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My first version of the Bitx20 is completed and works very well (I just made the receiver part), it was made using through hole components on individual pcbs that plugged together.

My next version is going to be surface mount (as much as possible) and use a Si5351 for the vfo and bfo.

I have now finished the coding part of this project but am wondering if I need to amplify the outputs of the Si5351 before they are fed in to the mixers?

For example, should I feed the vfo input to the first mixer through the last transistor amplifier (the one with the two 1k resistor divider at the base (Q7))?? For the bfo should this go through the transistor with a 1k in to the base and a 1k on the emitter Q9? (references are for the Ashhar Farhan, 2004 version of schematic)

Or is there a different way to do this?

Thanks for your help.

There have been several recent postings on this question. The output of the 5351 can be set at different levels. Do a search of recent conversations on this reflector.

73,

Todd K7TFC

Hi Todd,

Thanks for the reply, I have been reading the various posts on this this evening and have see lots of people discussing the code (I have written my own code for this) and seen lots of discussion about the level of the output signals. Currently mine is set to output 8mA, but I can change it if needed.

I have not really been able to find much about where the best place is to put the signal in except for one person who seemed say they put it directly in to the mixer coils via a 0.1uF capacitor.

I will keep looking just in case I managed to miss the posts where the signal injection is discussed.

<< I have not really been able to find much about where the best place is to put the signal in except for one person who seemed say they put it directly in to the mixer coils via a 0.1uF capacitor>>

Well, Farhan provided a DDS connector on the board for that purpose. Remove the existing VFO toroid to remove the VFO from the circuit.

73,

Todd K7TFC

I am creating the PCB myself, it it not a pre-designed one, I am just at the initial stage of re-working my original through hole design in to a surface mount one and so am removing the VFO and BFO circuitry.

I will look up the board you mentioned and see how the DDS input is implemented there - this should give a me a good idea of what components I need to remove / leave in place on my PCB.

Thanks again for the help.

>> I am creating the PCB myself, it it not a pre-designed one, I am just at the initial stage of re-working my original through hole design in to a surface mount one and so am removing the VFO and BFO circuitry.<<

Presuming you're using Farhan's schematic, he has the DDS connector? and signal insertion point shown. No need to examine the existing board.

Will you be placing the Si5351 and its associated xtal and I2C level-shifting components directly on your SMD layout or will you use the Adafruit (or EtherKit) breakout board and plug it onto your board?

73,

Todd K7TFC

Hi Todd,

I am building the Arduino part as a separate PCB, the ATmega328P plus associated components are going on one PCB with an Si5351 Adafruit board, OLED screen, rotary encoder, buttons, EEProm and beeper attached. This is all currently breadboarded up and working. My PCB is laid out for this part.

The other PCB will just be the Bitx20 with the VFO and BFO wires going from the Arduino board to this one.

I have been experimenting this afternoon - I plugged the Si5351 directly in to the Bitx20 VFO and BFO input points. The VFO I put in at the base of Q7 and the BFO directly in to the T3 mixer, both via a 0.1uF capacitor. The circuit I am using is the one shown on the following blog post:



My initial experiments did appear to work, the signal levels going in to these two places were slightly under the levels when using the original oscillators by approximately 0.2 - 0.3V. I did hear some morse code at around 14MHz but then all the signals appears to fade out for the rest of the day both with the Si5351 and the original oscillators back in place.

I am currently working on getting the PCB laid out for the Bitx20 using surface mount components.