It is truly a thing of beauty. Stephen VK2BLQ built it just as we designed it, so his build (like those of several others) serves as confirmation that this design is ready for the high school students.
Stephen writes:
Bill,
Don't worry, you are not alone out there.
Here is my build; sorry that the front panel is overexposed and hard to see, but it is plywood.
I did follow the schematic but due to the contents of the junk box there have been some component changes.
The only thing that I had to buy was the 3/16 x 50 mm (2 inch) brass screw.
My calculations for the coils for the PTO and BPF were a little bit off necessitating padding down the PTO with a further 100 pF (easier than remaking the coil and mounting) and removing a few turns from the T50-6 toroids.
Like other people have found: the audio takes off at full volume; I am thinking but not yet tried adding decoupling between R5 (15K) and C2(47 uF). It isn't the actual values of the electros as I had to use 100 uF so might be the audio output getting back into the earlier stage.
The tuning range I get is our 7000 to 7200 KHz and some shortwave stations above and below, Turning the screw is a little bit fiddly, but once tuned the vfo is quite stable and the audio sounds good.
Best wishes,
Stephen
VK2BLQ
I really like the ruler near the tuning control. Is that (I hope!) the frequency readout?
Posts
Well done Stephen. The notion of a 7mhz analog junk box VFO being stable is somewhat foreign to me! Paul VK3HN.
ReplyDeleteclean build!
ReplyDeletePaul: On the 7MHz VFO/PTO: Dean and I were both surprised by the stability of Farhan's Colpitts VFO. It is very simple. But it really works very well. 73 Bill
ReplyDelete