Wasn't this the basis of the TNS?

If so, it worked on impulse noise above the slow AGC level.

The ANC-4 doesn't even let the noise into the first RF stage!!

DD, W1MCE

Crazy George wrote:

Jason:

Very similar to what you are describing is popularly known as a "Noise
Blanker" Motorola introduced their design for mobile radios in 1959 as an
"Extender" In the same time frame, Collins offered a model for the S-Line
and KWM-2. I designed a tube model for GE's Progress Line radios, and I
forget who designed the solid state version. The concept has been described
in numerous places, so do a bibliographic search of Engineering Index, or
Scientific Abstracts, or whatever that school has access to. You also need
to familiarize yourself with the concepts involved in noise balanced
squelch, which was patented by Motorola back in the late 30s or early 40s.
It will tell you how to do the audio noise level measurement meaningfully
and apply it usefully.

--
Crazy George
Remove NO and SPAM from return address
"Jason Hsu" wrote in message
om...

THE BIG QUESTION: How do you measure the audio noise level in a
receiver? Does anyone here know of any circuits that show the overall
audio noise level?

Let me tell you what this is all about.

SIDE NOTE: Thanks again to those of you who helped me with the
SWR/wattmeter project I worked on last semester. This project taught
me more about ferrite cores, op amps, and diodes than ANY class
possibly could. I learned about stray capacitance and what rails
mean. I also learned that not all 1N34A diodes are alike.

In this coming semester, I will be working on an even more ambitious
project - an automatic noise canceller for 160m to 10m. It will
definitely be a control system, and it may even use DSP. The device
will also require a motor for automatically adjusting the controls.
The idea is to design and build an automatic version of the Timewave
ANC-4 or the MFJ-1025/1026 RF noise cancellers.

The ANC-4 and MFJ-1025/1026 are manual devices. There are automatic
noise cancellation devices, but their adjustments are at the audio
level rather than the RF level.

The back panel of my device will contain:
1. Connector for the signal antenna
2. Connector for the transceiver
3. Connector for the noise antenna
4. DC power connector

The front panel of my device will contain:
1. Power switch and the obligatory idiot light to show that the power
is on
2. 2 audio connectors: one connects to the transceiver, and the other
connects to an external speaker
3. Frequency range control for choosing the inductance values, as the
proper inductance values in the RF noise cancelling circuit varies
with frequency
4. Phase range knob so that the phase shifter can cover all 360
degrees
5. Manual noise phase knob
6. Manual noise gain knob
7. LED display to show the noise level
8. Noise phase adjustment push-button: Pressing this button activates
the control system to adjust the phase shift of the noise.
9. Noise gain adjustment button: Pressing this button activates the
control system to adjust the gain of the noise.

Other features:
1. I need to design my automatic noise canceller so that parts won't
blow up if I transmit 100W through it. This probably requires some
type of automatic bypass circuitry.
2. Transmitted power must not reach the noise antenna (at least not
without a great deal of attenuation)
3. It also needs a low insertion loss.
4. A preamplifier would be desirable.

How it would work:
1. You manually turn the phase and gain controls to the minimum
settings. (Or I could put in a reset button to do that. No, that
would add too much complexity to the circuit.)
2. You select the band using the band inductance switch.
3. You move the phase polarity switch to the negative setting. If
the noise cancellation procedure does not work, it probably means the
opposite setting is required.
4. Press the noise gain adjustment button. The device adjusts the
noise gain until a change in the signal level (or the S meter) is just
noted. (Some type of derivative function would come into play.)
5. Press the noise phase adjustment button. The device adjusts the
noise phase shift so as to produce a null in the signal level (or the
S meter).
6. Steps 4 and 5 could be repeated to make further adjustments.
There might be away to activate the control system with just one
button.

Does anyone know of circuits that measure audio noise? Making the RF
noise canceller automatic requires an audio circuit to monitor the
noise level. This noise level needs to be converted into a large DC
voltage, which feeds the motors that turn the variable capacitor and
potentiometer.

Jason Hsu, AG4DG