

[JohnnyGalaga]

Yes, but the info listed is different than what I got with trunker:

http://www.radioreference.com/modules.php?name=TRSDB&sid=4026

 

[loumaag]

Hmmm, if the orig. submitter made a typo it would fit with your data. If the 406.1625 was really 406.9625, it matches pretty much up with yours. Since Eric did the original update I will let him deal with it and the submitter as he may have already contacted him.

 

[WayneH]

In the downloads area there's a spreadsheet I created that will help out; it beats doing it by hand with Windows calculator. Also, try a search as there's a ton of info on this as it comes up a lot. Try it with my username in the poster field.

-Wayne