[TowerTalk] Modeling Tri-Band Yagi Antennas

[Tony]

Peter:

I specifically mentioned mid-sized tri-band antennas as having compromised f/b. The Optibeam 21 3 has wonderful specs but it’s a huge antenna weighing 220 lbs on a 46 foot boom! 

Too much load for my tower : )

Tony
Sent from my iPad

> On Feb 14, 2026, at 8:04 PM, dj7ww at t-online.de wrote:
> 
> Any example were the 20m monoband yagi is 10dB better then the tri-band
> antenna?
> It seems very unlikely to me, Optibeam 21-3 and 5-20 are my examples.
> 
> 73
> Peter
> 
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Tony
> Sent: Sonntag, 15. Februar 2026 01:14
> To: TowerTalk at contesting.com
> Subject: [TowerTalk] Modeling Tri-Band Yagi Antennas
> 
> All:
> 
> I've noticed that most tri-band Yagi antennas that cover 20,15 and 10 meters
> seem to have compromised F/B ratios on the 20-meter band. Some mid-sized
> antennas have peak F/B ratios of only 15db on 20M, which isn't terrible, but
> that figure is likely to get worse as you sweep across the band.
> 
> It must be a necessary trade-off in tri-band design since JK Antennas,
> Optibeam and others lean towards the same compromise, which is a shame since
> one would want that extra F/B performance on that band.
> 
> On average, a 20M mono-band Yagi outperforms the tri-band antenna by 10db or
> more, which seems pretty substantial.  I'm sure someone in the group has
> modeled tri-band antennas like the mid-sized JK and Optibeam, and it would
> be interesting to know what the criteria is for the 20M performance
> trad-off.
> 
> Tony -K2MO
> 
> 
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