Milliwatts and Microwatts

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Milliwatts and Microwatts
QRPp Milliwatts and Microwatts Arkiecon

Presented by Don L. Jackson

Topics QRPp - “low low power” QRSs - “slow” CW Slowfeld & other modes
Experiments on 30 Meters Computer Software Resources

What is QRPp ? QRP is low power, usually under 10 watts.
QRPp is even lower power, often in the milliwatt or even microwatt range.

Signal Strength Comparisons
100 w +50 dBm 10w +40 dBm 1w +30 dBm 100mw +20 dBm 10mw +10 dBm 1mw dBm 100uw dBm 10uw -20 dBm S9 S7+ S5+ S4 S2+ S0+ ? ??

HOW do we receive a very weak signal, often well below the noise level?

Methods for weak signals
Narrow Bandwidth Slow Data Rate Stable Frequency Control Long Time Integration Computer Assistance

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.

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.

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!!!

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.

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?

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.

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...

Back to Communications Theory
Lower data rate = narrower bandwidth Narrower bandwidth = lower transmitted power to maintain the “threshold of copiability”

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.

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.

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.

QRSs is... VERY slooooooow! Agonizingly slow! B-O-R-I-N-G !
Often sent at dot lengths of 20 seconds or longer

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”

Example: 90 second Dot 0.0133 wpm or 0.8 words/hour
bandwidth >= Hz 72,000x narrower than SSB (48 dB) 900x narrower than 12wpm CW (29 dB)

Stable and known frequency control of both transmitter and receiver
Needed Computer software Stable and known frequency control of both transmitter and receiver Patience

Introducing ARGO Windows Sound card Pentium 200 MHz or better
Price is right Works!

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...

What the computer does for us:
Presents the results visually in a waterfall display with frequency, level, and time.

Other QRSs modes FSCW - Frequency Shift CW DFCW - Dual Frequency CW
Slowfeld - similar to Hellscriber ...and many many more!

DFCW CQ DK1IS K Upper=Dash Lower=Dot

SLOWFELD

A Few 30 Meter Band Experiments

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."

The Players AA4XX - Paul Raleigh, NC ON5EX - Johan Zevergem, Belgium
WØCH - Dave Seneca, MO AE5K - Don Yellville, AR AKØB - Stan St Charles, MO N4SO - Ken Grand Bay, AL W8DIZ, N3AAZ, KD1YV, VE7SL, VE3FAL,ON6UL, AE4IC, N4HAY, K2UD, VE6KBS

Details February-March 2002 10.140 MHz. +/- Main beacons: AA4XX, ON5EX
Power 250 mw to 50 uw Call, power, “codeword”

AA4XX - Raleigh, NC Paul - AA4XX Wilderness Sierra S&S DDS VFO

DDS VFO in 100 degree heat chamber
AA4XX - Raleigh, NC DDS VFO in 100 degree heat chamber (2-3Hz/day)

AA4XX - Raleigh, NC

AA4XX - Raleigh, NC Antenna - 30 meter dipole fed with ladderline, about 60 ft. up in NE/SW orientation.

My first attempt and results...
Paul, Just downloaded Argo, installed it & tuned rig to (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 Z

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.

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.

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?

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]

Some Results AA4XX -> AE5K (785 miles) 200 microwatts good copy 100 microwatts missed 1 letter in codeword 7.8 million miles/watt

Some Results ON5EX->AE5K 250 mw - good copy 4600 miles 18,400 miles/watt

Even Better Results WØCH and AA4XX - 2 way contact Distance 892 miles Power 50 microwatts Mode: QRSS60 17,840,000 miles per watt !

Even Better Results Took 5 hours to complete exchanges WØCH was received at AA4XX using only 10 microwatts at one point

AA4XX transmitting “GL”

Difficulties Observed
Propagation - no path? QSB, QRM, QRN Multipath Frequency stability/accuracy Software crashes

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 mw or so were not audible. (rough estimate, depends on conditions of course)

The UTHT

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, MHz

Accomplishments with UTHT
5mw SM6LKM to W1TAG

Freeware for ham and hobbyist use. Good starting program, easy to use.

SOFTWARE Freeware, more extensive and sophisticated than Argo. By same authors.

SOFTWARE DL4YHF's Audio Spectrum Analyzer ("Spectrum Lab")
Due to its “Laboratory” nature, this analyzer is not as easy to use as ARGO. Freeware

SOFTWARE ON7YD’s QRS Program
software/qrs/qrs2.htm Freeware, makes easy to send QRSs and DFCW transmissions.

Slowfeld SOFTWARE http://www.qsl.net/zl1bpu/FUZZY/software/
G3PPT/Slowfeld.zip

Other Resources (nice distance computation)

My thanks to the following who contributed to this presentation:
AA4XX WØCH ON5EX AKØB N3AAZ NL9222 SM6LKM KA7OEI W1TAG W5CSJ (my wife who had to put up with all this) ...hope I didn’t miss anyone (if so, hollar)