In article ,
Ralph Mowery wrote:

As hams are not reqired to keep the spacing or deviation some areas did
go to 20 kHz spacing and 5 kHz deviation. Other areas went to 15 kHz
spacing and kept the 5 kHz deviation. If the rigs are not very well up
todate and the frequency and deviation set correctly there can be
problems with the 15 kHz spacing.

Yup. Here in NoCal, some parts of the 2-meter spectrum use 20 kHz
spacing, and others use 15 kHz. There was a proposal to move things
down to even narrower 12.5 kHz spacings a few years ago, but some
experiments (which I helped perform) demonstrated that a lot of the
then-available mobile and hand-held radios would suffer some pretty
severe adjacent-channel bleed-through - their IF filters aren't
sharp/narrow enough to avoid it. Getting people to cut their peak
deviation down to 2.5 kHz would also have been difficult (older radios
often don't have this available as an option, and those that do are
often easy to mis-adjust).

The 440 band is still on 20 kHz spacings. Keeping peoples' transmit
oscillators accurately centered within 1 kHz or so is harder, up at
those higher frequencies, and it pays to make allowance for some
amount of drift when doing the frequency planning.

In article ,
says...



Yup. Here in NoCal, some parts of the 2-meter spectrum use 20 kHz
spacing, and others use 15 kHz. There was a proposal to move things
down to even narrower 12.5 kHz spacings a few years ago, but some
experiments (which I helped perform) demonstrated that a lot of the
then-available mobile and hand-held radios would suffer some pretty
severe adjacent-channel bleed-through - their IF filters aren't
sharp/narrow enough to avoid it. Getting people to cut their peak
deviation down to 2.5 kHz would also have been difficult (older radios
often don't have this available as an option, and those that do are
often easy to mis-adjust).

The 440 band is still on 20 kHz spacings. Keeping peoples' transmit
oscillators accurately centered within 1 kHz or so is harder, up at
those higher frequencies, and it pays to make allowance for some
amount of drift when doing the frequency planning.

In NC, actually many of the southern states as the South Eastern
Repeater Association is the co-ordinating body, usually below 146 MHz
is 20 kHz and above 146 is 15 kHz spacing. As always there is some
oddball or non standard pairs being used.

At the state of the art and money wise it is difficult to go to the 12.5
kHz spacing. Even if the deviation is cut back to 2.5 kHz on the older
rigs it is my understanding they may produce enough 'trash' to cause
problems. The rigs will need to be designed to produce less phase
noise. As hams hold onto rigs for many years, going to much less than
15 kHz spacing and about 5 hZ deviation will take a long time if ever in
our lifetime.

I was licensed in 1972 and I think most everything around here was on
the 30 and 5 standards then. That was back when the ham rigs still
seemed to have IF filters of about 30 Khz or more. I remember the
Regency rigs did not even have a trimmer for the receive crystals.
As there were very few frequency counters many rigs were just tuned by
ear. Sometimes someone would have a rig with a discriminator meter and
the locals would just net to whatever he was on.




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Jeff wrote:

Yup. Here in NoCal, some parts of the 2-meter spectrum use 20 kHz
spacing, and others use 15 kHz. There was a proposal to move things
down to even narrower 12.5 kHz spacings a few years ago, but some
experiments (which I helped perform) demonstrated that a lot of the
then-available mobile and hand-held radios would suffer some pretty
severe adjacent-channel bleed-through - their IF filters aren't
sharp/narrow enough to avoid it. Getting people to cut their peak
deviation down to 2.5 kHz would also have been difficult (older radios
often don't have this available as an option, and those that do are
often easy to mis-adjust).

Hi

Just to point out that on 2m the Region 1 & 3 band plans used to use
25kHz spacing and moved to 12.5kHz about 20 years ago!!

The commercial world in Europe have used 12.5kHz spacing for even longer
on VHF.

Jeff

Adjacent channel interference is sometimes a problem, depending on the
width of your filters, the deviation of the adjacent station, and the
accuracy of the frequencies.
(FM stations often are accurate only to about 1.5 kHz and of course
when the station above you is 1.5 down it makes the interference worse)

While a 12.5 kHz spacing is used for repeaters here, generally the
frequency coordination is done in such a way that adjacent repeaters
are not 12.5 kHz apart.

In general, 12.5 kHz works well. Note that on 10m (and CB), the channel
spacing is only 10 kHz. That is more problematic, it requires a tiny
deviation and low audio cut-off frequency to do it well.