SDS100/SDS200: Stopping On Unlisted Frequencies

kq4chief · Jul 5, 2018

I monitor ONLY the "West Simulcast" on the Portland, Oregon P25 system. Last night, during very busy police and fire activity regarding fires and fireworks, I logged the frequencies the SDS100 was stopping on during transmissions. The majority of those frequencies are listed in the RR Database and in Sentinel for that system. However, the scanner occasionally stopped on a few frequencies that are not listed. How is this possible?

IAmSixNine · Jul 5, 2018

On a trunking system the control channel tells the scanner what voice channel and talk group is active.
So if the CC was not being decoded 100% accurate its possible the voice channel was given incorrectly to the scanner. But if it was passing audio then the frequencies could have been added for capacity and not listed in the DB.
Just my guess.

troymail · Jul 5, 2018

I think you are saying that you would sometimes see a displayed frequency during a voice call that is not listed in the RRDB for that specific site... if so, one possibility (giving the radio the benefit of the doubt) is that the RRDB listing isn't 100% complete/accurate.

Of course, there could be other reasons.....

kq4chief · Jul 5, 2018

Thanks for the feedback, guys! Yes, the unlisted frequencies the scanner stopped on had valid Portland police and fire transmissions. So the Control Channel is indeed in control!

troymail · Jul 5, 2018

kq4chief said:
Thanks for the feedback, guys! Yes, the unlisted frequencies the scanner stopped on had valid Portland police and fire transmissions. So, I guess the Control Channel can instruct the scanner to stop on certain frequencies even though they aren't shown in the Database?

Yes - for these type systems, all that is really needed is the "active" control channel frequency.... the others really don't matter until that control channel frequency changes....

FWIW - Some systems nearly never change their CC frequency - others rotate the CC over ALL site frequencies over time...

ofd8001 · Jul 5, 2018

As I understand it, part of the data in the control channel's data includes the frequency assigned for the voice conversation, which is what you see displayed.

It's possible the system is using a voice channel that isn't listed in the database. If so, an update to the database would be in order.

kq4chief · Jul 5, 2018

Thanks again. I'll continue to log the unlisted frequencies and submit a database update.

Ubbe · Jul 5, 2018

I believe your FCC are pretty good at having all information about granted frequencies to users. Maybe they have to due to the freedom of information act. You could take a look there to see what frequencies have been given to the Portland system.

/Ubbe

UPMan · Jul 5, 2018

Also, if you post the found freqs to this thread (in addition to submitting), might find some additional insight from users.

kq4chief · Jul 5, 2018

So far, the additional frequencies I found that are not on the list for the Portland P25 "West Simulcast" are:
852.38750
856.73750
857.46250
860.26250
However, these four are listed in the database for the old Portland analog system.

ChrisP · Jul 5, 2018

kq4chief said:
So far, the additional frequencies I found that are not on the list for the Portland P25 "West Simulcast" are:
852.38750
856.73750
857.46250
860.26250
However, these four are listed in the database for the old Portland analog system.

Since the analog system was taken down, I do believe the plan was to integrate some of those frequencies into the P25 sites as needed.

- Chris

SDS100/SDS200: Stopping On Unlisted Frequencies

kq4chief

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IAmSixNine

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troymail

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troymail

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Ubbe

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UPMan

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