In article ,
Tim Wescott wrote:

| For radio control on 6 meters using PPM -- what is the amount of
| frequency shift, and which direction is it (please don't just say
| 'positive' or 'negative' -- I need to know which direction is 'pulse'
| and which direction is 'not pulse').

http://www.nobugs.org/engineer/uav/futaba-rx.html and
http://users.belgacom.net/TX2TX/tx2t...h/tx2txgb1.htm may be of
some assistance, or at least there will be some pretty pictures.

Positive shift means that the frequency increases during a pulse, and
negative means it decreases. I don't think the exact amount of the
frequency change really matters, but I think it's normally around 1.5
KHz to 2.5 KHz.

Or, to make it really simple, for positive shift, `pulse' is about 2
KHz higher than `not pulse', and reverse it for negative shift. And
modern 6m stuff is positive shift.

| Yes, I know there's no standard -- what do manufacturer's do these days?

From http://www.fmadirect.com/detail.htm?item=1739&section=1 --

SPECIAL NOTE CONCERNING HAM BAND TRANSMITTERS: All current
transmitters use positive shift modulation. When you order for current
transmitters, your invoice will list the purchased item as 805FM50V2FJ
or 805FM53V2FJ. This receiver will work with all recently manufactured
transmitters. If you have an ACE transmitter or an old Futaba (prior
to around 1990), you will require an ACE version. Your invoice will
list the 805FM50V2ACE or 805FM53V2ACE. Please be advised, it is
unclear when Futaba changed from negative to positive shift
modulation. Unfortunately, unless you have access to test equipment,
you may not know if your old Futaba requires negative or positive
shift.

.... so it looks like there IS a standard now, at least on the six
meter band stuff. I've heard some say that this isn't true, that
brand X 6m RX didn't workt with brand Y 6m TX, but details were never
really given.

--
Doug McLaren,
Nine out of ten doctors agree that one out of ten doctors is an idiot.