[Lowfer] loading coil considerations for UWL at 185 kHz

[jrusgrove at comcast.net]

Eric

A reasonable estimate for the vertical wire is 6 pf/m ... but it gets tricky estimating the 
additional C of the top hat and environmental factors. This is where an impedance bridge comes in 
handy. An accurate measure of antenna C will yield an accurate calculation for loading coil 
inductance. One can guess at the antenna C but consider that a 20 pF error changes the loading coil 
inductance by a few mH. Winding a coil with this much inductance is not a trivial matter so it's 
nice to get in the ballpark on the first shot.

Before building the improved coil I'd recommend doing a quick and dirty 'cobble job' to the existing 
loading coil to bring the antenna to resonance. Add in the old moveable variometer coil you have 
laying around and add or remove turns as necessary on the main coil. This will also be a good 
opportunity to see if the adjustment range of the moveable coil is appropriate. When happy with the 
performance measure the inductance ... and make the new improved coil the same inductance.

Since you're currently seeing 1/2 watt transmitter power it would seem you're already close to 
resonance.

Jay W1VD  WD2XNS  WE2XGR/2

----- Original Message ----- 
From: "Eric Smith" <esmithmail at gmail.com>
To: "Discussion of the Lowfer (US, European, &amp,UK) and MedFer bands" <lowfer at mailman.qth.net>
Sent: Wednesday, February 16, 2011 10:11 PM
Subject: [Lowfer] loading coil considerations for UWL at 185 kHz


> HI all,
>
> I decided rather than try to modify the loading coil I have for 185 kHz I
> will build a new one.  The old one is on a PVC form, uses small gauge
> telephone frame wire, and has been modified several times already over its
> eight years.
>
> Antenna details:  8m tall #14 stranded Cu building wire, 2m diameter
> capacitance hat comprised of five #4 solid Cu radials and a #14 (estimated)
> copperweld halo.
>
>
>   - The original coil was sized (in terms of L) based on a model produced
>   from method of moments type software I found on Lyle's site called NF (a
>   stripped-down version of AO, his article says).  This coil currently, from
>   end to end, measures 7.3 mH.  However, I suspect this may be larger than it
>   needs to be.  I could use any help estimating a target for the new coil --
>   when winding a 7.3 mH coil it is tough to use a respectable size wire and
>   still have a favorable length to width ratio.  If this is the size I need
>   then fine, but I wonder..
>   - Suggestions on Litz spec and, if possible, a recommended supplier or
>   two?
>   - I'm planning to do this in the basket weave style.  I have not chosen a
>   material for form and rods yet -- suggestions?
>
>
> Thanks to all in advance,
> Eric  KD5UWL / WD2XFX
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