On 1 Jan 2008 at 13:35, g0opb wrote:
> Hi all,
> I have trawlled through all the files and posts (before getting
> too bored) and can find no referance to LO clock jitter. I note some
> ccts use D type flip flops with hysteresis in an attempt to make the
> edges faster! but this makes the problem even worse as the threshold
> voltages can move around significantly.
> Why am I concerned...about to order a softrock IF kit to play with and
> I dont think 74HC/T logic is fast enough when operating with a 32.5MHz
> clock (4X my RX 8.125Mhz IF).
> There is also a need to maintain a consistant Mark/Space ratio for any
> software I/Q gain-phase correction system to work correctly.
> Am I missing something, or is this a second order effect compared to
> other system limitations, like jitter may be completly swamped by my RX
> PLL 1st LO noise performance!
> Tony G0OPB
You can get 74AC parts that are pin for pin compatible and even available
in DIP packages. You can also get 74LVC parts in SOIC that are even
faster. Both are available from Mouser and DigiKey. A 74AC74 typically
clocks to 125 MHz and a 74LVC74 can go to 150 MHz(but operates at 3.3V)
Dave - WB6DHW