Hi Gary,
As preface, you are in my CQ160CW log. And lest someone have the idea that
the following is some kind of whining about QRP...
Particularly in a contest, I ENJOY trying to pull QRP stations out of the
noise, especially the ones I can manage to copy and the next guy can't.
Successfully working QRP puts points differential between me and those who
can't. I just have to make sure that doesn't cause me to lose my run
frequency.
But let's be clear headed about what QRP lays on the other end and what the
dB realities are.
For sake of argument, make the assumption that a 1.5 kW station should be
heard about as far as he can hear another 1.5k station. That would imply
similar noise levels at both ends and equivalent RX ant provisions.
Now place yourself geographically on either end of this station pair.
1500/5 = 300. Log 300 = 2.477. 10 log ratio = 24.77 dB, call it 25 dB.
25 dB out of the noise is 10 over S9 on a lot of S meters. In a few rigs,
like the K3, the S unit display can be calibrated. K3 "S unit" leds are 5
DB. 25 dB would be 5 K3 leds. Right now my local noise on the S meter is
tickling the S6 led. S6 plus 5 leds or 25 dB is just tickling 10 over 9.
The 1.5k station would have to be a real 10 over 9 in order for the QRP
station to just be right at the noise. 95% of the contest signals answering
my CQ's last night were below 10 over 9. For the QRP station to be 5 dB out
of the noise, the 1.5k station would need to be 15 over 9.
In RBN terms, the 1.5k station would need S/N of more than 30 at a node
local to the non-QRP end.
Some things QRP stations do (some necessarily) make copy even harder. There
is the myth that correct matching equipment for contest QRP is trail-grade,
AKA teeny. Teeny tuners, with small wires and small jacks and often with
160 as a poorly engineered afterthought, will sometimes add 2 or 3 dB loss.
The big QRO tuners are needed for their lack of loss.
This is not a put-down for on-the-trail QRP signals, just a dB evaluation
of same. Someone wants to run that, fine by me, just don't get on my case
for not being able to copy. Know what you're actually putting out.
QRP stations and teeny matching equipment are sometimes all that's possible
in tight spaces, where one may have the same volume as a stack of five or
six paperback novels to place the station. KX3's and all those kinds of
things. Particularly so in family occupied RV's and similarly disadvantaged
settings.
The very short antennas and extremely sparse (therefore lossy) 160
counterpoises sometimes can have three or four dB loss (and more) compared
to a well-counterpoised full size antenna.
That and the teeny tuner get us up to the 1.5k station needing to be 20
over 9 for QRP 5 dB out of the noise.
That certainly is my experience for much of QRP on 160.
I have an email somewhere from a QRP station that was using a coiled
antenna stapled to the basement ceiling, which was bare floor joists. He
made something like a dozen contacts in a contest, myself being one. I'm
not sure my ears are good enough for that any more.
73, Guy K2AV
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|