12.5 kHz & 25 kHz Range differences

Nickdap · Post by **Nickdap** » Wed Mar 20, 2002 5:36 am

Hey all,
What have all you guys noticed in range between narrowband and wideband? Narrowband seems to be where we are all going, down here at least, especially in the VHF Hi Band.
Thanks
Nick

RadioSouth · Post by **RadioSouth** » Wed Mar 20, 2002 1:43 pm

Shouldn't be any difference in range just audio quality. Motorola has xpand technology in the newer units to address this audio issue.

Tom in D.C. · Post by **Tom in D.C.** » Wed Mar 20, 2002 2:24 pm

In the USA wideband FM has not been used on the VHF FM public service and ham bands for many, many years. On UHF the transition was slower, and wideband continued in some services for many years, but today most of what you will hear on UHF is 5 kHz deviation transmissions. We also use a system between 470 and 512 kHz which uses what some call "sliver band" which is 2.5 kHz deviation in an effort to squeeze even more space out of the available spectrum. As was said in the post just above, it has nothing to do with power, but rather getting more out of the space available.

Tom, W2NJS
...in D.C.

Nickdap · Post by **Nickdap** » Wed Mar 20, 2002 5:46 pm

ahh i see, 5 Khz (25 khz) is what i meant my wideband. Why I ask is that i have heard that the is a difference in rx sensitivity on radio using 12.5 Khz channel spacing. ie haveing less sesitivity then a 25 khz radio.
Thanks
nick

what is the channel spacing for what you meant by wide band? i assume 30 khz

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<font size=-1>[ This Message was edited by: Nickdap on 2002-03-20 20:47 ]</font>

Tom in D.C. · Post by **Tom in D.C.** » Thu Mar 21, 2002 1:38 pm

It was 30 kHz on VHF and it was 25 kHz on UHF. There is some 6.25 and 12.5 on VHF, but it's mostly 15 kHz now, and lots of 12.5 on UHF, all depending on what your system/equipment was designed for in the sense of receive bandwidth. A narrow signal heard on a wideband IF radio can sound very low in volume.

Tom, W2NJS
...in D.C.

Will · Post by **Will** » Fri Mar 22, 2002 5:09 pm

Narrrow Band is what we run now, 30 khz occupied bandwith, 5khz deviation, on VHF, 25khz on UHF. Used to be 15khz deviation on 50 khz spacing back years ago.
Now the FCC got a bug up their *$%# and want us to go the one half the occupied bandwith, Narrow narrow band! On VHF the requirements are 12.5 or 11.25khz occupied b/w and 2khz dev., and 12.5 khz O B/W and 2.5 khz dev. on UHF. Also note TWO watts ERP now.
If you are presently licensed as 5khz deviation, 20K0F3, you can continue to use the Narrow Band 25khz.

Nickdap · Post by **Nickdap** » Fri Mar 22, 2002 6:55 pm

for as long as i can remember it was 5khz vhf/uhf, and now its 2.5 khz vhf/uhf. only ever used 5 khz tho, what the difference like? im setting up a narrowband system soon with out x-band.
nick

Vern · Post by **Vern** » Fri Mar 22, 2002 9:41 pm

This issue has confused me for several months now. Our county is going to a narrow channel operation on 154.2425 mHz. According to refarming documents I've read, new refarmed channels are 7.5 Khz away from the "old" VHF frequencies, IE 154.250 Mhz.
Now, a lot of new "narrow channel" capable radios will not accept the 154.2425 frequency. The frequency usually rounds off
to something weird when it is entered into the RSS.
Did the maufacturers goof here or what? Our new radios had to have a flash upgrade to accept the new frequency. Radios that support 2.5 or 7.5 Khz PLL steps seem to be the only radios that will work.

Post by **HumHead** » Sat Mar 23, 2002 12:10 pm

There are two different schemes for refarming wide band channels into narrow band.

The first is "on-center" frequency spacing. In an on-center refarming the new channels are centered on the old channel's center frequency, and the old band edge frequencies become new narrow band center frequencies. The up side of this is that this keeps the frequencies in a format taht older radios can handle. The down side is that the new center frequencies added at the previous band edges overlap into the adjoining wide band channels, so you have to convert an entire block of channels, not just a single one. You also lose two possible channels at the top and bottom end of the block.

The other scheme is "off-center" or "splinter" refarming. In off-center refarming the existing channel is divided in half with the new centers halfway between the old edge and center frequencies. This allows two new narrow band channels to fit neatly into the spectrum occupied by a previous wide band channel, without disprupting adjacent spectrum. The down side, as you have discovered, is that many older radios do not recognize the off-center frequencies as valid channel centers, and cheerfully "correct" your "error" by rounding up or down to what it considers the closest "real" channel center.