Diode ring mixers are messy.
The port driven by the local oscillator will have unwanted mixer products coming out of it.
Using a 6dB attenuator, most of that junk coming back out will get absorbed by the 50 ohms it sees.
If the unwanted products are not absorbed, they can be reflected back into the mixer to create yet more products
that can come out of one of the other ports.? Causes birdies in a receiver, spurs in the transmitted signal.
That attenuator would work pretty well here if the si5351 were capable of driving with 13dBm of power.
It would lose 6 dB going through the attenuator and the mixer would get 7dBm of power like it should.
In this case, since the si5351 can't give 13dBm, we should either add a fairly powerful buffer amp
between the si5351 and the 6dB pad and/or we should somehow do away with the 6dB pad.
Jerry
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On Tue, Sep 11, 2018 at 08:50 PM, Gary Anderson wrote:
What's the reason to? set-up the Si5351 to maximum drive @ "8 mA" ,3.3 V (Output Driver close to 50 Ohms at 1.65V per IBIS models ) just to send through a? series resistor, then to a? 50 ohm 6 dB pad?
I was confused, and even more so now? from Kee's post on V4 schematic with increasing series resistance before the 6bB pad ,rather? than decreasing Si5351 drive and winding transformers to match impendance.?
Flame Suit On.? Just wishing? to re-cap the well head so all may benefit from the refined uBITX .
Regards,
Gary AG5TX
