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Re: [IRCA] 9 Foot Longwave Box Loop (and other projects)
Theoretically, there is the possibility of trading additional ( switchable ) capacitance for the additional wire length. In traditional air-core MW loop designs this is the method used to tune the lower end of the AM band. I don't recall the math involved, and since it's essentially a range extender, it's easy enough to experiment. I've been planning on attempting that with one of my loops to see how far down I can get into the beacon segment of the band.
Russ Edmunds
Blue Bell, PA ( 360' ASL )
[15 mi NNW of Philadelphia]
40:08:45N; 75:16:04W, Grid FN20id
<wb2bjh@xxxxxxxxx>
FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'
AM: Modified Sony ICF 2010 barefoot
--- On Mon, 5/4/09, D1028Gary@xxxxxxx <D1028Gary@xxxxxxx> wrote:
> From: D1028Gary@xxxxxxx <D1028Gary@xxxxxxx>
> Subject: Re: [IRCA] 9 Foot Longwave Box Loop (and other projects)
> To: irca@xxxxxxxxxxxxxxxx
> Date: Monday, May 4, 2009, 11:50 PM
> Hello Again Rick,
>
> After adding three more turns of #18 wire to the 9' LW
> box loop, I now have
> 567 feet of wire in 22 coil turns, and a tuning range from
> 142 to 350 kHz.
> This should be OK for DX testing, so I'll probably
> wrap it up this way.
> It's amazing how much wire you need to add to get the
> tuning range a little
> lower, on LW.
>
> The coil turn spacing on the loop is actually wider than
> .25 inches,
> because although that was the width of the wooden spacers
> used with the circular
> saw to cut the wire slots, I forgot to account for the kerf
> width of the
> circular saw blade. The actual coil turn spacing is about
> .4 inches.
>
> The variable cap used in this project (and all the PVC
> loops) was a
> compact, 8:1 vernier drive single-section unit from the
> eBay seller
> "crystalradiosupply." This split-stator cap fits
> neatly inside of a section of 1.5"
> diameter PVC pipe, for waterproofing the loop tuning
> system.
>
> This LW box loop project was essentially an afterthought,
> after the
> construction of ten MW PVC-frame box loops of various
> sizes. The mail goal of the
> project was to design and test lightweight, structurally
> strong PVC frames
> for extremely large loop sizes-- a goal which was entirely
> successful.
> Refinements to some of the larger loops can probably be
> made for optimum
> performance, and I'm happy that Steve R. has expressed
> interest in making one of
> these LW box loops according to my design, for testing
> against his 1600'
> long wire. Living on a residential lot of .33 acre, I
> don't quite have the
> experimental freedom that he has, in deploying sizable LW
> antennas.
>
> 73, Gary
>
>
>
>
> In a message dated 5/4/2009 12:08:52 P.M. Pacific Daylight
> Time,
> k9ao@xxxxxxxxxxx writes:
>
> D1028Gary@xxxxxxx wrote:
> > The design was a basic one-loop coil system in a
> traditional box loop
> > (non-spiral) design, wound on a PVC support frame,
> tuned by a 4-400 pf
> capacitor
> > connected directly at the coil ends.
>
> Is that a split-stator of a single-section cap?
>
> > The coil windings are spaced by slots
> > cut in short sections of PVC pipe, which are offset
> from the main PVC
> > frame by 90 degree PVC "elbow" fittings.
> The spacing slots are
> separated by
> > .25", and are all symmetrically cut into the PVC
> by a circular saw with
> > multiple wooden spacers of identical .25" width.
> The 19 coil windings
> (of #18
> > wire) are then pulled tightly to ensure optimal loop
> symmetry, in a
> system
> > which apparently provides excellent nulling
> capability. The 490 feet
> loop coil
> > of #18 stranded wire tunes from 167 kHz to 444 kHz
> in the current
> setup,
> > but I plan to add a few more turns to drop the
> coverage down to 150
> kHz.
> > Photos of the loop and support structure are
> available upon request.
>
> I'd love to see anything you might have, but can wait
> for your article
> too.I know you must be busy.
>
> The split-stator cap and center-tapped loop primary
> winding improves
> loop symmetry and balance.
>
> As to the spreading of the windings, the spreaders that
> splay every
> other turn up and down in two (maybe more) sections help a
> lot in
> increasing the range of tuning. Let me know if photos of
> that might help
> exp[lain what it looks like. I used wide tongue depressors,
> but small
> round PVC pipe sections would probably work better in that
> big loop.
>
> Rick Kunath
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