[time-nuts] SDR Radio Opinion ?

[Magnus Danielson]

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