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. This has been a factor
on vhf for years, as noise levels tend to peak
at 6 meters (50 MHz). The MAIN reason that F.M.
is Vertical polarized is that for mobiles, it is
easy to construct an omni-directional antenna.
Most vhf manuals detail this effect! Jim NN7K

wrote:
Ken Bessler wrote:

Take 2 antennas on 6m - one is an inverted V and the
other a 3el quad. Both are mounted at near the same
height and fed with about the same length of coax.

Is it normal for the quad to be quieter?


Noise almost always arrives from multiple directions and from different
directions than the desired signal.

It is normal for ANY antenna to be quieter when it is more directional.
As a matter of fact, it is expected that S/N ratio is a direct function
of directivity of the antenna as long as the noise and signal are not
coming from the same direction.

To answer your question, it would be very abnormal if your quad (or
Yagi or any other directional antenna) was noisier than a broad pattern
antenna like your Inverted Vee dipole.


73 Tom

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

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

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. This has been a factor
on vhf for years, as noise levels tend to peak
at 6 meters (50 MHz). The MAIN reason that F.M.
is Vertical polarized is that for mobiles, it is
easy to construct an omni-directional antenna.
Most vhf manuals detail this effect! Jim NN7K

Dunno...I don't see much difference as far as the polarity
of the antenna. It's more the polarity of the noise source,
and it's radiator. I've got both horizontal and vertical yagi's
on 2m, and I've seen many times when the local line noise
was much worse when horizontal. But I blame that on the
noise being radiated mainly by horizontal power lines.
I see cases of noise with both polarities, or mostly
vertical, or mostly horizontal. Just depends on the source
antenna. You usually see appx 20db attenuation when
cross polarized.
As far as Ken's loop vs inv vee, if the vee is picking up more
noise, that just means the vee is the best antenna at picking
up that particular noise and at that direction and angle.
If he were to transmit on the two antennas, and receive
them from the noise source, using the sources antenna,
the vee would be received the strongest more than likely.
It's all reciprical. Noise is rf just like any other signal, and
obeys the same rules. If a certain antenna picks up more
rf of any type, noise, or desired, it's the best antenna of the
bunch to receive that source of rf. Thats one reason why I
often chuckle about "noise problems".. As long as it's not
local or common mode pickup from the shack, that just means
the antenna is working, and doing what it's supposed to do.
MK