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Old 09-26-2009, 10:29 AM
nd5y nd5y is offline
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Join Date: Dec 2002
Location: Wichita Falls, TX
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Quote:
Originally Posted by DaveNF2G View Post
Where would you need 2.5 kHz steps?

2.5 kHz is the specification for bandwidth of the signal, not distance between carrier center frequencies.
Don't confuse deviation and bandwidth. Let me clear some of this up.

In the private land mobile radio world, radios are specified as having:
2.5 kHz deviation = 12.5 kHz bandwidth = narrowband
5 kHz deviation = 25 kHz bandwidth = wideband

In the scanner world:
2.5 kHz deviation = 12.5 kHz bandwidth = FMN or NFM = narrowband
5 kHz deviation = 25 kHz bandwidth = FM
75 kHz deviation = 200 kHz bandwidth = WFM or FMW = wideband (FM and TV broadcasting)

All Part 90 certified VHF high band land mobile radios made recently have 2.5 kHz tuning steps so that they can operate on the 7.5 kHz spaced channels used on VHF High Band in the USA. The FCC channel allocations are spaced 7.5 kHz apart, but there are some gaps and you can't use 7.5 kHz tuning steps from one end of the band to the other.

Most FM only VHF/UHF ham gear made for the USA market won't do less than 5 kHz tuning steps because it isn't needed.
Almost nobody uses 2.5 kHz deviation on ham radio in the USA.
In Europe they do, because the 2m band only goes from 144-146 MHz and the repeater channels are spaced at 12.5 kHz apart.

Some ham rigs will transmit 2.5 kHz deviation but don't have narrow receive filters. My FT-7800R and VX-6R are like that.

You can still listen to NFM stations on 7.5 kHz channels with the average VHF/UHF FM ham rig with 5 kHz tuning steps because they have 25-30 kHz wide receive bandwidth. The filters in the receiver are so wide that you won't notice being 2.5 kHz off frequency.

There was a thread about this a while back. Somebody pointed out that at least one relatively new FM ham rig tunes in 2.5 kHz steps. I don't remember what radio it was.

If you want a radio that does 2.5 kHz steps, you need to download the owners manuals from the manufacturers' web sites and check the specifications.
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Tom

Last edited by nd5y; 09-26-2009 at 10:39 AM..
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