Channel Spacing/bandwidth etc.

rescuer · Post by **rescuer** » Tue Jun 06, 2006 5:30 am

I thought I had a partial understanding of all this but now I'm really confused.

All this is for VHF public safety frequency ranges. (154-155)

Take these frequencies as examples. 154.385, 154.400, 154.415. Are those not 15 kHz apart? If so wouldn't a new splinter frequency be 154.3925, 154.4075, 154.4225? If a radio says it does 12.5 /25 kHz spacing, it only appears that the 154.400 would be allowed.

I'm asking because I am looking for a new radio and I want to be able to use the new splinter channels.

Should channel spacing not say 7.5/15 kHz instead of 12.5/25KHz? Or is my idea of channel spacing totally off?

Midland even has a radio that says 12.5/25 Channel Spacing with 5.0/6.25 Channel Stepping.

Thanks,

k2hz · Post by **k2hz** » Tue Jun 06, 2006 5:56 am

Your understanding is basically correct. The confusion is between the channel frequency step which is 7.5/15 KHz and the signal bandwidth which vendors tend to specify at 12.5/25 because it makes the specs look better.

So, you need a radio with a synthesizer that actually operates on 2.5KHz steps to be capable of all the necessary 7.5/15 channels for VHF. Most older radios can not do this. Some "narrow band" VHF units made for governement and export do 5 and/or 6.25 steps and are not capable of the new FCC channels.

The FCC made a real mess in splitting the VHF 15 Khz channels in half. The 12.5 Khz signal bandwidth but only 7.5 KHz channel spacing means adjacent channel use is impractical without significant geographical separation. The UHF plan works fine, channel spacing and bandwidth is 12.5Khz.

HLA · Post by **HLA** » Tue Jun 06, 2006 7:48 am

i think what you are asking has two answers. 154.3925, 154.4075, 154.4225 are narrow frequencies because they are evenly divisible by 6.25. but on the other hand 154.400 or 154.6875 can be wide or narrow.

k2hz · Post by **k2hz** » Tue Jun 06, 2006 10:08 am

HLA wrote:i think what you are asking has two answers. 154.3925, 154.4075, 154.4225 are narrow frequencies because they are evenly divisible by 6.25. but on the other hand 154.400 or 154.6875 can be wide or narrow.

That is not correct. The frequency 154.6875 is designated as narrow band only in the FCC rules (note 27) as are all the non-15Khz step frequency.

The fact that some frequencies may be divisible by 6.25 as well as as 7.5 nothing to do with the authorized bandwidth.

It is true that some wideband radios have synthesizers capable of 6.25KHz steps and could be made to work (illegally) on those frequencies.

HLA · Post by **HLA** » Tue Jun 06, 2006 1:04 pm

154.6875 is one of the frequencies on my license and repeater and wideband right from the fcc.

Will · Post by **Will** » Tue Jun 06, 2006 1:56 pm

All the 154.6875 mhz licenses are for 11K2F3E which IS "narrowband",
+/- 2.5khz deviation.

License Search
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Radio Service = ALL
State = Indiana
Frequency Assigned = 154.6875

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HLA · Post by **HLA** » Tue Jun 06, 2006 2:24 pm

i could never find it on the website either but i have it hanging on my wall in my office.