[TowerTalk] OptiBeam OB2-40M

[Peter Voelpel]

Everything can be calculated and designed with help of EZNEC.
That's what I did for my 3-element fullsize yagi which works very well for
me.
I optimized it for best front to back within the most active section of the
band for SSB DX from Europe.
Also use a hairpin match to raise the impedance so made the driven element a
bit shorter.

Maximum gain is far outside the band which does not matter at all.

This the table for front to back and gain versus frequency the simulation
calculated and what I can confirm at least for front to back.

7.00 15.84 12.99
7.05 19.74 13.03
7.10 25.51 13.06
7.15 39.78 13.11
7.20 30.70 13.16
7.25 24.03 13.22
7.30 20.61 13.29
7.35 18.41 13.36
7.40 17.00 13.42
7.45 16.21 13.45
7.50 16.28 13.42

SWR: 1.23 at 7.00 1.07 at 7.14 1.36 at 7.30

I hope the tab format is kept.

73
Peter



-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Mike
Zak
Sent: Sonntag, 23. Mai 2021 22:31
To: towertalk at contesting.com
Subject: Re: [TowerTalk] OptiBeam OB2-40M

Is there a paper, article, YouTube video, Powerpoint deck, chapter in a
book, website, message-in-a-bottle, or anything else, that clearly and
succinctly describes the trade-offs and interactions between yagi gain,
pattern, and match?

A 15 minute session with EZNEC, and a candidate yagi design, is plenty
adequate for showing that there's some serious systems engineering involved
in coming up with the right set of trade-offs, starting with "which problem
are we trying to solve?"  But few of us are ever going to capture the ideal
design and then fabricate it.  So maybe if there was some insight around
these tradeoffs we could all do a better job with our selections of
commercially available products.

Did W4RNL ever do anything along these lines? Or W2PV?  How about the Telrex
archives?  Anyone have any suggestions for something that is readable by
mere mortals?

Mike, W1MU



From: TowerTalk <towertalk-bounces at contesting.com> on behalf of Jim Brown
<jim at audiosystemsgroup.com>
Reply-To: "jim at audiosystemsgroup.com" <jim at audiosystemsgroup.com>
Date: Sunday, May 23, 2021 at 3:11 PM
To: "towertalk at contesting.com" <towertalk at contesting.com>
Subject: Re: [TowerTalk] OptiBeam OB2-40M

YES! SWR is NOT an indicator of antenna performance.

73, Jim K9YC

On 5/23/2021 9:40 AM, Richard (Rick) Karlquist wrote:

On 5/23/2021 7:29 AM, VE6WZ_Steve wrote:
I have received a few direct email questions about this thread...
Just to be clear, the reason for inductor switching at the Yagi
elements is NOT only to get a "good, low SWR" match at the driver.

The "SWR" and "matching" at the feedpoint is really NOT the issue.

The real issue is tuning the REFLECTOR across the band.  That is what
determines the gain and F/B performance.
The PARASITIC element needs to be incremented across the band to
maintain maximum gain and F/B performance.

Yagi SWR has very little to do with performance.

Steve, ve6wz


Another great posting from Steve.  It seems like this point
has to be constantly repeated on TT to counteract marketing
hype and wishful thinking.  When I first got my MonstIR,
I did some experiments where I set the tuning for 40 CW
and then QSY'ed to 40 phone, without retuning the MonstIR.
Of course the SWR went way up.  I then used the custom
tuning feature to tweak just the driven element for SWR.
This did improve the VSWR somewhat, but the gain and F/B
were still lousy.  SWR bandwidth doesn't equal pattern
bandwidth.  And the MonstIR is a full size 3 element
design (yes, 70 foot elements), so it will tend to do
better than a shortened 2 element.

Rick N6RK
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