[TowerTalk] Loading Coils

[n0tt1 at juno.com]

RE: the high price of coils...Imagine what "they" are charging the
government
for those coils!  Our tax dollars at work.  It's like the $600 toilet
seat made
for aircraft....heh..heh, remember that fiasco?

Charlie, N0TT

On Mon, 4 Aug 2025 15:07:28 +0000 Bill Eisinger <Bill at theeisingers.com>
writes:
> I was one of the first purchasers of Gaylord's (N4SF) coils...they 
> are very well made and really the only option out there these days 
> if you need large inductors. He also sells some nice clips for 
> finding the tap point you need that can be tightened with a screw to 
> make a semi-permanent connection.
> 
> In my search for coils, I contacted B&W...they are still in business 
> but sell almost 100% to government purchasers but will do custom 
> orders with a minimum run of 10 units...that sounded OK...I figured 
> I could buy 10 and recoup my money by selling the extras... until 
> they quoted me a price of $33,000!
> 
> Bill, AA7X
> 
> 
> ________________________________
> From: TowerTalk <towertalk-bounces at contesting.com> on behalf of 
> Brian Beezley <k6sti at att.net>
> Sent: Monday, August 4, 2025 8:44 AM
> To: towertalk at contesting.com <towertalk at contesting.com>
> Subject: [TowerTalk] Loading Coils
> 
> "FWIW, your number for Q (673) agrees exactly with the number I get
> using Medhurst's 1947 formula."
> 
> 
> Interesting, Rick. I'm surprised you got the same result. I've 
> tried
> several methods of calculating coil Q. Skin depth is 
> straightforward.
> The proximity effect is another matter. I wound up using an 
> integral
> equation developed by G3RBJ. I modified an approximation it uses 
> for
> slightly better accuracy. The method yields the most accurate 
> results
> for the set of test coils I measured with my HP 4342A Q meter.
> 
> Q is not easy to accurately measure for big coils like those sold 
> by
> QCoil. The fields may extend quite a distance and interact with 
> nearby
> objects, such as the instrument enclosure or even your body. The 
> Qcoil
> photo shows the coil quite close to the HP 4275A. I wrote a utility 
> to
> let you remote a coil with a transmission line to minimize 
> interaction.
> The program recovers coil inductance and Q from what a Q meter 
> indicates
> for a remoted coil. The program is part of my Q meter utilities 
> listed
> near the center of this page:
> 
> https://k6sti.neocities.org/mu
> 
> I verified that the tiny zeros in the HP instrument do mean that 
> the
> digit is not necessarily accurate. So 6oo means Q is closer to 600 
> than
> to 500 or 700.
> 
> It turns out that QCoils is just a few miles away from me. I'm going 
> to
> contact the owner to see if he will loan me some coils that I can
> measure with my HP 4342A.
> 
> Brian
> 
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