Transcript Milliwatts and Microwatts Arkiecon - 2003 Presented by Don L. Jackson Topics QRPp - “low low power” QRSs - “slow” CW Slowfeld & other modes Experiments on.

Milliwatts and
Microwatts
Arkiecon - 2003
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Presented by
Don L. Jackson
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Topics
QRPp - “low low power”
QRSs - “slow” CW
Slowfeld & other modes
Experiments on 30 Meters
Computer Software
Resources
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What is QRPp ?
QRP is low power, usually
under 10 watts.
QRPp is even lower power,
often in the milliwatt or even
microwatt range.
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Signal Strength
Comparisons
 100 w
+50 dBm
 10w
+40 dBm
 1w
+30 dBm
 100mw +20 dBm
 10mw
+10 dBm
 1mw
0 dBm
 100uw
-10 dBm
 10uw
-20 dBm
 S9
 S7+
 S5+
 S4
 S2+
 S0+
?
 ??
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HOW
do we receive a
very weak signal,
often well below
the noise level?
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Methods for weak signals
Narrow Bandwidth
Slow Data Rate
Stable Frequency Control
Long Time Integration
Computer Assistance
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Communications Theory
The faster the signaling rate, the
more bandwidth you need.
The more bandwidth you have,
the more energy you need to
keep your signal above noise.
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Example: 12 wpm CW
 A dot is about 1/10 second long
 Rule of thumb: 3x dot length or 30 Hz.
 So this means that if we want to receive
a 12wpm CW signal, we’d need to use a
filter no narrower than 30 Hz.
 Going narrower that this will cause the
dots to run together making difficult
copy.
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Using a SSB filter
 2.4 KHz bandwidth
 2400 Hz is 80 times wider than 30 Hz.
 Will let 80 times energy through it
 Since our desired CW signal only takes
1/80 of the received energy, most of
what we get is NOT the desired signal.
 This is -19 dB disadvantage!!!
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Lesson Learned
 For best performance, we receive with a
filter that is no wider than the signal we
are trying to receive requires.
 If you have a wider filter than the signal,
you are receiving “extra” energy from
the noise that is “diluting” the desired
signal -- making the effective S/N ratio
worse.
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But I can hear a weak signal
as well with the SSB filter as I
can with the CW filter.
What’s the deal here?
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Psychoacoustics
Psychoacoustics - how the
brain perceives sounds.
Brain/ear capable of picking out
narrow bandwidths of signal in
presence of white noise or
signals removed in freq.
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But...
We are going to try to receive
very weak signals that are
below noise level
...so let’s look at how we can
do it...
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Back to
Communications Theory
Lower data rate = narrower
bandwidth
Narrower bandwidth = lower
transmitted power to maintain
the “threshold of copiability”
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Shannon’s Law
states that if you are willing to
transmit data infinitely slowly,
you could communicate with
infinitely narrow bandwidth and
infinitely low (not zero) power.
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Obvious Practical Limits
It should go without saying
that there are practical limits
to how slow you would go to
convey useful information in
a reasonable amount of time.
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Introducing...
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What is QRSs?
The term QRSs is derived from
QRS, an abbreviation that
means “Slow Down”
QRSs, by extension, would
imply very slow sending speed.
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QRSs is...
VERY slooooooow!
Agonizingly slow!
B-O-R-I-N-G !
Often sent at dot lengths of
20 seconds or longer
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But, QRSs...
Works!
Extremely narrow bandwidth.
Has been used to accomplish
worldwide LOWfer (very low
frequency) records.
Is almost impossible to decode by
ear.
Needs computer “assistance”
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Example: 90 second Dot
0.0133 wpm or 0.8 words/hour
bandwidth >= 0.033 Hz
72,000x narrower than SSB
(48 dB)
900x narrower than 12wpm CW
(29 dB)
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Needed
Computer software
Stable and known
frequency control of both
transmitter and receiver
Patience
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Introducing ARGO
Windows
Sound card
Pentium 200
MHz or better
Price is right
Works!
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What the computer does
for us:
With DSP/FFT, is able to
give us extremely narrow
bandwidth representations of
energy levels, averaging
over long periods of time,
and...
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What the computer does
for us:
Presents the results visually
in a waterfall display with
frequency, level, and time.
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Other QRSs modes
FSCW - Frequency Shift CW
DFCW - Dual Frequency CW
Slowfeld - similar to Hellscriber
...and many many more!
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DFCW
CQ DK1IS K
Upper=Dash Lower=Dot
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SLOWFELD
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A Few 30 Meter Band
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The start of it all...
On 9 Feb 2002 at 22:51, Paul Stroud
wrote:
Hi Gang,
You are invited to listen for weak signal
beacon AA4XX/B Sunday, Feb10th, from
20:00-02:00 UTC (3:00-9:00PM EST) on
10,140,000 hz.
This beacon will be running slow speed
CW, with 10 second dots and 30 second
dashes, commonly referred to as "QRSS10."
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The Players
 AA4XX - Paul
 AKØB - Stan
Raleigh, NC
 ON5EX - Johan
Zevergem,
Belgium
 WØCH - Dave
Seneca, MO
 AE5K - Don
Yellville, AR
St Charles, MO
 N4SO - Ken
Grand Bay, AL
 W8DIZ, N3AAZ,
KD1YV, VE7SL,
VE3FAL,ON6UL,
AE4IC, N4HAY,
K2UD, VE6KBS 33
Details
February-March 2002
10.140 MHz. +/-
Main beacons: AA4XX, ON5EX
Power 250 mw to 50 uw
Call, power, “codeword”
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AA4XX - Raleigh, NC
Paul - AA4XX
Wilderness
Sierra
S&S DDS VFO
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AA4XX - Raleigh, NC
DDS VFO in
100 degree
heat
chamber
(2-3Hz/day)
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AA4XX - Raleigh, NC
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AA4XX - Raleigh, NC
Antenna - 30 meter dipole
fed with ladderline, about
60 ft. up in NE/SW
orientation.
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My first attempt and results...
Paul,
Just downloaded Argo, installed
it & tuned rig to 10140 (with 800
hz. bfo offset) and there you
are! Just got the complete call.
Very exciting for this old timer!
Just wonder what power you are
running right now? Time of
reception has been 1832-1849Z
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Email comments...
It was a real treat to hear from
six stations who copied the five
letter codeword "GREEN" during last
night's 30M QRSS10 beacon session.
The beacon was running 1 milliwatt
output into a 30M dipole up 60
feet. Congratulations to the
following stations who confirmed
the codeword: N4SO, W0CH, AE5K,
ON5EX, ON6UL, AK0B.
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Email comments...
The most common comment that is
being received from the QRSS mode
listeners is that they want to try
to copy lower power levels.
With that in mind, the AA4XX beacon
will be running 500 microwatts
QRSS30 mode tomorrow (Wednesday).
The longer characters will
hopefully facilitate reception of
the 1/2 milliwatt signal.
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Email comments...
Next week we will continue
our downward plunge as
long as at least one of
our listeners decodes the
code word. This is really
getting interesting, isn't
it?
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Email comments...
Do you think I ought to
leave my antenna half
down on the ground? ;-)
(good ground wave?)
[AE5K, after receiving
AA4XX’s 200 microwatt
signal]
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Some Results
AA4XX -> AE5K (785 miles)
200 microwatts good copy
100 microwatts missed 1
letter in codeword
7.8 million miles/watt
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Some Results
ON5EX->AE5K
250 mw - good copy
4600 miles
18,400 miles/watt
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Even Better Results
WØCH and AA4XX - 2 way
contact
Distance 892 miles
Power 50 microwatts
Mode: QRSS60
17,840,000 miles per watt !
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Even Better Results
Took 5 hours to complete
exchanges
WØCH was received at
AA4XX using only 10
microwatts at one point
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AA4XX transmitting “GL”
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Difficulties Observed
Propagation - no path?
QSB, QRM, QRN
Multipath
Frequency stability/accuracy
Software crashes
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Conclusions
 QRSs is an “experimental” mode
 QRSs is a very viable mode using very
low power and computers.
 None of our antennas were
“spectacular”
 Signals under about 10-25 mw or so
were not audible. (rough estimate,
depends on conditions of course)
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The UTHT
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Ugly Transoceanic Hifer
Transmitter
 Built by SM6LKM
 Crystal oscillator BF245A (similar to
MPF102) JFET buffer with resonant
tank 74HC00 one gate for keying,
remaining 3 gates in parallel as "Power
Amplifier" Series tuned tank 4:1
transformer BNC output connector, +11
dBm @ 14.10111 MHz
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Accomplishments with UTHT
5mw SM6LKM to W1TAG
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SOFTWARE
http://www.qsl.net/padan/argo
Freeware for ham and hobbyist use.
Good starting program, easy to use.
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SOFTWARE
http://www.qsl.net/padan/spectran.html
Freeware, more extensive and
sophisticated than Argo. By same
authors.
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SOFTWARE
DL4YHF's Audio Spectrum
Analyzer ("Spectrum Lab")
http://www.qsl.net/dl4yhf/spectra1.html
Due to its “Laboratory” nature, this
analyzer is not as easy to use as
ARGO. Freeware
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SOFTWARE
ON7YD’s QRS Program
http://www.lwca.org/library/
software/qrs/qrs2.htm
Freeware, makes easy to send QRSs
and DFCW transmissions.
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SOFTWARE
Slowfeld
http://www.qsl.net/zl1bpu/FUZZY/software/
G3PPT/Slowfeld.zip
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Other Resources
http://www.indo.com/distance/
(nice distance computation)
http://www.ussc.com/~turner/qrss1.html
http://www.w0ch.com/qrss/qrss.htm
http://www.qsl.net/zl1bpu/
http://www.qsl.net/on7yd/136narro.htm
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My thanks to the following who
contributed to this presentation:
 AA4XX
 W1TAG
 WØCH
 W5CSJ (my wife
 ON5EX
who had to put up
with all this)
 ...hope I didn’t miss
anyone (if so, hollar)
 AKØB
 N3AAZ
 NL9222
 SM6LKM
 KA7OEI
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