[TowerTalk] Re: Yagi's (wrapup)

[Joe Reisert]

Art,

Some on this reflector read my comments on your 13 element Yagi and asked 
me how broad-band it was. I did some quick modelling but the results are 
tons of data and difficult to quickly sum up. However, despite this, I'll 
try my best to summarize.

Your 13 element Yagi has roughly the following gains, front to back and VSWR:

Freq. (MHz)  gain (dBi)      F/B (dB)    VSWR (based on 50 Ohms)  Comments

28.0             14.32            25.7           2.19:1
28.25           14.56            45              2.1:1 
            Looks good here
28.5             14.68            46              2.15 
             The design frequency.
28.75           14.74            39              2.65
29.0             14.73            33              6.1:1 
             Starting to crash
29.25            14.56           25.5           35.9:1 
           Impedance only a few Ohms!

So, it looks pretty good from 28.25 to 28.75 MHz.

My quick and dirty 28 MHz 6 element Yagi on same boom length is as follows:

28.0             15.34           20.35            1.43:1
28.25            15.59          24.60             1.31
28.5              15.86          28                  1.15
28.75            16.09          22                  1.06
29                 16.18         16.4                1.32
29.25             15.96         12.6                2.2 
          Starting to crash

I think I'll stick with my simpler design and direct 50 Ohm feed with less 
than half the aluminum!

73,

Joe, W1JR


At 10:51 AM 2/9/01 -0600, art unwin wrote:
>A big thanks to Joe for his input and time
>There are many "big boys " who have contributed
>to the envelope on yagi's and I also put Tom Rauch
>right up there with the experts. All of this is
>not about winning or loosing, it is about sharing
>and debating antennas and pushing the envelope of
>known boundaries.
>
>As a closing comment, there is the question about
>     'all that extra aluminum in the air'
>which is a fair observation to weigh against reaping
>any possible advantages.
>  When seeing pictures in magazines of
>multi towers, miles of wire, antenna farms I am
>not fully convinced that many hams would  compromise
>one iota in the fight for the title of 'top dog'.
>
>Unfortunately for me there is a limit as to how
>much aluminum I can put up into the air as with many who
>have limited sized lots...... So, as with the
>association of selsyns and prop pitch rotators.
>I also challenged the association of aluminum elements
>and yagi design which was made before I was born.
>
>I REJECTED that association sometime back and I do not use
>aluminum elements anymore.    Which means no more clamps
>and questions of continuity or loss of element tips in
>high winds or of loading under ice ,fatigue e.t.c.
>plus increasing demands upon rotators and boom to mast
>considerations.
>
>     In defense of the 'low' specs comment, made else where,
>at the edges of the band chosen. MY antenna was
>designed for 28.3 Mhz and above(Audio). But I could not
>in good conscience suggest comparison to the ARRL's 17th
>edition aproach to improving the High Gain Yagi,
>because that study covered a range  starting at 28.100
>All antennas are a question of compromise
>  For me to NOT supply those figures,
>even tho they are  not complementary, would be patently
>dishonest and could be taken as an attempt to deceive.
>
>
>Art Unwin KB9MZ........XG
>
>
>--
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