Electronics Forums > Help needed understanding the ANC-4 design

# Help needed understanding the ANC-4 design

Jason Hsu
Guest
Posts: n/a

 10-15-2003, 01:34 AM
http://www.timewave.com/Acrobat/ANC_4TW8x11a.pdf

The schematic is on the last page. Has anyone here worked with a
similar circuit? I'll explain what little I do understand so you can
build on this.

My questions:
1. What is the Q1 transistor for? Is Q1 an amplifier or just a
buffer? At DC, I notice that it's fed by a supply voltage just under
12V (only 20 ohms and some inductance away from 12V). The CR1 and CR2
large signals. Capacitors C3 and C2 couple the RF to ground. I
assume that R3, R4, and R8 play a role in determining the gain. (I
can't remember enough of FETs to show the exact relationship.) The RF
output must be the voltage across T1 and is not connected to ground.
The inductance provides RF impedance between Q1 and the power supply.
2. What does transformer T1 do? I notice that the not-quite-12V DC
(I'll call it 11.8V DC) is connected to two of the T1 windings. So if
the input of T1 is .01V RF, it extends from 11.79V DC to 11.80V DC.
Then the output would extend from 11.80V DC to 11.81V DC. Until I get
an answer from Timewave, any idea what the turns ratio and inductance
values might be? Does it play a role in the noise phase adjuster? Do
I need to treat this as a current transformer rather than a voltage
transformer?
3. How does the noise phase shifter work? How does noise phase
shifter work? Adjusting the value of potentiometer R6 is supposed to
change the frequency response. The phase shift should vary between
about -pi/2 and +pi/2 depending on how the pot is adjusted, but I'm
not getting anywhere in the simulations. The FREQ RANGE switch should
control where the phase shift equals 0, but I can't make any sense of
this, either. Unfortunately, information on the transformers is not
provided. But even assuming 1:1, 10:1, and 1:10 turns ratios on
FT50-43 toroids isn't helping. I must be thinking about the circuit
in the wrong manner. The adjustment for the noise gain seems
straightforward enough to me - the pot controls a simple voltage
divider.
4. What is the Q2 transistor for? It's also fed by a supply voltage
just under 12V (only 10 ohms and 2 inductors away from the 12V power
supply). Capacitor C8 seems to be like capacitor C2 - coupling
capacitor. I guess R9 and R10 play a role in setting the gain, like
R8, R3, and R4 in Q1.
5. What does transformer T2 do? The strange thing is that the DC
power supply is connected to the OUTPUT winding. I'm lost.
6. How does the noise gain work? Is the R12 pot a simple voltage
divider? I notice that C11 lies between R12 and Q3, so it has no DC
connection to it. I also notice that part of this pot is in parallel
to R37.
7. What does Q3 do? I don't remember my BJT transistor theory very
well either. The collector is 2 inductors away from the 12V power
supply and is thus connected at DC but isolated at RF. C12 is a
coupling capacitor, so R16 plays a DC role. R13, R14, R15, and R16
determine the gain.
8. How exactly does T3 work? Again, there is a DC supply voltage on
the output side.
9. What does Zener diode CR12 do? Do it, CR4, and CR3 play a role in
dealing with unexpected large RF signals, or am I off base here?

I don't yet understand the T/R switch at the bottom left of the page,
but I'll save that for another post.

Jason Hsu, AG4DG
usenet AAAAAATTTTTTTTT jasonhsu.com

ehsjr@bellatlantic.net
Guest
Posts: n/a

 10-15-2003, 02:35 AM

Jason Hsu wrote:
>
> http://www.timewave.com/Acrobat/ANC_4TW8x11a.pdf
>
> The schematic is on the last page. Has anyone here worked with a
> similar circuit? I'll explain what little I do understand so you can
> build on this.
>
> My questions:
> 1. What is the Q1 transistor for? Is Q1 an amplifier or just a
> buffer? At DC, I notice that it's fed by a supply voltage just under
> 12V (only 20 ohms and some inductance away from 12V). The CR1 and CR2
> large signals. Capacitors C3 and C2 couple the RF to ground. I
> assume that R3, R4, and R8 play a role in determining the gain. (I
> can't remember enough of FETs to show the exact relationship.) The RF
> output must be the voltage across T1 and is not connected to ground.
> The inductance provides RF impedance between Q1 and the power supply.
> 2. What does transformer T1 do? I notice that the not-quite-12V DC
> (I'll call it 11.8V DC) is connected to two of the T1 windings. So if
> the input of T1 is .01V RF, it extends from 11.79V DC to 11.80V DC.
> Then the output would extend from 11.80V DC to 11.81V DC. Until I get
> an answer from Timewave, any idea what the turns ratio and inductance
> values might be? Does it play a role in the noise phase adjuster? Do
> I need to treat this as a current transformer rather than a voltage
> transformer?
> 3. How does the noise phase shifter work? How does noise phase
> shifter work? Adjusting the value of potentiometer R6 is supposed to
> change the frequency response. The phase shift should vary between
> about -pi/2 and +pi/2 depending on how the pot is adjusted, but I'm
> not getting anywhere in the simulations. The FREQ RANGE switch should
> control where the phase shift equals 0, but I can't make any sense of
> this, either. Unfortunately, information on the transformers is not
> provided. But even assuming 1:1, 10:1, and 1:10 turns ratios on
> FT50-43 toroids isn't helping. I must be thinking about the circuit
> in the wrong manner. The adjustment for the noise gain seems
> straightforward enough to me - the pot controls a simple voltage
> divider.
> 4. What is the Q2 transistor for? It's also fed by a supply voltage
> just under 12V (only 10 ohms and 2 inductors away from the 12V power
> supply). Capacitor C8 seems to be like capacitor C2 - coupling
> capacitor. I guess R9 and R10 play a role in setting the gain, like
> R8, R3, and R4 in Q1.
> 5. What does transformer T2 do? The strange thing is that the DC
> power supply is connected to the OUTPUT winding. I'm lost.
> 6. How does the noise gain work? Is the R12 pot a simple voltage
> divider? I notice that C11 lies between R12 and Q3, so it has no DC
> connection to it. I also notice that part of this pot is in parallel
> to R37.
> 7. What does Q3 do? I don't remember my BJT transistor theory very
> well either. The collector is 2 inductors away from the 12V power
> supply and is thus connected at DC but isolated at RF. C12 is a
> coupling capacitor, so R16 plays a DC role. R13, R14, R15, and R16
> determine the gain.
> 8. How exactly does T3 work? Again, there is a DC supply voltage on
> the output side.
> 9. What does Zener diode CR12 do? Do it, CR4, and CR3 play a role in
> dealing with unexpected large RF signals, or am I off base here?
>
> I don't yet understand the T/R switch at the bottom left of the page,
> but I'll save that for another post.
>
> Jason Hsu, AG4DG
> usenet AAAAAATTTTTTTTT jasonhsu.com

or were you doing something on DSP? In any event, thanks
for posting the schematic! I'll look at it in detail when
I can, but I'll comment on the xsistors: for the FETs, the
voltage (signal) at the gate controls the current thru the
source-drain. For the bipolar, the current at the base
controls the current thru the emitter-collector. All of
them are amps that drive the transformers. At a glance,
the xformers appear to be auto-transformers to boost the
signal voltage.

mkelly@powerup.com.au
Guest
Posts: n/a

 10-15-2003, 01:56 PM
I wonder if they use fets as variable capacitors to tune the
resonant circuits? Works well in VFOs.

I will study it. I have one but this is the 1st time I've
seen
a schematic. Thanks

Murray vk4aok

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Joerg Electronic Design 37 05-31-2013 03:18 AM JW Electronic Design 58 05-16-2013 03:43 AM Flyndad123 Electronic Projects 6 04-16-2013 07:00 AM Jason Hsu Electronic Design 2 10-15-2003 01:56 PM Jason Hsu Electronic Basics 2 10-15-2003 01:56 PM