I am building a general purpose LF/MF/HF/VHF/UHF "crystal calibrator" using a Progrock and a QLG1.? But I am not sure how to deal with the RF outputs from the Progrock.? I do have them AC-coupled through 0.1 microfarad capacitors.?
The Si5351a data sheet only specifies it for a 5 pF load.? I've read in other places that 50 ohm loads result in poor crosstalk between the outputs.? But this is of little concern in the current application.? I am a bit concerned about heating....the Progrock is drawing >50mA with some combinations of output frequencies and the current does seem to depend quite a bit on the load impedance (even a few inches of open-circuited coax has a noticeable effect).? I also wonder about how well the Si5351a would react to an AC short.
I'm thinking about putting in a series resistor between the Progrock/blocking capacitor and the output of my box, or an L network of resistors, to reduce the loading on the Si5351a while providing a low impedance source (50 ohms perhaps), since there seems to be more output power than I need for this specific purpose.? At some point I may add a multiplier circuit to produce microwave harmonics - that would benefit from lots of drive, so I don't want to attenuate too much and have to amplify back up again.
Any useful thoughts on this topic?
73,
Steve VE3SMA
