n8zux
05-22-2003, 03:18 AM
Hi ;
# # #Anyone know where I can buy a open air Tuneable 270 mfd. capacitor ? I am building a Antenna tuner for HF. #I have limited time at a swap being I am doing an exam so anyone knows who still sells them PSE let me know & TNX.
That must be for a VERY low frequency! TOM K8ERV
K0CRX
05-22-2003, 05:51 PM
Also, gonna need a BIG box to put it in!!
I can't resist this one....
C = 0.2249 ( KA/d )
where:
C = capacitance in picofarads
K = 1.0006 in air dielectric constant
A = plate area in sq inches
d = distance between the plates in inches
0.2249 = metric to english conversion
Solving for A:
A = ( d * ( C/0.2249 ) ) / K
[ d = 1/8" for high voltage transmitting ]
A = ( .125 * ( 270,000,000 / 0.2249 ) ) / 1.0006
A = 150,000,000 sq inches
convert to sq ft:
A = 150,000,000 / 144
A = 1,041,667 Sq ft
convert to acres: [ one acre = 43,560 sq ft ]
A = 1,041,667 / 43,560
A = 23.91 acres [ single plate variable not practical!]
at 4 sq ft per plate [2' x 2']
Number plates = 1,041,667 / 4
Number plates = 260,417 plates
distance between plates = 1/8 inch
minimum thickness if plates for mechanical stiffness =1/16"
total plate thickness = 260,417*0.0625 = 16,276 inches
total air space = 260,416*0.125 = 32,552 inches
total cap length = 16,276 + 32,552 = 48,828 inches = 4069 ft = 0.77 miles
So as near as I can figure, disregarding end mounting hardware, and the pointer knob [hehehe] this thing would be 4 feet high [allowing room for plates to disengage] and 2 feet wide by roughly 8 blocks long [ using a standard city block of 1/10 mile ] ....
For a cap this big, I recommend a motor drive and use of a linear resistor for feedback to the remote indicator. A five horsepower 3 phase motor with a gear and chain drive should be adequate to rotate the cap. Don't forget the suppression caps for the motor... we wouldn't want any RFI problems with this bad boy...
Contact me here on the board for cost projections and contract negotiation. Contract will probably be best set up on a cost plus basis. Trucking this device from my lab to the transmitter site may take special permits so please be aware of these charges also.
BTW: I'm up for bidding on the matching coil too when you get ready for it.
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