John and all,
As soon as I get my presentation written I'll get started on replacing those caps as well as the parts you think are associated with the ripple. Here's my list of discrepant items so far:
1) 5 kHz radiated and conducted EMI susceptibility - EMI source is the CAN-Do switching power supply. No further action needed from me at this time. Amount of receiver filtering and shielding required is TBD pending top-level EMI review and possible modifications to CAN-Do module and enclosure. I stand ready to make any modifications or do any testing that the CAN-Do team requests.
2) Excessive ripple in the passband - I'll order parts next week and attempt to dig deeper into this.
3) 157 kHz spur - caused by Receiver switching power supply. Do you want to try to push the switching frequency higher to get it out of the passband? Or modify the circuitry to attempt to attenuate this spur? IF we end up with a two-compartment enclosure, with the digital circuitry separated from the analog, then this problem will probably go away with filtering.
4) Microphonics - I'm fairly certain that swapping those 5 ceramic chip capacitors for film will fix this one. I'll get parts on order next week.
5) Master oscillator frequency jumps - No further action needed at this time. Revise design on next rev to use analog TCXO instead of digital.
6) Lack of autonomy - No further action needed at this time. Revise both local oscillators on next rev to fixed tune receiver.
Have I missed anything?
73, Juan
-----Original Message----- From: John B. Stephensen [mailto:kd6ozh@comcast.net] Sent: Saturday, July 14, 2007 2:57 PM To: juan-rivera@sbcglobal.net Cc: eagle@amsat.org; Bill Ress; Dave Black (Home); Dave Black (Work); Dave hartzell; David Smith; Don Ferguson; Juan. Rivera (Home); Juan.Rivera (Work); Samsonoff@Mac. Com Subject: Re: Source of 70 cm Microphoncs Found
This is what we suspected earlier but couldn't prove. Those capacitors, plus
C54, need to be replaced with film capacitors similar to C23, C24, C52 and
C53.
73,
John
KD6OZH
----- Original Message -----
From: "Juan Rivera" juan-rivera@sbcglobal.net
To: "John B. Stephensen" kd6ozh@comcast.net
Cc: eagle@amsat.org; "Bill Ress" bill@hsmicrowave.com; "Dave Black
(Home)" dblack1054@yahoo.com; "Dave Black (Work)"
dblack@mail.arc.nasa.gov; "Dave hartzell" hartzell@gmail.com; "David
Smith" w6te@msn.com; "Don Ferguson" kd6ire@sbcglobal.net; "Juan. Rivera
(Home)" juan-rivera@sbcglobal.net; "Juan.Rivera (Work)"
Juan.Rivera@gd-ais.com; "Samsonoff@Mac. Com" samsonoff@mac.com
Sent: Saturday, July 14, 2007 18:18 UTC
Subject: Source of 70 cm Microphoncs Found
John,
The microphonics is caused by C19, C27 and C28 (.047uF 25V) and C50 and
C51
(.022uF 25V).
I found the best way to isolate this is to inject a CW signal into the
receiver, tune the signal in at the IF output using my TS-2000 in AM mode,
and then listen to the audio output while lightly tapping each component
one
at a time.
According to my research, barium titanate, the base ceramic material for
most ceramic SMD capacitors is inherently microphonic.
Juan