Rich. Can’t comment on the STEPPIR. However the performance degradation of
the yagi as you discuss at the band edges should be unaffected by the OWA feed.
Its more a function of the element spacing decisions of the rest of the yagi.
Makes the Transmitter happy, but doesn’t change some of the F/B or Gain vs
frequency curves of the traditional yagi I don’t believe. More of an expert on
OWAs might offer some additional guidance.
Ed N1UR
-----Original Message-----
From: Richard (Rick) Karlquist <richard@karlquist.com>
Sent: Thursday, April 30, 2020 8:07 PM
To: sawyered@earthlink.net; towertalk@contesting.com
Subject: Re: [TowerTalk] OWA Yagis was 40m 4el KLM - replacing linear loading
with coils
On 4/30/2020 4:15 PM, sawyered@earthlink.net wrote:
> In my view, the discussion on OWA yagis is about the element count and
> the
> I have all conventional yagis. The 2:1 bandwidth of the my yagis are
> 28000
> - 28750. 2100 - 21375. 14000 - 14300. 7000 - 7185. The amp is at
> full power up to 3L1 SWR. And I have most of my runs using LDF5-50.
> So in my opinion, for a given boom length, the trade of the OWA isn't
> worth the gain loss outside the 2:1 edges of the band. Especially
> because I am almost never running in those sections of the band - where gain
> is most important.
Unfortunately, the pattern of a Yagi can go all to hell as you move away from
the design center frequency, no matter what your ability of match it. The "2:1
VSWR bandwidth" doesn't tell you much about how the pattern holds up across
frequency.
I can easily illustrate this with my MonstIR. If I set it up for the bottom
end of 40, then drive it at the top end of the band, I can use the driven
element tuning (independent of the parasitic elements) to somewhat mitigate the
VSWR. But the pattern degrades considerably and I lose several dB or more of
gain.
> Like everything, there is no free lunch in engineering trade-offs.
At least in terms of performance ONLY, the SteppIR is a free lunch.
AFAIK, it beats anything else in terms of gain across the entire band, given a
boom length and number of elements. Yes, there are various non-performance
tradeoffs, but a properly working one is tough to beat. YMMV, but my MonstIR
has worked perfectly for over
10 years. BTW, the SteppIR driven element has an impedance of
22.2 ohms, and the loss in the transformer/balun is extremely low. I measured
in on a VNA before I put up the antenna.
There are alternate designs that emulate the SteppIR in a monobander by
individually tuning the elements using various modalities, such as motor tuned
or relay switched capacitors or inductors. They produce similar results if
properly implemented.
> Ed N1UR
>
Rick N6RK
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