EMRFD Message Archive 9404

Message	Date	From	Subject
9404	2013-11-23 06:14:29	wa5bdu	K3NHI calibrator for AD8307 power meter
Good morning. In using the K3NHI calibrator as described in Jan/Feb QEX and updated in the file section of this group, is it a requirement that the calibrator output be DC coupled to the AD8307, bypassing the input capacitors? TU / 73- Nick, WA5BDU
9405	2013-11-23 10:41:14	John Lawson	Re: K3NHI calibrator for AD8307 power meter
No, John Sent from my iPad
9406	2013-11-23 10:47:07	ha5rxz	Re: K3NHI calibrator for AD8307 power meter
I would say include those input capacitors in case there is any DC bias
9407	2013-11-23 10:57:15	Nick Kennedy	Re: K3NHI calibrator for AD8307 power meter
OK, thanks.  I was a little confused because there is a significant DC level (50%) on the output of the calibrator.  Then I read in VE7BPO's QRP Homebuilder that you shouldn't use any attenuators at the output of the calibrator and wondered if that was related to the DC level. I did some modeling of it in LTSpice.  I didn't see that an attenuator caused any problems with or without a blocking capacitor.  But using a capacitor reduces the power to a 50 ohm load by 3 dB, as would be expected.   OTOH, the AD8307 won't necessarily match what LTSpice shows since it's not true rms reading.  So here's where I have faith and move on.  With coupling capacitors in place. 73- Nick, WA5BDU