Hello all, power required is a lot less. The VSWR is excellent as it is
a mono band low VHF yagi. However sometimes things can go wrong and I
want the capacitor to survive my late night sleepy blunders!
I have a cap of the correct value with 0.02 inch spacing. I just 'looks'
too close spaced.
Regards
Conrad PA5Y
On 19/08/2017 14:26, Joe Subich, W4TV wrote:
On 8/19/2017 7:42 AM, Alek Petkovic wrote:
> I always thought, that for the loading capacitor, you just use the old
> "Power = V squared over R" formula.
That will give you average (RMS) voltage with SWR = 1:1. For peak
voltage, multiply by 1.414 (peak voltage of a sine wave): 316 * 1.414
= 447 V.
Your 1200V capacitor will do the job with adequate headroom., when
your system is all tuned and matched.
Multiply the peak voltage by the SWR for worst case peak voltage if
the voltage node occurs on the capacitor - 316 * 1.414 * 3 = 1340V.
A 1200 volt rated capacitor will be marginal in a *system* allowing
for a maximum SWR of 3:1 at 2 KW - it will be barely adequate when
the system is designed for 1500 W (1166 V).
73,
... Joe, W4TV
On 8/19/2017 7:42 AM, Alek Petkovic wrote:
I always thought, that for the loading capacitor, you just use the
old "Power = V squared over R" formula.
You know R is 50 Ohms, and you supposedly know the power, so you can
work out the voltage from there.
For example, for an output power of 2kW, V squared will be 100,000,
therefore V will be 316V.
Your 1200V capacitor will do the job with adequate headroom., when
your system is all tuned and matched.
73, Alek. VK6APK
On 19/08/2017 6:07 PM, Conrad PA5Y wrote:
Hello what is the rule of thumb for conservatively estimating the
required ratings for a load capacitor when used with a mono band
Pi-L tank circuit?
Anode voltage 2750V
Tube design RL = 2600 ohms
Q = 12
I have searched on the internet an I cannot find any really
convincing info, I have something that will stand 1200V but that is
marginal and will not survive a fault I expect.
Alternatively does anyone have a small vac variable around 40-60pF
that is around 3 inches/76mm? That will obviously do the job.
Also where can I buy a couple of Ohmite Z-50 chokes in Europe?
Anyone got one or two that they can spare?
Regards
Conrad PA5Y
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