Railfan Technology > RS pro 97 ?

I have a pro 97, radio shack. Am I right that the rr's went to 2.5mhz narrow band, and my receiver only gets down to 5mhz I will have difficulty receiving the channels?

Posted from iPhone

The problem is when there are two separate conversations going on in the 5 MHz that has now split into two channels. A 5 MHz radio would de-mod them both at the same time. The older radio can not be programmed to receive the individual splinter channel either.

Not many areas are using the splinter channels with 2.5MHz channels, if you don't have this problem, you're good for the moment. There is another issue with how loud the de-mod audio will be. Suspect this will be a bigger issue in Urban areas than out in the woods somewhere.


CPRR Wrote:
-------------------------------------------------------
> I have a pro 97, radio shack. Am I right that the
> rr's went to 2.5mhz narrow band, and my receiver
> only gets down to 5mhz I will have difficulty
> receiving the channels?
>
> Posted from iPhone

As a side note...if you're interested in ATCS Monitor, the Radio Shack Pro-97 is one of the few radios that can be modified with a tap and feed ATCS data through an iMic and into a Windows computer running ATCS Monitor.

Ryan Wilkerson
Fair Oaks, CA

Very good point, I missed that.
The scanner could be worth it's weight in ATCS-coins.

The narrower bandwidth will also provide reduced volume in that radio. Other than that, it shouldn't be a problem using it for the next few years. NXDN (digital) is coming and some places are using it now but it is going to be years before it becomes widespread.

John

CPRR Wrote:
-------------------------------------------------------
> I have a pro 97, radio shack. Am I right that the
> rr's went to 2.5mhz narrow band, and my receiver
> only gets down to 5mhz I will have difficulty
> receiving the channels?
>
> Posted from iPhone

I've used the budget version of the 97, Pro 92. Both made by GRE for Radio Shack. No problems listening to railroad conversations so far, and plenty left on the volume dial for loudness, so I'd say go ahead and start using it.

For earphone listeners having problems with volume after the narrow band conversion several years ago, find a cheap, modern earphone (for MP3 players and iPods) with lower impedance, and the sound should be louder. This isn't audiophile equipment, so no one should be worrying about lack of fidelity from mismatched impedances (a somewhat obsolete concern with modern electronics).

Good info from a PM about channel spacing, I also missed the units error, I was thinking in the RF world of both channels to be downconverted, rather than the Audio (kHz) whole radio reality:

" I believe you have MHz and kHz interchanged. The VHF channels were narrowbanded from 15 kHz spacing to 7.5 kHz, while the authorized was decreased from 20 kHz to 11.25 ( or 6 if using "digital technologies). See FCC 90.209 "

CPRR Wrote:
-------------------------------------------------------
> I have a pro 97, radio shack. Am I right that the
> rr's went to 2.5mhz narrow band, and my receiver
> only gets down to 5mhz I will have difficulty
> receiving the channels?
>
> Posted from iPhone

Either way, if the radio works keep it. Or make use of the ATCS Monitor ability.

Let's be clear about CHANNEL spacing and what a radio will tune. Prior to 2013, the VHF commercial frequencies (including the VHF railroad band) channel spacing was 25 kHz. That is what amateur radio is still today. In 2013, all of the other VHF frequencies were required go to "narrow band" spacing of 12.5 kHz. NXDN digital is VERY narrow band, with 6.25 kHz spacing.

Many older scanners and most amateur radios have a minimum of 5 kHz (or 0.005 mHz) spacing, so their tuning steps, for example, are 160.455, 160.460, 160.465, 160.470 mHz. The old AAR channel 23 was 160.455 and channel 24 was 160.470 mHz. 5 kHz spacing would tune those two channels with no problem. Watch what happens since narrow-banding. Channel 23 is now channel 023, still at 160.4550, and channel 24 is now channel 024 at 160.4700. But now there is a "splinter" channel, designated AAR channel no. 123 that is at 160.4625 mHz. That 5 mHz tuning step will not tune that frequency.

There is some indication, supported by some old, but still published FCC information that the railroads may not use the "splinter" channels in analog mode that are now available, but may start using them at some point for NXDN digital. My surmise is that, if deployment of NXDN digital is delayed (and many people think that might be likely), the railroads might change course and start using some of the splinter channels for analog communications.

So, a railfan may continue using a radio with 5 kHz spacing and likely not miss a lot, at least for awhile. If the radio will not tune at "narrow deviation" (usually a "W/N" menu option in the radio menu), audio and reception may be somewhat degraded when listening to a narrow-band analog transmission being made on the non-splinter channels. Personally, though, I would not go out today and buy a new radio for railfanning that did not have 2.5 kHz tuning steps.

Of course, when NXDN comes into common use, analog radios, regardless of tuning steps, will become less and less useful for railfanning as the NXDN conversion proceeds. Again, my personal surmise is that widespread NXDN use is still a few years away, but when it happens, it will progress pretty quickly. Remember, the major railroads have been purchasing NXDN-capable radio equipment in large quantities since around 2010.