[eagle] Re: Jim's Phase Noise Number!!

Jim Sanford wb4gcs at amsat.org
Mon Jun 11 18:20:59 PDT 2007


Juan:
I have seen, in my professional life, a similar situation where an 
inductor was radiating noise with unacceptable impact.  Replacing the 
inductor with a shielded version was more effective than any overall 
shield, tho those did work.

Good luck, and thanks again for all your hard work.

73,
Jim
wb4gcs at amsat.org


Juan Rivera wrote:

> Bdale,
>  
> Please refresh me on the function of the watchdog timer.  In the state 
> I was running, while observing the 3-second jumps, the receiver was 
> shut down but the CAN-Do module and dongle were both powered up (pins 
> 39 and 40 not connected to the receiver.)  I thought the module only 
> reset if it detected no heart beat from the dongle.
>  
> I think this evening I will fire up the receiver to recreate the noise 
> I've been seeing and then start playing with some brass sheet in front 
> of the inductor as a shield.  I tried probing all the pins with a 10x 
> scope probe connected to the SDR-IQ but I didn't see anything.  I'll 
> repeat that test with a 1x probe.  Based on last night I'm currently 
> thinking that the noise is radiated from that inductor rather than 
> conducted via the 40-pin connector.  There are receiver components 
> very close to that inductor.
>  
> 73,
>  
> Juan
> WA6HTP
>
>  
> On 6/11/07, *Bdale Garbee* <bdale at gag.com <mailto:bdale at gag.com>> wrote:
>
>     On Sun, 2007-06-10 at 20:04 -0700, Juan Rivera wrote:
>     > To my surprise the module jumps briefly to about 57 kHz at regular
>     > intervals of about 3 seconds.
>
>     Yes, that's the watchdog timer firing and causing a software reset.  I
>     have no doubt that the reset cycle causes a short-term variation
>     in the
>     current consumption profile on the board itself.  If the frequency is
>     power consumption dependent, note that it's likely to move around
>     a bit
>     during normal operation... might want at some point to look at
>     conditions with the CAN-Do! running at a "normal" 20ms update rate.
>
>     > My next plan is to probe all 40 pins by using a 10x scope
>     probe.  I'll
>     > start another log called CAN-Do Noise and start posting there as I
>     > start on this task.
>
>     As Lyle pointed out in an off-list email, the power supply on the
>     CAN-Do! widget was designed to be efficient, not necessarily to be
>     quiet.  Switchers always have noise issues... we've flown a lot of
>     them,
>     and this isn't the first time some filtering or shielding has been
>     required to keep everything happy.   You're doing the right things to
>     characterize what's going on, and we'll all help if/as needed.
>
>     We (the CAN-Do folk) are following your progress with great interest.
>     Augmenting the CAN-Do! documentation with some summary of your
>     findings
>     and mitigation approach to aid future users is something we'll look
>     forward to doing.
>
>     Bdale
>
>
>
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