Increase over what?
There are not that many tri band yagis with 5 elements on 20m
Peak f/b of my modified KLM 20m mono band yagis is 37dB on 14.175.
73
Peter
-----Original Message-----
From: Tony [mailto:73guddx@gmail.com]
Sent: Sonntag, 15. Februar 2026 03:22
To: peter.voelpel@t-online.de
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Modeling Tri-Band Yagi Antennas
Peter:
The JK 205 mono band Yagi has peak f/b of 28db. Assuming the same modeling,
and all things being equal, that?s a pretty substantial increase.
Tony K2MO
Sent from my iPad
> On Feb 14, 2026, at 8:04 PM, dj7ww@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@contesting.com] On Behalf Of
Tony
> Sent: Sonntag, 15. Februar 2026 01:14
> To: TowerTalk@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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