?

True, but a good approximation of the noise in the vicinity of the receiver antenna can be sampled and used to reduce the noise coming in along with the desired signal from the main antenna.? The noise from the secondary system, must, as you point out, be as close as possible to the noise being picked up by the primary antenna.? Cancellation is, of course, incomplete, so elimination is not possible, but quite significant reduction is indeed possible and has been proven in the field.? Needless to say, the noise receiving system must not pick up much of the desired signal.? This can be effected both by operating the two receive systems on dissimilar frequencies, and also by utilizing a receive antenna location that will pick up the closest possible envelope to the noise the primary antenna receives but picks up a minimal amount of the desired signal.

How much improvement is available?? Results vary widely with the nature of the noise and the environment in which the noise is being received.? Still, the reduction is often very, very worthwhile!

As always, your mileage may vary!!

Mike/
K5MGR
_____________________________________________

?

?

?

It seems to me, that since noise is neither correlate-able or stochastic, elimination is not possible. Also the multiple antenna theory is out the window since RF generated noise travels at the speed of light. 73 – Mike

?

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

908-902-3831

?

?

Another technique for reducing or eliminating noise was to introduce
local noise to the front end of a receiver from a local "noise antenna."
The amplitude and phase of that noise could be adjusted to, hopefully,
cancel the noise received by the signal antenna.

Early BC-342 and BC-312 receivers featured a noise suppression circuit
of this type. War Department TM 11-850 states that the noise antenna
was intended to eliminate ignition noise when the receiver was mounted
in a vehicle.

By the time my BC-342-N was born (1942), the noise antenna and
associated circuitry were omitted, so that circuit may not have worked
well. The September, 1946 revision of the TM notes that spare parts
were no longer available for the noise suppression circuit and
recommends removing it if any of the components fail.

MFJ has featured at least one similar unit, the MFJ-1026, which is now
listed as sold out. There are other such units available but I have no
experience with them.

73,

Maynard
W6PAP

?

Well, you are speaking of _random_ noise, like natural radio noise
but blankers are intended to work on periodic signals such as ignition
noise.

On 6/9/2024 5:11 PM, Mike Feher wrote:

It seems to me, that since noise is neither correlate-able or
stochastic, elimination is not possible. Also the multiple antenna
theory is out the window since RF generated noise travels at the speed
of light. 73 – Mike

Mike B. Feher, N4FS

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

I am seeing a picture in my mind of a kitchen with motorcycle parts
all over. Smells strongly of gasoline and kerosene. I don't remember
where this comes from. Some low life I once had as friends (maybe my
brother). Its not just wives, I would probably kill if someone did this
to MY kitchen (except me).

On 6/9/2024 7:07 PM, Bob wrote:

Tom, Kinda like rebuilding a carburetor on the kitchen table! LOL
Bob W4JFA

On Sun, Jun 9, 2024, 8:55 PM Thomas Latimer via groups.io
<> <tlatimer4@...
<mailto:[email protected]>> wrote:

__
And I wonder how many of them, *if married*, are no longer with us
??? hahahahaha

Tom Latimer

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

?

It IS periodic, not random. Each noise pulse has a definite
signature. It is well above average random noise. A noise blanker of any
sort desensitizes the signal channel during the noise pulse. In fact,
the pulse can be singular. It is important that the timing is correct,
that is, if the blanker or the channel it blanks, has too much time
delay the pulse and hole do not coincide. Mostly they do and digital
circuits can provide delay where necessary to synchronize them.
Perhaps I should not have said periodic but there is a better term
for non-random which I am not thinking of at the moment (blanking on it).
The kind of noise that you can't cancel is random noise generated
in two different places, such as in the receiver vs: from space via an
antenna. They don't cancel, they combine.

On 6/9/2024 6:26 PM, Mike Feher wrote:

Rich – Ignition noise is far from periodic. It may approach that at a
constant speed, and may be somewhat predictable in the same vehicle
where the receiver is. An SX117 for example and most others are used at
home and are subject to numerous noise sources, the combination of which
is anything but periodic. 73 – Mike

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

908-902-3831

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

Tom, Kinda like rebuilding a carburetor on the kitchen table! LOL
Bob W4JFA

On Sun, Jun 9, 2024, 8:55 PM Thomas Latimer via groups.io
<> <tlatimer4@...
<mailto:[email protected]>> wrote:

__
And I wonder how many of them, *if married*, are no longer with us
??? hahahahaha

Tom Latimer

Rich – Ignition noise is far from periodic. It may approach that at a
constant speed, and may be somewhat predictable in the same vehicle
where the receiver is. An SX117 for example and most others are used at
home and are subject to numerous noise sources, the combination of which
is anything but periodic. 73 – Mike

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

908-902-3831

?

Well, you are speaking of _random_ noise, like natural radio noise
but blankers are intended to work on periodic signals such as ignition
noise.

On 6/9/2024 5:11 PM, Mike Feher wrote:

It seems to me, that since noise is neither correlate-able or
stochastic, elimination is not possible. Also the multiple antenna
theory is out the window since RF generated noise travels at the speed
of light. 73 – Mike

Mike B. Feher, N4FS

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

?

It seems to me, that since noise is neither correlate-able or stochastic, elimination is not possible. Also the multiple antenna theory is out the window since RF generated noise travels at the speed of light. 73 – Mike

?

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

908-902-3831

?

?

Another technique for reducing or eliminating noise was to introduce
local noise to the front end of a receiver from a local "noise antenna."
The amplitude and phase of that noise could be adjusted to, hopefully,
cancel the noise received by the signal antenna.

Early BC-342 and BC-312 receivers featured a noise suppression circuit
of this type. War Department TM 11-850 states that the noise antenna
was intended to eliminate ignition noise when the receiver was mounted
in a vehicle.

By the time my BC-342-N was born (1942), the noise antenna and
associated circuitry were omitted, so that circuit may not have worked
well. The September, 1946 revision of the TM notes that spare parts
were no longer available for the noise suppression circuit and
recommends removing it if any of the components fail.

MFJ has featured at least one similar unit, the MFJ-1026, which is now
listed as sold out. There are other such units available but I have no
experience with them.

73,

Maynard
W6PAP

It seems to me, that since noise is neither correlate-able or
stochastic, elimination is not possible. Also the multiple antenna
theory is out the window since RF generated noise travels at the speed
of light. 73 – Mike

Mike B. Feher, N4FS

Another technique for reducing or eliminating noise was to introduce
local noise to the front end of a receiver from a local "noise antenna."
The amplitude and phase of that noise could be adjusted to, hopefully,
cancel the noise received by the signal antenna.

Early BC-342 and BC-312 receivers featured a noise suppression circuit
of this type. War Department TM 11-850 states that the noise antenna
was intended to eliminate ignition noise when the receiver was mounted
in a vehicle.

By the time my BC-342-N was born (1942), the noise antenna and
associated circuitry were omitted, so that circuit may not have worked
well. The September, 1946 revision of the TM notes that spare parts
were no longer available for the noise suppression circuit and
recommends removing it if any of the components fail.

MFJ has featured at least one similar unit, the MFJ-1026, which is now
listed as sold out. There are other such units available but I have no
experience with them.

73,

Maynard
W6PAP

There are some, who put entire chassis in the dishwasher as long as things like transformers.

From our file department.

K2WH

?

Another technique for reducing or eliminating noise was to introduce
local noise to the front end of a receiver from a local "noise antenna."
The amplitude and phase of that noise could be adjusted to, hopefully,
cancel the noise received by the signal antenna.

Early BC-342 and BC-312 receivers featured a noise suppression circuit
of this type. War Department TM 11-850 states that the noise antenna
was intended to eliminate ignition noise when the receiver was mounted
in a vehicle.

By the time my BC-342-N was born (1942), the noise antenna and
associated circuitry were omitted, so that circuit may not have worked
well. The September, 1946 revision of the TM notes that spare parts
were no longer available for the noise suppression circuit and
recommends removing it if any of the components fail.

MFJ has featured at least one similar unit, the MFJ-1026, which is now
listed as sold out. There are other such units available but I have no
experience with them.

73,

Maynard
W6PAP

Can't read the whole book:-) Look at any of the classical receivers,
say a Hallicrafters S-40. That has a series diode noise limiter. I think
the S-20R has a shunt limiter. Series limiters began to appear in the
early 1940s. They were "automatic" in that the clipping level depended
on the carrier strength. For AM signals the carrier would set the
limiter for about 100% modulation, keeping the distortion fairly low
(still had distortion). When there was no carrier, in between stations,
the clipping was lower. When used with a BFO the BFO was the carrier and
might prevent effective noise reduction. Receivers with shunt limiters
often had a front panel adjustment. It could be set to minimize
distortion on AM and to provide fairly deep clipping for CW where audio
distortion was not critical.
There were many variations of noise limiters, for instance see the
schematic for the Hammarlund SP-200 Super-Pro which uses a triode
limiter and the patented limiter in the RCA AR-88. The AR-88 limiter is
pretty effective.
Most limiters work at audio. They limit or clip off the peaks of the
detected audio. This has no effect on noise that gets into the AVC. The
AVC tends to integrate the noise pulses which affect it just as a
carrier would and tend to desensitize the receiver.
A noise blanker, following the idea of J.J.Lamb, works at the IF
frequency. The wider the band where its applied the better. The blanker
sees pulses, like impulse noise from ignition, which are above a pre-set
threshold, and produces DC pulses from them which are applied to a gate
circuit which cuts off the IF channel during the noise. This prevents
the pulses from getting to the AVC detector so they have no effect on
the sensitivity of the receiver. At least that is how its supposed to
work. But, the bandwidth where the pulses are detected must be wide
enough so it does not stretch out the pulses or cause them to be
smeared. If too narrow the muting signal will be too broad and reduced
in amplitude so the muting will become obvious and reduced in
effectiveness. In addition, the bandwidth of the circuit where the
muting pulses are applied must also be wide enough to the "holes"
punched in the signal are not stretched out. Modern noise blankers do
this fairly well but the first attempt at a practical embodiment, namely
the NB in the SX-28, did not work very well. Probably neither Lamb or
the Hallicrafters engineers fully understood the requirements. In fact,
there is a service letter for the SX-28 from Hallicrafters showing how
to competely disable and remove the Lamb noise blanker and replace it
with a conventional series noise limiter.
The arrangement in the SX-117 is not a noise blanker since it
doesn't poke holes in the IF signal. Rather it is a peak limiter working
in the IF rather than for detected audio. It is able to limit the peaks
of the IF signal which is similar to the effect of the noise blanker in
that it prevents large noise pulses from being integrated by the AVC
detector and causing the AVC signal to desensitize the receiver. Of
course it also affects the audio, reducing the audibility of the noise.
However, since it is not seeing detected carrier as it would following
the detector, its clipping level is not controlled by the signal
strength and it can clip modulation peaks unless some method is
available to reduce the input signal to the limiter to a low level where
the modulation peaks are not too much affected. It will have the virtue
of working well for CW and SSB where no carrier appears in the IF. The
effective carrier is the BFO, which is injected at the detector (either
diode or product) at a point after the clipping circuit. Since the
carrier for AM is part of the signal at IF it does affect the level at
the clipping diodes and can be distorted. The instruction book suggests
reducing the RF gain. That reduces the level everywhere the AVC or
manual gain works, including the level at the clipping diodes.
So, since probably the receiver will be used more often for CW and
SSB than for AM this system works quite weil and is much simpler than a
true noise blanker. Perhaps there should also have been a conventional
audio limiter available for AM but it would have cost something to have
it and the necessary switching.
Hallicrafters had a lot of innovative circuits over they years,
some worked well, some, like the Lamb blanker, were not embodied well
and didn't work so well. BTW, Lamb also invented the single crystal IF
filter. I think National was the first to employ it but Hallicrafters
was not far behind. It became universal in better quality receivers.
FWIW the best of the crystal filter circuits is the one patented by
Hammarlund and first used in the HQ-120-X.
I am writing too much. I hope this is of some interest.

On 6/8/2024 7:16 PM, don Root wrote:

Back to noise? stuff only

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

Back to noise? stuff only

?

Well, that's useful to know. Actually, I have some Kroil, my local
hardware store just began to stock it along with gun cleaning stuff.
I agree that recommendations for cleaning based on experience would
be valuable to the list. I also use Barkeepers Friend and also Zud which
appears to be identical. I also use plain toothpaste for cleaning
delicate items and polishing plastic. It works as well as the expensive
special plastic polishing cleaners.
This problem is interesting because Hallicrafters used an unusual
noise limiter arrangement. It would be interesting to know what other
receivers use it. Namely, a diode clipping limiter in the IF rather than
detected audio. In the SX-117 it serves to keep the noise peaks from
activating the AVC, which is the purpose of the Lamb type noise blanker,
but is much simpler. However, it does not have the advantage of the
"automatic" series noise limiter found in older receivers of minimizing
distortion on AM. It should work better for CW or SSB where the BFO in
the usual set up makes the noise limiter inactive.
Hallicrafters was the first to use the Lamb type blanker (in the
SX-28) but it did not work well there and I suspect they did not quite
understand how it works.

On 6/8/2024 8:00 AM, Jim Whartenby via groups.io wrote:

Richard
I am recommending penetrating oil to clean and lube switches and pots.
Kroil, Deoxit and the like are effective but are also expensive.? Just
trying to point out that there are alternatives to name brand items
which also do a decent job at a very reasonable price.

Perhaps we should share some cleaning tips on the reflector.? I am sure
that there are many products that do a decent job and are less
expensive.? I can recommend Bar Keeper's Friend for general metal
cleaning, it works well for me.? For wood cabinets, waterless hand
cleaner also does a decent job without harming the remining finish.
Regards,
Jim

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998 ?

Richard
I am recommending penetrating oil to clean and lube switches and pots.
Kroil, Deoxit and the like are effective but are also expensive.? Just
trying to point out that there are alternatives to name brand items
which also do a decent job at a very reasonable price.

Perhaps we should share some cleaning tips on the reflector.? I am sure
that there are many products that do a decent job and are less
expensive.? I can recommend Bar Keeper's Friend for general metal
cleaning, it works well for me.? For wood cabinets, waterless hand
cleaner also does a decent job without harming the remining finish.
Regards,
Jim