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

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

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.

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
> 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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