I also wonder if a 1/1 balun would help. I think it'll isolate the coax from the loop.

----- Original Message -----
From: Tom Fowle  <[log in to unmask]>
To: [log in to unmask]
Date: Sunday, December 13, 2015 6:50 pm
Subject: Re: Report on 10M Loop Project, and Request for Feedback

>
>
> 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