Squelch open delay? 396XT

[dracer777]

Wirelessly posted (MOT-QA30/00.72 UP.Browser/7.2.7.5.610 (GUI) MMP/2.0)

Hello peoples, i'll be quick and to the point.

When I'm scanning conventional channels, I miss maybe .5 seconds of audio when squelch opens. Enough that when the dispatcher does a status check, I will completely miss the "code 4" and just hear an instant open and close squelch. I have turned the P25 waiting time in the system settings to 0ms. And I thought at first it was because it didn't catch the traffic due to scanning 20 channels. So I put it on hold, on the specific channel, with the same result.

This isn't a huge issue and I can easily just deal with it, but if anyone has a recommendation, that would be great.

The channel I am scanning is 159.270 with a CT of 136.5 if it makes a difference. Thanks guys!

[jclarkr6]

You might try eliminating the PL (or "CT") tone. I had the same problem with my 396XT and eliminating the PL tone seemed to fix the problem. I think that the scanner takes an extra half second or so to pick up the PL tone sometimes and that is why you are missing the beginning of some transmissions. This is just my opinion; I hope it helps!

[dracer777]

Originally Posted by jclarkr6

You might try eliminating the PL (or "CT") tone. I had the same problem with my 396XT and eliminating the PL tone seemed to fix the problem. I think that the scanner takes an extra half second or so to pick up the PL tone sometimes and that is why you are missing the beginning of some transmissions. This is just my opinion; I hope it helps!

AHA! Thanks jclarkr6, that worked. Instant open squelch. Much thanks.

[jclarkr6]

Originally Posted by dracer777

AHA! Thanks jclarkr6, that worked. Instant open squelch. Much thanks.

You're welcome, dracer777! I'm glad that you're able to hear all of the action again. Happy Scanning!

[UPMan]

That should have had no affect unless:
a) There are interfering signals causing the PL to be difficult to discriminate, or
b) (most likely) The channels is not programmed with the correct modulation (i.e. FM or AUTO instead of NFM).

PL detection is within a few (certainly fewer than 500) milliseconds.

[jclarkr6]

Originally Posted by UPMan

That should have had no affect unless:
a) There are interfering signals causing the PL to be difficult to discriminate, or
b) (most likely) The channels is not programmed with the correct modulation (i.e. FM or AUTO instead of NFM).

PL detection is within a few (certainly fewer than 500) milliseconds.

Thanks for the additional info, UPMan. I think that in my case there must be something interfering with the signal that makes it difficult to immediately detect the PL tone. I have only encountered this problem on one frequency so far (154.815 in Mattoon, IL) and I know for a fact that the modulation for that frequency was set to AUTO. The other frequencies that I use a PL or DPL tone for all seem to work correctly. I just had to remove the PL tone for 154.815.

[UPMan]

AUTO on that frequency would result in NFM (sorry, I see I had my parenthetical backwards in my post...NFM or AUTO would cause a problem if the actual transmission is FM, unless you have modified the band defaults).

[dracer777]

Wirelessly posted (MOT-QA30/00.72 UP.Browser/7.2.7.5.610 (GUI) MMP/2.0)

I do have mine set to FM. After listening today, I think I still have the same issue. It seems to be better with no PL, but I can't tell if I'm just imagining it. I'll try NFM to see if that works.

[UPMan]

The other symptom you should note for mismatched modulation is if the channel is significantly louder than other channels, you likely have it set to NFM when it should be FM. And the obverse...if it is quieter than other channels you have it set to FM when it should be NFM.

The PL decode delay could still be caused by other interference (but setting the correct modulation is a desired thing to do regardless).

[tampatracker]

UPMan, how do you know from the RR database when it should be FM vs. NFM, or is it a matter of experimentation? Afterthought: Upon searching thru some databases for here in FL. I'm seeing FM along with FMN, is this the key perhaps?

[DaveNF2G]

You probably can't tell from the RRDB. There is much confusion over FM, WFM, and NFM among scanner users. Much of that is the fault of the manufacturers for assigning their own definitions to the terms. (The same situation exists regarding "Motorola" and P25 trunking.)

As a rule of thumb, beyond UPMan's suggestion above about relative volume, you can presume most of the time that UHF frequencies are NFM. VHF frequencies are likely to be NFM if the fourth digit after the decimal is a 5 (i.e. 154.3475). Other frequencies are being changed from FM to NFM as agencies attempt to comply with the FCC's narrowbanding mandate. If a local FM frequency gets much quieter (lower relative volume) suddenly, it has probably been narrowbanded.

Another indicator of narrowbanding might be a change from CTCSS (PL) to DCS (DPL) without a change in frequency.

[UPMan]

The "MODE" column is supposed to indicate this. (I think RRDB uses "FMN" for "NFM"). Also, if you open the license page for the frequency, FM channels are going to have a FCC Emission designation starting with "20". NFM will usually be "11" or "13" or some other value much smaller than "20."

Uniden Modulation Definitions

[tampatracker]

Thank you, gentlemen, that clears up that mystery for me. Thank you both for the quick response.... John.

[Avery93]

I am having this delay problem on my BCT15. In another thread a while back I was told to change the modulation, this certainly helped while holding on a channel, squelch usually opens up in less than 50 ms. However while actually scanning, it can take up to 2 seconds on some channels, and when mobile I've actually had it never open up. Its very inconsistent, on one transmission it can be barely noticeable, but the next could take 2 seconds. When I turn the PL tones off while scanning there's almost no delay. I'm pretty sure it isn't interference, I've had it in different buildings and vehicles with the same results.

[Kennrth]

Is there a delay when using autodetect?

[UPMan]

If you mean PL search, no.

[Avery93]

Originally Posted by Kennrth

Is there a delay when using autodetect?

No, because it isn't waiting on the tone to open squelch. It opens squelch on a transmission and then detects the tone.


So UPMan, do you know what could be causing this? Could my scanner have a bad tone decoder?

[jclarkr6]

Originally Posted by UPMan

AUTO on that frequency would result in NFM (sorry, I see I had my parenthetical backwards in my post...NFM or AUTO would cause a problem if the actual transmission is FM, unless you have modified the band defaults).

I did not realize that this could happen with the AUTO setting. I've changed the modulation for the appropriate frequencies. Thanks for that tidbit, UPMan!

[UPMan]

Common confusion. AUTO does not mean "autodetect" (I get it, now), it means "automatically use the band's default value." Starting with the "X" models, you can edit the band default values so if your area has little narrowband, you can change the band default to FM (then "AUTO" would equal "FM" instead of the "NFM" that is the default for most bands and is the current FCC licensing requirement for new licenses.

[rvictor]

Perhaps the setting could be labeled "DEFAULT" at some point down the line.

Dick