[Milsurplus] Improving RU Selectivity.

[Hubert Miller]

Neat. This may have me rethinking getting rid of all my RUGF stuff.
One thing I wondered about, tho. With regenerative feedback, when in CW mode, do the RF stages track well enough that the narrowed selectivity window aligns with the BFO frequency ?

So I have added another thing to my must-try list. Looking at the schematic, I see the 78 tube has an independent suppressor grid. Raising this grid above AC  ground will allow plate to
control grid capacitive feedback. This is how the Halli S-38 and S-140 and Knight Star Roamer developed their selectivity and BFO.
-Hue


>Was listening to a 75-meter AM QSO with the RU-15 receiver this morning. There were the usual SS-SOBs needlessly crowding the AM Window.  Made a short video of how easily one can improve the selectivity of the receiver with just a piece of wire and a few minutes spent fiddling with it.



Ran a wire from the antenna post to near the third tube from the rear.  Adjust how much wire, how near the tube.  Fine-tune with the ANT TUNE knob.  It's touchy- too much coupling will motor-boat.  Regen will also pull the tuning some so you'll need to zero-best.  When you find the "sweet spot," you can easily hear the "rushing noise" as you tune across each sideband of the AM signal.  In fact, you can get it TOO narrow, distorting the audio.  The improvement can be dramatic.  Here's the video:



https://goo.gl/photos/wBK2dKmkFukYjR3A9



73 Dave AB5S



P.S. Once you get it narrowed on a carrier, it's much easier to zero-beat the BFO correctly.



Sent from my Ain't Smart Phone.


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