Getting a buzz, the wrong way

[Tony Estep]

I dragged my scope up to the shack to measure the voltage on antenna A when
I transmit on antenna B. I got the answer to that, but I also got a look at
a sorry phenomenon that probably affects a lot of others on this reflector.

If you have a wire antenna, disconnect it, put 50 ohms across the coax and
hook it to your scope. If you are like me, you will see a hideous waveform
of mixed harmonics of 60 hz, along with a witch's brew of various components
of hash and buzz. And not a small amount, either; I have more than 200 mV
RMS of that crap coming in on one of my antennas. It's like a vlf 1mW qrpp
transmitter feeding directly into your receiver, while you're trying to
listen to HF. And I live in a fairly sparse suburban neighborhood -- it has
to be worse as you move in closer to town. Of course, 99.9% of it doesn't
make it through the bandpass filters in the rx, but there are just enough of
those evil buzzy harmonics that do get in, and end up right on top of the
weak signals we're trying to hear. I guess we all know that the noise is
there, but seeing it on your scope with such a pronounced amplitude is a sad
experience.

73,
Tony KT0NY
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[Mike WA8BXN]

Tony,
 
I think its closer to 0% of the 60 Hz stuff will really make it into a good
receiver. Take a look with your scope at what gets past the first tuned
circuit of a receiver. Noise that you hear in a receiver is really at the
frequency you are tuned to, not a harmonic of 60 Hz. Some simple receiver
circuits can hum on signals but I think the effect is for a reason different
from picking up 60 Hz on the antenna.
 
 
73 - Mike WA8BXN
-------Original Message-------
 
From: Tony Estep
Date: 1/7/2011 10:05:06 PM
To: Elecraft
Subject: [Elecraft] Getting a buzz, the wrong way
 
I dragged my scope up to the shack to measure the voltage on antenna A when
I transmit on antenna B. I got the answer to that, but I also got a look at
A sorry phenomenon that probably affects a lot of others on this reflector.
 
If you have a wire antenna, disconnect it, put 50 ohms across the coax and
Hook it to your scope. If you are like me, you will see a hideous waveform
Of mixed harmonics of 60 Hz, along with a witch's brew of various components

Of hash and buzz. And not a small amount, either; I have more than 200 mV
RMS of that crap coming in on one of my antennas. It's like a vlf 1mW qrpp
Transmitter feeding directly into your receiver, while you're trying to
Listen to HF. And I live in a fairly sparse suburban neighborhood -- it has
To be worse as you move in closer to town. Of course, 99.9% of it doesn't
Make it through the bandpass filters in the rx, but there are just enough of

Those evil buzzy harmonics that do get in, and end up right on top of the
Weak signals we're trying to hear. I guess we all know that the noise is
There, but seeing it on your scope with such a pronounced amplitude is a sad

Experience.
 
73,
Tony KT0NY
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[k6dgw]

I only did this twice.  The first time was pretty discouraging, I'm a
little less than 200 km from the old Middletown CA LORAN-C station, and
I was seeing around a half a volt of very obvious LORAN pulses.  It
didn't affect me on 160 directly, but ... the USCG shut down LORAN-C in
2009-2010, and now the K3 NB works great on 160.  Never did before.  I
remember as a kid, in So. Central Los Angeles, our TV antennas brought
the 300-ohm twinlead down to a window where it connected to a lightning
arrestor, and then went inside.  You could put your fingers across the
two terminals and feel the buzz.  You didn't want to lick your fingers
first :-)  Without LORAN-C, my noise peaks are running around 100-150mv,
we're in a moderately rural area.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2011 Cal QSO Party 1-2 Oct 2011
- www.cqp.org

On 1/7/2011 7:04 PM, Tony Estep wrote:

> If you have a wire antenna, disconnect it, put 50 ohms across the coax and
> hook it to your scope. If you are like me, you will see a hideous waveform
> of mixed harmonics of 60 hz, along with a witch's brew of various components
> of hash and buzz. And not a small amount, either; I have more than 200 mV
> RMS of that crap coming in on one of my antennas.
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[Don Wilhelm-4]

  Tony,

That is the reason receivers have bandpass filters - to filter out all
that off-frequency trash.
Yes, there is a lot of stuff that can be seen on any antenna.  I see
much of the same in my very sparely populated suburban/rural area - I
cannot see any neighbor's house and I am sitting in the middle of 11
acres with a 1/4 mile driveway.

If you want a better picture, put a bandpass filter for the band of
interest between the antenna and the 'scope, and you should see a much
more clear picture of what the receiver is "seeing".

73,
Don W3FPR

On 1/7/2011 10:04 PM, Tony Estep wrote:

> I dragged my scope up to the shack to measure the voltage on antenna A when
> I transmit on antenna B. I got the answer to that, but I also got a look at
> a sorry phenomenon that probably affects a lot of others on this reflector.
>
> If you have a wire antenna, disconnect it, put 50 ohms across the coax and
> hook it to your scope. If you are like me, you will see a hideous waveform
> of mixed harmonics of 60 hz, along with a witch's brew of various components
> of hash and buzz. And not a small amount, either; I have more than 200 mV
> RMS of that crap coming in on one of my antennas. It's like a vlf 1mW qrpp
> transmitter feeding directly into your receiver, while you're trying to
> listen to HF. And I live in a fairly sparse suburban neighborhood -- it has
> to be worse as you move in closer to town. Of course, 99.9% of it doesn't
> make it through the bandpass filters in the rx, but there are just enough of
> those evil buzzy harmonics that do get in, and end up right on top of the
> weak signals we're trying to hear. I guess we all know that the noise is
> there, but seeing it on your scope with such a pronounced amplitude is a sad
> experience.
>

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[Jim Brown-10]

On 1/7/2011 7:04 PM, Tony Estep wrote:
> If you have a wire antenna, disconnect it, put 50 ohms across the coax and
> hook it to your scope. If you are like me, you will see a hideous waveform
> of mixed harmonics of 60 hz,

If you see a lot of 60Hz and its harmonics on a scope as you have
described here, I would STRONGLY suspect a "pin 1 problem" in the scope.
The most common form of a Pin 1 Problem is the mis-connection of a cable
shield to internal circuitry rather than to the equipment chassis.
Another common form is the connection of the power system equipment
ground (the Green wire) to internal wiring, rather than to the chassis.

With either (or both) of these design errors, any current flowing on
either or both of those leads (the cable shield and/or the green wire)
flows through the equipment, creates a voltage drop on that wiring that
is added to the signal path and amplified. If it is modulated RF, it is
often detected, and is a common cause of RFI.

73, Jim Brown K9YC
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[George & Jan]

Actually it is more than likely there is no "Pin #1" issue here!
The scope is just giving you an accurate representative of what it is
actually picking up from the antenna feeding a very high input impedance
over the full bandpass of the input amp.

BTW - For those of us who have a living in professional audio, video and RF,
the proper term for what you call the "Pin #1" problem is a Ground Loop - or
at least that is the term we have used for the 50 years I was in radio & TV
broadcasting & video production.

George
AI4VZ
- - - - - - - - - - - - - - -

If you see a lot of 60Hz and its harmonics on a scope as you have
described here, I would STRONGLY suspect a "pin 1 problem" in the scope.

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[Tony Estep]

On Wed, Jan 12, 2011 at 2:10 PM, George & Jan
<[hidden email]>wrote:

> Actually it is more than likely there is no "Pin #1" issue here!
>

Right, that's not it. The resistance between my scope's cable shield and the
chassis of the scope is 0.0 milliohms. And if it was a defective cable or
wiring setup on the scope, it would be present on antenna #2 and in fact
everything else I hooked up to my scope. Antenna #2 shows none of the 60-hz
harmonics, for whatever reason.  It also has nothing to do with the ground
on my other equipment, since no other equipment is involved when the scope
is put on the antenna. It's just a bunch of hash that has 60-hz harmonics
and garbage overlaid on it. I received about a dozen emails from other guys
who tried the same thing and observed the same sorry mess coming in on their
antenna, even those with fairly rural locations.

I realize that the low-frequency garbage I see on the scope isn't getting
through the receiver to my headphones; my original post was mainly just to
lament the sad state of the ether, filled with so much ugly junk. As a side
note, however, I must say that I hear more HF noise on antenna #1 than on
#2, so it's tempting to believe there's a link between all the LF noise it
picks up and the HF noise.

Anyway, if you are having a cheerful day and are looking for a downer, scope
all your antennas and see what you find.

73,
Tony KT0NY
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[Jim Brown-10]

On 1/12/2011 12:10 PM, George & Jan wrote:
> For those of us who have a living in professional audio, video and RF,
> the proper term for what you call the "Pin #1" problem is a Ground Loop - or
> at least that is the term we have used for the 50 years I was in radio&  TV
> broadcasting&  video production.

Sorry to disagree George. Yes, we have used the words "ground loop" to
somehow describe the coupling of hum and buzz into audio systems, but
the words don't make sense if you try to draw an electrical circuit that
demonstrates what you are talking about. As a teenager, and subsequently
as an EE, I struggled to find any logic in anything I had seen on the
topic. Indeed, the problem with the term "ground loop" is that it causes
VERY muddy thinking and outright stupid conclusions about what are good
and bad methods of bonding equipment together, to the power system, and
to a ground system.

The first rational drawing I've ever seen was prepared by Bill Whitlock,
the excellent engineer who owns Jensen Transformers.  Before joining
Jensen more than 25 years ago, Bill designed consoles for Quad Eight and
studios for Capitol Records. Bill uses that drawing to clearly show how
hum, buzz, and noise is coupled into both balanced and unbalanced audio
systems.  There are excellent tutorials on his website. google to find
it. Bill is also the guy who showed conclusively that when interrupting
the shield of balanced cable between line ins and outs to prevent shield
current, that the interruption must be on the receiving end, not the
sending end.  He did this by showing that a noise rejection in a
balanced interconnect is the result of a balanced Wheatstone bridge,
where the impedances of source and receiver are elements of the bridge.
He was recently made a Fellow of the AES for his many contributions to
our understanding of these issues.

I have adapted and expanded upon Bill's drawings for my own tutorials
and lectures. You can see them in
http://audiosystemsgroup.com/HamInterfacing.pdf   which addresses how
these issues should be handled for the UN-balanced connections in a ham
station. There's a lot more about these issues on my website.

http://audiosystemsgroup.com/publish.htm

73, Jim Brown K9YC
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