DDS spectral "purity" ?


Steve and other have discussed the spectral purity, or lack thereof, from our inexpensive DDS modules and accessories. Playing around a bit today with a spectrum analyzer, I made a "home movie" of a sweep from one my my very early builds of a Type-2 PHSNA

PHSNA Type-2 (push-pull transformer output)
Type-2 AD-9850 module with on board filter removed
Standard 30 Mz version LPF on the PHSNA
The ERA-3+ running with a bit too much bias, at ~ 40 mA
Using the WinPHSNA app with 9600 baud Bluetooth communications
Sweep from 1 MHz to 40 MHz, with 100 kHz steps
Rigol DSA-815TG analyzer

SA vertical divisions 10 dB (top = +10 dBm)

SA horizontal divisions 10 MHz (0 to 100 MHz scan)

It's too big (12 MB) for Yahoo to allow into the Files or Photos areas, so here's the URL for it on my web page

The cinematography will not earn me any Red Carpet time, but it's interesting to watch the wheat field march across the screen. Gives a good feel for the limitations of inexpensive test gear. Make popcorn, call the kids. It's rated "G" and is just over minute long.

Jim, N5IB

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