Very interesting HMP frequency change

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Very interesting HMP frequency change

Postby Minus1 » Thu Jul 26, 2018 11:12 am

HMP Birmingham (aka Winson Green) "M2JG" has recently moved to 450.7 MHz (still using 136.5 CTCSS).
They'd previously been using 452.9/466.8 for at least 40 years.

I've managed to track down the new input/mobile freq. It is 460.7 MHz (also using 136.5 CTCSS).

This is interesting for multiple reasons:
1. 450.7 is presently all by itself in the middle of the desert.
2. The new pairing is exactly a 10 MHz split, as are a few existing TETRA transmissions at 454/464.
This suggests that a 10 MHz split is being implemented across much of the UHF band. Which would do a lot to tidy up the present mess that has evolved over many decades :thumbup:
3. The new M2JG mobile freq is within the existing HMP base station band 460.5-460.75. So are they going to realign this entire band, moving the mobile freqs currently at 467.0-467.25 to 460.5-460.75, and the base freqs currently at 460.5-460.75 to 450.5-450.75 ?
This would also free up 467.0-467.5 (possibly for more PMSE?)
4. Note that 450-450.5 is not usable as the base end of a base/mobile pair as 460.0-460.5 is already paired with 453.5-453.9875 (unless they plan to move that too).

Has anyone else found any new HMP transmissions at 450.5-450.75?

If this 10MHz split continues to be implemented , it may progress to affect the airport band at 455 MHz; and the fireground channels at 457 MHz.
It could even mean a gradual realignment of the 456/461.5 base/mobile pairing to 456/466.
Something to remember if transmissions suddenly disappear…
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Re: Very interesting HMP frequency change

Postby warlock01 » Sun Jul 29, 2018 11:55 am

hi minus 1,, a long time ago when the police used that band there was two splits as you will possibly know 13.900 and 10 mhz, the 10 meg split was for the tx's 450.000 to i think 451.000 ,then 13.900 upwards, tnx for the prison info though, i scan that band from time to time and there is some constant data on 450.5375 and 450.5625, no idea what it is ,
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Re: Very interesting HMP frequency change

Postby Minus1 » Sun Jul 29, 2018 4:56 pm

I've picked up some signals on 450.5375 and 450.6625 near Bedford in the past, but I didn't have the time to try and track them down.
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Re: Very interesting HMP frequency change

Postby jimh » Sun Jul 29, 2018 9:19 pm

All of the HMPs in the Bristol area are 450/460Mhz (-10Mhz splits) now, and are TETRA. One of them used to be 460/467Mhz split analogue, then moved to encrypted DMR, now TETRA (but in the clear !).
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Re: Very interesting HMP frequency change

Postby Minus1 » Mon Aug 13, 2018 4:15 pm

It's got more interesting, The secondary channel that used to be on 460.55 has now popped up on 452.55, input is 462.55. Both ~136.5
Again a 10 MHz split. So we might assume that 452.5 to 452.75 is going to be allocated to the Home Office, paired with 462.5-462.75 (Which already includes some Fireground input freqs).
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Re: Very interesting HMP frequency change

Postby Davie Boy » Wed Aug 15, 2018 2:16 pm

That is interesting... I hope this is a new bandplan for prisons...

I used to enjoy listening to HMP Notts on 451.100 and until recently ish... HMP Birmingham on 452.900... both were analogue with a good signal to me and both have disappeared... :sad:

I assumed they went to tetra but this has got me hopeful... anyone heard anything...?
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Re: Very interesting HMP frequency change

Postby Minus1 » Thu Aug 16, 2018 7:10 am

This is what I have found so far.
All these band are 0.25 MHz wide, and use a 10MHz split between repeater input and output.
It is not possible to extend the bands because there are existing systems either side; but this 10MHz split may be indicative of a long term plan.

Any HMP base transmissions that dissappear from the old HO 25k channels in 450-452.975 range, and from the 460.5-460.75 band, may pop up in 450.5-450.75 or 452.5-452.75.
It remains to be seen what will happen to 467.0-467.25 if all HMP comms switch to a 10MHz split.
One obvious possibility is the moving of Fireground input freqs from 462 to 467.

450.5 - 450.75 New HMP repeater output?
452.5 - 452.75 New HMP repeater output?
457.0 - 457.25 Fireground simplex/repeater output

460.5- 460.75 currently HMP repeater output => new HMP repeater input
462.5 - 462.75 Fireground repeater input => new HMP repeater input (Cue more problems from illegally used US FRS/GMRS radios!)
467.0 - 467.25 currently HMP repeater input => ?

Official information from OFCOM is sparse and out of date as usual:
https://www.ofcom.org.uk/__data/assets/ ... rvices.pdf
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