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Old 01-05-2014, 11:05 AM
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Default FDNY Tac channels narrowband?

Doing some checking over the eair with a measurement receiver, all the traffic I'm seeing on the FDNY simplex tac channels (486.1125, etc) appears to be narrowband. But the database still lists these as wideband (FM vs FMN).

Anyone have an authoritative answer if all the FDNY portables have indeed been converted to narrowband? The traffic I'm seeing (from the 3rd alarm on W 43rd) this morning definitely is, but that's only a small sample compared with the whole department.. If they are now narrowband, the database should probably be updated.

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Old 01-05-2014, 12:09 PM
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That doesn't sound right.

We had tested narrow band at the rock but then when Tband was exempt stopped.

There is a waiver for the channels that are not Tband
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Old 01-05-2014, 2:09 PM
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Interesting; the units I was getting this AM at the 3rd alarm were alll def within narrowband specs (as measured over the air).
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Old 01-05-2014, 2:53 PM
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Quote:
Originally Posted by blaze View Post
Interesting; the units I was getting this AM at the 3rd alarm were alll def within narrowband specs (as measured over the air).
Measuring over the air can be a pain, How strong was the signal you where trying to measure.
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Old 01-05-2014, 4:33 PM
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Quote:
Originally Posted by KC2OBW View Post
Measuring over the air can be a pain, How strong was the signal you where trying to measure.
Measuring over the air is indeed tricky; the main challenge is that you don't know how modulated the signal is. But there are a few tricks.

A not great way is to look at the maximum deviation over time, in the hopes that a fully modulated signal will eventually fill the passband. But that takes a while.

It's easier if there's a standard level in the signal somewhere. PL tones on an otherwise unmodulated signal can work if you know the exact specs of the transmitting radio, but the levels vary too much among vendors and even models to be a reliable method in general.

MDC code signals work well for this, and fortunately FDNY uses MDC (at least on the portables). Once you know the standard levels for MDC at various bandwidths, it's a snap to determine the bandwidth with the right receiving equipment as long as the signal peak is about 10 or 20 db above the noise floor.

My technique is to capture the spectrum P/Q with an SDR and then look at it offline with software (much easier than doing it in real time, since you can isolate the MDC part of the transmission this way.).
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Old 01-05-2014, 6:52 PM
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Ok. Maybe your problem there. FDNY does not use MDC on the portable radios.
It's a 7 digit ID using Motorola tps system. If you look on a scanner like the pro96 you see DG when the I'd goes then FM for voice.
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Old 01-05-2014, 6:58 PM
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Quote:
Originally Posted by tbendick View Post
Ok. Maybe your problem there. FDNY does not use MDC on the portable radios.
It's a 7 digit ID using Motorola tps system. If you look on a scanner like the pro96 you see DG when the I'd goes then FM for voice.
OK, maybe it wasn't a portable I was measuring, because it was very definitely MDC.
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Old 01-05-2014, 7:02 PM
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Only MDC is on dispatch and that's all narrowband.
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Old 01-05-2014, 7:10 PM
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Originally Posted by tbendick View Post
Only MDC is on dispatch and that's all narrowband.
Ah, interesting. I believe it was Fieldcomm (on CMD1 or maybe HT5, not sure) that I actually measured, and it was definitely transmitting an MDC code. I'm wondering if ithey might have a misconfigured mobile radio set to narrowband if it's all supposed to be wideband there.

I'll have double check with signals from more radios next time I'm near a fire and with the right equipment.

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Old 01-06-2014, 10:21 AM
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Probably a radio that was reprogrammed

The xts3500 radios are all wideband
Even EMS TAC2 is wideband , that way they didn't need to reprogram the fire radios when ems went narrow.
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