UHF Trunking Question

[rjp3637]

Hello all,

I've been trying to figure out how to program a 400mHz trunking system into my Pro-95 using Win95 and the more I try to figure out the base/offset/spacing parameters the more confused I get.

The system I am trying to program has the following setup:

-----
Motorola Type II
Base: 406.100
Offset: 25.0

406.1000, 406.2500, 406.7500, 406.8500, 408.4500, 408.7000, 408.9000, 409.7500, 410.3750
-----

OK, I can figure out the base frequency, that's pretty obvious...

Next I look at the offset, and see 25.0kHz, I can partially understand that, it seems obvious but I'm not entirely sure of exactly how it works. :?

Lastly, I look at the channel spacing... Here's where I'm totally confused! From this list the channels are not consistently or evenly spaced! What would I enter for the Step Size in Win95? :?:

Thanks for any help in advance

Ray

 

[DaveH]

The Database sometimes uses a confusing notation which
originated with the BC245. Offset and Spacing are mixed
up. Use:

Base = 406.100
Offset = 380
Step = 25.0 (or whatever the PRO-95 calls it)

That should work.

Dave

 

[joepaigejr]

You would probably put this in the Motorola UHF-Lo Settings in the upper right part of your bank settings in Win95.

 

[rjp3637]

OK...

I follow what you say about the base but both the step size and offset are still confusing me :?

Can someone out there give me a brief description of how step size and offset refer to. In the previous example it would seem that the step size would be consistent in term of what you would see in the frequencies of the system, but that is not the case in the example :roll:

What then does the offset refer to? Is the 380 in the example refer to kHz or what :?:

Ray

 

[joepaigejr]

380 decimal is 17C hex. Next go to this thread http://www.radioreference.com/modul...p;file=viewtopic&t=3122&highlight=17c . Look at Wayne's first response on 3/24.

 

[DaveH]

Offset is a channel number which corresponds to the lowest possible frequency in the range in question (Moto systems have three ranges...you are only dealing with one. The other two may not, or ever be used, so don't worry). This does not mean that channel 380 must be used in the system...it is only a reference point.

Moto systems don't send out actual frequencies, only channel numbers which the radios interpret.

Offset 380 is fairly standard for systems like this. This means that channel 380 corresponds to the base 406.100MHz. The step (increment) is 25kHz, so channel 381 would be 406.125MHz, channel 382 is 406.150, and so on. If you decode the hex channel numbers from Trunker, you can calculate their frequencies, if you know the base and offset.



Dave

 

[joepaigejr]

Dave,

I monitor DC MPD and sometimes get comms below 380 (in hex). How do I interpret these freqs, and how would I calculate the freqs?

Thanks,

Joe

 

[DaveH]

The channel numbers below 380 (17c hex) are inputs to the channels above 380. There are three sub-ranges for each. You don't need to bother with them unless you want to figure out what the input/output pairs are.

Dave

 

[joepaigejr]

Thanks, Dave. I would be interested in how to calculate them.

 

[mpdonala]

DaveH you seem pretty smart about the 400 mHz Trunking. I am working with a multiple offset system what are the other off sets you are refering to. I am trying to get the Ft Carson System in Colorado to work if you need the freq's you can get them from the RR Data Base any help would be appreciated. THANKS Mark

 

[WayneH]

Thanks, Dave. I would be interested in how to calculate them.

Input freqs aren't calculated any differently. From my experience the ranges - number of channels per range - is the same. You're really just working with different base freqs that are addressed with 000 to 379 instead of 380 to 759. The difficulty is when you're working with UHF Gov systems in that the tx versus rx 'repeater offset' is not standardized.

Regarding Ft. Carson.....what's the problem? Is the database incorrect in that there are more than one range?

-Wayne

 

[mpdonala]

The info for Ft. Carson does not work you can input it and it will track but nothing is ever heard. Havn't dealt with uhf tracking to often so I don't know if the offset is wrong or I need an additional one or what. Just looking for thoughts. Have several military bases here and I have one working but I can't get Ft. Carson to work. Thanks Mark

 

[mshadwick]

When programming a UHF trunked system, do you enter just the control channel or do you enter all the channels in to the bank?? Ft Chaffee AR has a Motorola system that is P25 with 3 Control Channels.

406.9875
407.3875
407.5875

I have entered them using 406 as the base, 12.5 spacing and 380 as the base in 3 different banks. It locks on, but does decode anything.

Manually scanning 406-410 I decode the voice channels.

I am missing something in the setup?

 

[kikito]

Have you guys changed the settings to Table with the FUNC 3 menu?

Are the freqencies set to MO?

Are the banks set to MO?

 

[mshadwick]

Uniden BC250 with the channels set to Motorola Type 2 UHF.