[Antennas] 2m Cubex Quad

[Sam Morgan]

John Luthy wrote:
> I have a 4 ele. cubex Quad that I would like to retune.  It is
> currently resonate around 146.0 mhz and I would like to move it to
> 144.5 mhz.  I know it's not that far from where I want it now but the
> swr really starts to climb when I use it below 144.3 mhz.
> 
> I have several verticals for 2m fm work and use the quad for 2m ssb
> only, and my icom 746 is really agresive about cutting back power when
> it sees a less than perfect match.
> 
> So my question is. What are my options for retuning the antenna?  I am
> open to all possibilities from adding wire to it, a tuning stub, a
> variable cap, or I suppose I could just use a transmatch at the
> transciver.
> 
> Thanks for your consideration
> John
> N7JL
> 
this is going to be strictly guess work on my part, been way to many years since 
I played with the quads and their formulas. But hopefully this plus others 
comments will point you in the correct direction.

1st the loop calculations are 1005/freq.=length around total loop
also 251/freq.=length of a side (from the only handbook I have left)

so:
251/146= 1.72' per side = 20.6" per side
251/144.5= 1.74' per side = 20.84" per side

so what I'm saying is the sides of the driven element would need to be 
lengthened by about .24 x 16 = 3.84 sixteenths of an inch on a side.

you would/may need to tweak the gamma or what ever is used for impedance matching.

this may cause problems with the reflector as you may be approaching it's length 
with the driven element, so it might need lengthening also.

another possibility is the spacing of the elements and/or the length of them.
I seem to remember as you approach the resonance freq of the reflector the swr 
jumps up. So... possibility is you could just tweak the reflector length by 
making the sides ...say 1/4 of an inch longer and see what happened. I'd say try 
this first as it doesn't mess with the driven element and the matching network. 
Although some tweaking there might be needed if you do find the larger reflector

Ok now lets hear the real antenna experts on the list expand on this , or blow 
it completely out of the water. ;-/ GL with playing with the antenna.

P.S. best I could find was this:
http://www.cubex.com/spec.htm#2%20METER

YELLOW JACKET

     * 4 Elements
     * Center Freq. 145.5 MHz
     * Weight = 2.5 lbs
     * Turn Radius = 26"
     * Gain dbi = 9+
     * FBR = >25db
     * Beam Width (hpp) = 60d
     * Wind Load (sq. ft.) = 0.4
     * Boom Length = 48"
     * Boom Dia = 1"
     * Fiberglass Spreader arms
-- 
GB & 73's
KA5OAI
Sam Morgan