Rich Measures wrote:
>G3SEK wrote:
>>Pulling some example figures out of the air, consider a suppressor that
>>consists of 100 ohm resistor paralleled by 100nH. In series with that is
>>say 200nH of connecting lead inductance between the tube and the pi-
>>tank. At 100MHz, this network transforms into 1058 ohms in parallel with
>>279nH.
>>
>Out of the air, indeed. . How about going through the calculations, Mr
>White?
>
Out of the air, like hell!
You are in the business of selling and advising your customers on RF
networks, Rich. Why should I have to spoon-feed you with basic network
theory that you should already have digested?
But here we go again...
0. This is a demonstration of an impedance transformation effect, so
we're going to assume ideal component behavior.
1. 100nH at 100MHz is +j63.83; 200nH at 100MHz is +j125.66
2. Now transform 100 ohms paralleled by +j63.82 transforms into its
series-equivalent. The equations (as posted last weekend) are:
Rs = Rp*Xp^2 / (Rp^2 + Xp^2) Xs = Rp^2*Xp / (Rp^2 + Xp^2)
Answer: 28.30 in series with +j48.05
3. Add the +j125.66 in series, to get 28.30 +j170.71 (still series-
connected)
4. This is now NEW NETWORK that includes the external 200nH. Transform
this new network back into its parallel-equivalent:
Rp = (Rs^2 + Xs^2)/Rs Xp = (Rs^2 + Xs^2)/Xs
Answer: 1.058K in parallel with +j175.40
5. At 100MHz this is 1.058K in parallel with 279.17nH - voila!
This impedance transformation is no less true than the impedance
transformation that happens in your pi-network. That can be handled
using exactly the same tools.
Real-life networks are more complicated but those same tools will still
handle them, if you include all the stray reactances and losses. It only
gets more complicated, not any different.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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