[Amps] ceramic caps, and 1kW power sampler/atten

[John T. M. Lyles]

I agree about the lousy tempco of high value ceramics. I have 22 x 
2000 pf Draloric 5 kV ceramic pancake style caps on a 1 MHz cavity I 
am designing right now. The caps have N2200 coefficient, but we are 
sweating over it. I think I am about to double the ferrite (it has a 
tempco of +1 mu unit per deg C approx) and half the caps. Also, using 
only 300 Watts to drive it from a solid state amp. I have some very 
nice old 200 pF caps, with N750. Get down to 100 pF or less, and the 
ceramic isn't so temperature sensitive. NEVER USE higher value 
CERAMIC DOORKNOBS IN A TUNED CIRCUIT FOR TUNING, unless you either 
compensate for them, really derate them, and pray for good conditions.

For the 1 kW sampler, Bird already makes power attenuators that are 
part dummy load (1 to 2.5 kW air cooled I think) and part attenuator. 
We use them just for that, spectrum analysis of RF amps driving 50 
Ohms, and also using a network analyzer to do power sweeps of RF PAs. 
If you can buy one, get it. Works well.

John
K5PRO
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