This page courtesy of WB9DLC and Ramsey Electronics



    QRP Works!

               


 

1000 WATTS vs 1 WATT: UNDERSTANDING THE DIFFERENCE

Before we move on, I would like to share with you a practical formula about transmitter power that I clung to in my younger years when I could not afford anything other than my original Novice CW transmitter, even well after I got my Extra Class license. First, some theoretical facts we should know:

Next, there are three practical facts to remember:

 

The following example shows RST reports to be expected, in exact theory, at various power reduction levels. We will start with the classic 1000 watt station which gets a report of "10 db. over S-9" measured on the receiving station's S-meter.

Assume identical dipole antennas at both stations. Our chart does not start at the proverbial "30 db. over S-9" and work itself down to S-1 for reasons that will become obvious.

S9+10 db. 1000 watts output
S9 100 watts output
S8 25 watts output
S7 6.25 watts output
S6 1.56 watts output
S5 .39 watts output

We can see that it becomes easy to play games with such numbers. For example, an RST of 439 is a legitimate report which permits reasonably effective communication.  But, do we believe that the transmitting station illustrated above could really produce a 439 signal by running .0013 watt?  If we say "probably not", we also ask why not, and then we would get the seminars about perfect antenna matching, transmission line losses, and so forth.

Under good propagation conditions, SSB signal reports of "20 over S-9" and more can be given without even needing 1000 watts or a beam antenna.  Assuming the "+20" is an accurate report, consider this example of power reduction over the same path:

S9+20db. 1000 watts
S9+10db.
100 watts
S9 10 watts
S8 2.5 watts
S7 .625 watts
S6 .156 watt
S5 .039 watt
S4 .0087 watt!

Under reasonably good band conditions, particularly at 10 or 14 MHz and on up, the above correlation of signal reports to power output becomes realistic.

 

"S9+20" is what amplifier users expect to give and receive to justify their investment and power consumption. Most commercial transceivers have typical output in the 60-200 watt range, and S8-9 reports are taken for granted.

Actually, 15-25 watts is a far more practical operating power than most amateurs and equipment vendors realize today...and the thousands of QRP enthusiasts will confirm that getting a solid 579 running 3-4 watts is no big deal.

If all the above theoretical signal reports are based on both the transmitting and receiving stations using simple dipole antennas, we can also see that the use of some 10db gain antenna such as a beam or quad by either station could move the S7 for .625 watt up to S8, and that a similar antenna used at the other station could give the under 1 watt signal a further boost over S9!

On the other hand, if you hear a 1000 watt station producing a moderate signal such as S4 or S5, you can reasonably assume that you will not have a lot of luck over that path right now with the theoretical S1 signal level of your QRP transmitter. (This point highlighted by Mike - WB9DLC)

While these figures also can be used to show how nice it is to have a power amplifier and beam antenna, they indeed serve to show that reasonable signal levels indeed are achievable with low power and a dipole antenna.

"QRP" enthusiasts have their own rituals, jargon, strategies, QRP operating conte sts, magazine columns and books, and convention get-togethers. They constitute a vital segment of the amateur radio community, because they consistently demonstrate the feasibility of low-power communication. In fact, the most avid QRP enthusiasts would not regard communication with a Ramsey transmitter especially challenging, since they prefer the new world of milliwatt operation, known as "QRPp"! And, yes, the ones who have conquered the "milliwatt" world ARE setting records with "milliwatt" tests. With the world record set in 1970 between Alaska and Oregon on ONE microwatt, think about it this way: your Ramsey QRP transmitter is almost one million times more powerful than the transmitter used in that historic test!

 

WHO SHOULD USE A "QRP" TRANSMITTER?

There is a philosophy that "Novices" should not get started with a very low power transmitter. The reasoning is that most newly-licensed amateurs need to build up the confidence that comes with actually making contacts and that they do not need the additional challenge and pressure of low-power operation.

There is some wisdom in this view, but that opinion should not make newcomers apprehensive about trying a Ramsey QRP transmitter, IF:

Sources:

WB9DLC andRamsey Electronics

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