Leo wrote in message . ..
On 9 Feb 2004 15:25:04 -0800, (N2EY) wrote:
Leo wrote in message . ..
I understand that Morse is good for getting through poor conditions
better than voice.
Much better than any form of analog voice.
Makes sense, it is narrowband and binary (well,
tri-state if you count the spaces...) encoded.
Exactly.
From the experimenting
(read: fooling around) that I have been doing over the past couple of
months, I have been repeatedly amazed with the ability of BPSK-31 to
get clean copy through pretty bad conditions. Even DX signals that
appear as weak vestiges on the waterfall display can be easily decoded
with near 100% accuracy, using just a PC sound card as an interface.
The soundcard is only part of the system. The decoder is quite smart,
in that
it stores and examines the received data and does a "best fit"
decoder. You can read all about it at several websites.
Good point - I've compared it to RTTY from the decoding standpoint -
RTTY seems to be much more prone to losing characters or dropping out
entirely when the signal is weak or noise is high.
Part of that is the modulation method used and part is the encoding.
There's a good explanation of the varicode philosophy and the PSK31
modulation method on a number of websites.
btw, PSK31 in BPSK mode works at around 45-50 wpm. The speed depends
on the exact text sent because the length of each character varies,
but the average character is 6 to 7 bits long.
But it's important to realize what constitutes "poor conditions".
Against purely amplitude noise it's quite robust. But against phase
noise of various
types it is not robust at all. All depends on the situation.
Frequency stability of my old Heath TX is a problem, but I'm working
on it.....
What rig is it?
Heath SB-400. The Pride of 1964 
Amazing how well a 40 year old box full of glowbottles is still
useful, huh?
15 Hz stability from a one-tube Hartley is pretty decent.
With a narrowband signal like this, it doesn't take much drift! I'm
seeing a frequency decrease of up to 15 Hz, beginning a few seconds
after keying. B+ to the VFO appears to be well regulated - maybe not
tight enough though. Might have to replace the 0A2 with a few zeners
- haven't tried that yet....
First try replacing the 0A2 regulator and 6AU6A oscillator tubes -
different
ones may have slightly different characteristics.
But the real problem may be that the heater voltage is changing when
transmitting, rather than the B+. Another possibility is that heat
from the
6146s and power supply may be causing a bit of drift, because PSK31 is
a very
high duty cycle mode and a lot of heat gets dissipated on transmit.
One cure to consider is to build an external VFO, either LC or
synthetic, to do the job. The SB-400 LMO tunes 5.0 to 5.5 MHz, and it
tunes "backwards" (5.5 MHz on the VFO is the low end of the band
selected). Such a VFO could be mounted
externally to eliminate any changes to the rig itself.
I copied the heterodyne scheme of the Heath SB-series for the
Southgate Type 6 transceivers, btw. Found some Heath filters at the
1978 Rochester hamfest and
built a rig around them. Now it's on "standby" duty since the Type 7
entered service about 10 years ago.
Now there's something that will get through when nothing else will.
Not really. You will find times when the PSK-31 signal is clearly
audible in the speaker, well above the background amplitude noise, but
the decoder cannot make sense of it because the phase distortion is
too bad.
Haven't experienced that yet - at least when I see that, I'll know
what is causing it!
Exactly.
And, it types itself out, too. (that's a real boon for the perennially
lazy - like me)
It was meant as a replacement for conventional RTTY - as a "keyboard
to keyboard" mode. For example, the speed was chosen to be about what
*average* conversational keyboarding hams use.
btw, the code used in PSK-31 uses shorter symbols for the most common
characters and longer ones for the least common. Just like Morse code,
which is where the designers got the idea.
Didn't know that - great idea, though!
Yup. Even the use of 00 for a character space was derived from Morse.
I believe that BPSK-31 was created within the amateur community -
Yup - G3PLX, and a number of folks who helped him by testing it out on
the air and others who have developed software packages. A local ham
of my acquaintance (one of those longtime 20 wpm 1x2 Extras with
multiple EE degrees - we share two alma maters, btw) was one of the
team who helped test it out.
PSK-31 is another great tool in the toolbox, but not a replacement for
good old Morse Code.
Haven't formulated an opinion on that one yet - stay tuned!
Consider that it takes a lot more hardware to implement PSK31, and
that
the requirements of that hardware are much more stringent than what is
required to implement Morse code.
Consider also that Morse code, as used by hams, is an aural mode, but
doesn't
require talking. Thus it can be used in a number of situations where
other
modes can't. For example, it's not safe to drive and work PSK-31, but
mobile
Morse operation is safely enjoyed by many hams. Using voice is often
out of
the question when it is of prime importance not to disturb other
family members.
And when cost, size, weight and battery power considerations are
paramount, Morse code equipment is the natural choice. Check out the
new KX1 at
http://www.elecraft.com
for an example of what can be done with modern Morse code radio
equipment.
73 de Jim, N2EY