15-03-2017, 09:57 AM
(15-03-2017, 02:16 AM)Nowhere-Man Wrote: Here is a discovery I made tonight I decided to share. It came from something in ARRL where reactance in resonant circuits compared to loads on the circuit is discussed. It states if power dissipated across the load on the resonant circuit (such as a transmitter) is about 10 times as great as the power lost in the inductor and capacitor, then power lost in reactance will be greater overall. So I did the following:
VAC in = 230
XL and XC at resonance = 250 R
Load on circuit (transmitter) = 3000 R
So, 230/250 reactance = current 0.92 amp. To get voltamps I get 211 dissipated power.
Then the load of 3000 watts (real power) I get current = 0.07 amp and watts = 17.6
So the power in the resonant circuit is now BIG.
Here is what gave me a kick: Divide the load wattage into the Voltamp power which is 211/17 and lo and behold 12. And ARRL in their sums gives 12 as the circuit Q.
I think my maths here is correct but, if not, apologies in advance.
Although pointless I admit, I like doing this kind of numbers game.
Don't forget that reactance doesn't dissipate power.
Also don't forget that in a parallel resonant circuit connected to an AC voltage source the voltage across the inductor and the capacitor will be the same as the source voltage, however that's not the case with a series resonant circuit, in that situation it's sometimes easy to forget that although the reactance's cancel out the individual reactance's are real and the voltages developed across them are only limited by the current flowing through R, in some situations those voltages can be very nasty.
Lawrence.
