Richard,
So far as I can tell, your math is correct.  I aggree with others, fixing it
will most likely make no audible difference for RX.

You should be able to remove pipe from only two opposite segments of the
loop, it will be a bit "squished" that way but much less work and again
shouldn't make any operational difference.

but if you're being obsessive, go haead and cut some off all the sections,
what the heck! <GRIN>

I wonder if placing a small varriable capacitor across the feed point would
let you adjust for a better match, but again, probably no difference on RX
and you'd have to have an analyzer available to fiddle with it.

Tom Fowle WA6IVG

On Sun, Dec 13, 2015 at 06:58:55AM -0800, Richard B. McDonald wrote:
> Hi!
> 
>  
> 
> I want to report on my 10M full wave loop (FWL) project, and ask for
> feedback on it.  My aim was a resonant antenna at 28.4 MHz for RX only on my
> TS-2000.  I viewed this project as practice for the antenna I *really* want
> to make - an 80M FWL for both RX and TX (inspired by Ron).
> 
>  
> 
> To make my loop, 14 gauge insolated stranded copper wire sits inside 1" PVC
> ~12' atop my wooden shack.  It is in the shape of an octagon.  I measured
> the length of the wire at 1005 / 28.4 = 35.39', which I rounded to 35.5'.
> There is a 25' run of 75 ohm coax (the kind for TV, which I was told is fine
> for RX antenna purposes like this) properly soldered to the ends of the
> wire.
> 
>  
> 
> So, my friend from our ham club measured this antenna with his analyzer.  It
> turned out to be resonant at 25.5 MHz : (  Now, only because I am obsessed
> with my project and by way of learning, I should like feedback on the
> following:
> 
>  
> 
> 1)      I am told that one thing affecting resonance is the "velocity
> factor" of the wire.  Apparently, the insulation of both a) the wire itself
> and b) the PVC affects the velocity factor.  I have no idea what "velocity
> factor" is, nor how it affects the calculated length of a wire for a FWL as
> per the above.
> 
> 2)      To bring the resonant frequency up to 28.4 MHz, I *think* I need to
> decrease the size of what I have built.  Is that right?  "Decrease" as in
> shorten rather than "increase" as in lengthen?
> 
> 3)      To decrease the size of my loop, I plan to cut 6" (0.5') off each of
> the eight sides of the octagons for a total of 4' (including obviously the
> wire therein).  Check my math (reasoning) on this.  28.4 / 25.5 = 1.11;
> meaning I am too big by 11%.  0.11 * 35.5 = 3.9; say 4'.
> 
>  
> 
> Incidentally, even though my loop is a little off, it seems to RX better
> than my 43' vertical does on 10M.  Some have said that for RX only this
> resonance differential is insignificant.  In other words, they say that even
> if I tune my loop precisely to 28.4 MHz, on 10M it would be imperceptible as
> to 25.5 MHz for RX.  What do you think about this?
> 
>  
> 
> 73,
> 
> Richard KK6MRH