Using polystyrene caps and with the VFO not having any buffer stage the
device fed by a 9v PP battery drifts not more than 20 Herz in 30 minutes.
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What kind of battery is a 9v PP battery? And, it would likely be helpful to
know what the Inductor is that the negative temperature coefficient of the
poly cap is compensating for. Is that drift specification for the first 30
minutes after turn on or after the oscillator has been on for a couple of
days?
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A 9v PP battery is a standard battery pack , alkaline /NiCad / NiMH as
used in all sorts of consumer electronics incl battery operated smoke
alarm devices. Dimensions :45x25x17 mm. Available all over the world.
The battery is 'velcro-ed' to empty space on the board
I did not use dedicated neg temp coeff components ,but used 4 recycled
polystyrene caps from the junk box.

FET is 2N3819 but any other HF FET would do.
The tuning cap is a air variable cap (old style trimmer ,silver plated
plates and ceramic body) with added reduction gear/scale in front panel.
Adjustable inductor with core is from Toko .It is mounted on its side,
soldered to PCB material plane.
There is a compact foil trimmer for fine adjustment

Since double sided PCB board was used , I drilled many holes in the
material and soldered through hole pieces of wire ,such that the 2
copper planes are connected at many places.

The 20 Hz stability is reached after applying power to the circuit for
approx 20 minutes in a room with a stable temp.

The power supply connection to the circuit is via an insulated pin which
sits on a tiny board island (having used a special PCB foil cutter which
removes a tiny ring of copper material) .
Although I also could have used an upright 10 MegaOhms (1/4 W) resistor
serving as pin and 'insulator'.

The unit is built onto an 2mm thick piece of aluminium bent as an L

Summarising : A typical little project using predominently junk box
components, with success resulting from using RF friendly components
and shortest possible connections between frequency determining elements.

I don't have a web site to post to ,but can take a pic and send it to
those interested, by email

You can contact me by e-mail by removing abcxyz from my NG address


Frank GM0CSZ / KN6WH

now almost fully migrated to Linux (using Mandriva 2007.1 distro)