Wednesday, 27 January 2016

The Power-Lore and QRP Philosphy.

QRP operation refers to transmitting at reduced power while attempting to maximize one's effective range. The term QRP derives from the standard Q-code used in radio communications, where "QRP" and "QRP?" are used to request, "Reduce power", and ask "Should I reduce power?" respectively. In practice it is a large and growing movement within the field of radio communication; both amateur and professional. The QRP fraternity has been growing exponentially and more and more QRP clubs are thriving world wide and in a scant two decades QRP operation has become a way of life for a plural wing of radio enthusiasts and is proliferating rapidly. It is evident now that working with QRP power levels isn’t a handicap; as it was once thought..!! It's just an arbitrary restriction of the one technical aspect of radio that has consistently worked against the interests of amateur operations. Set aside power, and you are left with skill, inventiveness, ingenuity, challenge, and enthusiasm that are very similar to the attractions of low power operation with added fun at lower cost along with the incentives of simplicity of designs and portability.

The Power Lore: Most amateurs use approximately 100 watts on HF and 50 watts on VHF/UHF. Though in some parts of the world, like the U.S. and Russia; they can use up to 1,500 watts. So many radio operators believe that higher the power the longer the distance you can work with. But it is a myth and nothing more than a philosophy of quasi lore. First; a little primer on power versus gain. Keep in mind that one S-unit on a properly calibrated receiver is equal to 6 db. To get a one S-unit gain you have to quadruple your power output. In other words, you would have to go to 20 watts to increase your signal strength by 6 db or one S-unit from your 5 watts. Conversely, to reduce your signal strength by 6 db or one S-unit, you need to go down to 1.5 watts from your 5 watts. Although it varies considerably due to many factors, one S-unit is about the minimum change in signal strength to be just noticeable. Here's a table comparing various power levels to 5 watts. An explanation follows.

Forget about logarithms and focus on the business end of the equation, the received signal. Signal strength is measured in S-points, which you can usually read directly from a meter on your radio. Your concern when transmitting is how many S-points you are generating at the receiving station. The more the better you believe. It may sound astounding but it is wrong scientifically. In the first place, if your signal is perfectly copiable at S-7, increasing the strength to S-9 achieves absolutely nothing other than hissing out atmospheric noise and grunting IMDs. If you want to increase your signal level by one S-unit, for example, look in the last column for 1.00 and you'll see you have to raise your power to 20 watts to get that change. I think it is very telling to look at the figures below 5 watts. Some folks think it is much 'greater' to get a QSO at 2.5 watts than with 5 watts. In reality there is only about 1/2 S-unit difference between the two powers, hardly noticeable at the receiving end. To drop your signal 2 full S-units requires going down to a little above 1/4 watt. Curious about the S-unit difference between say 100 watts and 1 watt? Just add the absolute values in the last column for 100 and 1 watts (2.17 + 1.17 = 3.34 S-units). I think the table helps explain a lot about why QRP can be so successful. Oh, although it is not in the table, the difference between 1,000 and 5 watts is 3.84 S-units. If a kW signal is S9, your QRP will be around S5 all other things being equal. You can have fun with the table and learn more about power and signal strength ratios. If a kW signal is S9, your QRP will be around S5 all other things being equal; and you are reasonably workable with quite visceral signals..!!

Don't believe….? Ok, let's look at the power ratio in action. Say you are transmitting with 5 watts and a station gives you a report of S-5. Now double your power to 10W and what happens? Your power output has increased by 3dB and the received signal has increased by the same 3dB, which is... wait for it.... one half of one S point. Double your power again, to 20W, and the received signal is now one whole S-point stronger. Double it again, to 40W and we are at 1.5 S points. Again, to 80W and we are at 2 S points improvement on our original 5 W signal. 80W is near enough to what your typical "100W" transmitter puts out, and by now you should see what little difference an additional 20W would make. In summary by going from 5W to 80W we have increased the received signal strength by all of two S points. The reverse is true; if you are copying an 80W station at S9 and he reduces power to 5W, you will still be copying him at S7.

But let's not leave it there. Start at 100W and add 3 dB at a time by doubling power- you go to 200, 400, 800, 1.6Kw. We doubled power 4 times, picking up 12 dB or.... wait for it.... 2 S points. Talk about diminishing returns! The only caveat is that the S-meters on most radios, if they are calibrated at all, are set for the standard S9 at 50uV input- at any other input, larger or smaller, they are notoriously inaccurate.

Thus the effectiveness of QRP communication, and the quality of QRP equipment, can be explained very easily with a little math. I hear you groaning, but it is very simple math and in fact you can witness its effectiveness, yourself in practice. A major factor in the continued growth and success of QRP is the cohesiveness of the QRP community. It is a community in all senses of the word, from local clubs to national organizations.

Less Frustation More Satisfaction: The downside of wanting to be a DXer if you only have an average station - which is all most of us can afford - is that the joy of making an unexpected DX contact is experienced less often than the frustration of when you don't work it. You only have to listen to the behavior of people in pile-ups to see what I mean. Many of them sound stressed. They don't sound as if they are having a good time. Is there pleasure to be had in shouting the last two letters of your call into a microphone for half an hour, especially if at the end of it you have nothing to show for it? I don't think so. A few of the high-power guys like to claim that it's their ears that do all the work during a QRP contact. "QRPers brag about working DX with milliwatts but it's the guy other end who does all the work to make the contact" is a typical comment. But if you believe that QRP operators brag about making a contact, you don't understand the QRP mentality at all. What the QRP op feels is a sense of wonder that such a tiny amount of power can propagate a signal to the other side of the world. The QRO op at the other end can feel that too. And from the comments I sometimes get ("your QRP is doing great" etc.) I think that the grumpy guys who think QRP just makes work for them are in the minority.

Further Thoughts: The reason I think all this is important is that QRP amateur radio is something which is achievable by all. A high power, DX-capable station is achievable by a minority. Some simply can't afford it. Others don't have the opportunity to erect big antennas, or simply don't want to displease family members or annoy the neighbors. Be honest: how many non-hams think antennas are attractive? QRP is cleaner than QRO and does not advocate RF pollution. Advancements in RF practice are on and new avenues for QRP and QRPp (Very low power communications) are opening. Several weak signal digital modes like CCW, JAT63/65, WSPR,WSJT and QRSS are becoming popular among designers and operators. The program WSJT, is created by Nobel Prize winning Princeton professor, Joe Taylor, K1JT. Its purpose is to send and receive various weak signal modes for meteor and ionospheric scatter as well as EME (moonbounce) on VHF and UHF bands. And, it’s both free and well supported. On the other hand QRSS is a derivative of the CW Q-Signal QRS for "Please lower your code speed". By using extremely slow CW, it is possible to use a computer sound card and special software to extract CW characters from below the audible noise floor. Morse code element lengths of 10 to 30 seconds (or even longer) per dot are commonly used.

Amateur VLF operators have used QRSS techniques to span the Atlantic at 136 KHz and to receive very weak VLF beacon transmissions from distant locations. By adopting these same techniques, QRP operators can push the envelope of very low power HF communications.

                    A 6 milliwatt QRSS contact in action.

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