[eagle] Re: Jim's Phase Noise Number!!
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:
> 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.
> 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
> 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
> and mitigation approach to aid future users is something we'll look
> forward to doing.
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