Re: [IRCA] 9 Foot Longwave Box Loop (and other projects)

[Rick Kunath <k9ao@xxxxxxxxxxx>]

D1028Gary@xxxxxxx wrote:
> A 9-foot (diagonal) PVC-framed box loop was built for LW reception, using  
> 1.25" diameter PVC for rigid framing. About 490 feet of #18 wire was wrapped 
> in  19 turns across the PVC frame, with the frame offset from the coil for 
> maximum  performance. Using the standard tuning capacitor from eBay's  
> "crystalradiosupply," this monstrous antenna tunes from 167 kHz to 444 kHz,  
> providing serious gain on any frequency near resonance. Not being a particularly 
>  active LW DXer, I assume this tuning range is suitable for some LW DXing 
> :>)  Otherwise, I'll just add a few more turns to get the coverage down to 
> 150  kHz.

I'm wondering about the turns arrangement Gary.

I take it that this is a traditional box-loop design and not a spiral 
loop? I've never seen decent loop balance out of any spiral design I tried.

Assuming you used a solenoidal loop winding scheme, is the primary 
winding center-tapped and this connected to the split-stator tuning 
capacitor frame?

Also, what is the inter-turn spacing on the primary winding? I generally 
use about a half-inch, maybe less for longwave, but not less than 3/8 inch.

Did you spread the turns of the primary winding using non-metallic 
spreaders to reduce the inter-turn capacitance and increase the tuning 
range? Generally the turns need to be separated from each other, i.e. 
every other turn above and below the spacing spreaders, at least two 
spreaders per side, but in the case of a big loop like yours you may 
need more. This also stiffens the loop winding nicely. I can send along 
a photo showing how I accomplished this on my loops. This has the effect 
of reducing the loop winding's distributed capacitance. This distributed 
capacitance is effectively in parallel with the tuning capacitor, so by 
spreading the windings you get the loop to tune higher in frequency with 
minimum capacitance on the tuning cap. This actually gives you a wider 
range of frequencies covered by any cap, so you can add more turns if 
needed to get the lower end down and still tune up high on the other end.

Rick Kunath

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