Saturday, 13 March 2010

Not-so-Superhet goes Multi-Band

Today I added a bandswitch to the SuperHet receiver (Blogs passim).

The band change operation requires a 4-pole switch so I was limited to 3 band operation, as a 4 pole, 3 way rotary is the best Maplin have to offer (order code: FF76H).

I needed the bandswitching components to be fairly well organized to squeeze them into the already crowded chassis (and to be able to get at and use the trimmer capacitors) so I made a PCB and fixed it to the switch using a bracket made of scrap steel. Here's the unit from the component side (which faces down when installed, so I can get at the trimmers when the chassis base is removed) ...

and the copper side...

You can see from the "top" photo that I've only populated (with coils at least) two of the available three bands. This because I'm going to be changing the main tuning capacitor from the big three-gang unit currently in place to a two-gang device I got yesterday on ebay. The change is to buy some more space on the chassis to add a reduction drive so I can tune the receiver more easily.

The rig now can switch between two bands, arranged to start with the 80 and 40m amateur bands (but the local oscillator drifts pretty badly on the higher band at the moment).

...-.- de m0xpd

Cold-blooded update:
the VFO drifts on BOTH bands - more work required!

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