VHF RECEIVE CONVERTER


 

RF AMP/MIXER

 

 

RF AMP/MIXER

For Q1 and Q2 I used a pair of 3SK45 dual gate FET's. Most VHF N-Channel dual gate mosfets should work fine. I have used 3SK88, BF961, and BF981 FET's in this circuit. If you decide to use a GaAsFET for Q1, you will probably need to use a Zener diode to reduce the drain voltage to a safe level. L1 is 5 turns of 1mm copper wire, tapped at 1 turn,coil diameter 7mm, L2 and L3 are 5 turns each. T1 primary is 9 turns on a Toko 10mm former (old IF transformer) T1 secondary is 2 turns. The screening can and outer ferrite cup are not used.

 

LOCAL OSCILLATOR

Q3 is a BF256 or similar VHF JFET. The 116 MHz crystal is a 7th overtone type. I built several oscillators using bi-polar transistors. All of them were unreliable. This simple oscillator starts first time, every time, and has an output of several volts. L4 is 5 turns, tapped at 2 turns, 7mm inside diameter. L5 is 5 turns with a ferrite tuning slug.

 

This converter is very sensitive. I can hear the Waterford repeater, about 160KM away. Reception of weak signals is superior to most commercial 2M rigs.

 

DANGER HIGH VOLTAGE! This converter is not likely to kill you, but you could very easily kill it! If you are using a HF transceiver as the IF, make sure that you don't accidently operate the transmitter. A few watts of RF into the IF output will almost certainly destroy Q2.


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