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Re: Si5351 output power

 

I think I would have gone for the power in the sine wave that's under those harmonics and divided the 0.8 Vpk by sqrt(2) to get the power of the fundamental.

FWIW and regarding appropriate loading of the Si5351, in this case regarding cross-talk, here's a tidbit I saved from the list a year ago:

September 6, 2018

Here¡¯s a bit of info from Allison KB1GMX on cross-talk between the outputs of the Si5351a¡¯s channels which could be an issue if you use one for BFO and one for LO or similar. A possible cure is to drive higher than 50 ? impedances with the outputs:

I also did the measurement with higher than 50 ohm load and got?

remarkably better result.

Hint:? drive the load using a 74LVT04 or one of the friends of that part

or any cmos buffer.??The output is loaded with CMOS gate and the?

CMOS inverter can be loaded heavier.

And AB7VF said: Read somewhere a test that suggested better results with 80 ohms rather than the spec-ed 50. Jim

73, Nick - WA5BDU


On Tue, Dec 17, 2019 at 11:23 AM Michael Maiorana <zfreak@...> wrote:
I'm just looking for a sanity check (please).

Square wave output from an Si5351 is 3.2V p-p unloaded. Into a 50 ohm resistive load it drops to 1.6V p-p. Average voltage of a square wave is 1/2 p-p value, so Vavg is 0.8V. Power into the resistor (assuming a pure square wave) is (0.8V)^2/50 or 12.8mw. Converting to dBm 10*(Log(12.8/1)) = 11dBm.

11dBm is more than enough to meet the 7dBm drive requirements of a diode ring mixer. However, I'm reading conflicting info on the Si5351's ability to directly drive a diode ring mixer.

Any advice or guidance will be greatly appreciated.

These little Si5351 demo boards from Ebay are amazing for the measly $3.50 that they cost. They have onboard linear LDO regulator and logic level converters so you can drive them direct from an Arduino running at 5V. 4 wires connected to an Uno and some sample code and I was making clocks in less than 10 minutes. What an age we live in!

Mike M.
KU4QO
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