My Voltage Tuned VFO - Have I gone crazy? : Video posted Feb 9, 2025

 Video posted on Feb 9, 2025 :: https://youtu.be/_SEzhTw6DcY

Resources for 'Voltage Tuned VFO'::

 

 

Above — Complete schematic of the voltage tuned VFO

 

 Above — Varactors on a scrap of PC board.  "Zoomed in heavily".

 

Above — Photo of the 3.5 MHz VCO ( voltage tuned VFO).

 

Above — Photo of a 5 MHz low pass filter I built 30 years ago using PL-259 connectors (PL-259 to BNC adapters in-situ). Currently most use SMA connectors, although some in the mid-to-late 2000's employed BNC connectors.

 

Above —  Some of my low pass "bench" filters. I also have band pass and high pass bench filters in my collection All filters I made after 2017 used SMA connectors. Most are not shown.

 

Above — Output of 3.5 MHz voltage tuned VFO into a 50 Ω terminated DSO channel.

  

Above — Output of 3.5 MHz voltage tuned VFO into a 50 Ω terminated DSO channel with the 5 MHz bench low pass filter in the signal chain.

Frequency Doubler [ 3.5X to 7.X MHz ]

Above — The KO4BB frequency doubler. I added a wide band output circuit (32 turns to 5 turns) -- plus a low pass filter of my design.  Q1 + Q2 form a standard, series-pass voltage regulator.  Q2 functions as the feedback amplifier -- but also works as a temperature compensating voltage reference. Clever design by KO4BB.

Above — The doubler output into a Spectrum Analyzer. The 10 dBm  input signal @ ~3.5 MHz signal lies down 53.5 dB indicating stellar full wave suppression by the Q3/Q4 pair.  I did not match Q3 and Q4.

 

 

Above — Output of the doubler into a DSO.