Programming the GRE 500/600 scanners for rebanded Motorola trunked systems
- Thread starter WayneH
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mikey60
Member
DonS
Member
Mike (V)... you might want to change the text in your "Custom Frequency Tables" dialog shown above. As I'm sure you're aware, the tables are used for more than just "only MOT VHF/UHF" TSYS objects (i.e. any MOT or P25 TSYS where the TTables setting is "custom").
ka3jjz
Wiki Admin Emeritus
Thanks to you and Mikey60 for those screen shots. I will capture them and post them in the GRE software article. Then everyone can point to this, rather than to the otherwise-unrelated Win96 article. Clarity is important! 73 Mike
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mikey60
Member
DOH! I guess I better fix that! (Shows you how often I look at that screen).
Thanks Don!
Mike
ka3jjz
Wiki Admin Emeritus
Mikey60, when you get that changed, please send me a JPEG of that screen, and I will update the wiki. The email is ka3jjz@NOSPAMnetscape.com (remove the NOSPAM, of course) 73 Mike
mikey60
Member
Highpockets
Member
Don, Mike has the offsets in his table and you don't, is there really any difference if you put the offset in or not?
DonS
Member
Yes, it matters.
After lookiing at Mike's table more closely, I don't believe it will work*. With the base frequencies shown (which match mine), all of the offsets except the first and fifth (base frequencies 851.0250 and 868.9750) should be zero. That is, it should look like my table.
*Mike's table will work for any system that only uses channel number 0-719. Any system that uses channel numbers above 719 will have incorrect voice frequencies calculated.
Highpockets
Member
Tom_G
Member
Don and Mike,
I don't think any of us could ask for better product support...
Thanks for all your efforts...
I don't think any of us could ask for better product support...
Thanks for all your efforts...
mikey60
Member
Hmmm, I'll have to go back and look at that, I thought I copied it directly from what Wayne had originally posted. I'll look again.
Mike
ka3jjz
Wiki Admin Emeritus
Mike V - I will hold off posting the changed chart until you get a chance to validate your findings. I would like to get a correct chart posted, not one that has potential errors. Thanx. 73 Mike
mikey60
Member
Yeah, the one on there is incorrect due to my misunderstanding of how offsets work on 800MHz systems. I've corrected the tables for the next release, but haven't been able to get it put up on the site yet.
Mike
I have the GRE600, will the same thing work for me---custom and reband?
thanks
thanks
mikey60
Member
DonS
Member
To clarify... the offsets work the same on all MOT and P25 systems. When the radio receives a "call grant"-type message, it looks at the channel number contained in that message. It then looks for a "table entry" that contains that channel number, based on each table entry's "ChLO" and "ChHI" values. If it finds such an entry, it calculates the voice frequency using:
Fv = Fbase + Fstep x (Channel - Offset)
where:
Fbase = the entry's "Base Frequency" value
Fstep = the entry's "Step Size" value
Offset = the entry's "Offset" value
Channel = the channel number from the control channel message
I think the misunderstanding (i.e. "Offset" usually equal to "ChLO") probably comes from how people are sometimes told to figure out the "ChLO" and "ChHI" values when they only have Base, Offset, and Step settings. We've told them (usually in reference to VHF or UHF OBT systems) to:
1. sort their entries by offset value
2. set each entry's "ChLO" to its "Offset" value
3. set each entry's "ChHI" to one less than the "Offset" value of the next entry, or 759 if this is the last entry
For example, given the RR DB's listed table entries for the San Mateo County, CA system, we'd come up with table entries of:
Code:
ChLO ChHI Offset Step Base
380 559 380 12.5 482.0000
560 759 560 12.5 488.0000For the "rebanded" 800 MHz systems, though, we already have a known set of table entries, and don't need to do any such ChLO/ChHI derivation.
It should be clear from the formula above that the values for Offset and Base Frequency are intimately tied together. Each entry defines a range of Channel -> Frequency mappings, where the first frequency in the mapping depends on both Base Frequency and Offset.
In the UHF example above, the two ranges start at (have first voice frequencies of) 482.000 and 488.000 MHz. The "default" 800 MHz tables are laid out somewhat differently, though: the Base Frequency doesn't usually equal the first voice frequency in the range - since the Offset value is zero. For example, the range for channels 720-759 has a first voice frequency of 866.000MHz, not 848.000MHz. If one wanted to make these tables "look like" the user-derived VHF/UHF tables (i.e. Offset = ChLO), then one would have to change both the base frequency and offset values. The 720-759 range would get a new offset of 720 and a new base frequency of 866.000MHz. That is, these two table entries are equivalent:
Code:
ChLO ChHI Offset Step Base
720 759 0 25.0 848.0000
720 759 720 25.0 866.0000
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mikey60
Member
Thanks Don, I understand my mistake now! 
Mike
Mike
qlajlu
Silent Key
I think you guys need to extend a "Thank you" to Highpockets. He was the one that asked the question pointing out that error.Thanks Don, I understand my mistake now!
Mike
Today i used Win96 (thank you Don) to set up a rebanding for my PRO96 on a northern suburb of Chicago=NWCD-Arlington Hts ILL, Motorola Type11 analog-digital 3600baud system...I followed the first post (Wayne) description, all freqys are from 851-853, entered the new 7 freqys, clicked on 3600-800mgz-multi-table, proceded to put in the first two sets of freqys, base, offset, CH-lo, CH-hi....I then "erased" all the rest as it mentioned you only need the first two freqy limits if not over 860....I then downloaded to my PRO96-1.3ver...I live 55 miles from this system so next week i hope to visit the area to see if it works...This system was just rebanded and from local accounts Motorola changed the # ing system of the freqys...Does my procedure sound correct....Thank You
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