With this done I could start progressing towards building the amplifier strip, but first I wanted to check how things were doing so far, in particular, the SBL-1 DBM (Double Balanced Mixer, the left hand silver box with legs) and its Dual Gate Mosfet buffer, needed testing. So after adding the first trimmer capacitor, which gave me a convenient point to connect, and tacking on the resistor chain that takes the supply to the buffer (these become permanent later in the amplifier) I set up a simple test.
With the unit powered, a few checks with the frequency counter were done to check that the oscillator 42MHz was running and appearing in all the right places - particularly the output of the buffer! This done, I fed the mixer with a 28MHz +5dBm signal from my Marconi 2955, and looked for an output
So the mixer is working. 5dBm is a little low for proper testing (around 3mW), and the input to the mixer is designed to be 10dBm (10mW), but 5dBm is the most I can get out of the test set! Next step the pre-driver amp. Another fiddly little 7t air wound coil needed. But, before this, me and Sam had a job to do - run a CAT5e cable to Sams bedroom! This took up most of the day!
In the absence of the specified BF199, ive substituted a 2N3904 in this position. The completed pre-driver section, and the above mentioned, now permanent, resistor chain, can be seen on this photo below. At this stage, getting hungry and it being late, I did a final test, before finishing off for the night.