+ WHAT ABOUT THIS QRO AND QRP THING?
by Ed Ewell, K7DXV - Associate Editor for Training - ewell@e-isco.com
You know most of the transceivers we have on the air operate at
100 watts of output power. Well is this enough power, or too much?
Some stations insist on running QRP, or reduced power, and will
this be enough to provide reliable communications?
You have to QUADRUPLE (X4) your signal to DOUBLE your signal
strength at
the receiver. If you drop your power by one-fourth, your receiver signal
strength will be one-half less, or drop 1 S-unit.
You are working a station running 100W and he is S8. If he drops
his power to 1/4th, or 25 W, his signal strength should drop about
1-S-unit,or to S7. If he drops another 1/4th, to about 6W, he should
drop another S unit, or to about S6. We see the difference between 100W
and 5W QRP is about 2 S-units. You can see that running 100 watts of power
is not always necessary, so do we do it just because it feels good?
Now let us drop down more to 1W that is about another S-unit, then to
250mW another S-unit, etc. OK, we are getting down to the S4 noise level on
40M. At this power level we hope the guy on the other end has only a S3
noise level on his end.
Low power QRP stations transmit at 5 watts or less, and operate CW
modes most of the time. The above example of power levels is not
a problem because if the received signal is at the noise floor, (the S
meter level with no receive signal) or above, QRP signals will be heard
with no problem on CW.
Stations that operate on SSB at reduced power will have usable
signals at 25 watts of power. Yes you may operate lower than this
However you have to be above the noise level for clear communications.If the bands are good, and propagation is good, you will not need to
operate at high levels of power on transmit.
Why use a linear amplifier at 1500 watts of power? The stations that use
amplifiers are usually net control stations, relay stations, stations that
have to communicate with stations that have poor antennas, receivers,
temporary antennas, and are in high noise levels. ARES stations can be in
poor locations and receiving conditions can be noisy. The relay station can
usually hear the portable stations, also net controls can hear them, but
all stations need to receive net control or the relay station. The
amplifier can help when needed.
This has been a presentation about power levels, I did not consider the
receiver sensitivity , antenna type, noise levels, or propagation.
Ed Ewell 73 K7DXV