|
Mine is remarkably stable.? It drifts a few Hz in the first few minutes, but nothing noticeable after that.? I wasn't able to find the original diodes anywhere in the USA - there were a couple on eBay at a stiff price.? So, I used the 1N459A which was recommended as a suitable replacement by someone on the forum a long time ago.
73, Floyd
|
Hi Floyd,
My neighbor has an electric fence which gives regular pops when listening to 40M. The NB reduces those quite a bit, but not completely. Now that you mention it, I might try replacing the diodes anyway, and see if it works any better.
The VFO on mine drifts quite a bit, even after nearly half an hour. How stable is yours?
Cheers,
Peter - VK2AN
|
Hi Peter.? Nice to hear from someone who has an SX-117.? Yes, mine had a problem with one of the diodes in the circuit - it wasn't shorted, but had a resistance of around 60 ohms in each direction.? After replacing the diodes, it appears to be working.? At this time, I have no noise here so can't comment on the effectiveness.? Now when I turn the NL on, strong CW signals (S9 + 20 dB) drop in level maybe 3-5 dB according to the S-Meter.? I don't hear any artifacts often associated with turning on a noise limiter in the presence of strong signals close in frequency.
73, Floyd - K8AC
|
It seems to me that no-one has actually answered your question.
I have an SX117 and the NB certainly doesn't reduce the signal to S1. It causes a very slight drop in audio on AM but almost no noticeable decrease on SSB. It does seem to be somewhat effective on pulse type noise, but not as effective as the modern ones.
I suspect yours has a fault.
Cheers,
Peter - VK2AN
|
Hello all,
Thought I would weigh in on this thread.?
I have an ANC-4 that I decided was not working. Sometimes there seemed to be an effect, othertimes none. So I sent it back to the factory for evaluation. This was $60 plus shipping both ways to learn there was nothing wrong with the unit.
I did chat with two folks at TimeWave and learned the following:
As the ANC-4 works by sampling noise, then inverting the noise signal and adding it to the main signal, it will only be successful if the noise on both antennas is matched. The manual recommends a short dipole close the ground for the noise antenna, but the folks at TimeWave said to use whatever works. That is to say, you should arrange the noise antenna as vertical, horizontal, or whatever just so you can ge the same noise signature and level on both antennas.
There is a level control on the ANC-4, but the range may not be sufficient to match both signals.?
I was told that the unit only works properly if there is a well characterized single noise source. That is, ?there should be something "tangible" to detect, invert and cancel.?
For random grunge from scores of SMPS sources coming from all directions in your neighborhood, the ANC-4 is likely to be ineffective. On the otherhand, if your neighbor's garage plasma cutter runs 24/7 you might just be able to zap it away.
This is the best case to sign off with "YMMV", as it certainly will.
Cheers,
=Randy= WB6MAI
toggle quoted message
Show quoted text
On Sat, 2024-06-15 at 20:41 -0400, don Root via groups.io wrote: Hello all. I just read the ANC-4 ?blurb.? ?It seems to me that if the noise comes from? wiring in the house, use a small noise ¡°antenna /wire near the¡± sourse or maybe near the wiring, but if the noise is from outside power lines, use a longer outdoor wire.? They ??leave the whole type of main antenna to be a mystery. No wonder ?there are reports that it works well and others that it is bogus. ?IMO the noise? location[s] and the antenna combinations used is missing, and must be a very big topic.???? don ? ? The ANC-4 by Timewave is a very effective device for limiting local noise. ?I get more than 40dB reduction, sometimes more, so that weak signals stand out against an almost silent background. ?MFJ makes a similar device. ?These devices use an active RF circuit to amplify the offending noise from a separate antenna, and then beat it against the same noise in your main antenna. ?They really work. I see some used ones online around 125 bucks. ? Preston WJ2V
On Jun 10, 2024, at 1:52 PM, Maynard Wright, P. E., W6PAP via <ma.wright@...> wrote: ? The use of a noise antenna and associated circuitry is independent of
the nature of the noise, whether or not it's periodic and whether or not
it's random.
Ideally, the signal antenna would receive the signal plus the offending
noise and the noise antenna would receive just the noise. The combining
network would be adjusted to combine the two signals so that their time
domain noise components would be equal in amplitude but opposite in
polarity so that they would cancel and leave only the desired signal at
the input to the receiver.
There are several potential difficulties that make this system less than
perfect in most, if not all, implementations, but it may reduce the
noise enough to be useful in some situations.
73,
Maynard
W6PAP
On 6/9/24 17:11, 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 ¨C Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
908-902-3831
*From:* [email protected] <[email protected]>
*On Behalf Of *Maynard Wright, P. E., W6PAP via
*Sent:* Sunday, June 9, 2024 7:31 PM
*To:* [email protected]
*Subject:* Re: [HallicraftersRadios] SX-117 noise limiter behavior
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
|
Hello all. I just read the ANC-4 ?blurb.? ?It seems to me that if the noise comes from? wiring in the house, use a small noise ¡°antenna /wire near the¡± sourse or maybe near the wiring, but if the noise is from outside power lines, use a longer outdoor wire.? They ??leave the whole type of main antenna to be a mystery. No wonder ?there are reports that it works well and others that it is bogus. ?IMO the noise? location[s] and the antenna combinations used is missing, and must be a very big topic.???? don ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Preston Douglas via groups.io
Sent: Tuesday, June 11, 2024 11:19 AM
To: [email protected]
Subject: Re: [HallicraftersRadios] SX-117 noise limiter behavior? The ANC-4 by Timewave is a very effective device for limiting local noise. ?I get more than 40dB reduction, sometimes more, so that weak signals stand out against an almost silent background. ?MFJ makes a similar device. ?These devices use an active RF circuit to amplify the offending noise from a separate antenna, and then beat it against the same noise in your main antenna. ?They really work. I see some used ones online around 125 bucks. ? Preston WJ2V
On Jun 10, 2024, at 1:52 PM, Maynard Wright, P. E., W6PAP via <ma.wright@...> wrote: ? The use of a noise antenna and associated circuitry is independent of
the nature of the noise, whether or not it's periodic and whether or not
it's random.
Ideally, the signal antenna would receive the signal plus the offending
noise and the noise antenna would receive just the noise. The combining
network would be adjusted to combine the two signals so that their time
domain noise components would be equal in amplitude but opposite in
polarity so that they would cancel and leave only the desired signal at
the input to the receiver.
There are several potential difficulties that make this system less than
perfect in most, if not all, implementations, but it may reduce the
noise enough to be useful in some situations.
73,
Maynard
W6PAP
On 6/9/24 17:11, 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 ¨C Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
908-902-3831
*From:* [email protected] <[email protected]>
*On Behalf Of *Maynard Wright, P. E., W6PAP via
*Sent:* Sunday, June 9, 2024 7:31 PM
*To:* [email protected]
*Subject:* Re: [HallicraftersRadios] SX-117 noise limiter behavior
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
-- don??? va3drl
|
The ANC-4 by Timewave is a very effective device for limiting local noise. ?I get more than 40dB reduction, sometimes more, so that weak signals stand out against an almost silent background. ?MFJ makes a similar device. ?These devices use an active RF circuit to amplify the offending noise from a separate antenna, and then beat it against the same noise in your main antenna. ?They really work. I see some used ones online around 125 bucks. ?
toggle quoted message
Show quoted text
On Jun 10, 2024, at 1:52 PM, Maynard Wright, P. E., W6PAP via < ma.wright@...> wrote:
The use of a noise antenna and associated circuitry is independent of the nature of the noise, whether or not it's periodic and whether or not it's random. Ideally, the signal antenna would receive the signal plus the offending noise and the noise antenna would receive just the noise. The combining network would be adjusted to combine the two signals so that their time domain noise components would be equal in amplitude but opposite in polarity so that they would cancel and leave only the desired signal at the input to the receiver. There are several potential difficulties that make this system less than perfect in most, if not all, implementations, but it may reduce the noise enough to be useful in some situations. 73, Maynard W6PAP On 6/9/24 17:11, 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 ¨C Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
908-902-3831
*From:* [email protected] <[email protected]>
*On Behalf Of *Maynard Wright, P. E., W6PAP via
*Sent:* Sunday, June 9, 2024 7:31 PM
*To:* [email protected]
*Subject:* Re: [HallicraftersRadios] SX-117 noise limiter behavior
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
|
The use of a noise antenna and associated circuitry is independent of
the nature of the noise, whether or not it's periodic and whether or not
it's random.
Ideally, the signal antenna would receive the signal plus the offending
noise and the noise antenna would receive just the noise. The combining
network would be adjusted to combine the two signals so that their time
domain noise components would be equal in amplitude but opposite in
polarity so that they would cancel and leave only the desired signal at
the input to the receiver.
There are several potential difficulties that make this system less than
perfect in most, if not all, implementations, but it may reduce the
noise enough to be useful in some situations.
73,
Maynard
W6PAP
toggle quoted message
Show quoted text
On 6/9/24 17:11, 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 ¨C Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
908-902-3831
*From:* [email protected] <[email protected]>
*On Behalf Of *Maynard Wright, P. E., W6PAP via groups.io
*Sent:* Sunday, June 9, 2024 7:31 PM
*To:* [email protected]
*Subject:* Re: [HallicraftersRadios] SX-117 noise limiter behavior
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
|
See the Collins 136B-2, used with the KWM-2 for details. This uses a
separate antenna such as the broadcast receiver whip, as a noise antenna.
FWIW, for the other meaning, i.e. a squelch, while they are mostly
found on FM receivers there are some HF communication receivers that
have them. These are used to eliminate noise between periodic
communications.
toggle quoted message
Show quoted text
On 6/10/2024 5:34 PM, Richard Knoppow wrote: Drake R4B and some other models. Also, Collins used a blanker with
separate antenna in some transceivers, have to look at the specs to jog
my memory.
On 6/10/2024 5:20 PM, Jim Whartenby via groups.io wrote:
I've looked and have not found a radio that uses a noise blanker.
All I
have seen is clippers which remove noise spikes above a set level.? The
guitar guys mention it but it is a squelch gate which is open below a
set value and closes above this set level.? So audio is muted for very
low passages; one assumes to remove background hiss.
Regards,
JIm
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
I always heard them called "duckers" although a ducker is really a
special application. I agree, a different animal.
toggle quoted message
Show quoted text
On 6/10/2024 5:37 PM, Mike Langner wrote: Noise blankers in Amateur Radio and in commercial sound installations ¨C
two very different animals!
Yes, noise blankers, typically called audio noise gates, are quite
common in performed music and in broadcasting.? I¡¯ve built a number of
studios for talk radio that use several microphones feeding a mic mixer
that automatically mutes any mic that nobody¡¯s talking into at the
moment.? Here¡¯s a typical example:
<> of one kind I¡¯ve
installed with great success.? There are also individual mic processors
that perform the same task along with compression, equalization, and
other voice enhancements:
<> .? I would expect to find some of these among the AM aficionados that use converted AM broadcast transmitters and inhabit 3885 and vicinity.
In PA systems they¡¯re great at stopping feedback when a person stops
talking and a compressor might otherwise raise the gain to the point of
feedback ¡°howling.¡±
These are completely different from noise blankers that we use on HF for
receive signal noise reduction.? The kind of noise blankers that reduce
ignition and similar noises typically cut off the IF or RF signal in the
receiver when a separate receiver and antenna receives the impulse noise
that we desire to be reduced.
Is there a version that works within a single receiver?? Yes, although
its effect isn¡¯t quite a great as the two antenna and receiver version.
Info on the single on-frequency version, sometimes called a noise
silencer, can be found here:
<> .
Incidentally, they also work well for lightning static.
For typical background hiss, atmospheric static, and the like, they¡¯re
practically worthless.
And now I¡¯ll just fade back into the background noise!
Interesting stuff!
Mike/
K5MGR
___________________________
Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@... <mailto:mlangner@...>
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Noise blankers in Amateur Radio and in commercial sound installations ¨C two very different animals!
Yes, noise blankers, typically called audio noise gates, are quite common in performed music and in broadcasting.? I¡¯ve built a number of studios for talk radio that use several microphones feeding a mic mixer that automatically mutes any mic that nobody¡¯s talking into at the moment.? Here¡¯s a typical example: of one kind I¡¯ve installed with great success.? There are also individual mic processors that perform the same task along with compression, equalization, and other voice enhancements: .? I would expect to find some of these among the AM aficionados that use converted AM broadcast transmitters and inhabit 3885 and vicinity.
In PA systems they¡¯re great at stopping feedback when a person stops talking and a compressor might otherwise raise the gain to the point of feedback ¡°howling.¡±
These are completely different from noise blankers that we use on HF for receive signal noise reduction.? The kind of noise blankers that reduce ignition and similar noises typically cut off the IF or RF signal in the receiver when a separate receiver and antenna receives the impulse noise that we desire to be reduced.
Is there a version that works within a single receiver?? Yes, although its effect isn¡¯t quite a great as the two antenna and receiver version.? Info on the single on-frequency version, sometimes called a noise silencer, can be found here: .
Incidentally, they also work well for lightning static.
For typical background hiss, atmospheric static, and the like, they¡¯re practically worthless.
And now I¡¯ll just fade back into the background noise!
Interesting stuff!
Mike/
K5MGR
___________________________
Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@...
|
Drake R4B and some other models. Also, Collins used a blanker with
separate antenna in some transceivers, have to look at the specs to jog
my memory.
toggle quoted message
Show quoted text
On 6/10/2024 5:20 PM, Jim Whartenby via groups.io wrote: I've looked and have not found a radio that uses a noise blanker.? All I
have seen is clippers which remove noise spikes above a set level.? The
guitar guys mention it but it is a squelch gate which is open below a
set value and closes above this set level.? So audio is muted for very
low passages; one assumes to remove background hiss.
Regards,
JIm
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
I've looked and have not found a radio that uses a noise blanker.? All I have seen is clippers which remove noise spikes above a set level.? The guitar guys mention it but it is a squelch gate which is open below a set value and closes above this set level.? So audio is muted for very low passages; one assumes to remove background hiss. Regards, JIm
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
Thanks jim, but first, is/has this topic swung to dealing with ignition noise only?? For an SX-117 ??? . interesting discussiuons, but what is the scope of it? Help..I¡¯M lost??? ¡. again. don ?
From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Monday, June 10, 2024 3:58 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] SX-117 noise limiter behavior ? Read the enclosed excerpt from TM 11-310.? The first page shows the noise antenna circuit and lists all design changes to the series of receivers.? I would think that the noise antenna would be short so as to only pick up ignition noise.? Anything longer would subtract form the signal of interest. Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy On Monday, June 10, 2024 at 01:55:22 PM CDT, don Root <drootofallevil@...> wrote: Maynard, your theory sounds mostly good, but we need some details on what is called an antenna; will it work with my 10 feet of haywire antenna? ? ? The operation of a noise antenna and associated circuitry are
independent of the nature of the noise, whether or not it's periodic and
whether or not it's random.
Ideally, the signal antenna would receive the signal plus the offending
noise and the noise antenna would receive just the noise. The combining
network would be adjusted to combine the two signals so that their time
domain noise components would be equal in amplitude but opposite in
polarity so that they would cancel and leave only the desired signal at
the input to the receiver.
There are several potential difficulties that make this system less than
perfect in most, if not all, implementations, but it may reduce the
noise enough to be useful in some situations.
73,
Maynard
W6PAP
--
don??? va3drl
|
Thanks jim, but first, is/has this topic swung to dealing with ignition noise only?? For an SX-117 ??? . interesting discussiuons, but what is the scope of it? Help..I¡¯M lost??? ¡. again. don ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Monday, June 10, 2024 3:58 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] SX-117 noise limiter behavior? Read the enclosed excerpt from TM 11-310.? The first page shows the noise antenna circuit and lists all design changes to the series of receivers.? I would think that the noise antenna would be short so as to only pick up ignition noise.? Anything longer would subtract form the signal of interest. Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy On Monday, June 10, 2024 at 01:55:22 PM CDT, don Root <drootofallevil@...> wrote: Maynard, your theory sounds mostly good, but we need some details on what is called an antenna; will it work with my 10 feet of haywire antenna? ? ? The operation of a noise antenna and associated circuitry are
independent of the nature of the noise, whether or not it's periodic and
whether or not it's random.
Ideally, the signal antenna would receive the signal plus the offending
noise and the noise antenna would receive just the noise. The combining
network would be adjusted to combine the two signals so that their time
domain noise components would be equal in amplitude but opposite in
polarity so that they would cancel and leave only the desired signal at
the input to the receiver.
There are several potential difficulties that make this system less than
perfect in most, if not all, implementations, but it may reduce the
noise enough to be useful in some situations.
73,
Maynard
W6PAP -- don??? va3drl
|
True: my BC-342, BC-312, etc. manual suggests routing the noise antenna
near the engine of the vehicle whose ignition noise is troublesome.
Maybe when the receivers weren't used in vehicles where that was
convenient, the noise suppression wasn't very useful and that's possibly
why it was discontinued, even to the point of not supplying spare parts
for the existing circuits.
73,
Maynard
W6PAP
toggle quoted message
Show quoted text
On 6/10/24 13:31, Richard Knoppow wrote: I see, since the two noise signals are coherent its possible to
cancel it by phasing. Would work on man made noise where the signal and
noise can be separated.
On 6/10/2024 1:12 PM, Maynard Wright, P. E., W6PAP via groups.io wrote:
Hi, Richard,
The system I described is not the same as the noise blanker internal to
the receiver. The circuitry that the Signal Corps used, and that has
been implemented by MFJ and others, works prior to the first RF
amplifier of the receiver and collects signals from two antennas. The
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
I see, since the two noise signals are coherent its possible to
cancel it by phasing. Would work on man made noise where the signal and
noise can be separated.
toggle quoted message
Show quoted text
On 6/10/2024 1:12 PM, Maynard Wright, P. E., W6PAP via groups.io wrote: Hi, Richard,
The system I described is not the same as the noise blanker internal to
the receiver. The circuitry that the Signal Corps used, and that has
been implemented by MFJ and others, works prior to the first RF
amplifier of the receiver and collects signals from two antennas. The
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Hi, Richard,
The system I described is not the same as the noise blanker internal to
the receiver. The circuitry that the Signal Corps used, and that has
been implemented by MFJ and others, works prior to the first RF
amplifier of the receiver and collects signals from two antennas. The
idea is to collect a signal contaminated by noise from one antenna and
just the noise from the second and then combine the two to cancel the
noise. The two antenna inputs on the BC-342 family are "SIGNAL ANTENNA"
and "NOISE ANTENNA." In the BC-342, the circuitry is internal to the
receiver but, if used, is inserted between the antenna and the first RF
stage. Other implementations are in separate boxes that connect to two
antennas and the input to the receiver.
To your question, Don, it depends on where the noise originates. If the
noise is local to your home, a short antenna that minimizes pickup of
the desired signal but receives the noise might be just the right thing.
You would then twiddle the amplitude and phase adjustments of the
combiner to minimize the noise in your receiver.
If the noise is from some distance away, you might have to fiddle with
positioning of the noise antenna so that the signal is minimized while
the noise is maximized. If you are receiving a signal from the same
direction from which the noise is coming, this may be difficult.
73,
Maynard
W6PAP
toggle quoted message
Show quoted text
On 6/10/24 12:33, Richard Knoppow wrote: A further note: The purpose of the blanker is more to prevent pulse
noise from desensitizing the receiver by being seen by the AVC as
signal. Although the noise pulses may be very short their amplitude can
be very high. The AVC system tends to integrate these pulses and causees
the AVC to desensitize the receiver. Also, and important, the presence
of these high amplitude pulses in the IF path can cause intermodulation
which can significantly exaggerate their effect. Also, narrow bandwidth
IF filters tend to stretch out the pulses, causing ringing and further
exaggerating their effect. Actually, the "holes" from the blanker may
also be stretched, also causing some strange effects.
In general, this type of noise eliminator works mostly for impulse
noise like ignition noise (does it exist any more?) and not for lower
level noise from arcing or of the sort generated by electronic circuits.
There are digital noise eliminators which do work pretty well for these.
I have some more but am blanking on a couple of names I need,
researchers into communication theory at Bell Labs. They showed that the
conventional idea of the effects of _random_ noise are not quite true.
So maybe more in a a while.
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Don Read the enclosed excerpt from TM 11-310.? The first page shows the noise antenna circuit and lists all design changes to the series of receivers.? I would think that the noise antenna would be short so as to only pick up ignition noise.? Anything longer would subtract form the signal of interest. Regards, Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
Maynard, your theory sounds mostly good, but we need some details on what is called an antenna; will it work with my 10 feet of haywire antenna? ?
From: [email protected] [mailto:[email protected]] On Behalf Of Maynard Wright, P. E., W6PAP via groups.io
Sent: Monday, June 10, 2024 2:22 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] SX-117 noise limiter behavior ? The operation of a noise antenna and associated circuitry are
independent of the nature of the noise, whether or not it's periodic and
whether or not it's random.
Ideally, the signal antenna would receive the signal plus the offending
noise and the noise antenna would receive just the noise. The combining
network would be adjusted to combine the two signals so that their time
domain noise components would be equal in amplitude but opposite in
polarity so that they would cancel and leave only the desired signal at
the input to the receiver.
There are several potential difficulties that make this system less than
perfect in most, if not all, implementations, but it may reduce the
noise enough to be useful in some situations.
73,
Maynard
W6PAP
--
don??? va3drl
|
A further note: The purpose of the blanker is more to prevent pulse
noise from desensitizing the receiver by being seen by the AVC as
signal. Although the noise pulses may be very short their amplitude can
be very high. The AVC system tends to integrate these pulses and causees
the AVC to desensitize the receiver. Also, and important, the presence
of these high amplitude pulses in the IF path can cause intermodulation
which can significantly exaggerate their effect. Also, narrow bandwidth
IF filters tend to stretch out the pulses, causing ringing and further
exaggerating their effect. Actually, the "holes" from the blanker may
also be stretched, also causing some strange effects.
In general, this type of noise eliminator works mostly for impulse
noise like ignition noise (does it exist any more?) and not for lower
level noise from arcing or of the sort generated by electronic circuits.
There are digital noise eliminators which do work pretty well for these.
I have some more but am blanking on a couple of names I need,
researchers into communication theory at Bell Labs. They showed that the
conventional idea of the effects of _random_ noise are not quite true.
So maybe more in a a while.
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
The reverse phase cancellation is not how I understand the blanker
to work although I think there are noise eliminators that do work this
way. My understanding is that the signal from the noise antenna is
detected and converted into a DC pulse which is applied to a gate in the
signal path which cuts it off momentarily for the length of time the
pulse lasts. Since both the detection and gating can be done where the
bandwidth is fairly wide the rise and fall times of the gating signal
can be made quite short. The device must be such that there is not an
excessive time delay between the noise pulse in the receive chain and
the muting or gating signal. Presumably, there is some delay in both
signal and noise channels and they can be matched by careful design. The
advantage of this system over the type of noise gate that picks up the
signal from the IF is that the bandwidth of the noise pulse can be
narrower and the rise and fall times of the pulse are shorter thus
reducing the amount of time the signal channel is cut off.
I am pretty sure Collins used this system, perhaps in its first
mobile transceivers. Also, since the kind of noise pulse the blanker is
supposd to work on is very short it will have a spectrum well into the
the HF or VHF range so that a short antenna antenna can be used and
desired signals will not get into the blanker.
Again the blanker works by shutting off the signal path briefly
during the noise pulse.
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On 6/10/2024 11:22 AM, Maynard Wright, P. E., W6PAP via groups.io wrote: The operation of a noise antenna and associated circuitry are
independent of the nature of the noise, whether or not it's periodic and
whether or not it's random.
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Floyd - K8AC
Peter E
don Root
Mike Langner
Jim Whartenby