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G8MNY > TECH 27.03.24 10:50l 84 Lines 4296 Bytes #999 (0) @ WW
BID : 4173_GB7CIP
Read: IU4JRU GUEST
Subj: QRO v QRP
Path: IZ3LSV<I0OJJ<GB7CIP
Sent: 240327/0947Z @:GB7CIP.#32.GBR.EURO #:4173 [Caterham Surrey GBR] $:4173_GB
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Jun 203)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
For years I have run as much QRO as I could muster. The main reason of course
is to be heard as far as possible and increase the chance of working that Dx,
or even having a contact at all. Also having a very small footprint with QRP
can mean your constantly fighting to keep your frequency on a busy band.
SIMPLE MODEL
Here is a simplistic statistical view of what power does in terms of range,
usable signal area covered, and hence the chance of a QSO.
(based on +6dB = to double the range and 4x the area of a usable RF signal).
Power 1.5W 6W 25W 100W 400W 1500W
.Ä~~~~Ä. /
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_--_ / \ Ý
-- / \ Þ Ý Þ
o () ( ) ( ) ( ) ³
-- \ / Þ Ý Þ
~--~ \ / Ý
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Range 1 2x= 2 2x= 4 2x= 8 2x= 16 2x= 32
Area 1 4x= 4 4x= 16 4x= 64 4x= 256 4x= 1028
S meter(3dB/Div) S1 S3 S5 S7 S9 S9+6dB
QSO Chance:1.5W 100% 400% 1600% 6400% 24000% 102000%
Chance:400W 0.4% 1.6% 6.4% 25% 100% 400%
CHANCE
Now chance is strange thing and much Dx is worked with QRP, often due to the
extensive endeavour of keen QRP operators, and the use of very quiet sites.
With HF of course there is multiple hops and this model will show step skip
effects too (rings of skip areas of "NO GO" & "GO" etc). Noise QRN at Rx end
and QRM from other station or modern electronics QRM, all impinge greatly on
the contact chance.
At VHF the curvature of the earth and hills can be the limiting factor.
BEAMS
By increasing the ERP with a beam, the range is increased, but not generally
the footprint area. That depends on stack/bayed configuration. (less lost into
space etc.) The actual chance of a contact therefore is often not increased,
but the amount of Dx is!
QRO HOGGS
Of course it is worth saying, if all were to run QRO, the bands will be jammed
with large signals, Lots of Rx overload effects and some Tx splatter. Look for
splatter by switching sideband and with no Noise Blanker as theu make the Rx
very non linear! So the number of total QSO might well decrease! To avoid T
splatter linears should be properly set up with a 2 tone test. Due to the under
run exciter PA used, when driving a high power PA, with a good PA with some
reserve, the result can actually be a better cleaner signal than the exciter
alone at full power, or a splattering hilltop QRP station with flat battery!
QRO ALIGATORS
Not being able to Rx weak signals well, while running QRO, greatly cuts down
the contact chance, to just those also running QRO! So a QRO station should
endeavour to have a better than average Rx set up.
NOISE FLOOR
Here I use a 2nd Noise cancelling aerial with JPS ANC-4 to give 1-5 S points
improvement, as well as Noise ignoring BHI DSP LS for typically a further 12dB
noise reduction. Also Narrow filters help, and with modern wideband Rx designs,
a high Q manual T tuner, as a preselector can reduce wideband front end noise!
ASYMMETRIC QSOs
Often an asymmetric QRO to QRP contact is possible, where a dual QRP QSO would
be unlikely due to both weak signals with QRN & QRM at each station, and with
more chance of "defending the frequency". A good one way path makes all the
difference & corrections needed in the weak direction get through much quicker.
See my Tech bul "Stacking, Baying or Boxing Ant","BHI Noise Eliminating DSP LS"
"AF 2 Tone Test Osc Design". "QRO Dummy Loads" & various PAs.
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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