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Thread: Precission RF Signal Generator Kit

  1. #1
    Junior Member
    Join Date
    Jul 2016
    Pineville, KY 40977

    Precission RF Signal Generator Kit

    I worked on a RF signal generator using LTSpice which allows you to sample the raw signal in an oscilloscope to measure its amplitude, where that sample is divided down by a precision voltage divider 1000 times resulting in a uV signal for use to test and align radio receivers. Since you can measure the signal 1000 times higher than the desired output level, you can accurately set the level of the output using an oscilloscope, where you are not limited by the oscilloscope's sensitivity. A 1% precision resistor is required for the voltage divider. And since the mV level for the most part is up out of the noise floor of the oscilloscope and stray noise in the shop, the measurement ability is certain. This allows one (either a hobbyist or radio shop tech) to test receiver sensitivity, or to set the S meter calibration to S 9 as required. A good shielded enclosure is advisable, along with a well filtered power supply.

    The circuit has other features such as a frequency counter sampling port and a mV output for the raw un divided RF signal for a higher level of RF output for other test purposes besides that of testing receivers, such as for test bench design.

    As a kit this can be built as a mere circuit board where the builder can then add the tuning capacitor, coils and an enclosure as well as the RF connectors. Also a complete kit could be made that comes complete with a built in frequency counter and a multi turn geared reduction drive on the tuning knob. However a cheaper kit without the frequency counter can be made, the user adds their own freq counter.

    The kit sold as a mere circuit board with its parts, perhaps minus the tuning cap and coils, can be built by the user for a single band or multiple bands. In LTSpice it works from down near to 100 kHz up to around 200 MHz. The limiting factor of the circuit is the buffer amplifier transistor which is a 2N2222 while the VFO transistor is a J310 FET. the VFO tank circuit is designed so that it also acts as a filter to filter itself of harmonics, seeing the circuit diagram you would see how this is and understand it.

    I plan to move onto designing the PCB layout with DIP Trace.

  2. #2
    Excellent post. Thank you very much!!I have long been interested in this topic. Thank you.

  3. #3
    Junior Member
    Join Date
    Nov 2017
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