On my printer now (in PETG) thanks
Hi Colin/Allg4eml wrote: ↑Sun Jun 13, 2021 10:01 amHi Mike,
I did consider adding a bias T to the board but decided to keep it simple as I suspect most people will already be powering the LNB using their normal receive setup. Likewise I considered adding a connector for the reference output but I think most people will be simply adjusting to get the correct down converted frequency of one of the QO-100 beacons.
The 25MHz reference is already DC blocked and terminated with a 75 ohm resistor on the board, so I might add a test point so that it can be extracted and measured. The level is quite low though because it is taken directly from the TCXO output and attenuated to prevent any pulling.
The LNB is using a VCTCXO with the tuning voltage supplied by a PIC10 processor’s PWM output. That limits the resolution of the adjustment to about 200Hz steps. The rest of the circuitry is using an RT320M chip the same as the Octagons.
They did actually originally design the LNB with a Trimpot for adjustment. (I have a prototype one that Jon, the UK based designer, sent me to try) However the problem was making it adjustable and still keeping it waterproof. It also only had a single turn trimpot so accurate adjustment is quite fiddly. That seems to be the main reason for switching to using the PIC.
I guess a possible upgrade might be to replace the 2ppm VCTCXO with a 0.5ppm one but the adjustment resolution might then become a problem.
I doubt there is any chance of getting a flanged version, the market is too small.
KiCAD can import Eagle files so I tried that. It might be useful to make a few changes to the PCB - e.g. to include some mounting holes and arrange for it to fit in some standard box. That is, only if Colin doesn't mind.g4eml wrote: ↑Sat Jun 12, 2021 4:12 pm
I have designed a simple interface using an Arduino Nano and three push buttons which is able to adjust the LNB. Having done this my LNB is now always within 1Khz of the correct frequency at room temperature.
It is also possible to control the LNB from a PC connected to the Arduino USB port which opens up the possibility of automatic adjustment.
Full details, including the Adjustment specification, Arduino code and PCB design are in my Github at https://github.com/g4eml/Bullseye-Calibrator