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').

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

Thanks in advance.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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.

Doug McLaren wrote:

In article ,
Tim Wescott wrote:
-- snip --

... 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.

That was useful, but I forgot to ask:

Is the space (no pulse) frequency the nominal frequency, or is it (more
sensibly IMHO) 1/2 the shift below -- or at least _some_ amount below
the nominal?

If I were designing such a rig I would have the space frequency (off, no
pulse, whatever) be 1/2 of the shift _below_ the nominal frequency, and
the mark frequency be 1/2 of the shift _above_. I may shade the space
frequency to be a bit closer to the nominal frequency to balance out the
spectrum, but I doubt that I'd stick it right onto the nominal frequency.

Thanks again.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

In article ,
Tim Wescott wrote:

| That was useful, but I forgot to ask:
|
| Is the space (no pulse) frequency the nominal frequency, or is it (more
| sensibly IMHO) 1/2 the shift below -- or at least _some_ amount below
| the nominal?

Do not know.

--
Doug McLaren,
We can hike anytime. This is our chance to see cars driving. --Homer Simpson

The shift for the FM (frequency shift keying) is up to +1500 and -1500
about the nominal frequency. This is true for 72 MHz or 50 MHz. This is
used on 53 MHz but is not mandated on this band since the channels are
100 KHz wide.

Dan Thompson

Tim Wescott wrote:
Doug McLaren wrote:

In article ,
Tim Wescott wrote:
-- snip --

... 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.

That was useful, but I forgot to ask:

Is the space (no pulse) frequency the nominal frequency, or is it (more
sensibly IMHO) 1/2 the shift below -- or at least _some_ amount below
the nominal?

If I were designing such a rig I would have the space frequency (off, no
pulse, whatever) be 1/2 of the shift _below_ the nominal frequency, and
the mark frequency be 1/2 of the shift _above_. I may shade the space
frequency to be a bit closer to the nominal frequency to balance out the
spectrum, but I doubt that I'd stick it right onto the nominal frequency.

Thanks again.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

IFLYJ3 wrote:
The shift for the FM (frequency shift keying) is up to +1500 and -1500
about the nominal frequency. This is true for 72 MHz or 50 MHz. This is
used on 53 MHz but is not mandated on this band since the channels are
100 KHz wide.

Dan Thompson

Thanks Dan. It has to be fairly close in to meet the spectral
requirements, of course -- I just didn't know what the relationship was
between nominal and reality.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

On Mon, 20 Mar 2006 13:09:32 -0800, Tim Wescott
wrote:


That was useful, but I forgot to ask:

Is the space (no pulse) frequency the nominal frequency, or is it (more
sensibly IMHO) 1/2 the shift below -- or at least _some_ amount below
the nominal?

If I were designing such a rig I would have the space frequency (off, no
pulse, whatever) be 1/2 of the shift _below_ the nominal frequency, and
the mark frequency be 1/2 of the shift _above_. I may shade the space
frequency to be a bit closer to the nominal frequency to balance out the
spectrum, but I doubt that I'd stick it right onto the nominal frequency.


You got my curiosity up so I dragged in the ol' service monitor to see
what my 9C was doing. All of the pix were with the freq error meter on
the 1.5KHz range and the scope scale was on the +/-1.5KHz range.

The first was using a FP-TP-FM module on 08 (50.960MHz):

http://www.mindspring.com/~sbhopper/FP-TP-FM_08.jpg

Modulation is +/-1500Hz. The freq error meter is showing about 1KHz
low, but I am assuming it is the service monitor adjusting to the
non-symetrical deviation.


The second pic is with a FT-TP-FM module on 60 (72.990MHz):

http://www.mindspring.com/~sbhopper/FP-TP-FM_60.jpg

Inverted from the 6 meter.


The third pic is with the TP-FSM syntesized module set to channel 60:

http://www.mindspring.com/~sbhopper/TP-FSM_60.jpg

Same as the crystal module except the modulation is just a tad lower.

FWIW,
David - WD4JKH



--
David - WD4JKH

Valid email:

David Hopper wrote:

On Mon, 20 Mar 2006 13:09:32 -0800, Tim Wescott
wrote:



That was useful, but I forgot to ask:

Is the space (no pulse) frequency the nominal frequency, or is it (more
sensibly IMHO) 1/2 the shift below -- or at least _some_ amount below
the nominal?

If I were designing such a rig I would have the space frequency (off, no
pulse, whatever) be 1/2 of the shift _below_ the nominal frequency, and
the mark frequency be 1/2 of the shift _above_. I may shade the space
frequency to be a bit closer to the nominal frequency to balance out the
spectrum, but I doubt that I'd stick it right onto the nominal frequency.



You got my curiosity up so I dragged in the ol' service monitor to see
what my 9C was doing. All of the pix were with the freq error meter on
the 1.5KHz range and the scope scale was on the +/-1.5KHz range.

The first was using a FP-TP-FM module on 08 (50.960MHz):

http://www.mindspring.com/~sbhopper/FP-TP-FM_08.jpg

Modulation is +/-1500Hz. The freq error meter is showing about 1KHz
low, but I am assuming it is the service monitor adjusting to the
non-symetrical deviation.


The second pic is with a FT-TP-FM module on 60 (72.990MHz):

http://www.mindspring.com/~sbhopper/FP-TP-FM_60.jpg

Inverted from the 6 meter.


The third pic is with the TP-FSM syntesized module set to channel 60:

http://www.mindspring.com/~sbhopper/TP-FSM_60.jpg

Same as the crystal module except the modulation is just a tad lower.

FWIW,
David - WD4JKH



That pretty much says it all. I guessed that +/-1500 was the number to
shoot for -- apparently your TX (Futaba?) agrees with me.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

Tim Wescott wrote:
Doug McLaren wrote:

In article ,
Tim Wescott wrote:
-- snip --

... 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.

That was useful, but I forgot to ask:

Is the space (no pulse) frequency the nominal frequency, or is it (more
sensibly IMHO) 1/2 the shift below -- or at least _some_ amount below
the nominal?

With 2kHz shifts I'm not sure that this is particularly relevant. Most
of the receivers probably have bandwidths of 10kHz or more.

Ideally the center frequency would fall in the center of the passband
of the receiver, following your "1/2 the shift below" if the center
frequency were truly accurately calibrated. And the receiver bandwidth
would be simlar to the FSK spacing. But things have always been much
looser than this.

If I were designing such a rig I would have the space frequency (off, no
pulse, whatever) be 1/2 of the shift _below_ the nominal frequency, and
the mark frequency be 1/2 of the shift _above_. I may shade the space
frequency to be a bit closer to the nominal frequency to balance out the
spectrum, but I doubt that I'd stick it right onto the nominal frequency.

1kc at 50MHz is 20 ppm, and 30 or 40 years ago when I did 6M remote
control I'm pretty sure that most of the crystals would've truly
struggled to meet this spec. Some of the transmitters used LC circuits
for tuning (I am not kidding!) and receive bandwidths were as wide as
100kHz or more. But that kind of slop was going away as the tube
transmitters disappeared :-).

Of course the Gonset portable sets (transmitter and regen receiver both
tuned only by LC's) set truly abysmal standards for stabilities and
bandwidths. Maybe I'm being too pessimistic in extrapolating their
specs to today!

Tim.

Tim Shoppa wrote:

Tim Wescott wrote:

Doug McLaren wrote:


In article ,
Tim Wescott wrote:

-- snip --


... 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.


That was useful, but I forgot to ask:

Is the space (no pulse) frequency the nominal frequency, or is it (more
sensibly IMHO) 1/2 the shift below -- or at least _some_ amount below
the nominal?


With 2kHz shifts I'm not sure that this is particularly relevant. Most
of the receivers probably have bandwidths of 10kHz or more.

Ideally the center frequency would fall in the center of the passband
of the receiver, following your "1/2 the shift below" if the center
frequency were truly accurately calibrated. And the receiver bandwidth
would be simlar to the FSK spacing. But things have always been much
looser than this.


If I were designing such a rig I would have the space frequency (off, no
pulse, whatever) be 1/2 of the shift _below_ the nominal frequency, and
the mark frequency be 1/2 of the shift _above_. I may shade the space
frequency to be a bit closer to the nominal frequency to balance out the
spectrum, but I doubt that I'd stick it right onto the nominal frequency.


1kc at 50MHz is 20 ppm, and 30 or 40 years ago when I did 6M remote
control I'm pretty sure that most of the crystals would've truly
struggled to meet this spec. Some of the transmitters used LC circuits
for tuning (I am not kidding!) and receive bandwidths were as wide as
100kHz or more. But that kind of slop was going away as the tube
transmitters disappeared :-).

Of course the Gonset portable sets (transmitter and regen receiver both
tuned only by LC's) set truly abysmal standards for stabilities and
bandwidths. Maybe I'm being too pessimistic in extrapolating their
specs to today!

Tim.

Current spec is 20kHz channels, so you have to be better than that.

You are correct that I should expect significant offsets, however -- I
should have been thinking in those terms.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/