[eagle] Re: Source of 70 cm Microphonics Found

Juan Rivera juan-rivera at sbcglobal.net
Sat Jul 14 16:44:00 PDT 2007

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 at comcast.net] 
Sent: Saturday, July 14, 2007 2:57 PM
To: juan-rivera at sbcglobal.net
Cc: eagle at amsat.org; Bill Ress; Dave Black (Home); Dave Black (Work); Dave
hartzell; David Smith; Don Ferguson; Juan. Rivera (Home); Juan.Rivera
(Work); Samsonoff at 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 








----- Original Message ----- 

From: "Juan Rivera" <juan-rivera at sbcglobal.net>

To: "John B. Stephensen" <kd6ozh at comcast.net>

Cc: <eagle at amsat.org>; "Bill Ress" <bill at hsmicrowave.com>; "Dave Black 

(Home)" <dblack1054 at yahoo.com>; "Dave Black (Work)" 

<dblack at mail.arc.nasa.gov>; "Dave hartzell" <hartzell at gmail.com>; "David 

Smith" <w6te at msn.com>; "Don Ferguson" <kd6ire at sbcglobal.net>; "Juan. Rivera 

(Home)" <juan-rivera at sbcglobal.net>; "Juan.Rivera (Work)" 

<Juan.Rivera at gd-ais.com>; "Samsonoff at Mac. Com" <samsonoff at 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






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