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Milliwatts and Microwatts

Arkiecon - 2003

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Presented by

Don L. Jackson

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TopicsQRPp - “low low power”QRSs - “slow” CWSlowfeld & other modesExperiments on 30 MetersComputer SoftwareResources

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

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Methods for weak signals

Narrow BandwidthSlow Data RateStable Frequency ControlLong 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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PsychoacousticsPsychoacoustics - 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 TheoryLower 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/hourbandwidth >= 0.033 Hz72,000x narrower than SSB

(48 dB)900x narrower than 12wpm CW

(29 dB)

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Needed

Computer softwareStable and known

frequency control of both transmitter and receiver

Patience

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Introducing ARGO

WindowsSound cardPentium 200

MHz or betterPrice is rightWorks!

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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 modesFSCW - Frequency Shift CWDFCW - Dual Frequency CWSlowfeld - 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 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

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Details

February-March 200210.140 MHz. +/-Main beacons: AA4XX, ON5EXPower 250 mw to 50 uwCall, 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 copy100 microwatts missed 1

letter in codeword7.8 million miles/watt

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Some Results

ON5EX->AE5K250 mw - good copy4600 miles18,400 miles/watt

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Even Better Results

WØCH and AA4XX - 2 way contact

Distance 892 milesPower 50 microwattsMode: QRSS6017,840,000 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, QRNMultipathFrequency stability/accuracySoftware 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

http://www.qsl.net/dl4yhf/spectra1.html

DL4YHF's Audio Spectrum Analyzer ("Spectrum Lab")

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

http://www.qsl.net/zl1bpu/FUZZY/software/

G3PPT/Slowfeld.zip

Slowfeld

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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

Other Resources

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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)