Low Q Long Yagis by G4CQM for Terrestrial VHF/UHF DX'ing

05-02-2021... In past years Long Yagis were the number one choice for most serious DX'ers, those old designs created by adopting basic principles along with trial and error including a generous testing regime... Derek G4CQM presents a selection of modernized VHF/UHF Low Q Long Yagi designs optimized with K6STI's YO7 Professional version software and calibrated with NEC-2. Limitations associated with NEC-2 have been carefully avoided as there are no tapered or bent elements, no junctions, and no close proximity spacings. Unique element mounting clips designed by Derek avoid the need for correction by conforming to the DL6WU mounting directive. This requires that each element is raised more than the boom radius (r) above boom. A special tuning technique conceived by G4CQM gives rise to a low average Q-factor with subsequent wider bandwidth than older traditional designs, critical in delivering a stable antenna. From experience the very best designs occur when YO7's unique algorithm and NEC-2 concur... For kits and parts to build these designs contact Richard Mason G6HKS for full details, specifications and prices.
Just to be clear the DE requires 5/8th Inch (15.875mm) OD tube, whilst the parasitic elements are all 3/16th Inch (4.7625mm) OD rod.

Old Vs New - Average Q-factor comparison

Understanding YO7

To reduce screen clutter, YO7 does not label the figures displayed within the Yagi patterns. They are as follows (shown in yellow font):

1. Frequency
2. Forward Gain
3. Front-to-Rear Ratio
4. Input Impedance
5. Standing-Wave Ratio
6. Elevation Angle or Gain FOM

YO displays elevation angle for Yagis over ground and gain figure-of-merit for single-Yagi, free-space models.

YO defaults to a generalized definition of front-to-back ratio.

The notation 12.7-j15.4 means a resistance of 12.7 ohms in series with a reactance of -15.4 ohms.

Z stands for impedance.

The lambda symbol (λ) means wavelengths.

YO uses a generalized notion of standard front-to-back power ratio to characterize pattern quality. Conventional F/B is the ratio of forward power (at 0 degrees) to that radiated in the opposite direction (at 180 degrees).

YO's generalized F/B is the ratio of forward power to that radiated within a specified region to the rear of the antenna. This is called front-to-rear ratio (F/R).

Yagi designs maximizing conventional F/B often have large backlobes at angles other than 180 degrees. Much better patterns result when you optimize a Yagi for F/R.

The F/R region begins at 180 degrees and extends forward to a specified angle (90 degrees by default).

Finally... Element lengths shown in the tables are half lengths.

Legal

• 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.

• MY WEBSITE DOES NOT USE COOKIES, EXTERNAL LINKS MIGHT!

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• Numerical Electromagnetics Code (NEC) latest news here!

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• VE7BQH Antenna Tables - A short historical analysis with comparisons and comment by G4CQM