TheRadioBoard

It's a long way from 50 to 2000 MHz! You don't see many lumped-circuits at 2 GHz, and you see even fewer stripline circuits at 50 MHz. Diode mixers are popular at millimeter wavelengths because, with sufficient LO drive, they can give wider dynamic range, and they're cheaper. But they need a low-noise active stage ahead of them. If I were going to use a diode mixer, it would be balanced, not single-ended. If you have to develop a large LO signal you might as well get the benefits of balancing.

Active devices have no net loss like diodes, and for VHF and lower frequencies they are cheap and easily obtained. The gain of an active mixer will offset losses in filters, and require much less LO drive. At 50 MHz a J310 used as a mixer has a noise figure low enough that he may not need an rf amp; with a diode mixer he almost certainly would. Remember, this converter is going in front of a regen IF, and will be used with a simple antenna; it only needs a low noise figure, not dynamic range.

73,

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http://kr1s.kearman.com/
http://qrp.kearman.com/

It's alive!

I rebuilt the thing from the ground up, using new transistors just in case (but still the 2SK192A substitute). I planned the layout more carefully to allow minimum lead lengths and a compact layout. It now oscillates, using the original 33uH chokes I had. I have to set the quench control to minimum resistance, then when I crank up the regeneration control, I hear the rushing sound of super regeneration. If I move my hand too close to the coil (1 cm or so) it will stop oscillating, so it seems very prone to outside influence.

I haven't heard any signals on it yet - again, not sure if there is no 50MHz activity here, or if my set's frequency is even in the ballpark. I did manage to pick up some unknown harmonic of my grid dip oscillator's signal though, so the thing is definitely receiving.

Looking forward to some more experiments with this VHF set. Thanks to all for the advice. I also still would like to try the regenerodyne idea, after I get some more of an understanding of mixers.