Topband: Vertical for 160/80?

[PaulKB8N at aol.com]

Jerry,
 
The Cushcraft MA-160V vertical happens to be 35' tall.  I believe  there is 
a capacitance hat at 23' with an inductor of unknown value just  under the 
hat.  The hat spokes are 48" and there are 8 of  them.  Above that is a 
"stinger", an adjustable element that can be  lengthened or shortened to bring 
the system to resonance.  The OD of your  element is larger than that of the 
MA-160V, suggesting that the size of the coil  needed may be marginally 
smaller to bring the system to resonance.
 
There is a user manual available online that details the construction of  
the antenna.  It is really very simple, 23.5 feet of aluminum, inductor,  
hat, and adjustable aluminum "stinger" in that order.  Read the eHam  reviews, 
they are overwhelmingly positive, especially for an antenna  of this size. 
 
You might check with some of the eHam reviewers about replicating the  
design, the value of the inductor being the only unknown.  I believe  Cushcraft 
even has the inductor listed as an individual part number.   Perhaps they 
would sell you one separately.  If there is anything more  to this design that 
I might have missed, I can't determine it from the  manual.  Users?
 
Perhaps more intriguing is that you might be able to tap the inductor for  
80M and short out the unneeded inductance via a control cable inside the  
aluminum tubing.  This design probably isn't optimized for that band, but  it 
may still outperform at least some of the alternatives.
 
I'm somewhat familiar with the design because I have a tree branch at 35'  
that would support a wire version of this design and is inside a cluster of  
trees that would hide the entire antenna, a must in my covenant-restricted  
neighborhood.
 
YMMV, but it is a proven design that should be easy to replicate.  I  don't 
encourage pirating of commercial designs, but emulating this for  
comparison against other designs is well within the spirit of ham radio antenna  
design IMHO.  Good luck!
 
73,  Paul, K5AF
 
 
In a message dated 10/25/2011 12:14:52 A.M. Central Daylight Time,  
k3bz at verizon.net writes:

I have  an aluminum tubing vertical that I no longer need to use on 40M. 
Bottom 18’ is  3” OD; rest is 1” OD, length is adjustable to max 35’. I’m 
looking for details  of a good way to use this  as part of a vertical for 160M 
(and/or 80M)  that might be better than an inverted el.  Ideas?

73,    Jerry K3BZ
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UR RST IS ...  ... ..9 QSB QSB - hw? BK