Bi-Lateral IF AMP Stage
G4GXO Bi-Lateral Amp Design
I use two of these amps in my radio. The first one follows the TUF1 DBM and I modified the circuit as follows. At the point marked Gain, I used a
voltage divider of 3.3K in series with 6.8K (6.8K to ground) and there is a
0.1 ufd bypass connected to 12 Volts and the other end of the 3.3K. The idea is to supply a fixed 8 volts to the stage. If you want to be precise an 8 V regulator would work fine. In this stage I used a Dual Gate Mosfet (3N211, 3N209 and a 40673) all work nicely. Taylor mentions the use of a DGM. I looked at W7ZOI's website and based on his data for biasing a DGM, I modified this stage as follows. R9 connects directly to ground. LED 1 & 2 are eliminated as is C1. R7 was paralled with a 39 ohm resistor (effectively it is now 30 ohms) and the R7 and 39 Ohm resistor are connected directly to ground. You will have to "diddle' with the turns ratios of T1 and T2. In my case the primary of T1 had to match 50 Ohms and in the case of the secondary of T2 I was looking into something around 200 ohms.
In the second circuit used after the Crystal Filter you once again have to
match from the filter to the primary of T1 and the circuit was built with
the J310's and the LED's. For the Gain I experimented with a FET analog
switch that is set for an output of 8 volts with no signal. On RX the gate
of the switch is fed with AGC voltage which reduces the Drain Voltage. and on Tx there is no AGC voltage so it floats back up to 8 volts (max gain). I did not include an S meter --no space but drive an LED -- when the LED just lights --I call that S9. Max Brilliance is "way over s9".