Jim and Bill,
Thank you for the compliments. I'm having more fun with this little SDR tool that just about anything I've played with in a long time. I just got started looking at EMI coming off of the CAN-Do module and I've already made an interesting discovery. I made a hairpin single-loop sniffing coil a while ago out of a piece of coax to sniff the internals of the receiver and I already knew that it would also work at the low noise fundamental frequencies that we're seeing from the CAN-Do module, so I pressed it back into service.
Holding the sniffer near the CAN-Do's inductor I see this:
As we already know, I can set the fundamental frequency by varying the input voltage, so I set it to 50 kHz by adjusting the input to 13.69 volts. I then captured this display. To my surprise the module jumps briefly to about 57 kHz at regular intervals of about 3 seconds. I think this has to do with it resetting because it's not happy. I've forgotten the details. 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.
73,
Juan
WA6HTP
-----Original Message----- From: eagle-bounces@amsat.org [mailto:eagle-bounces@amsat.org] On Behalf Of Jim Sanford Sent: Sunday, June 10, 2007 7:46 PM To: Bill Ress Cc: eagle@amsat.org Subject: [eagle] Re: Jim's Phase Noise Number!!
Bill:
-110 dbc/hz at 10khz offset is what I REMEMBER in my response to the
question, "What is a good phase noise number to shoot for in a microwave
narrowband (ssb/cw) system?"
My memory may very well be WRONG, which was the point of asking my question.
I agree with you, looks like -90dbC at 10 KHz, but given what Juan's
already said about his sources, and the uncertainties of the SDR-IQ,
that may be VERY good!
Do you have a different answer to my original question, "What is a good
phase noise number to shoot for in a microwave narrowband (ssb/cw)
system?" If so, I'd like to engage in that conversation, both for
Eagle and for my terrestrial microwave station.
I agree with your assessment of Juan's work -- ABSOLUTELY EXEMPLARY!!!!!!
Thanks & 73,
Jim
wb4gcs@amsat.org
Bill Ress wrote:
Jim,
Where did the -110 dBC/Hz at 10 KHz come from? And at what frequency?
That's pretty aggressive using straight forward VCO's and PLLs. From
Juan's data with his snappy SDRIQ, it looks like that the 70 cm is
doing about -90 dBc/Hz at10 KHz. I thought that's what I read from his
early HP8566B dtata.
My straight forward S2 RX downconverter PLL LO does -100 dBc/Hz at 10
KHz.
We'd better get a good read on this since, if real, it forces more
sophisticated LO designs.
Great work Juan!!
Regards...Bill - N6GHz
Jim Sanford wrote:
I think I remember Bob's answer as -110dbc at 10 KHz offset.
Thanks & 73,
Jim
wb4gcs@amsat.org
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