[ICOM] Icom 2720 deviation adjustment

[Gary Pearce KN4AQ]

At 05:13 PM 3/20/2006, you wrote:
>Does anyone know how to increase the deviation on a 2720? My audio
>is awfully weak, and I can't find a deviation control on the unit.


You don't have the radio in the "FM Narrow" mode, do you?

I don't have a 2720, but I downloaded the manual and in SET MODE you have a 
"nAr-On" "nAr-OF" setting.  Looks like it should be in "OF".

If the setting is correct ("OF"), then there's something else wrong and I 
can't help you.  I will, though, add two mini-lectures: "deviation 
controls" and "the new Narrow FM Mode".  Forgive me if this is old news to 
you...

DEVIATION CONTROLS
When hams want more transmit audio on FM radios, they often reach for the 
deviation control and crank it up.  This does have the effect of raising 
the average audio level.  But it also has the effect of letting voice peaks 
go beyond the =/- 5 kHz bandwidth that the system is designed for.  The 
result is that they may "chop" out of a receiver's IF filter and have the 
receiver's squelch close on voice peaks.  They may also splatter onto 
adjacent channels and cause interference.  Without a service monitor, you 
can't tell for sure where to set the deviation control.

The "deviation control" is more properly called the "deviation LIMITER 
control".  It's real job is to set the limit on audio peaks.  What hams 
really want for adjusting their transmit volume is a "mic gain" 
control.  Unfortunately, few FM radios are equipped with a mic gain control 
- at least not an adjustable one.  The mic gain settings in most FM radios 
are fixed.  The problem is, fixed at what?

A little time spent listening to 2 meter FM conversations will show that 
audio levels are all over the map, though I'd say that "too low" outnumbers 
"too high" by a wide margin.  Some of this is just poor microphone 
procedure - holding the mic too far from the lips.  But a lot of it is 
radio settings that just don't match the voice and style of the operator.

There's currently no good solution.  You can learn the characteristics of 
your particular radio and maybe improve your audio a little.  But you have 
to adapt to it, and it should be the other way around.

I'd like to see FM radios with HF style audio controls - mic gain and some 
speech compression.  That could help make FM sound a lot better.  Of 
course, we'd have a lot of miss-adjusted radios, and a certain contingent 
of hams who deliberately miss-adjust their radio because they want to be 
LOUD!!!  And endless arguments about what the "right" settings are.

Come to think of it, maybe we're better off the way we are.

Then again, maybe we'd get more people back on the air because they'd have 
something new to talk about.


THE NEW "NARROW" FM MODE
The "FM Narrow" mode is designed to make ham radios compatible with the 
"new" commercial analog modulation standards, and they'll be useful should 
hams ever decide to modify their repeaters to use less spectrum.  Our 
current standard is +/- 5 kHz deviation.  The new scheme is 2.5 kHz or 
less.  There's also an upper limit on frequency response.  Some radios use 
special processing in the transmitter and receiver that expands the 
effective frequency response at the expense of sounding odd on 
non-processed receivers.

FRS radios, for example, operate at this narrow modulation scheme.  All 
commercial and public safety radios will be required to adopt it (or 
digital) eventually.

If you have your radio set in this narrow mode, your audio will sound 
pretty low to other hams who are operating "standard" FM.

The term "narrow" may confuse some long-time FM operators.  +/- 5 kHz 
deviation has been called "Narrowband FM" for a long time, following a 
commercial change from +/- 15 kHz "Wideband" deviation.  This happened back 
in the 60's, and it "surplussed" a lot of radios, triggering the original 
amateur radio two-meter FM boom.

Today, "narrow" refers to the 2.5 kHz or less deviation limit.

73,
Gary KN4AQ
former FM guru....