[Amps] WLW 500 kW transmitter

[Will Matney]

Jeff,

If you get the chance, take the tour as I did. You'll be impressed when you see the modulation transformer, it's a monster. I know the very coils your talking about that have the shields in between. The coils look to be out of tubing of some sort. The shielding kind of reminds you of the way shopping carts are made, hi hi! You'll need to reference some transformer books on this that shows using pancake coils. I remember seeing something online at a university about them, but can't remember where. A google search may find them using pancake coils, etc. I think I have some info here in a transformer book, and will try to locate the one it's in. To my opinion, those shields will have to be taken into account on the formulas also. Oh by the way, believe it or not, most of the book work is missing on this transmitter! Where it went, I don't think nobody knows.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 5/16/06 at 6:20 PM Xmitters at aol.com wrote:

>Hello:
>
>I'm doing a mathematical analysis on the RF PA of the WLW 500 kW
>transmitter, 
>which consists of three 167 kW RF amplifiers into a combiner. The RF 
>amplifiers are RF transformer coupled; the primary and secondary are
>pancake coils, 
>the primary being of about 4 turns and the secondary of about 2 turns,
>both 
>about 80 inches in diameter.
>
>I'm wondering if someone here might direct me to a text book that would
>allow 
>me to calculate the likely coupling coefficient and mutual inductance. I
>have 
>checked many of the famous references (Henny, Terman, ITT Ref Data, etc.)
>and 
>have not found anything for two coupled pancake coils.
>
>I do not have exact dimensions for the primary and secondary RF coils;
>only 
>approximations based on photographs. The coils look like they are
>separated by 
>about 4 to 5 inches with a faraday screen between them. I hope to get to
>the 
>site this Summer to make some physical measurements.
>
>Based on my approximate dimensions from the pictures, I've done some 
>preliminary calculations and it looks like a mutual inductance of 4 uH and
>a k of . 
>143 would make it all work. That coefficient of coupling of .143 seems
>high to 
>me, how about you? It would be difficult if not impossible to get unity 
>coupling with an air core transformer, but I'm not sure if even the .143
>coupling is 
>a practical value. Coupling coefficients found in some of my old textbooks
>for 
>low power stuff like receivers, etc. usually run .001, .005 which makes me 
>think my number is too high. The k value depends on a lot of things, so I
>just 
>don't know. Do you think that a k of .143 would even be realizable?
>
>Thanks,
>
>Jeff Glass
>Northern Illinois University
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