September 18, 2012

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Analyze This! ... The Desert Ratt 2
and other "Regen" Receivers

One of the easiest and best performing receivers to build, the "regen" offers a unique and incomparable operating experience.
Once you hear the characteristics whistles and pops when tuning in a station, you'll think of your grandfather's radio in his den while
you lay listening to the 1939 Yanks pound the Philadelphia Athletics
. And you'll also hear dynamic range and crystal clarity that is hard
to duplicate with others receivers ... even today!


Many of us have built transmitters - QRP or otherwise - but how many have built a receiver?  It's actually not too difficult to do it with some of the integrated circuits around these days, Gilbert mixers like the SA512 and the like.  But have you ever considered whipping up a "regen" receiver?  What a ball it can be and you'll impress the neighborhood teen (and yourself) with how simple it can be, yet still give incredible listening pleasure. 

This episode of CWTD will overview the basics of a regenerative receiver, and go through some classic designs that are really fun and easy to build.  And per usual, we spotlight one specific design, that of the Desert Ratt by designer and homebrewer extraordinaire Paul Harden NA5N, and we'll analyze it from the ground up ... with the detail and discussion perhaps you'll even catch the bug to build your own regen!

73, George N2APB  & Joe N2CX

Audio Recording ... (Listen to the MP3 podcast)

Discussion Notes:

<20:05:24> "Paul - wa0rse": I have a box of tubes that I'd like to put to use!
<20:07:28> "George - N2APB": Loooooove tubes here!
<20:09:32> "Paul - wa0rse": :) I got it...
<20:09:55> "Joe N2CX": Edwin Armstrong
<20:10:34> "Paul - wa0rse": My first transmitter was a single 6L6 crystal-controlled loaner from my Elmer, W0AUS.
<20:13:24> "Joe N2CX": It makes a distinctive sound when it "bloops" into oscillation hence their moniker of "blooper"
<20:13:29> "Paul - wa0rse": No, but I wanna!
<20:14:16> "Paul - wa0rse": My first receiver was a crystal set with a cat's whisker :(
<20:16:01> "Paul - wa0rse": Whoa! That's cool, Rich!
<20:16:10> "Dave AA3UR": My first: Knight Kit Span Master (top of page)
<20:20:08> "Alan W2AEW": would you call it a homodyne?
<20:20:48> "Pete - WB2QLL": Corrrectly designed regens don't "bloop".
<20:28:07> "Joe N2CX": A homodyne is somewhat different - search for the homodyne wiki
<20:29:13> "Joe N2CX": Oops the wiki sez that the dc rx is a homodyne...
<20:33:00> "Joe N2CX": Small correction adding an RF amp does not make a superregen
<20:37:41> "Joe N2CX": Hum modulation is discussed as the last bullet in "Regen Negatives"
<20:43:19> "John ZL1AZS": Another resource:
<20:45:48> "Joe N2CX": Plus the regen control is like a manual choke!
<21:04:11> "George - N2APB": Moving hand around the antenna can pull the oscillator if not properly isolated.
<21:04:44> "George - N2APB": Q2 is a common-emitter design.
<21:05:03> "George - N2APB": Stable 3V regulated voltage helps with stability.
<21:05:33> "George - N2APB": Regen controlled by varying a resistor in the emitter to control the amount of current in the circuit, and hence the degree of oscillation.
<21:06:29> "George - N2APB": The varicaps vary from 8-90pF, by providing a variable voltage 0-9V with the tuning pots.
<21:07:06> "George - N2APB": Q3 is an emitter follower used to isolate the detectors from the oscillator Q2 ... otherwise direct connection would "pulls" the oscillator unpredictably.
<21:08:21> "George - N2APB": Q4 is used as a splitter transistor to present differential signals to the op amp, thus doubling the drive level to the amp.
<21:08:56> "George - N2APB": Sometimes need to be careful about putting a speaker on the front panel because the vibrations will affect the regen stage!
<21:09:06> "Alan W2AEW": 1N4001's used as varactors - interesting
<21:11:48> "Al K8AXW":
<21:12:26> "Frank N3PUU": I find a bunch of pictures of the 3 (some on njqrp), but not a 2 yet
<21:12:58> "Ted - AB8FJ": The build on QRP-Tech was the WBR design published in QST a few years ago.
<21:13:19> "Ted - AB8FJ": I built it using the board from FAR Circuits and found the same problems with very low audio output
<21:13:46> "Ted - AB8FJ": Seems that there was speculation that a kit for the Desert Ratt was going to be offered. Did that ever happen?
<21:15:21> "Alan W2AEW": but the turn count would have to change
<21:17:44> "Frank N3PUU": Here's a built desert ratt 2:
<21:20:02> "Kevin - kb3omm": Possibly using the copper as an electrostatic shield between the primary and secondary
<21:23:43> "Pete - WB2QLL": Looks like a toroid on the 3 here:
<21:23:44> "Pete - WB2QLL":
<21:26:52> "Craig -KC2LFI": Like to see a good regenerodyne circuit.
<21:32:47> "Ted - AB8FJ": Great topic. Thanks guys!
<21:32:48> "Kevin - kb3omm": 73
<21:33:18> "Terry WB4JFI": Thanks for all the work Joe and George. 73
<21:33:26> "Charles WC5MC": Really fun topic tonight
<21:33:27> "Frank N3PUU": great job guys, that was a good session.. 73!
<21:33:33> "Todd K7TFC": Yes, many, many thanks!

SESSION NOTES .... Analyze This! ... The Desert Ratt 2, and Other "Regen" Receivers

"A regenerative radio receiver is unsurpassed in comparable simplicity, weak signal reception, inherent noise-limiting and agc action and, freedom from overloading and spurious responses. The regenerative radio receiver or, even super-regenerative radio receiver or, "regen" if you prefer, are basically oscillating detector receivers. They are simple detectors which may be used for cw or ssb when adjusted for oscillation or a-m phone when set just below point of oscillation. In contrast direct conversion receivers use a separate heterodyne oscillator to produce a signal. " ... Ian Purdie, VK2TIP, as an intro to the Charles Kitchin N1TEV regen receiver project.

The Twinplex design ... a simple 1-tube regen with superb performance for the simplicity offered.
(See Greg Latta's beautiful AA8V Twinplex web page ...



More Regen Positives

Regen Negatives

Regens are similar to Direct-Conversion Receivers


Three Classic Books on Building and Understanding Regen Radios


And the best of them all ... by Bruce Vaughn, NR5Q:
(available from Electric Radio ... )


The Ultimate Regen Receiver, by Bruce Vaughn, NR5Q 








K4XAF version of the NR5Q Ultimate Regen Receiver, named the "NRQ-62"



You can read all about K4XAF's building and operating fun with the NR4Q Ultimate Regen Receiver
by visiting ...





Tips on Building Regen Receivers

    Much advice taken from saged regen gurus N1TEV ...

    And from NA5N ...


Avoiding "ground" loops in the regenerative receiver

Building the cabinet to house the regenerative receiver


Regen Grounding and Antenna

Tuning a Regen Receiver


High Performance Regenerative Receiver Design, by Charles Kitchin, N1TEV




N1TEV High Performance Regen Receiver, as featured and published by the ARRL in QEX for Nov/Dec 1998
(See full technical PDF article in References below.)



Regen Short Wave Receiver, by Charles Kitchin, N1TEV



Building the N1TEV Regenerative Shortwave Receiver



A Simple Regen Receiver For Beginners ... another wonderful Charles Kitchin design ...





Neighborhood teen building up a Boy Scout Regen at Chez N2APB




The "Desert Ratt 2" Regen Receiver, by Paul Harden NA5N



Analyze This! ...





1. Jerry Haigwood, W5JH ...

2. AA8V Twinplex ...

3. NRQ-62 Ultimate Regerative Receiver, by Jim Stoneback K4XAF ...

4. A Short Wave Regenerative Receiver Project, by Charles Kitchin N1TEV ...

5. Radio Receiver Basics ...

1.   6.  Some Recent Developments in the Audion Receiver, by E H Armstrong, Proceedings of the IRE (Institute of Radio Engineers), volume 3, 1915, pp. 215–247 ... <>

7.  National Radio SW-3 “Thrill-box" ...  <>

8. Knightkit Ocean Hopper Regnerative Receiver ... <>

9. NA5N “A Regenerative Receiver” ... QRPp Vol IV Number 1 March 1996 pp. 12-15

10. NA5N Desert Ratt 2 schematic ... <>

11. Desert Ratt Description ...

12. History of the Desert Ratt ...

13. A Simple Regen For Beginners, by Charles Kitchin, N1TEV ...


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