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Am I missing something or can't the software be changed to account for the difference? Our VFO has a timing constant in the code that is changed to account for variations in the 125MHz crystal on the AD9850 board. Indeed, one of our users uploaded an Excel app that calculates the constant for you. (Thanks, Norbert.) My guess is that something could be done in software to account for the differences.

Jack, W8TEE

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From: "special@... [BITX20]" <BITX20@...>
To: BITX20@...
Sent: Tuesday, December 6, 2016 10:15 AM
Subject: [BITX20] Si5351a VFO boards.

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Hi all.

Just a word of warning/advice.

The Si5351 based VFO (clock) boards produced by Hans (QRP Labs) and Adafruit are not directly interchangeable for use within the many Arduino based VFO sketches that are appearing out there.

The reason for this is that the boards use different crystal frequencies for their operation.

The QRP Labs board is based on a 27MHz crystal while the Adafruit board is based on a 25MHz crystal.

Although both boards have the same basic 7 active connections (Gnd, Vcc, SCL, SDA, OP1, OP2, OP3) and while they CAN theoretically be used virtually interchangeably, you will need to compensate for which board you are using within the coding within the relevant .ino sketch file when using an Arduino based version.

The QRP Labs VFO is designed around Han's version of the Si5351 board and the VFO will not produce the correct output frequencies if an Adafruit board is kludged into it instead.

It can be done but at the low price and high quality of Han's kit it really isn't worth the effort - and I prefer Han's boards anyway :-)

Slim G4IPZ