Saturday, November 07, 2009

5-5.5Mhz VFO


For my FT-102 I have been using the FT-107 VFO but it's like killing flies with a cannon since I make no QSO's at the moment and it could be used for the FT-107. After decided to use an homebrew vfo it's time to build one.
Transistor is a 2N3819 (no MPF102 in the "LES", local electronic shop). Variable capacitor is salvaged from an old radio and honestly I didn't measured it, also the capacitors of the tuned circuit were more or less dropped in the circuit til I have the 5-5.5 Mhz range. Toroid core is an T50-2, black and red with 30 turns and "middle" point at around 8 turns from ground. wire is 24 swg.
I reduced the power supply to 6v to try to improve on the stability. Since I didn't measured before I can't give you info if it did improve!
The "varicap" diodes are 2 red led's and give me around 10Khz offset in the highest vfo frequency (around 5.6Mhz). It tunes from around 4.9Mhz.
You can see in the video the initial drif. I hope that after placed in a box it will get betther. Anyhow made some tests after warming up (and the frequency counter removed) and it doesn't look that bad.

video

Not finished yet since I still need to put the buffer and find a nice box, will do that when needed.

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