Finally … The page you’ve all been waiting for. On the left is a photograph of the
trace of a real 40MHz filter which was previously aligned using my DG8SAQ VNWA. Admittedly
As previously mentioned, the RF output from the Sweep Generator and the RF input to the Lin/Log Amp are unusual in that although they resemble the small connectors found on the rear of RA17s, they are in fact different since the centre conductor is a receptacle as opposed to a pin.
As can be seen from the photograph below, I managed to obtain a much better trace by fashioning short connections between the connector outer and the coax braid. In time I shall look into making dedicated leads for connection to TP2 and TP3 on the RA17. But until then I think you will agree it is quite fascinating to see this bespoke piece of test gear actually working.
More on the Marker Generator, left:
I now have the 5 markers correctly set. This was actually very easy to do. The way
it works is remarkably simple. The smaller of the two variable inductors is used
to set the centre marker on 40MHz (the Crystal Oscillator). The coax lead carries
the auxiliary swept signal from the sweep oscillator. The taller of the two cans
contains two tuned circuits in series which are themselves in series with the anode
of one of the EF91s. I haven’t figured out precisely how it works, other than I can
tell that some form of mixing is taking place, but the bottom core adjusts the +/-