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I love my BC780XLT. I recall reading somewhere that this model is not upgradable to 12.5khz channels. However, I see that one of my menu options for Step Size certainly includes 12.5khz as an option, as well as 7.5 and even 5.

How will the new band plan actually affect me? Will, for example, Kitsap SO go from 155.43 to 155.4175? If so, I would have thought, OK, I can just change the step size and enter the new freq. Ahh, but I did try that and no matter what the step size, the radio rounds the freq to 155.420 or 155.415.

Narrow banding and step size are not the same.
MANY people ( and radio makers/sellers ) have the two confused.
Most of VHF, UHF and 800 ( & 700 / 900) will have to go to narrow band by 2013.
The difference will be reducing the audio FM deviation from 5 khz to 2.5 khz maximum.
MOST agencies will stay on the same frequency(s), but have the reduced deviation.
Some will get new channels that are "between" the old steps.
That's the reason for the whole process, narrow the deviation, and make "empty" (sort of ) channels between the old channel spacing.
If you try to listen to narrow band transmissions on a wide band radio, the audio level (volume) will sound very low, but might be use able in some cases.
But, if someone goes to use the "in between" channel, your wide band radio won't filter it out, and you will suffer interference.
So, once things go to NB from WB, you really want to have a radio that does:
1) Narrow band or wide band BY CHANNEL. ( Not all one or all the other )
2) All the possible step sizes, also by channel.

This affects part 90 licenses, not marine band, GMRS, VHF-Low, or any of the Hambands.

So the radio has some logic on what frequencies it will tune... and 155.43 - 0.0075 is 155.4225, not 155.4175.

I don't have a BC780, but my BC796 will take 155.4225 as -
find an empty channel
enter 155.0 (or anything)
menu down to stepsize and set 7.5
use the menu option (1) to alter the frequency to 155.4225

As petnrdx notes, this just sets the center frequency of the tuner. The bandwidth should be set as MODE=NFM. My experience is that even the newest scanners don't really change their selectivity to properly reject adjacent channels, they just alter their audio response so that the voices come out at proper volume.

With the lack of selectivity plus the FM "capture effect", you don't have to be tuned to the precise frequency to get decent reception. Being 2.5 or even 5 kHz off will usually work okay.

And to confuse things a bit, when you get to steps of 6.25 kHz, many scanners round off the last digit of the displayed frequency - but really use the correct value internally.

My experience is that most commercial portable and mobile radios exhibit this very same behavior...

_________________
"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

Some (commercial) radios are better than others.
'Theoretically' the narrow band capable radios have filters that will make the front end narrow.

Here is how I test wide band rejection:
I take the radio I want to test, and program it on a (simplex) frequency and set for narrow.
I then take another radio, programmed to the same freq, but set for wide band.
I then transmit on the wide band radio and vary how much voice I give it.

A good (narrow band) radio will actually "clip" as the received signal deviates wide and heavy.

Not all radios are so good....

Also, test like this both with, and without, CTCS/DCS squelch.

Whats interesting is with my ASTRO Saber, regardless if the 12.5 or 25 khz setting is set on the personality, if you send either a narrowband or wideband signal, it will receive and adjust accordingly.

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Support Search & Rescue: Get Lost!
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It would be interesting to look at the shop manual for some of these radios. A good radio would have dual mechanical IF filters or something adjustable like a varactor-tuned electronic IF filter.

Thats similar to how we test... Curious which makes and models you have found to be better... Our testing has been primarily Motorola at this point. Be nice to know whats out there though...

_________________
"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

JFF, are you sure your Astro Saber works that way.
That would not make much sense to me.
How would it know if the signal it was hearing is supposed to be wide or narrow and be able to filter out adjacent channels?
In general, I know some of the earlier radios that did WB and NB did the filtering in DSP.

I've mostly tested the ICOM landmobiles.
For the most part they "pass".

Some of them clip more readily when CTCS / DCS is invoked.
In fact, some clipped with CTCS/DCS EVEN when both TX radio AND RX radio were set to same bandwidth!

Found some fixes for that tho.

Jeff,

what setting are you referring to? If it's under the Astro setting, there is a "wide" setting that is for use with digital simulcast systems. You should leave that at C4FM.

Jim

The 2013 narrowbanding/refarming only applies to frequencies from 150mHz to 512mHz (with a few exceptions as you listed that are not under part 90), not above 512mHz.

I have not seen any radio manufactures that have bandwidth, and step size confused (resellers, yes but if they have that confused, then I would not want to deal with them). Some manufactures may refer to channel steps as channel spacing, it can be, and is confusing and some people miss-read that. Motorola may say a VHF radio is 2.5kHz, they are referring to the channel step, or spacing, not the deviation. With 2.5kHz steps the radio will let you program in 153.83000 (a valid channel in the FCC plan), 153.83250, 153.83500, 153.83750 (the next valid channel in the FCC plan, 7.5kHz up from the last) and so on. There are a lot of two way radios that will do narrow band 12.5kHz B/W but not 2.5kHz steps. When ODF went narrow band a few years ago they had to dump all of their Bendix King EPH radios (some were only a few years old) due to the fact the EPH would not do the 2.5 steps and they could not program in all of their new channels.

The narrow band bandwidth is 12.5KHz, and that will give you a max of 2.5kHz deviation on a FM transmitter.

Jim

N7MAQ: No, I know better than that :P Its the 12.5 or 25 khz settings under TX...it has no effect on the RX.

Me and Mr. Russ the other day when he was making up narrow and wide audio samples for his presentation to the OSSA on the subject, we discovered this when we tried to use my ASTRO Saber as the RX Radio; you could not tell the difference between narrow and wide on it, but if we used his Kenwood, we could.

_________________
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Support Search & Rescue: Get Lost!
http://www.mwave.org

Where in the CPS are you seeing a "narrowband" and "wideband" setting?

Jim

My bet is that the radio has some sort of audio gain that is messing with you. Unfortunately if you set the radio to narrow and you still can hear full deviation from a radio transmitting "wideband", your radio is probably not going to handle someone using an adjacent channel close by very well at all.

Im about to test my NOS Astro Spectra Ive had hanging around to see how well it does and now with what your posting my faith that it will do well has faded a little...

In fact Im going to get my service monitor right now before I install this thing...


Update- The Astro Spectra easily passes my tests... Much better than the CDM its replacing...

_________________
"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."