development of the "Desert Ratt" regenerative receiver design
 

The "Desert Ratt" is a clever design for a sensitive and well behaved
shortwave regenerative radio. It has been doing the rounds in various
forms since 1994, and quite a few people added new twists.

As I kept seeing roughly the same stuff popping up all over the place,
and found it somewhat hard to keep track of which version was an
improvement over another one, I did a bit of investigation to figure
out who did what, and what the direction of development was.

Read it all at:
http://webfools.net/filippo/desert-ratt.html

BR

Filippo/SpamHog
N1JPR/I2
http://filippo.ru.ru

Hi,

I have a question about the Desert Ratt 2... do you have any idea what
the dimensions of the form for the onboard coil are?

Thanks,

The Eternal Squire

SpamHog wrote:
The "Desert Ratt" is a clever design for a sensitive and well behaved
shortwave regenerative radio. It has been doing the rounds in various
forms since 1994, and quite a few people added new twists.

As I kept seeing roughly the same stuff popping up all over the place,
and found it somewhat hard to keep track of which version was an
improvement over another one, I did a bit of investigation to figure
out who did what, and what the direction of development was.

Read it all at:
http://webfools.net/filippo/desert-ratt.html

BR

Filippo/SpamHog
N1JPR/I2
http://filippo.ru.ru

SpamHog,

Here's another question:

I've been building the Desert Ratt 2 today, starting with the audio amp.
Problem is that I am getting attenuation rather than amplification.

I have questions about the biasing network surrounding Q4. R9 and R10
are specified as 1.2K (1200 ohm). The schematic states that the
emitter and collector voltages should be 3.0 Volts. However, my version
develops an collector voltage of 7.2 Volts and an emitter voltage of 1.7
Volts. My base voltage is 1.8 Volts (which is in the ballpark of what
the schematic states as should be 2.0, I am not nearly as worried about
that one.

I had used a 2N3904 as recommended. On the assumption that the
transistor could be bad, I subbed a 2N2222. Same result.

It seems to me there might be a misprint with respect to the values of
R9 and R10.

Any ideas?

The Eternal Squire

The Eternal Squire wrote:
Hi,

I have a question about the Desert Ratt 2... do you have any idea what
the dimensions of the form for the onboard coil are?

Thanks,

The Eternal Squire

SpamHog wrote:

The "Desert Ratt" is a clever design for a sensitive and well behaved
shortwave regenerative radio. It has been doing the rounds in various
forms since 1994, and quite a few people added new twists.

As I kept seeing roughly the same stuff popping up all over the place,
and found it somewhat hard to keep track of which version was an
improvement over another one, I did a bit of investigation to figure
out who did what, and what the direction of development was.

Read it all at:
http://webfools.net/filippo/desert-ratt.html

BR

Filippo/SpamHog
N1JPR/I2
http://filippo.ru.ru

I have questions about the biasing network surrounding Q4. R9 and R10
are specified as 1.2K (1200 ohm). The schematic states that the
emitter and collector voltages should be 3.0 Volts. However, my version
develops an collector voltage of 7.2 Volts and an emitter voltage of 1.7
Volts. My base voltage is 1.8 Volts (which is in the ballpark of what
the schematic states as should be 2.0, I am not nearly as worried about
that one.

The voltages on the schematic are wrong.
Whatever the base voltage is, the emitter
should be 0.6 to 0.7 volts lower. Then
you can calculate the emitter current as
Ve/Re (around 1 mA in this case). The
Collector voltage is approximately Ie/Rc
lower than the supply voltage, or something
around 7V here.

The fact that your emitter voltage is only
0.1V less than the base voltage says that
either the transistor is bad (which you seem
to have eliminated, you have a bad or wrong
value component, or a wiring mistake.

I'd suggest disconnecting C15, C16 and
C17 to isolate the stage, and repeating the
dc measurements.

73, John - K6QQ

John Moriarity wrote:
I have questions about the biasing network surrounding Q4. R9 and R10
are specified as 1.2K (1200 ohm). The schematic states that the
emitter and collector voltages should be 3.0 Volts. However, my version
develops an collector voltage of 7.2 Volts and an emitter voltage of 1.7
Volts. My base voltage is 1.8 Volts (which is in the ballpark of what
the schematic states as should be 2.0, I am not nearly as worried about
that one.


The voltages on the schematic are wrong.

Yep. I had used LTSPICE to figure that one out. Collector and Emitter
DC voltages measured are same as on simulation, NOT on schematic!
AC voltages on nodes 3 and 8 from simulation agree with same on
schematic. I should measure the AC voltages.

-------------cut here-------------
Version 4
SHEET 1 1052 772
WIRE -16 224 32 224
WIRE 144 384 208 384
WIRE 272 384 320 384
WIRE 304 96 304 128
WIRE 304 16 144 16
WIRE 144 16 144 96
WIRE -80 224 -160 224
WIRE -160 384 -160 416
WIRE 32 224 32 240
WIRE 32 320 32 560
WIRE 320 464 144 464
WIRE 144 464 144 496
WIRE 144 272 144 384
WIRE 576 352 576 400
WIRE 368 176 144 176
WIRE 432 176 576 176
WIRE 576 176 576 272
WIRE 576 176 592 176
WIRE 32 224 80 224
WIRE 32 640 32 720
FLAG 144 496 0
FLAG 304 128 0
FLAG -160 416 0
FLAG 32 720 0
FLAG 576 400 0
SYMBOL npn 80 176 R0
SYMATTR InstName Q1
SYMBOL res 128 80 R0
WINDOW 3 -83 76 Left 0
SYMATTR Value 1200
SYMATTR InstName R1
SYMBOL res 128 368 R0
WINDOW 0 -44 67 Left 0
WINDOW 3 -82 105 Left 0
SYMATTR InstName R2
SYMATTR Value 1200
SYMBOL cap 272 368 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C1
SYMATTR Value .1µ
SYMBOL cap -16 208 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 36 34 VTop 0
SYMATTR InstName C3
SYMATTR Value .1µ
SYMBOL res 304 368 R0
WINDOW 3 48 65 Left 0
SYMATTR Value 100000000
SYMATTR InstName R3
SYMBOL res 560 256 R0
SYMATTR InstName R4
SYMATTR Value 100000000
SYMBOL Misc\\battery 304 0 R0
SYMATTR InstName V1
SYMATTR Value 9
SYMBOL voltage -160 208 R0
WINDOW 3 -85 -33 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value SINE(0 .1 400)
SYMATTR InstName V2
SYMBOL res -176 288 R0
SYMATTR InstName R5
SYMATTR Value .01
SYMBOL Misc\\battery 32 544 R0
SYMATTR InstName V3
SYMATTR Value 2.2
SYMBOL res 16 224 R0
SYMATTR InstName R6
SYMATTR Value 10000
SYMBOL cap 432 160 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 36 34 VTop 0
SYMATTR InstName C4
SYMATTR Value .1µ
TEXT -246 506 Left 0 !.tran 0 .01 0 .001
--------------------cut here-----------------

Whatever the base voltage is, the emitter
should be 0.6 to 0.7 volts lower. Then
you can calculate the emitter current as
Ve/Re (around 1 mA in this case). The
Collector voltage is approximately Ie/Rc
lower than the supply voltage, or something
around 7V here.

The fact that your emitter voltage is only
0.1V less than the base voltage says that
either the transistor is bad (which you seem
to have eliminated, you have a bad or wrong
value component, or a wiring mistake.

I'd suggest disconnecting C15, C16 and
C17 to isolate the stage, and repeating the
dc measurements.

73, John - K6QQ



Or I should report the emitter voltage more
exactly. I'll verify this. Tell me something,
how terrible an idea is it to use disk ceramic
for C15, C16, and C17? I have heard of
disk ceramics being capable of conducting DC
if made badly.

Thanks,

The Eternal Squire.

PS: LTSPICE is the ham's best friend! I
think it would be worthwhile to post the
entire SPICE file for the Desert Ratt 2,
wouldn't THAT be something!

Or I should report the emitter voltage more
exactly. I'll verify this. Tell me something,
how terrible an idea is it to use disk ceramic
for C15, C16, and C17? I have heard of
disk ceramics being capable of conducting DC
if made badly.

The disc ceramics should be ok, as long as they're
good.

I've never built this circuit, I'm just looking at it
as a paper exercise. DC measurements will usually
locate the problem. Spice may be overkill ;-)

GL & 73,

John - K6QQ

Dear Mr. Moriarity,

Well, I finally used to scope to prove to myself
that I wired the phase splitter correctly.

I placed 100 mV p-p 1000 hz sine signal into C15. I get
proper 100 mv p-p 1000 hz sine signals that are
180 out of phase into pins 2 and 3 of U1.

R12 seems to be misspecified as well. On the
pdf schematic, R12 shows as "10W". I assumed
at the time that the W was simply a misconverted
omega symbol, so I had soldered in a 10 Ohm
resistor there.

U1 does not amplify at all!!! So, I figured
that perhaps it was a mis-typed "K". So I tried
a 10 K resistor.

With a 10K resistor as R12, I got a VERY nice
volume that filled the entire room. The only bad
news is that when I remove the input signal, I get
about 400 hz motorboating.

I wired a pot in place of R12, and found that the
threshold resistance was somewhat below 800 Ohms.
Much less than that, and U1 did not amplify. But
any value needed for U1 to amplify caused at least
a few hz of motorboating.

Please keep in mind that I am using ground plane
construction and that both leads and traces are
reasonably short.

Also keep in mind that I constructed only the
phase splitter and audio amp stages. Basically,
everything between C15 and the speaker, along with
the necessary D1/LED1/R4 voltage regulator.

My remaining hypothesis is this: Is it that I have
too much gain in U1? Should
I change the value of the capacitor, C18,
between pins 1 and 8 of U1 to adjust the maximum
gain in the hopes this will kill the motorboating?

I don't know how else to solve the motorboating
problem, especially in a circuit that NA5N billed
as inherently resistant to motorboating according
to the explanation sheet.

Again,

The Eternal Squire


John Moriarity wrote:
Or I should report the emitter voltage more
exactly. I'll verify this. Tell me something,
how terrible an idea is it to use disk ceramic
for C15, C16, and C17? I have heard of
disk ceramics being capable of conducting DC
if made badly.


The disc ceramics should be ok, as long as they're
good.

I've never built this circuit, I'm just looking at it
as a paper exercise. DC measurements will usually
locate the problem. Spice may be overkill ;-)

GL & 73,

John - K6QQ

The Eternal Squire wrote in message news:

R12 seems to be misspecified as well. On the
pdf schematic, R12 shows as "10W".

Any resistor will do, as long as it can dissipate 10 watts!
Did you try with a 10W resitor?
I used a 25W one and it works perfectly ;)

Nonsense aside, I just dropped a line to Paul Harden at the VLA -
which btw is pro'lly the biggest RF-receiving system on this planet.
I hope he will find some time off his VLA retrofitting project to
visit here and clarify.


I made a few changes to the History file at
http://webfools.net/filippo/desert-ratt.html
adding a later version of Charles Kitchin's beginner oriented receiver
- one with a still lower part count, the result of a few month's
experimenting.



Also, a related matter:

Charles Kitchin mentioned that his bipolar designs for beginners have
become extremely popular, although his JFET ones perform much better.

a) Did anyone try the circuits proposed in Charles Kitchin's article
on "High Performance Regenerative Receiver Design"?

b) How does it compare to this
http://www.electronics-tutorials.com...o-receiver.htm
and to the DR?

c) Is the article still available? Is there a link I should add to the
DR history?

tnx es 73 de n1jpr/i2

The Eternal Squire wrote in message news:

R12 seems to be misspecified as well. On the
pdf schematic, R12 shows as "10W".

Any resistor will do, as long as it can dissipate 10 watts!
Did you try with a 10W resitor?
I used a 25W one and it works perfectly ;)

Nonsense aside, I just dropped a line to Paul Harden at the VLA -
which btw is pro'lly the biggest RF-receiving system on this planet.
I hope he will find some time off his VLA retrofitting project to
visit here and clarify.


I made a few changes to the History file at
http://webfools.net/filippo/desert-ratt.html
adding a later version of Charles Kitchin's beginner oriented receiver
- one with a still lower part count, the result of a few month's
experimenting.



Also, a related matter:

Charles Kitchin mentioned that his bipolar designs for beginners have
become extremely popular, although his JFET ones perform much better.

a) Did anyone try the circuits proposed in Charles Kitchin's article
on "High Performance Regenerative Receiver Design"?

b) How does it compare to this
http://www.electronics-tutorials.com...o-receiver.htm
and to the DR?

c) Is the article still available? Is there a link I should add to the
DR history?

tnx es 73 de n1jpr/i2

Dear Mr. Moriarity,

"Mister Moriarity"??? ;-) How about "John"?

R12 seems to be misspecified as well. On the
pdf schematic, R12 shows as "10W". I assumed
at the time that the W was simply a misconverted
omega symbol, so I had soldered in a 10 Ohm
resistor there.

Ten ohms is the "right" value, looking at a LM386
data sheet.

U1 does not amplify at all!!!

The LM386 should have plenty of gain if wired
correctly with these values. Something is very
wrong!

I am also suspicious of the connection of pin 7
on the LM386. I would disconnect it from the
junction of R12 and Cwhateveritis, and separately
bypass it to ground with a 10 microfarad cap
(plus side to pin 7). You might even get away
with not connecting pin 7 at all!

73, John - K6QQ

Hi, "John"!

I looked up an LM386 data sheet from National.
I also consulted your advice.

It turns out that the best solution is to
strike C18 and R12 completely, and to change
C20 to 10 microfarad.

Looking at the original schematic, it makes a
lot of sense... if you're trying to amplify
100 millivolt p-p of audio into 1 V (1000 millivolt)
p-p of audio, we clearly only need a factor
of 10 amplification, a.k.a. 20 decibel.

This is best accomplished simply by leaving
the connection between pins 1 and 8 open,
which by the way programs the LM386 for
its default 20 decibel amplification.

I found that R12 between pin 5 and pin 7 simply
provided a greater chance of a ground loop, so
eliminating that provided less chance of
motorboating even at 20 decibel amplification.

Then I took your advice to simply bypass
pin 7 to ground with a 10 microfarad capacitor.
This was easily enough done by changing
C10 from .1 microfarad to 10 microfarad.

With 100 millivolt p-p coming into the phase
splitter, the scope reads a clipped sine wave
at several volts... meaning that I have plenty
of gain to spare, I should even crank down the
input a little.

Because of the LM386 is amplifying a differential
signal, our effective amplification is actually
a factor of 20... so it would seem that nominal
input signal is actually 50 millivolt.

So, I believe that I have a working version of
that section of the circuit. I think I will
work on the detector portion (Q3) next, and
try injecting a 20 millivolt rf carrier at
14 Mhz.

I'll be back in a couple days with the results.

The Eternal Squire


John Moriarity wrote:
Dear Mr. Moriarity,


"Mister Moriarity"??? ;-) How about "John"?


R12 seems to be misspecified as well. On the
pdf schematic, R12 shows as "10W". I assumed
at the time that the W was simply a misconverted
omega symbol, so I had soldered in a 10 Ohm
resistor there.


Ten ohms is the "right" value, looking at a LM386
data sheet.


U1 does not amplify at all!!!


The LM386 should have plenty of gain if wired
correctly with these values. Something is very
wrong!

I am also suspicious of the connection of pin 7
on the LM386. I would disconnect it from the
junction of R12 and Cwhateveritis, and separately
bypass it to ground with a 10 microfarad cap
(plus side to pin 7). You might even get away
with not connecting pin 7 at all!

73, John - K6QQ

With a 10K resistor as R12, I got a VERY nice
volume that filled the entire room. The only bad
news is that when I remove the input signal, I get
about 400 hz motorboating.

Squire-

I believe R12 should be ten ohms. It provides a load at higher frequencies
where the speaker or headphone impedance might be too high for stability.

The motorboating is most likely feedback via the power supply line. Therefore,
the ten ohm series resistor should be higher (perhaps 100 ohms?), and the
filter capacitor at the IC's power terminal could be increased.

73, Fred, K4DII

Fred,

Maybe R12 needs to shunt the speaker to ground, rather than the
output of U1. If R12 is needed just for AC response, then it doesn't
make sense for it to conduct the DC between pins 5 and 7. By
shunting the speaker it should force the speaker impedance closer
to 10 ohms. I'll try that.

The Eternal Squire


Fred McKenzie wrote:
With a 10K resistor as R12, I got a VERY nice
volume that filled the entire room. The only bad
news is that when I remove the input signal, I get
about 400 hz motorboating.

Squire-

I believe R12 should be ten ohms. It provides a load at higher frequencies
where the speaker or headphone impedance might be too high for stability.

The motorboating is most likely feedback via the power supply line. Therefore,
the ten ohm series resistor should be higher (perhaps 100 ohms?), and the
filter capacitor at the IC's power terminal could be increased.

73, Fred, K4DII