WB9DLC      QRP Works!


The following has been extracted from the Ramsey Electronics Manual for their QRP transmitters.  It is one of the best documents that I have seen showing why QRP works.  I hope that Ramsey doesn't mind me sharing it.  The explanation about QRP is in it's entirety - including the reference to 'Ramsey Transmitters'. 

Ramsey Electronics has gotten out of the radio business



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:

  • 1. An "S-unit" on a receiver's S-meter or in the R-S-T system consists of a 6-decibel increase or decrease of output power received from a transmitter.

  • 2. Power needs to be increased four times or 400% to result in a true 1 S-unit or 6db RST gain.

  • 3. Reducing output power down to 25% of previous power should result in an S-Meter or RST drop of only one 6-db unit.

  • 4. A 10-decibel increase in signal strength requires a power increase of ten times!

Next, there are three practical facts to remember:

  • 1. The R-S-T system was designed originally for the human ear and was based on typical receiver performance of over 50 years ago.

  • 2. Modern receiver design permits signals which are technically "weak" in measured decibels to sound quite good (ie: 569-579) to the ear.

  • 3. The human ear is sensitive enough to appreciate a 1 or 2 db change in signal strength, which is why moderate changes in output power often result in more dramatic signal report changes. (In fact, the value of a decibel was determined to be that increment of sound change which the ear could detect!)


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
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 contests, 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!



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:

  • 1. This is where your budget is.

  • 2. You can count on somebody to help you with assembly.

  • 3. You can count on somebody to listen to your signal during initial tests.

  • 4. You have a reasonably good receiver.

  • 5. You have space for a normal, no-compromise antenna for the band
    you wish to operate, either a standard dipole, or the "inverted V" dipole, or quarter-wave vertical.