BinaryRock

I've been playing with the TCXO calibration of these boards. The vast majority of the correction factors are between -150PPB and -350PPB. I calibrated these boards earlier today when the wood stove was going and the boards were at 83F.

Now, the boards are 70°F and I am checking them again at 10MHz. I am seeing, on average, 30PPB difference. I have to subtract about 30PPB to bring them back to 10.000 000 0. The boards are about 0.2Hz to 0.3Hz higher at 70°F from when I calibrated them at 83°F.

The datasheet shows an operating temp range of -40°C to 85°C and a 0.5PPM across that range. That's 4PPB per °C if I interpret that correctly. 83°F - 70°F is 13°F, and that's a difference of 7.2°C. 7.2°C * 4PPB = 28.8 PPB. The temperature drift I am measuring seems to be spot on with the specs.

All this is to say, don't bother chasing that last tenth of a Hz if you calibrate.

SuperLid gave me an idea for a new walkie talkie mode.

In this mode, there are 4 pins that individually choose one of 4 channels, and those channels are determined by soldering channel numbers to the solder pads as chunks of 6-bit binary for each channel. The software looks up the frequency for that channel and subtracts 455kHz from it. When PTT is brought low (or high, has a switch), it adds the 455kHz back to it. So now you can pick any 4 standard channels, control them from the factory channel switch, and it does the 455kHz shift automatically. All other modes remain the same.

To use this mode, you would feed the oscillator the same signal and reroute the channel selector wires to operate the channel pins instead of having those switches selecting crystals.

Updating the sketch and website instructions tonight to reflect these changes. I will try to make a full video demonstrating each mode and its options this weekend so people don't have to read the instructions.