Ok, so mostly I am a DDS and Arduino kind of guy, they just work, they don’t drift and they are super simple. But sometimes, you get that “Retro” kind of nostalgia happening and a desire to build something rock bound. I have a ton of crystals in matched pairs for 7mhz, enough to cover the whole CW portion to 7.050. So i thought, what the hell, I will make a Super VXO, and incorporate it into a transceiver if it proves to be stable enough.
So i went looking for a suitable circuit to modify to suit my parts bin and needs. And i came across this one above. Varactor tuning is nice, as getting quality air variable caps and reduction drives is impossible, so varactors are must. The only thing i changed is the inductor as I do not have any Toko IF coils, and the only other thing i changed was to add an unbalanced to balanced transformer to split the signal in to, one for the receiver and the other for the transmitter. The original article and associated info for this Super VXO can be found HERE!!
Laid the board out in Sprint Layout, and after ironing out the bugs with the help of Ben VK6FBLJ who put his eyes over the layout and noticed all the errors, the gerbers were then converted to gcode for routing.
Could fit 2 boards on the one sheet of FR4 the above picture is the boards on the mill deck still after routing and v-cutting in two.
And this is the finished board after being cleaned with steel wool and a coat of PCB lacquer being applied. They have come up rather nice looking. More to come on this, after they have been built and tested to see how stable they are.
Most of the parts are installed, I threw in a pair of 10mhz xtals for testing with, they will not be the what is used in the final board, but are good enough for testing purposes. Just have the inductors to wind, 10 turn pot to wire up and the 8v regulator to install and it is ready for smoke test. Oh and i was able to find a MV2109 varactor in my semi conductor box, so, no cheeping out and using a silicon rectifier.
Well i cannot get this thing to start oscillating. Have tried just about everything i can think of, will post back when i work out what the case is.
7 thoughts on “Super VXO”
Inductance of the oscillator coil shall not exceed 15 uH! Try an other FET also.
Been a long time since i looked at this, but if i recall i used maybe 3 or 4 uH inductance and I tried a few different fets and could not get it to oscillate, I know a lot more now than I did when i built this, so i should dig it out and see if I can make it work.
Hi, change R5 to 1 MOhm. 73 de YO3HJV
I will dig it out of the junk pike later and give it a go. Thanks.
C4 is 100 nF… in other schematics the value of the series capacitor of the inductance is only 100-150 pF. With the varicap maximum capacitance the sum of the fixed and variable capacitance should be around 100 pF. The oscillacion does not starts if the value of the LC is not suitable with the quartz
Also missing a diode from gate (anode) to ground (cathode) of the FET, in parallel with the 100 k resistor. see the schematic here: http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/VXO_10MHz.gif
I dont even remember what I did with this project. I know i got it working, but that was 6 years ago.