The following is an exhange on the Aprssig mailing list about how to setand the deviation for 1200baud packet radio. I found WA8LMF's response to be very helpful Stephen has kindly agreed to let me post here as I  am sure that others will find it useful (and I'll be able to find it in the futiure -grin)

My original post was

> I have old school packet question for you all from someone who is still
> learning....
>
> In an attempt to be a good citizen, I have picked up a deviation meter
> and am going round tweaking various trackers and digis that I use or
> am responsible for rather than using the traditional "by ear" method.
>
> I have several TNCs and radio combinations in use but there is always
> a difference in the low and high tone deviation, e.g. when my OT1+ has a high tone deviation of 2.4KHz, the low tone is only at 1.5Khz. I
> understand that this is normal and why from
> (http://www.febo.com/packet/layer-one/transmit.html ) but my question is what do I set the deviation at for the high and/or low tone at for
> a 12.5KHz channel? I asked this question on the UKAPRS forum and got
> several different answers (ranging from 0,9 to 2.4KHz). Whilst I
> appreciate the time that has been put into providing these replies, I
> am not much further towards knowing which is right so am asking a
> larger audience.
>
> I am not trying to start a fight, I just want to understand!
>
> Thanks in advance for your help es 73
> Steve M0BPQ

And WA8LMF, Stephen responded:

The answer is "It depends" ! Many parts of Europe are now using
narrower deviation than the traditional standard of 5 KHz peak
deviation. (The Euro versions of many Japanese radios now have menu
options for either 2.5 or 5 KHz peak deviation.)

In North America, where 20 or 25 KHz channels and 5 KHz peak FM
deviation still prevail for amateur radio , the high tone should be set
at about 3 to 3.5 KHz deviation. [Commercial land-mobile &
public-safety users in the US are under a federal government mandate to "narrow-band" to 2.5 KHz in the next year or two. Amateur radio is not
affected, except that soon there will be a flood of cheap surplus
commercial hardware that will be illegal for commercial users.]

In Europe, in areas where the 12.5 Khz channels / 2.5 KHz peak
deviation are used (and the radio receivers have narrower IF filters) ,
the setting would be about half the above, or around 1.5 to 1.75 KHz.

In general, one wants the highest deviation on data to correspond to
about 60-70% of peak, in order to allow some tolerance for the
transmitter (or receiver) not being precisely on channel. If you
deviate to the maximum peak value (i.e. 5KHz or 2.5 as the case may be),
and the receiver was off frequency by even only 500 Hz, some of the
significant modulation sidebands would fall outside the edge of the
receiver passband, creating severe distortion and a high data error
rate.

Stephen H. Smith wa8lmf (at) aol.com
EchoLink Node: WA8LMF or 14400 [Think bottom of the 2M band]
Skype: WA8LMF
Home Page: http://wa8lmf.net

MB7UBP coverage plot - compare to M3SXA-10!

After returning from M3SXA’s place I fired up the remote rig set up to see if I could find some folks to work in the IARU 144/432 contest. Unfortunately I received several reports of bad audio and it looks like RF was getting into the Ethernet cables or RRC system at the radio end. This shows one major problem with the RRC/FT-847 combo – most of the radio functions are not available via the CAT system so it was impossible to tweak the mic gain or RF power settings to see if I could make things work at a distance. As my 8 month old son was sick in bed with a cold I couldn’t get direct access to the radio so had to give up. I did get access to the radio on Sunday and threw a handful of snap on ferrites at all the cables in the Ethernet network and audio chain. I also put my Ethernet network switch inside a metal box in case that was susceptible to RF. After taking the control half of the station to the remote end I readjusted all the levels including the DVK whilst listening on another RX. I sounded OK to me, but by that time the contest was over. I will have to get on for the 432 UKAC this week to try it out.

I finally got my act together and sorted out the gear for Steve M3SXA to run an APRS I-gate from his QTH in North West London so I popped over there at the weekend and helped him get everything set up. For once things went smoothly and Steve is now gating items from all over west London and even to the southern stretch of the M25, which is a real step forwards in coverage.  The plots from aprs.fi below look great, the darker red the square the more packet have been received from it: