P1225 2.5 kHz PLL?

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P1225 2.5 kHz PLL?

Postby aaknitt » Sat Apr 18, 2009 3:48 pm

Working on a grant and I'm trying to determine what various VHF radios are capable of. I know the VHF P1225 is narrowband capable, but does it have a 2.5 kHz channel step size (i.e. can be be programmed on all VHF splinter channels or just some of them)?

Thanks in advance,

Andy
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Re: P1225 2.5 kHz PLL?

Postby laramiecountyCERT » Tue Apr 21, 2009 11:13 am

I could not get the 1225 that we use at work to go any lower than 12.5Kh for the spacing. If anyone has any other suggestions that would be great.
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Re: P1225 2.5 kHz PLL?

Postby Will » Tue Apr 21, 2009 1:50 pm

In the days of the P1225 and M1225 the "narrowband" channel step was 6.25 kHz. They also do the 5kHz step.
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Re: P1225 2.5 kHz PLL?

Postby laramiecountyCERT » Tue Apr 21, 2009 4:57 pm

Could this be with a different radio set? Is there a series of radios for the P1225 in serial number or the like that will do the narrow band? If I can get them down to the new standard we can use them instead of getting CP200 to replace them.
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Re: P1225 2.5 kHz PLL?

Postby fineshot1 » Tue Apr 21, 2009 10:01 pm

aaknitt wrote:Working on a grant and I'm trying to determine what various VHF radios are capable of. I know the VHF P1225 is narrowband capable, but does it have a 2.5 kHz channel step size (i.e. can be be programmed on all VHF splinter channels or just some of them)?

Thanks in advance,

Andy


I think you are confusing things on this issue. There is NO 2.5khz channel step on vhf hi band. There is a 2.5khz deviation max for the new narrow band step which is 7.5khz for some portions of the vhf hi band and for uhf the new narrow band is 6.25khz.
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Re: P1225 2.5 kHz PLL?

Postby aaknitt » Wed Apr 22, 2009 3:47 am

fineshot1 wrote:I think you are confusing things on this issue. There is NO 2.5khz channel step on vhf hi band. There is a 2.5khz deviation max for the new narrow band step which is 7.5khz for some portions of the vhf hi band and for uhf the new narrow band is 6.25khz.


I understand that the channel spacing is 7.5 kHz. However, VHF hi band is split into several segments. Within these segments the channel spacing is 7.5 kHz, but between segments the channel centers aren't on multiples of 7.5 kHz, which is why a 2.5 kHz channel step is needed to operate on all splinter channels in the VHF hi band. A radio with 6.25, 12.5, or 7.5 kHz channel step size will be able to operate on some of these splinter channels, but not all of them. I've attempted to explain it in more detail here:

http://radioetcetera.googlepages.com/NBChannelIssue.pdf

There are many radios from this vintage that are narrowband (2.5 kHz deviation) capable but can't properly be programmed onto some of the 7.5 kHz spaced splinter channels. Apparently the P1225 is one of those radios, which is what I was after (Thanks Will!).

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Re: P1225 2.5 kHz PLL?

Postby fineshot1 » Fri Apr 24, 2009 10:10 am

Andy - between 150 - 162 there is not one big block of consegutive 7.5khz channels steps. Portions of this range could not be changed
to 7.5khz steps(ie: the RC & RT channels as an example). This range is made up of smaller portions some of which have different
channel step sizes. If you can PM me with your email address I can send you a pdf file with the breakdown, or if you have a copy of
one of the last police call publications and still have the CD Rom supplied with it the file is on that CD Rom and is called " ConsolCD1x.pdf"
and has a lot of other usefull info as well.
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Re: P1225 2.5 kHz PLL?

Postby Tom in D.C. » Fri Apr 24, 2009 2:05 pm

FWIW, and not to confuse the issue but in the interest of getting information out there, I once owned a UHF Vertex VX900 that had programmable channel steps of 1.25 kHz, so you could put the frequency almost anywhere imaginable in the band. It's probable that having one of these units and having it set up wrong could also raise hell with adjacent channel users.
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Re: P1225 2.5 kHz PLL?

Postby fineshot1 » Fri Apr 24, 2009 5:38 pm

Tom in D.C. wrote:FWIW, and not to confuse the issue but in the interest of getting information out there, I once owned a UHF Vertex VX900 that had programmable channel steps of 1.25 kHz, so you could put the frequency almost anywhere imaginable in the band. It's probable that having one of these units and having it set up wrong could also raise hell with adjacent channel users.


Tom - after looking over the specs for the VX-900V this seems a bit confusing.

The channel spacing is 12.5/25/30Khz and the PLL steps are 1.25/2.5/5/6.25Khz

I could be wrong but I think the PLL steps are a fine tune for the receiver, don't think
that has an effect on the transmitter but this one seems clear as mud. Perhaps someone
else can clear this one up.
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Re: P1225 2.5 kHz PLL?

Postby aaknitt » Fri Apr 24, 2009 6:34 pm

fineshot1 wrote:I could be wrong but I think the PLL steps are a fine tune for the receiver, don't think
that has an effect on the transmitter but this one seems clear as mud. Perhaps someone
else can clear this one up.


PLL steps are for both the transmitter and receiver. The PLL step (or channel step) dictates what frequencies you can and can't program the radio to operate on. In this case, a 1.25 kHz PLL step means that it's possible to program the radio to operate on frequencies that are 1.25 kHz off-center of the FCC-defined channels. That doesn't mean anyone should do it...just that the radio is capable of it.

The PLL is the phased locked loop, which is a digital circuit that ensures the radio is on the correct frequency. Because a PLL is a digital device, it can only be programmed to "lock" on a finite number of frequencies for a given reference oscillator. The smaller the PLL step, the more frequencies that the radio could be programmed to operate on. From a practical standpoint, there is no reason to produce a radio with a PLL step smaller than what is required to operate on the FCC-defined channels. When the FCC changes the channel centers (or the planned channel centers), it causes some radios to go obsolete because their hardware was designed for the old channel plan.
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Re: P1225 2.5 kHz PLL?

Postby Tom in D.C. » Sat Apr 25, 2009 6:05 am

The radio had a 1.25 kHz step in it that was programmable, and I did on several occasions, just for the hell of it, set in some of those nutty new channels the FCC is now assigning. However, this was the UHF radio, not the VHF one. The RSS for the VHF radio did not display the 1.25 capability so I would assume it didn't have it, but I've sold both radios so don't mess with that setup anymore, although I do still have the disks for both bands of the 900.
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Re: P1225 2.5 kHz PLL?

Postby fineshot1 » Sat Apr 25, 2009 9:26 pm

aaknitt wrote:
fineshot1 wrote:I could be wrong but I think the PLL steps are a fine tune for the receiver, don't think
that has an effect on the transmitter but this one seems clear as mud. Perhaps someone
else can clear this one up.


PLL steps are for both the transmitter and receiver. The PLL step (or channel step) dictates what frequencies you can and can't program the radio to operate on. In this case, a 1.25 kHz PLL step means that it's possible to program the radio to operate on frequencies that are 1.25 kHz off-center of the FCC-defined channels. That doesn't mean anyone should do it...just that the radio is capable of it.

The PLL is the phased locked loop, which is a digital circuit that ensures the radio is on the correct frequency. Because a PLL is a digital device, it can only be programmed to "lock" on a finite number of frequencies for a given reference oscillator. The smaller the PLL step, the more frequencies that the radio could be programmed to operate on. From a practical standpoint, there is no reason to produce a radio with a PLL step smaller than what is required to operate on the FCC-defined channels. When the FCC changes the channel centers (or the planned channel centers), it causes some radios to go obsolete because their hardware was designed for the old channel plan.


Well then, the vertex VX-900V model would seem to be what you are looking for. I do not recall if any of the motorola
models have this kind of programing capability but its new to me. Always thought the smallest step was 5khz until
now. Anyway, if you have that CD you can look over that file I referred to and see how that portion of the vhf-hi band is
broken up into smaller portions with different channel step sizes.
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