ARRL FUD about BPL
 

Jim Nye wrote:
Unfortunately, the technically unsophisticated do not recognize the
difference between coherent and non-coherent noise, and this makes it
easy for the ARRL to spread its FUD. But the fact is that, if BPL
signals are heard at all, they are coherent (have a predictable phase
and amplitude) and therefore can be completely removed at the
receiver. This can be done in many ways, most of which amount to
nulling the BPL signals by introducing an identical signal which is
180 degrees out of phase with the original. As a matter of fact, most
current HF transceivers have what they call a "noise reduction" option
already built into them which uses the nulling method to accomplish
its goal.

?? I'm not aware of ANY HF transceivers that contain nulling-type noise
reduction circuitry. (and as an active contester with 30 years in ham
radio, I'm aware of pretty much every transceiver available)

Many transceivers do include a "noise blanker". This works by detecting
unusual peaks in signal strength and temporarily muting the receiver.
They can be very effective against some types of noise, such as gasoline
engine ignitions and electric fences. I have no idea how they do
against BPL.

There are external nulling units available - MFJ makes one. Such
devices may be impractical for many types of amateur operation - they
require readjustment when making substantial changes in frequency.

The coherency (assuming it exists) of BPL signals doesn't affect the
effectiveness of either type of noise reduction. (I suppose a third
type of noise reduction would be possible that would take the coherency
into account.)
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Jim Nye wrote:

On Tue, 19 Aug 2003 14:02:48 GMT, Doug Smith W9WI wrote:

Jim Nye wrote:

Unfortunately, the technically unsophisticated do not recognize the
difference between coherent and non-coherent noise, and this makes it
easy for the ARRL to spread its FUD. But the fact is that, if BPL
signals are heard at all, they are coherent (have a predictable phase
and amplitude) and therefore can be completely removed at the
receiver. This can be done in many ways, most of which amount to
nulling the BPL signals by introducing an identical signal which is
180 degrees out of phase with the original. As a matter of fact, most
current HF transceivers have what they call a "noise reduction" option
already built into them which uses the nulling method to accomplish
its goal.

?? I'm not aware of ANY HF transceivers that contain nulling-type noise
reduction circuitry. (and as an active contester with 30 years in ham
radio, I'm aware of pretty much every transceiver available)

Many transceivers do include a "noise blanker". This works by detecting


The Icom 746PRO contains such a circuit, which is separate from its
noise blanker function. Basically, the 746 samples slightly out of
band signals in order to determine the probable phase and amplitude
of coherent interference, and then it subtracts them from the in-band
signals. I believe that several of the Yaesu FT series transceivers
can do the same thing.

In any case, that's not the primary point of the post. The point is
that the ARRL has conveniently neglected the coherency property of BPL
leakage signals.



If the signal has predictable phase and amplitude, then it conveys no
information whatsoever. Otherwise I'd want an internet experience that
could predict what I want to download an do it for me. If it really
worked it could predict the content and create it on my machine. My
internet connection would be truly virtual.

Wow!

I don't think so.


craigm

In article ,
Jim Nye wrote:
[big snip]

The Icom 746PRO contains such a circuit, which is separate from its
noise blanker function. Basically, the 746 samples slightly out of band
signals in order to determine the probable phase and amplitude of
coherent interference, and then it subtracts them from the in-band
signals. I believe that several of the Yaesu FT series transceivers can
do the same thing.

In any case, that's not the primary point of the post. The point is
that the ARRL has conveniently neglected the coherency property of BPL
leakage signals.

This is true of a carrier; however, this property you call "coherency"
will disappear to the extent that the interfering signal is modulated, and
will effectively vanish if the modulation rate is high enough.

So the ARRL is alarmist about this new brand of interfering signal,
because a special case of it (unmodulated) that will not appear in the
real world could be dealt with by new hardware that cost more than my last
car?

The most charitable thing I can say is that you & I have different takes
on the word "alarmist".


--

R F Wieland Newark, DE 19711-5323 USA 39.68N 75.74W
Icom R75 Heathkit GR-81 Inverted-L in the attic
Reply to wieland at me dot udel dot edu

Jim Nye wrote:
?? I'm not aware of ANY HF transceivers that contain nulling-type noise
reduction circuitry. (and as an active contester with 30 years in ham
radio, I'm aware of pretty much every transceiver available)

Many transceivers do include a "noise blanker". This works by detecting

The Icom 746PRO contains such a circuit, which is separate from its
noise blanker function. Basically, the 746 samples slightly out of
band signals in order to determine the probable phase and amplitude
of coherent interference, and then it subtracts them from the in-band
signals. I believe that several of the Yaesu FT series transceivers
can do the same thing.

How does it determine which slightly out of band signals are broadband
noise and which are actual signals?

I can see a system where, for example, when tuned to 7006KHz the noise
reduction samples 6999KHz and subtracts what it finds there from the
signals on 7006. *Assuming* that the noise is consistent in phase and
amplitude across frequency (I'm not so sure that's a valid assumption
with BPL) I can see that cancelling the interference.

*Unless*...

there's a real live *signal* on 6999. Say, a MARS station running RTTY
morale traffic or a LSB drug-trafficing pirate or someone who wasn't
watching his VFO dial close enough or whatever. Haven't you now
frequency-converted that signal right on top of the guy you're listening
to on 7006? Admittedly 180 degrees out of phase, not that that makes
any difference...

The MFJ and similar systems work by sampling the *same* frequency
spectrum, but using a *different antenna*. This antenna (hopefully) has
a much worse signal-to-noise ratio - or better put for this application,
a much better noise-to-signal ratio! - than the normal station antenna.
In other words, it puts out mostly noise and very little signal.

You can then subtract the second antenna's output from that of the main,
reducing and hopefully completely nulling the noise while only slightly
if at all weakening the desired signal.

In any case, that's not the primary point of the post. The point is
that the ARRL has conveniently neglected the coherency property of BPL
leakage signals.

The coherency property is meaningless to the vast majority of amateur
radio operation.

Virtually none of the equipment is designed to take advantage of it.
And even if MFJ-type cancellation circuitry *was* present in most ham
receivers, the necessity for readjusting every time you change frequency
would make it useless for many hams.

--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com