Base Freq / Offset / Step

[dmc541]

How/where can I find the Base Freq / Offset / Step numbers for the trunking system in my area? I have a Police Call guide book but it does not give me these numbers. The used freq in my area are 453.1000, 453.62500, 453.9000, 460.1000 (primary control channel), 460.25000, 460.45000 and 460.60000.

I need these numbers to program the Pro-2096 from RS.

Any help would be greatly appreciated.

dmc541

 

[DELCOLHFC]

Welcome aboard!
Where are you and what system is it you are trying to monitor?
Have you tried looking in the "RR Database"? Just click on the tab at the top of this page.

 

[fmon]

At the top of this page, click on RRWiki then under General Information, click on Trunking, then click on Motorola, then determining Base/Step/Offset...

 

[fmon]

The system is Umatilla Co OR

Using Brian Cathcart's calculator, I may have something which will work.

Press PGM>TRUNK>FUNC + 2 and enter the following:
453.0000 then ENTER
380 then ENTER
/\ to 25.0KHz then ENTER

FUNC + 3
/\ to Table on line 4 then ENTER

Edit :BTW, you'll need at least the CC programmed in the bank with these settings and the bank and freq set to Mot.
SCAN

 

[DaveH]

Frequencies in the 453MHz and 460MHz range is a sure sign that
at least two of the three ranges of VHF/UHF Moto systems is in use.
A single base/offset/step is not going to work for the whole system.
Each range needs its own base/offset/step exactly defined and
programmed. Thus can be one of the more difficult tasks.

First, it might be arrived at by guesswork, but if not, there could be
a lot of frustration. I suggest someone in the area of the system run
Trunker or Treport software on it. Get at least one channel number
for the 453MHz channels and at least one for the 460MHz channels.
That would be enough to narrow it down. The only other variable
would be step size. The way around this is to capture two channels
per range, and by simple calculation the step size can be determined.

By the way Frank, the step size could be 12.5kHz or 25kHz, so
using 25kHz may or may not be correct. Another thing I recently
discovered, the stepsize is not necessarily the same in every range.

Dave

 

[fmon]

I agree Dave, it will likely be frustrating and Trunker or Treport is the best method to try to find the needed data. I think Trunker is suggested in my directions provided to get more help for setting this type system up. And there could very well be two ranges.

I used one of the freqs provided by dmc541 and found his system with the Motorola search feature in RRDatabase and found the freqs looked like they should offset at 12.5 or 25. Logic would also suggest the base would be at or below the lowest freq.

Then I opened Brian's Excel VHF/UHF Mot calculator program and tried some variables. What fit with 460.1000 as CC was to use its Hex Value as 298, and affset of 25 KHz which produced a base of 453.0000.

Also, other Hex Values to match the voice freqs were in the tables using 25 as offset but totally unusable with 12.5.
180 Calculated freq > 453.1000
195 Calculated freq > 453.6250
1a0 Calculated freq > 453.9000
29e Calculated freq > 460.2500
2a6 Calculated freq > 460.4500
2ac Calculated freq > 460.6000

I provided a shoe for dmc541 to try on, if the settings are correct for the lower range (assuming there is two) then he will receive traffic on some of the system. If it is correct and only one range exist, then he will receive the total system. If the data entered is incorrect, He will likely see or hear nothing.

 

[dmc541]

Hey thanks for the info. I'm going to try some of it. I have found out more info since my first posting.

The base is 406.0000

And the step is 25 KHz.

Now is that enough to figure the offset?

Thanks again for the help,

Don

 

[dmc541]

Hey thanks for the info. I'm going to try some of it. I have found out more info since my first posting.

The base is 406.0000

And the step is 25 KHz.

Now is that enough to figure the offset?

Thanks again for the help,

Don

 

[loumaag]

Emphasis added

Hey thanks for the info. I'm going to try some of it. I have found out more info since my first posting.

The base is 406.0000

And the step is 25 KHz.

Now is that enough to figure the offset?

The Offset is the easiest as the the first one is always 380 or 0x17c in Hex. Your base frequency above is impossible given the frequencies used on the system. With a base freq of 406.000 and a step size of 25KHz, the highest frequency in the system can only be 415.4750.

As others have said, a single channel number and correspoinding frequency will go far into giving the proper base/set/offset for the system.

I will tell you that it is possible to run the 32 bit version of Trunker and feed it with direct audio into your soundcard from the speaker/earphone jack of you radio (no disriminator tap) and it will run well enough to get the frequency channel info (as it is repeated over and over again) that is needed for this task. See this thread in the forums.

 

[loumaag]

I forgot, as this has nothing to do with scanner software, I am moving it to the scanner forum.

Sorry, meant to put that in the last post.

 

[loumaag]

Well this is getting silly. After forgetting to move the thread, and then doing so, I realize I should look at the system. Looking at the submission from Aug 8, 2004 (the one that provided the frequencies) I find that the submitter actually sent in the Trunker file. So, using that and what Brian's great spreadsheet, I have come up with the following:

            Offset
Base        hex/dec      Space
453.0125   0x17c/380     6.25 Khz
460.0125   0x21a/538     6.25 Khz

Of course the second base was a guess, but just tried to match the first one for choice.

I would appreciate it if others looked at the dump and point out any flaws:

c v453.1000,18a,ffff,c7b
  v453.6250,1de,ffff,db0
  v453.9000,20a,ffff,ffc
 d 460.1000,228,ffff,0
  v460.2500,240,ffff,f5d
  v460.4500,260,ffff,c13
  v460.6000,278,ffff,e4a

 

[fmon]

Well this is getting silly. After forgetting to move the thread, and then doing so, I realize I should look at the system. Looking at the submission from Aug 8, 2004 (the one that provided the frequencies) I find that the submitter actually sent in the Trunker file. So, using that and what Brian's great spreadsheet, I have come up with the following:

            Offset
Base        hex/dec      Space
453.0125   0x17c/380     6.25 Khz
460.0125   0x21a/538     6.25 Khz

Of course the second base was a guess, but just tried to match the first one for choice.

I would appreciate it if others looked at the dump and point out any flaws:

c v453.1000,18a,ffff,c7b
  v453.6250,1de,ffff,db0
  v453.9000,20a,ffff,ffc
 d 460.1000,228,ffff,0
  v460.2500,240,ffff,f5d
  v460.4500,260,ffff,c13
  v460.6000,278,ffff,e4a

Lou, I'm getting the base for the upper range at 459.0250 vs 460.0125 with 228 hex for the CC 406.1000.

The lower range sure fits though.

 

[DaveH]

            Offset
Base        hex/dec      Space
453.0125   0x17c/380     6.25 Khz
460.0125   0x21a/538     6.25 Khz

Of course the second base was a guess, but just tried to match the first one for choice.

That looks like it should work. The only minor tweak I would
suggest is changing base 2 to 460.0000 and offset 2 to 537.

This is the first Moto system I've seen that uses 6.25kHz step,
but surely one of the first of many. Too bad some older scanners
can't handle that stepsize.

Dave

 

[dmc541]

Hex numbers

So do I need to build two different banks with the above infomation one for the 453 numbers and one for the 460 numbers?

I have been told the four lower sets of numbers are the one used for the rotating control channel they switch to ever night at midnight

Will my scanner let me put in two different sets of info?

When I put in the off set of 380 or 537 is there any thing I need to do the the hex numbers (0x17c & 0x21a) or are they the same thing?

So far I have tried these but not two different banks. I'm such a novice.

Thanks again for all your help,

Don

 

[fmon]

Don,
Below is an annotated export of the system from Win96 with the two setups indicated by Lou above. If DaveH is correct then the second settings would be modified accordingly.

You cannot do this double setup with the scanner keyboard. If your scanner has two current active CC's (453 and 460), then you can use one group in a bank and the second in another bank.

Pendleton OR                     
MO      Base         Offset Step   CH Lo  CH Hi
1       453.01250    380    6.5    380    537
2       460.01250    538    6.5    538    759
3600    multi table                
0    Umatilla OR     453.10000    MO    0    
1    Umatilla OR     453.62500    MO    0    
2    Umatilla OR     453.90000    MO    0    
3    Umatilla OR     460.10000    MO    0    
4    Umatilla OR     460.25000    MO    0    
5    Umatilla OR     460.45000    MO    0    
6    Umatilla OR     460.60000    MO    0

I have been told the four lower sets of numbers are the one used for the rotating control channel they switch to ever night at midnight

If this is true, then you only have one system. You can surly find this out by manually stepping through each of the 6 frequencies and listening for CC noise. You'll need to do this for four days and this should give you one of the following conclusions:

1. no CC noise=no system or you are out of range to the tower
2. one CC noise=one system\site
3. two CC noise=two systems\sites

 

[dmc541]

A big thanks

Frank

This is what I have found that finally worked. And I have to say without the help of Dave's high range numbers and Lou's low range numbers AND long phone call conversations with Frank I could not have got this done. He was great to work with. A true gem in a big ocean!

And to the county's radio guy who told me that there was no such thing as base freq, step and offset Pattooee to you!!!!!!!!!!!!!!

Thanks again Frank! God bless! Keep in touch.

Don

Base Offset Step
Bank 1 453.0125 380 6.25
Bank 2 460.0000 537 6.25


Pendleton OR
MO Base Offset Step CH Lo CH Hi
1 453.01250 380 6.25 380 537
2 460.00000 537 6.25 538 759
3600 multi table
0 Umatilla OR 453.10000 MO 0
1 Umatilla OR 453.62500 MO 0
2 Umatilla OR 453.90000 MO 0
3 Umatilla OR 460.10000 MO 0
4 Umatilla OR 460.25000 MO 0
5 Umatilla OR 460.45000 MO 0
6 Umatilla OR 460.60000 MO 0

 

[fmon]

Thanks for the kind words.

Don is using two Pro-96's, one with the current CC locked out and scanning the other 6 freqs in FM and the other trying to set it up correctly to follow the traffic in Mot trunking.

Actually, I only helped him set the FUNC + 3 table for each bank (failed using multi table) and to use a second bank with the upper range settings. Without input by Lou and Dave, we would still be fishing. Lou admitted his upper range was a guess, so I'm still scratching my head on how Dave came up with his settings for that range. But it surely works because Don is apparently tracking the system correctly with the two banks and related settings, and the voice traffic received on the FM Mode scanner matches the voice traffic now received with the Mot Mode scanner with correct ID's indicated.

If he were using Win96, these would be the settings.

[/color] Pendleton OR                     
 MO      Base         Offset Step   CH Lo  CH Hi
 0	 453.01250    380    6.25    380    536
 1	 460.00000    537    6.25    537    759
 3600    multi table                
 0    Umatilla OR     453.10000    MO    0    
 1    Umatilla OR     453.62500    MO    0    
 2    Umatilla OR     453.90000    MO    0    
 3    Umatilla OR     460.10000    MO    0    
 4    Umatilla OR     460.25000    MO    0 
 5    Umatilla OR     460.45000    MO    0    CC on 08/05/05
 6    Umatilla OR     460.60000    MO    0

Apparently the 460.xxxx freqs rotate CC duty each night.

Without Win96 he is forced to use (apparently successfully) two banks with settings as indicated in previous post.

1 453.01250 380 6.25
2 460.00000 537 6.25

Strange, when the scanner stopped on a TG in bank 2, the VC freq displayed was 460.09375 instead of 460.10000. Changing the step to 12.5 naturally changed the VC to a freq above 460.10000 and he lost the audio, so 6.25 must be correct because that is the only way scanner will receive audio.

All in all, we have a camper in Pendleton and should soon start noting RRDatabase changes on the system.

 

[DonS]

Without Win96 he is forced to use (apparently successfully) two banks with settings as indicated in previous post.

1 453.01250 380 6.25
2 460.00000 537 6.25

What happens when the scanner stops in bank 2 on a channel below 537? Or in bank 1 on a channel above 536? Unless the scanner is "smart enough" to avoid such things (and I don't think it is), you should get some invalid voice frequencies.

 

[dmc541]

I'm going to check this closer tonight but I'm all but sure that if the number is one of the 3 in the 453.xxxx the scanner locks into bank 1. If it locks onto one of the 4 in the 460's it locks into bank 2. A bank 1 lock, is right on the number, a bank 2 lock is just below the number.

I'll let you know as the time goes on,

Thanks,

Don

 

[fmon]

What happens when the scanner stops in bank 2 on a channel below 537? Or in bank 1 on a channel above 536? Unless the scanner is "smart enough" to avoid such things (and I don't think it is), you should get some invalid voice frequencies.

Talking with Don last night 08/06, he is getting some invalid voice freqs at this time in both banks, but ID's appear with audio. Wouldn't Win96 correct this by setting Extended Tables with Multi tables under 3600 CC, and of course, using one bank? Giving the other settings are also correct, base etc...