wrote:
Try this test, wire a small 2.5 MHh RF choke across your antenna and
check the before and after noise levels. They will not change.

Cecil Moore wrote:
Obviously a false statement based on limited knowledge and
experience.

When did you do that test?

Around 1990 to cure the arcing at the coax connector
during clear-sky high-wind conditions in the Arizona
desert. When I got rid of the coax and used ladder-line
all the way to the tuner, I discovered that the 4:1 balun
in the MFJ tuner accomplished the same anti-arcing function
so hams using ordinary 4:1 voltage baluns are equalizing
that charge before it can arc.

When did you compare other antennas, like noise on plummer's delight
antennas?

The noise was the arcing of the coax connector at the input
to my IC-745 which woke me up at night and scorched my rug
after I disconnected it and laid it on the floor. Seems
obvious that going from arcing to not arcing changes the
noise level. I was afraid to turn the transceiver on during
the arcing process. If I had known I was ever going to have
this conversation with a doubting Thomas, I would have hung
an o'scope on it. The condition is well known to most desert
hams but I had just moved there from Silicon Valley. I never
experienced the condition in Silicon Valley or East Texas.

Installing the RF choke across the antenna feedpoint
cured the problem. I'm not talking about plumber's delight
antennas here. I am discussing Yagis and other antennas
whose driven elements are center-fed dipoles where there
is no DC path between the driven elements.

How many Yagi's have floating driven elements without ground paths?

It only takes one red car to disprove the assertion
that all cars are white.

All the Yagis that I have built used isolated dipole
elements and it only takes one to demonstrate the clear-
sky high-wind noise problems in the Arizona desert. Every
Arizona desert ham running bare isolated HF elements with
no DC path to ground will encounter the problem sooner or
later. The problem has been discussed here on this
newsgroup in the past, possibly while you weren't
reading it. As I remember, one ham solved the
problem with a 10K 3 watt carbon resistor across the
feedpoint.

It seems apparent to me that the problem occurs in very
low humidity conditions. That would include dust and
dry-air snow. And the dust doesn't have to be visible to
the naked eye. I've seen it happen with clear-sky and
seemingly clear-air conditions with high winds and low
humidity. I suspect dust/pollen particles too small to
see still carry a dry-air charge.
--
73, Cecil http://www.qsl.net/w5dxp

Ian White GM3SEK wrote:
This makes the choices quite complex, and makes generalization
impossible. Quote an example, and someone else will quote you a
counter-example.

Seems the assertion should be that precipitation noise
can exist on some antennas but not on others.

Just one other thing: PLEASE let's not talk about elements being
"grounded", way up there at the top of a tower.

How about "DC grounded"?
--
73, Cecil http://www.qsl.net/w5dxp

wrote:
People actually seem to think the little particles voving through the
air charge the antenna to a different potential than the air around the
antenna, and that a "dc" path to earth or "dc" path around an element
somehow magically stops RF noise.

Please don't accuse people of believing in magic until you
understand the physics involved.

There's no magic involved. Dry-air dust and snow particles
certainly can transfer a charge to an uninsulated wire in
the air. It is simple physics to realize that when a highly
charged particle touches a conductor, the charges between
the two objects will be equalized. It would be magic if the
particle and the wire did NOT equalize their charges by
transferring excess differential charge when they come
into contact.

Given a dipole where one element has a DC path to ground
and the other element is floating with respect to ground,
it is reasonable to expect the charge between the two
elements to be different and they often are. The difference
in charge will build up to the point where the smallest gap
between the two conductors arcs. In my configuration in
the Arizona desert, that gap existed at the coax connector
at the transceiver and it did indeed arc badly. It woke me
up and scorched my rug after I disconnected it from my
transceiver. The arc was bright enough to light up the
room and certainly caused RF noise. The wind was blowing
around 30 mph and there wasn't a cloud in the sky.

Given an extreme relative charge between the element with
a DC path to ground and the element without a DC path to
ground, anything that will bleed off that charge will cure
the problem. An RF choke works. A 4:1 voltage balun works.
A resistor works.

Perhaps we can convince a desert ham to hang an o'scope
on a clear-sky, dry-air system on a windy day and report
back here with some results. Many other hams have reported
the same thing during a dry-air snow storm.
--
73, Cecil http://www.qsl.net/w5dxp

wrote:
People actually seem to think the little particles voving through the
air charge the antenna to a different potential than the air around the
antenna, and that a "dc" path to earth or "dc" path around an element
somehow magically stops RF noise.

Let's say we have the following bare-wire dipole system
link coupled to the receiver (in fixed font).

|
| dipole element A link coupled
| -////-
+--------------------------------------------------///////--+
|
+-----------------------------------------------------------+
|
| dipole element B
|

Let's assume one highly charged particle hits dipole element
A and transfers half of its charge. Element A will then have
an excess charge one half of which will migrate through the
link while equalizing the charge between element A and element
B. That charge migration/equalization no doubt results in an
RF noise pulse.

This experiment can easily be performed by anyone.
Rub one's leather soles on a wool carpet, touch one side of
the dipole, and listen for noise in the receiver. Guaranteed,
it will be there.

Now multiply the above by millions of charged particles
randomly encountering the bare-wire dipole. The charge on
each side of the dipole will never be exactly equal. Thus,
continuous broad-band noise will be continuously transferred
through the link as long as the particles are transferring
charge to the antenna. That's what some hams are hearing
during dry-air dust and snow conditions. Some have even reported
being able to hear individual particle collisions from large
snowflakes.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
Ian White GM3SEK wrote:
This makes the choices quite complex, and makes generalization
impossible. Quote an example, and someone else will quote you a
counter-example.

Seems the assertion should be that precipitation noise
can exist on some antennas but not on others.

Living in this climate, I don't have any particular view or experience
about static noise (but ironically we're just about to get one of our
few thunderstorms of the year... better go and do something about that).

Just one other thing: PLEASE let's not talk about elements being
"grounded", way up there at the top of a tower.

How about "DC grounded"?

By all means; so long as we never forget to include the "DC" part.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian White GM3SEK wrote:

Tom Ring wrote:

wrote:

How many Yagi's have floating driven elements without ground paths?


None on VHF/UHF/SHF that I build and anyone I know builds. Maybe on
HF it's different. I don't know why it should be, though.

Although normally all the other elements float on anything but 6 meters.


You're both over-generalizing. In VHF/UHF/SHF yagi construction it's
quite common to find driven elements connected to the boom or floating.
The same choice or a different choice may be made for the parasitic
elements.

There are many different reasons for these choices, including:
* size of elements and boom
* mechanical strength requirements
* effect of boom on element resonance (depends on mounting method)
* long-term effect stability of element resonance
* feed impedance of driven element (affects choice of feed method)
* number of elements involved
* perceived or actual effects of "static".

This makes the choices quite complex, and makes generalization
impossible. Quote an example, and someone else will quote you a
counter-example.

Just one other thing: PLEASE let's not talk about elements being
"grounded", way up there at the top of a tower.




Maybe I should have defined what I meant when I said floating. I think
we have been talking about a DC grounded element, and that's what I
meant with respect to floating.

Virtually all of the homebrew yagis that I have seen, and most of the
commercial are gamma match, or T match. The gamma is not going to carry
the ground through, but is used almost exclusively on 6 meters where
driven elements are rarely insulated from the boom. 2 through 432 are T
matches and that DC grounds the driven element regardless of how it's
mounted. Going up we see mostly loop yagis, and I've never seen one of
those that's not grounded. I know there are regular (non-loop) yagis
used 902 and up, but I never seen one to see how they are driven.

So, for me anyway, the generalization works.

And I'm just watching Silverstone, Ian, so don't tell me how it went!

tom
K0TAR

wrote:
I don't have a lifetime to spend picking nits with Cecil, but I do
resent his immediate implications I haven't looked at the closely for a
long time.

Do you think the people who report the problems that you haven't
experienced and don't understand resent your assertion that they
believe in magic? The actual magical thinking is asserting that
charged particles don't transfer part of their charge to bare
wire antennas.

In my experience the vast majority of noise people complain about is
caused by corona from the element or something in the immediate area of
the element.

That may be true but we are not discussing corona noise. Exactly
where do I go wrong in the following explanation?

1. A highly charged particle encountering one element of a bare
copper wire dipole will transfer approximately half its charge
to the wire.

2. A charge unbalance between the two elements of a dipole will
cause a differential current to flow in a link coupled system.

3. The differential current may be detected by an RF receiver.

Now I'm sure there will be some cases where people disagree with this,
but anyone who can A-B-C test antennas will find that other than a pop
or arc across a dielectric from antennas that accumulate enough charge
to exceed charge leakage the only thing that really matters is how
"pointed" the antenna is and how exposed the points are to the air
around the antenna.

This is simply a false statement. Many desert hams, like
myself in the 1990's, have experienced another kind of noise.
I've never experienced it from snow, but I can understand
how it could happen with snow falling through dry air. The
snow phenomenon has been reported here on this newsgroup.

All that crud hitting the antenna isn't significantly different in
potential than the air around the element, it just has a lower
impedance.

Absolutely false! Charged dust particles are a fact of life
in the Arizona desert. There is often not enough moisture in
the air to discharge them. Your limited experience is showing.
How often does the relative humidity get down to 10% with
high winds and dust in Georgia?

As a matter of fact, it is rather silly to claim the particles
discharging make noise and then at the same time claim that a DC path
somehow reduces or eliminates that noise.

I didn't claim it "reduces or eliminates that noise". I claimed
it eliminates arcing which is certainly a type of noise.

The CLOSER the antenna would
be allowed to float to the potential of the particles the LESS change
in potential would occur. Pulling the element to earth would make each
tiny discharge worse and make more noise, not less.

My problem was that 1/2 of the antenna was at DC ground potential
and the other half was floating which is typical of a store-bought
G5RV. That seems to cause the worst case of arcing. But it is simple
physics to realize that each particle acts independently. The charge
transfer from each particle causes a tiny differential current between
the two elements of the antenna. Millions of unsynchronized collisions
per second certainly would produce differential RF noise.

A link-coupled balanced dipole system would probably never arc but
there would be a differential noise pulse through the receiver as
described in the graphic in my other posting.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
wrote:

Your argument makes perfect sense. Cecil, I was suprised that you actually had arcing to the point of scorched carpet. What voltage do you think this potential represents? Is this a relatively constant voltage. By that, I mean is there usually SOME voltage difference during days or weeks? My naieve question is: Could this serve as a trickle charge for a battery when not used for RX/TX?

Cecil Moore wrote:
1. A highly charged particle encountering one element of a bare
copper wire dipole will transfer approximately half its charge
to the wire.

2. A charge unbalance between the two elements of a dipole will
cause a differential current to flow in a link coupled system.

3. The differential current may be detected by an RF receiver.

Only when it is AT THE FREQUENCY the receiver is tuned to.

So when you provide a DC path that does not short the antenna at radio
frequencies, it does nothing.

The only exception to this is if the charge actually causes something
to arc, but even then it is a long term buildup of charge.

This is simply a false statement.

You can a call me a liar if you like, but it doesn't change the facts.


All that crud hitting the antenna isn't significantly different in
potential than the air around the element, it just has a lower
impedance.

Absolutely false! Charged dust particles are a fact of life
in the Arizona desert. There is often not enough moisture in
the air to discharge them. Your limited experience is showing.
How often does the relative humidity get down to 10% with
high winds and dust in Georgia?

I haven't lived in Georgia all my life. Most of my experience with this
is actually in Ohio, but on other reflectors like TowerTalk everyone
seems to share the same common experiences.

As a matter of fact, it is rather silly to claim the particles
discharging make noise and then at the same time claim that a DC path
somehow reduces or eliminates that noise.

I didn't claim it "reduces or eliminates that noise". I claimed
it eliminates arcing which is certainly a type of noise.

We agree there. So why are you arguing?

If it charges the antenna to the point where a dielectric fails the
sudden change will make a terrible noise and may even cause damage.
This is why no one should have a large element high in the air that
does not have a leakage path.

The CLOSER the antenna would
be allowed to float to the potential of the particles the LESS change
in potential would occur. Pulling the element to earth would make each
tiny discharge worse and make more noise, not less.

My problem was that 1/2 of the antenna was at DC ground potential
and the other half was floating which is typical of a store-bought
G5RV. That seems to cause the worst case of arcing. But it is simple
physics to realize that each particle acts independently. The charge
transfer from each particle causes a tiny differential current between
the two elements of the antenna. Millions of unsynchronized collisions
per second certainly would produce differential RF noise.

In that case a ground on the floating side would make no difference, or
if anything make it worse. Think about it, or draw it on paper. The
charge differential (as you say above) is between the floating
particles and the earth. The greater the charge difference, the larger
the amount of charge transferred (as you said above).

If we agree on what you say above, the "millions of unsynchronized
collisions" would not impart less charge to the antenna when it is
closer to earth potential, they would impart more.

The fact is a dc path doesn't change a thing with one single exception,
the dc path prevents an antenna from building a charge in the
capaciatnce of the system, and prevents that voltage from building to
the point where some dielectric fails. Indeed that happens, and that is
why large high antennas should have a leakage path to earth.

Even on a clear calm day my 160 dipole at 300 feet, if I let the coax
dangle a few feet above earth, will knock a person for a loop when
touched. Inactive power lines, when open circuited, have to be clamped
to ground for the same reason. On a windy day the recharge rate of the
dipole is faster, and faster still in inclement weather.

When the weather is bad, there is corona off the antenna that makes a
sizzling sound that starts out as a series of slow pops and builds to
the point where it almost turns musical or tonal. If lightning flashes
even far in the distance, it immediately stops and rebuilds. The higher
the antenna and the sharper and more extended the ends, the worse the
problem is. Even when no moisture is hitting the wire.

73 Tom

wrote:
You can a call me a liar if you like, but it doesn't change the facts.

Being ignorant doesn't make you a liar. The fact is that
many hams have experienced charged particle noise. Your
denial of such doesn't change the known facts.

The meaning of most of your posting escapes me so I will
just summarize my position.

When I lived in the Arizona, clear-sky wind-driven charged
dust particles transferred lots of energy to my bare-wire
G5RV. It caused arcing whether the outside braid was grounded
or not. It only happened when the wind was blowing and
the humidity was very low.

I'm not sure what your point of disagreement is so help
me out.

Do you agree that a charged particle will transfer energy
to the bare wire in a dipole when it touches it? If not,
why not?

If the antenna were link coupled, do you agree that the
above transferred energy will try to equalize between the
two dipole elements? If not, why not?

Do you agree that the equalizing of the charges between
elements would cause a current to flow through the link?
If not, why not?
--
73, Cecil http://www.qsl.net/w5dxp