Nitpicking re. the glorious Desert Ratt 2 regen RX
 

The Desrt Ratt HR regenerative receiver has a good reputation, and I'd
love to build one, but I am a quite mediocre homebrewer... If I can
get some potential problems out of the way I can better concentrate on
the many others that will surely crop up!

These are my doubts w.r.t. the DR2 as described in the .PDFs on Paul
Harden's page:
http://www.aoc.nrao.edu/~pharden/hobby/DR2.pdf
http://www.aoc.nrao.edu/~pharden/hobby/DR2descr.pdf .
Can anyone comment on any of these points?

1) Tuning Coil
--------------
The PDF mentions inductance, number of turns and wire gage,
but leave us in suspense apropos the coil former:
"T1 is wound directly on the PCB". Uh?
I guess anything 5-6uH will do, but I can't keep from wondering...

2) Tuning Varicap
-----------------
"R5 sets the current across D2-D3" The reverse resistance on such
rectifiers is huge, much greater than R5 (10kohm). I noticed that Paul
Harden N5AN once offered V/C measurements on diodes for use as varicaps
(http://www.kkn.net/archives/html/QRP.../msg00360.html)
There, one sees a 1N4148, forward biased. From the specs one gleans
that this diode has a sizeable current when forward biased at voltages
within a reasonable tunng range - but we're talking about something
quite different here. What gives?

3) Q2 (oscillator) biasing
--------------------------
The resistor between C6 and C7 is not rated. A base bias on an regen's
oscillator can be rather, well, critical....

4) IC Amplifier
------------
R12 is indicated as "10W".
What would a reasonable resistance rating be?

5) Voltage Regulator
--------------------
The text says that the drop across the forward biased LED1
is 1.3-1.8V, while across the Si rectifier D1 is 0.7V.
In series they'd sum up to 2 - 2.5V, but on the circuit
one reads a total drop of 3.0V, i.e. up to 1 V higher.
Charles Kitchin's design fed the oscillator just 2.1V...
Would 2.5V be enough? Or, do LEDs come with a wide variety
of voltage drops?


TIA to everyone!

I hope this will encourage others to experiment with this circuit.

Filippo (SpamHog)
N1JPR/I2