Hi Bill,
I find the usual formula for the ratio of Rac/Rdc = d*sqrt(mu*f/rho) very
unsatisfactory for small diameters, since as d gets smaller the ratio cannot
get less than 1. The same is true for low values of frequency. Instead I use a
couple of series approximations to the Bessel functions.
So I checked your figures and found for AWG #12 at 185kHz, a ratio of 3.6 and for #8 a ratio of 5.56, quite close but slightly higher than your figures.
The point you made is of course why it is better to use properly made Litz wire
to keep the advantage of thicker wire.
73, John, G4CNN
-----Original Message-----
From: "Ashlock,William"<[email protected]>
To: [email protected]
Date: Sat Mar 16 12:32:42 PST 2002
Subject: LF: TX Loop antenna conductors
All,>
I get a bit perturbed when I see comparisons of various loop conductors
using Rdc values since the 'skin effect' within the conductors causes the
Rac to be much higher at the frequencies we use.
To prove the point, I calculated the 'skin effect' of two different loop
conductors. For #12 (2.05mm) at 185k the Rac/Rdc came out to 3 and for #8
(3.26mm) the Rac/Rdc was 5. Even though the Rdc for #8 is over 2.5 times
lower than #12 for the same length, the Rac is only about 35% lower. This
amounts to a mere 2.6db signal improvement, assuming no soil loss. With
typical soil loss factored in, the signal improvement would be less than 2.2
db.
Bill A
*********************************************************************
This footnote confirms that this e-mail message has been scanned for
the presence of known computer viruses by the MessageLabs Virus
Control Centre. However, it is still recommended that you use
local virus scanning software to monitor for the presence of viruses.
*********************************************************************
___________________________________________________
GO.com Mail
Get Your Free, Private E-mail at http://mail.go.com
| 