PRO 39 mod

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Dec 19, 2002
Vista, CA
Is it possible to modify the pro39 scanner freq step size for narrowband FM?
That scanner has a standard step size in the VHF-HI band of 5KHz and in the UHF band of 12.5KHz. Modifying it for a different step size wouldn't be worth it for two reasons:

1) Too much effort and may not even be feasible with the hardware inside;

2) The IF filter in the scanner is already wide enough so that you can get "close enough" using the regular step size on VHF (UHF is already fine unless you need to go to 6.25KHz step sizes in which case see below).

If you're trying to hear, for example, a station on 151.3175MHz then just set your scanner on either 151.315MHz or 151.320MHz (first is 2.5KHz lower while second is 2.5KHz higher); either should get you close enough but try both and use the one that works best for you.

Your scanner's internal filtering is broad enough so that 2.5KHz differences make little difference to the reception unless the signal is very very weak. 2.5KHz is only half of 5KHz which is what your scanner's step size is on VHF.

The same goes for UHF for those few signals you might encounter which may be at 6.25KHz steps though the filter would have more of an effect due to the wider spacing.

You may have to just deal with hearing closely spaced adjacent channels using this method, however. So if you are trying to hear 151.3175MHz and are programming in 151.315MHz in to do so then you will have to live with hearing possible strong interference from strong stations on 151.310MHz and 151.325MHz (and perhaps further out in frequency depending on your filtering).

"Narrowbanding" affects the "sound" of the station relative to your scanner so that it won't be as "loud" to you as it might have been before the station "went narrowband" soyou may need to increase the volume and you may hear more background noise ("hiss"). Radios that actually can handle "narrowband" signals correctly, like the professional radios the users have, assuming they are programmed correctly, compensate for this but you'll just have to deal with it on your scanner.

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