[CQ-Contest] 2nd harmonic - engineer's perspective

[Jukka Klemola]

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