144MHz Tx Converter GW4RWR

Introduction
This is similar to the 70MHz converter, except that more filtering stages were needed to suppress the LO.

J310 push pull mixer, five stages of filtering, BF998, two BF199 and MRF237 final. Throughout the construction, I couldn't believe how difficult it proved to suppress the LO. I just couldn't get >45dB suppression until all stages after the mixer were shielded. I remain amazed that the little Mizuho MX2 produced clean o/p with a single PCB and just 7.8MHz IF.

Implementation
Swinging the volts on G2 of the BF998 gives about 10dB of power control. If this voltage in series with a reversed 1.5V battery the variation could be increased to ~40dB, but about 10dB variation is all I aim to have, for setting the drive to an external amplifier.

Commentary
The BF998 stage produces -30dBm. I would have liked followed that with just the 2 x BF199 stages, but couldn't get more than a few mW out. Adding the MRF237, which has more gain than my stock of 2N3866, and RF is output now well over 1W, some 11dB more than I need to drive the PA! There's now a lot of attenuation in line, on the rear panel "break out" loop.
LO is 60dB down.