Re: a simple spur fix

Vince Vielhaber

Take an existing raduino and disable the si5351. Bring the i2c lines off to an external si5351 board, like the adafruit. Put the buffers on that board. Get the display and nano away from the si5351. Audio beat problem is gone. Design of a new raduino or redesign of the old is no longer necessary.

Now you can find out of the buffers will solve any of the problems. If it does, moving the si5351 to the main board (with buffers) will solve the need of another board. Add a header to the raduino board for i2c for now for an external board.


On 11/10/2018 10:37 AM, Jerry Gaffke via Groups.Io wrote:
This might be an opportunity for somebody to create yet another new Raduino
Add buffer amps to all three clocks from the si5351 to help solve the
spur problem.
Choose a processor clock that won't beat with the BFO, creating audio
tones cases
where the Nano's 16mhz ceramic resonator happens to fall on an unlucky
frequency .
Communicate with a host processor via well filtered 3v UART lines
that go off to a well shielded USB-to-UART dongle.
Processor is a little beefier, something like an STM32F*, not pressed
for memory space,
more IO pins, and with the horsepower for a few simple digital modes
such as PSK31.

This could easily be used to upgrade old v3 and v4 uBitx's.

Jerry, KE7ER

On Sat, Nov 10, 2018 at 06:41 AM, Jerry Gaffke wrote:

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.


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