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Friday, February 18, 2011

VFO = Very Frustrating Object

I immensely enjoyed Solder Smoke -- The Book, and have given it as gifts to several friends. It has rekindled the homebrewing spark, and I have been operating only homebrew gear this year as a result. My transmitter is a rockbound 40 meter rig, and I am using a HF regen receiver.

Tiring of QRM on 7.030 MHz, I decided to cobble up a VFO. Well, you know how that can take on a life of its' own. I decided to build a Hartley oscillator at 3.5 MHz, and then double it to 7.030. The initial stages of the oscillator and buffer went well, but then I ran into a brick wall with the doubler, which performed admirably as an attenuator, but nothing else. The circuit was simple enough, but it just wouldn't work. For a week I tweaked and tuned, to no avail. (as a result of all this effort, my wife said VFO must mean Very Frustrating Object). Then this morning I was going over the circuit again, and discovered that one side of the doubler tank circuit capacitor was grounded, and not supposed to be. It seems the knob shaft of the variable cap was in contact with the metal front panel, and being grounded out. I corrected the problem, and almost shouted EUREKA! when the doubler sprang to life and generated a big and perfect sine wave exactly at 7030!

I just wanted you to know that the story of your doggedness in tracking down the cause of harmonics on one of your homebrew rigs provided moral support to help keep me coming back again and again.

So, thanks again for the inspiration Bill.

Hey, I hope you are going to FDIM this year. If so, you should bring a good supply of SSTB. I bet you would go home with new junk, but no books.

73 de KD7KAR
Rob Pursell

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