On 08/06/2013 02:08 AM, John Ackermann wrote: > The DTV dongles are very cute and really great educational devices, > but one thing to keep in mind is that they have 8 bit A/D converters > and consequently pretty limited dynamic range. And the frequency > accuracy/stability is pretty horrific for anyone on this list. :-)
Hacking a lock-up PLL to lock the 28,8 MHz crystal to say 10 MHz isn't too hard. Dividing the 10 MHz by 25 and the 28,8 MHz by 72 gives a 400 kHz comparator frequency, so it's not too hard to do. The crystal is in a traditional inverter feedback setup with two caps, so lifting a cap and inserting a varicap between it and ground is easy enough. The software have a switch that enables it to operate the RTL-chip not on the default 0 Hz IF but shifted, use that to avoid the 1/f noise near 0 Hz. I have hacked a bias tee and filter which provides +5V on the antenna connector for a LNA. Nice to have SMD inductors and caps lying around. Cheers, Magnus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
