This circuit was developed by Luigi Falcone, I1FLC. He uses seven plug in coils covering 3.0 to 30Mhz in a Colpitts oscillator circuit. The coaxial socket J2 permits connection to a frequency meter when required. The coils are wound on Teflon formers with two "female" sockets which plug-in to two "male" sockets on the instrument. TR2 forms a DC amplifier permitting the use of a 1mA FSD meter with sensitivity controlled by R7. With TR1 switched off (via S2) the instument forms a field strength meter/RF sniffer.
|3.0 - 4.5||30||21||75||59.6|
|4.0 - 5.8||25||21||63||47.8|
|5.0 - 7.5||19||17||47.5||23.5|
|7.5 - 11||10||17||25||10.25|
|10.5 - 16.0||11||11||27.5||5.55|
|15.0 - 22. 0||6||11||15||2.5|
|20.0 - 31.0||6||9||15||1.8|
It is important that the oscillator components are mounted rigidly and not subject to "hand capacitance effects" in use.
If a somewhat larger value variable capacitor was used with a slow motion drive the number of coils to tune 3 to 30 Mhz could be reduced.
Back to Test Equipment Page
Back to Home Page