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.


Nick, WA5BDU