Wet Weather and Q-factor...


Stability in yagi designs is directly related to Q, those where the value is high will suffer from wet weather due dielectric loading effects caused by sticky water droplets.

In my previous study I looked at average Q-factor between 144 - 146MHz...

The following comparisons take into consideration a much greater frequency range 140 - 150Mhz, this clearly shows the cut-off frequency at the HF end. This also reveals the range in which unwanted out of band signals will be reduced!

As a point of reference competitor designs and the famous DL6WU 10 element standard give a handle on the likely outcome.

Thanks to John Lemay G4ZTR for providing dry and wet analysis of the CQM14DXL long yagi design.

Provided that the cut-off is well above the desired upper bandwidth limit then good to reasonable stability will be the outcome.

When conducting tests odd quarter waves in the feedline should be avoided otherwise impedance transformation can magnify changes! Insertion of a temporary quarter wave section (343mm with Vf of 0.66) into the feedline at the shack end will show if a fault condition/problem is present... If no fault exists then introducing the quarter wave section will make no difference to measured SWR... To be certain do this test when the antenna is dry and then wet!

73

Derek Hilleard G4CQM


WA6XX 6 ele

WA6XX Average Q-factor 66 (140-150MHz)

 


WS8C9 8 ele

WS8C9 8 element Average Q-factor 35 (140-150MHz)

 


DL6WU10 10 ele

DL6WU 10 element Average Q-factor 27 (140-150MHz)

 


WAXXX10S 10 ele

WAXXX10S Average Q-factor 64 (140-150MHz)

 


WA10XX 10 ele

WA10XX Average Q-factor 39 (140-150MHz)

 


KSC11LFA 11 ele

G0KSC 11 element LFA Average Q-factor 114 (140-150MHz)

 


EF0213M 13 ele

YU7EF EF0213M Average Q-factor 370 (140-150MHz)

 


144NX13S 13 ele

144NX13S Average Q-factor 360 (140-150MHz)

 


144NX14 14 ele

 

144NX14 Average Q-factor 161 (140-150MHz)

 


CQM14DXL 14 ele

CQM14DXL Average Q-factor 623 (140-150MHz)

 

DRY
WET

 

G4CQM's Antennas...

  • THESE YAGI ANTENNA DESIGNS ARE NOT FOR COMMERCIAL USE OF ANY KIND WITHOUT PRIOR CONSENT!
  • Private experimenters are free to use these designs for their own personal enlightenment. However, no guarantee or warranty is offered or implied.
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