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:
Sent: Saturday, July 14, 2007 2:57 PM
To:
Cc:
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" <
To: "
Cc: <
(Home)" <[email protected]>; "Dave Black
(Work)"
<[email protected]>; "Dave hartzell"
<[email protected]>; "David
Smith" <[email protected]>; "Don Ferguson" <
(Home)" <
<[email protected]>; "Samsonoff@Mac. Com"
<[email protected]>
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
>
>
>
>