Jim - NN7K wrote:
Not to mention that noise is normally a phenonmen of the Vertical Plane
(which , depending on how steep your inverted "vee" is, will contain some
vertical component, while the yagi/quad is Horizontal to the plane.

Quads are a lot less noisy than Yagis when the wind
is blowing in the Arizona desert. Quads have a DC
short across the feedpoint that reduces noise from
static buildup.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
Quads are a lot less noisy than Yagis when the wind
is blowing in the Arizona desert. Quads have a DC
short across the feedpoint that reduces noise from
static buildup.

Virtually all Yagi's have dc paths to discharge the elements.

The primary reason a quad is quiter is it has no sharp protruding ends
that are sticking way out in the air.

As a matter of fact if you research the quad, it was initially used to
eliminate corona at radio station HCJB.

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.

73 Tom

wrote:
As a matter of fact if you research the quad, it was initially used to
eliminate corona at radio station HCJB.

Yep, designed by my distant cousin, BTW.

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.

Obviously a false statement based on limited knowledge and
experience. Any ham living around Phoenix will be glad to
enlighten you.

That's exactly how I eliminated the noise and arcing on my
first bare-wire G5RV installed in Arizona. I didn't measure
the change in noise level but it went from arcing at the coax
connector to not arcing at the coax connector which was
acceptable to me.

If the driven element on a Yagi is an uninsulated dipole, it
is susceptible to wind driven noise on the driven element just
like my G5RV was.

Just because you have never experienced that type of noise in
Georgia doesn't mean it doesn't exist in Arizona. I dare say
you haven't experienced a lot of things that exist in reality.
Mary G. comes to mind. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore 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.

Obviously a false statement based on limited knowledge and
experience.

When did you do that test?

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

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

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.

tom
K0TAR

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.



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

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.

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

The entire topic and people's reactions about precepitation noise is
fascinating.

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.

Certainly it is possible for a conductor very well insulated from earth
to charge to the potential of the static field around the antenna, and
flash over to "ground" through some path that breaks down. Of course
only a fool would have equipment that allows that to happen while large
antennas are being used or connected. This is an entirely different
thing than the corona discharge that makes what people typically call
"P-static".

73 Tom

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

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:
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