Technology & maths enthusiasts out there, let's calculate it.
Simplifying the figures for average joes, but in realistic ballpark for
relatively large stations.
Our case is:
Output power 1000w = 60dBm
160m antenna gain on 160m approx or less than 9dBi (irrelevant in
calculus)
160m antenna gain on 80m approx or bigger than -15dBi
..for this maths experiment we are dealing with a 160m antenna that is
really poor on 80.
To create some thoughts for the technically minded, a full wave 160m
loop shows much more gain on 80 than -15dBi.
Looking at the amplifier, harmonic rejection Pi approx or worse than
40dB, harmonic rejection PiL approx or worse than 50dB.
Optimistic case:
Harmonic's power budget for 80m:
Output power on 80m case Pi: 20dBm
Antenna gain on 80m -15dBi or bigger
-> The harmonic's ERP on 80m is +5dBm or bigger.
For comparison a real signal on 80m:
Antenna gain +10dBi
Output power+60dBm
-> ERP 70dBm.
The real measured signal is S9+35dB at a normal station in range for the
first skip.
So difference between ERP +5dBm to +70dBm is 65dB.
Difference to S9+35dB signal is 65dB .. yielding S9-30dB signal.
S unit is 6dB.
That will show S3 on a calibrated meter.
We all know that is well audible for stations having a low noise level.
To attenuate the harmonic:
In case PiL, S1.
In case stub, closing on noise.
In case PiL + stub, even closer to noise - or in noise.
Double stub + PiL, should really start to vanish.
73,
Jukka OH6LI
_______________________________________________
CQ-Contest mailing list
CQ-Contest@contesting.com
http://lists.contesting.com/mailman/listinfo/cq-contest
|