Re: question about "lambda" (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 23 Aug 2007 18:36:49 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: question about "lambda" (fwd)

Hi Matthew,

Tesla list wrote:

>This is exactly what I needed, thank you! So with the wavelength being taken 
>into consideration, where would be good spot for the primary coil to be? I 
>am currently using a helical primary, but hope to switch to a pancake 
>primary soon.
>  
>
First, the primary should be at the opposite end of the hv end. 
Secondly, coupling will identify it's placement with a fixed geometry. 
Whatever your current helical coil is, you'll need to get the coupling 
to a usable level. If the helical is a wide as I think it is, your 
coupling may actually be very low (can you confirm the primary diameter 
again?). Often, when helical's are built, the secondary is adjusted 
above it. This occurs because the coupling was too high and coil to coil 
distance is the only thing that can fix that. But, if the helical is 
made wide enough, then it can be raised higher and higher.

>Also, is there any tips on using a oscillascope to find the frquency of the 
>secondary? I've tried it before, but the oscillascope wouldn't give a clear 
>reading. I though I heard somewhere that a signal generator could be used in 
>conjunction with a oscillascope somehow.
>  
>
Yes, use a signal generator connecting the base of the secondary to the 
generator output. You'll then be able to read the signal on the 
oscilloscope. Place the scope probe horizontal with the toroid and about 
1 coil length away with maybe a 4" piece of wire in the probe end to act 
as an antenna. Adjust the signal generator frequency until you see 
voltage amplitude rise. The point at which the amplitude is greatest is 
the fundamental frequency. It's good to calc your fundamental first, 
then adjust the generator below that frequency by some amount before you 
start adjusting the generator. It's good to do this with everything in 
position (primary and topload).

Take care,
Bart