I5TDJ developed the following very sensitive preamplifier which replaces the 74HC4046

This circuit gives 50mv sensitivity to 50MHz. The output of the 74AC00 drives the PIC directly bypassing the 74HC4046.

Piero used a DFD with the IC-202S two meter rig. It triples a 15MHz VXO to 45 MHz and then triples it again to 145MHz. Piero took the signal after the first tripler and set DFD to multiply by 3. The signal was taken from the junction of R25, R26 and C39 through a 100pf capacitor and about 12" of RG174U.

For those applications that do not require this much gain I played with just the final stage of I5TDJ's design.

Using a 2N3904 this little amplifier gave a gain of about 15 at 6MHz and dropped to about 3 at 50MHz.

It has a rather low input impedence so for those who need to decrease the load on their VFOs an emitter follower can be added.

It is probably best to put this preamplifier in the radio to buffer the radio from the cable capacitance.

The 5V DC can be borrowed from the DFD at the output of the 78L05.