Re: a simple spur fix

Jerry Gaffke
 

Unless we add an amp to each of the three clocks between the si5351 and the mixers,
we are trading off si5351 crosstalk, local oscillator injection level, and reflections due to 
driving the mixer from a source impedance higher than 50 ohms.
All three of these factors will contribute to spurs.
One might replace the 100 ohm and 75 ohm resistors of my previous email
with small pots, then try various settings to find the best compromise.
 

On Fri, Nov 9, 2018 at 08:37 PM, Jerry Gaffke wrote:
I suggest each si5351 clock pin drive a series DC blocking cap and a series 100 ohm resistor
into the mixer port.  Assuming the si5351 has not hit its 8ma current limit, the mixer will
see a source impedance of 50 ohms (internal to the si5351) plus that 100 ohm resistor, so 150 ohms.
Add a 75 ohm resistor from mixer port to ground, that in parallel with 150 ohms makes
it a 50 ohm source impedance for the mixer.

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