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/

In article ,
Tim Wescott wrote:

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

Current spec is _10_ KHz channels. Sure, our (72 MHz) channels are 20
KHz apart, but that's because there's channels for other things
(pagers, industrial R/C, wireless microphones) in between our
channels.

--
Doug McLaren,
"Give me ambiguity, or give me something else!"

Doug McLaren wrote:

In article ,
Tim Wescott wrote:

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

Current spec is _10_ KHz channels. Sure, our (72 MHz) channels are 20
KHz apart, but that's because there's channels for other things
(pagers, industrial R/C, wireless microphones) in between our
channels.

The hazelnuts (or something) are blooming in Oregon, and I'm getting the
early spring allergies.

I had my head stuck in the 6m band, which gives exclusive 20kHz
channels. Yes, 72MHz RC is 10kHz.

I think I need to start tattooing this to my forearms.

--

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

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