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Thanks Phil.

I checked three more air vars. from my stock ranging up to 400 pf and they all had a D very close to 7%. I also checked a glass piston (6 Pf) and it measured just below 7%. This isn’t making sense to me since I used the original 160 I mentioned to measure the Q of my loading coil using Tongue’s method and it was just over 150 with a calculated Rs = 15 ohms. This would not be possible if the cap ESR is 44 ohms.

I checked the bridge again using a CDE dipped mica (1000 pF) and the D was 0.3% and Y5P 3900 pF ceramics measure 0.6% which gives me some confidence that the bridge is OK. I will try a mica with a know series R added and see if it measures as expected.

I suspect there is something wrong with how I am measuring this but can’t figure what it is.

Neil