On Tue, 19 Jun 2012 12:59:43 -0500, Boomer wrote:
(snip)
After at least an hour of
conversation we got to the fact that I had built a portable loop antenna
for 2 meters as a direction finder. He pointed out how sharp the null
was when this antenna was pointed (edge on) toward the source station.
He then said to take this antenna and then turn it horizontal and see if
I could hear anything. Voila. Nothing at all was heard.
(snip)
ISTR with my portable shielded loop, when its horizontal, its omni;
when its vertical, max received signal is when the edge is pointing to
the tx. The null happens when the plane of the loop is at right angles to
a line to the tx.

On 6/20/2012 7:24 AM, W5DXP wrote:
On Wednesday, June 20, 2012 2:12:09 AM UTC-5, NM5K wrote:
If an antenna were immune to noise, it would be immune to all
signals.

Don't forget the effects of polarization. At my previous QTH, my horizontal dipole was about 2 S-units less noisy than my vertical even when communicating with remote vertical antennas.
--
73, Cecil, w5dxp.com


I'm not. I'm just trying to show that an antenna can't tell what
is noise, and what is an actual desired signal. To the antenna,
they are both the same. RF.. One can not magically filter noise,
without filtering the actual signals along with it.
This applies more to the small receiving loop, comparing shielded
to non shielded, but also would apply in most any other case.
I'm fairly comfortable saying the claims of reduced noise pickup
with shielded loops is a myth. I've compared them, and I saw no
difference here. And that includes the usual far field signals,
but also closer local noise, such as monitor noise from the shack,
etc..
I never saw any difference with that type of local noise either.
Both types picked it up equally well if it was there.
And both types could null it out equally well, if from a single
source.

NM5K wrote:
I'm not. I'm just trying to show that an antenna can't tell what
is noise, and what is an actual desired signal. To the antenna,
they are both the same. RF.. One can not magically filter noise,
without filtering the actual signals along with it.
This applies more to the small receiving loop, comparing shielded
to non shielded, but also would apply in most any other case.

Say, you have interference with a local origin and a signal with
a remote origin, wouldn't it be possible to tell the two apart?

E.g. by using two antennas. The received signal is the same on
both antennas but the noise is different. This can be used to
cancel out the local noise but keep the remote signal. Phasing boxes
that operate on this principle are commercially available, so maybe
it is possible.

On 6/20/2012 11:14 AM, Rob wrote:
NM5K wrote:
I'm not. I'm just trying to show that an antenna can't tell what
is noise, and what is an actual desired signal. To the antenna,
they are both the same. RF.. One can not magically filter noise,
without filtering the actual signals along with it.
This applies more to the small receiving loop, comparing shielded
to non shielded, but also would apply in most any other case.

Say, you have interference with a local origin and a signal with
a remote origin, wouldn't it be possible to tell the two apart?

E.g. by using two antennas. The received signal is the same on
both antennas but the noise is different. This can be used to
cancel out the local noise but keep the remote signal. Phasing boxes
that operate on this principle are commercially available, so maybe
it is possible.


Sure, but that's a whole different thing entirely.
That's nothing to do with the antennas themselves.

NM5K wrote:
On 6/20/2012 11:14 AM, Rob wrote:
NM5K wrote:
I'm not. I'm just trying to show that an antenna can't tell what
is noise, and what is an actual desired signal. To the antenna,
they are both the same. RF.. One can not magically filter noise,
without filtering the actual signals along with it.
This applies more to the small receiving loop, comparing shielded
to non shielded, but also would apply in most any other case.

Say, you have interference with a local origin and a signal with
a remote origin, wouldn't it be possible to tell the two apart?

E.g. by using two antennas. The received signal is the same on
both antennas but the noise is different. This can be used to
cancel out the local noise but keep the remote signal. Phasing boxes
that operate on this principle are commercially available, so maybe
it is possible.


Sure, but that's a whole different thing entirely.
That's nothing to do with the antennas themselves.

But once you move a bit further away and consider the two antennas
and phasingbox together as a single antenna, it suddenly is capable
of telling apart local noise and distant signal. That is promising.

On 6/19/2012 12:59 PM, Boomer wrote:
There is the knowledge amongst most hams who work low bands that a loop
antenna has much less noise than a dipole at the same height. This is
especially true in a suburban area. The ability to hear the other
station in a qso is profoundly effected by the noise level heard in your
receiver.

I just had a very long conversation with a fellow ham who has been
experimenting with antennas for over 50 years. He has lived in the same
rural place all that time. He has no homes anywhere near his own. His
noise level in his receiver is not much reduced by using a horizontal
loop. He does like loops and his most used antenna is a 160 meter quad
loop vertically mounted with its top at 200 feet.

Anyway I was trying to understand why my loop antenna reduced my noise
level in my receiver by so many S units. After at least an hour of
conversation we got to the fact that I had built a portable loop antenna
for 2 meters as a direction finder. He pointed out how sharp the null
was when this antenna was pointed (edge on) toward the source station.
He then said to take this antenna and then turn it horizontal and see if
I could hear anything. Voila. Nothing at all was heard. I finally
understood the reason for the remarkable noise immunity of the loop
antenna. The loop simply nulls all noise and signals from its edge on
plane. So, any signals from nearby homes, power lines, and industry are
received by me at this very low angle of radiation. They are nulled out.
I receive only high angle radiation. This is also true of transmitted
signal and thus the large amount of gain it has as an NVIS antenna. This
is not magic, just physics.

My 75 meter transmitted signal in the day stops at about a 300 mile
radius. This is fine for me. It may not be fine for others. I regularly
talk to California from Michigan during the night on 75. This same
antenna works DX on 40. I do not understand why at this point. I have
received an S9 signal report from Barcelona Spain on 40. It also works
other bands, but its performance on 40 meters is better than any other
band. In any case my interest in this subject was piqued when someone
here said that it was just mythology that loop antennas had any more
noise immunity than a dipole. I knew this was not true from my own
experience but wanted to understand why. '

So in finishing up, a horizontal loop probably offers little noise
immunity when operated in the countryside where you have no nearby
sources of interference. It offers a lot of noise suppression when
operated in the city or suburban areas.

Michael


As I said above, I am not talking about atmospheric noise. I am
suppressing the local noise generated in my community by various
electrical and electronic devices. These are close enough to arrive
where I live from an extremely low angle. This low angle is exactly what
my loop "magically" nulls out.

I understand now that when I use it at multiple wavelengths that it no
longer behaves as it does where it is a single wavelength on 75 meters.

All the contrarians keep citing atmospheric noise cannot be suppressed
with a loop. Please read my post above more carefully. I do not make
that claim. If you read carefully you will see that I am trying to
suppress ".... So, any signals from nearby homes, power lines, and
industry are received by me at this very low angle of radiation....."

Now if you are claiming this does not work, then say so rather than
talking about atmospheric noise.

Those of us who live in a suburban area bombarded with local noise know
very well which antenna will be more quiet. At least those who have
tried a loop. I suppose there are some suburban areas without noise. I
have not lived in one.

I always prefer empirical evidence over theoretical postulates. Those
who prefer to defer to a theory over evidence are welcome to do so. I
like to use what actually works.

There appears to be an anti-loop antenna feeling among some people. I
have no such innate prejudice against most antennas. I have tried
various types of antennas and use what works best where I live. I found
the random wire antenna and the G5RV to be the worst performing of all
antennas I have tried. If I had no room for a loop, I would use a folded
dipole. After that, I would use a simple 1/2 wave dipole. I have tried
the double bazooka but found it only marginally wider in bandwidth than
a dipole and heavier and more difficult to support.

I do admit that I find the wide spread acceptance of the G5RV by new
hams to be a mistake. I certainly understand why they might originally
chose this antenna. It claims operation from 75 meters to 10 with just a
102 foot length. This is an attractive specification, but comes with a
serious performance cost.

Michael

On 6/20/2012 12:05 PM, Boomer wrote:

As I said above, I am not talking about atmospheric noise. I am
suppressing the local noise generated in my community by various
electrical and electronic devices. These are close enough to arrive
where I live from an extremely low angle. This low angle is exactly what
my loop "magically" nulls out.

I see little if any chatter about atmospheric noise.
The only mention I've made of it was to say if the noise is
from overhead, the horizontal loop will receive it very well.
As will a dipole, turnstile, and many other antennas.


I understand now that when I use it at multiple wavelengths that it no
longer behaves as it does where it is a single wavelength on 75 meters.

Also the height above ground in wavelength should be considered.

All the contrarians keep citing atmospheric noise cannot be suppressed
with a loop. Please read my post above more carefully. I do not make
that claim. If you read carefully you will see that I am trying to
suppress ".... So, any signals from nearby homes, power lines, and
industry are received by me at this very low angle of radiation....."

Now if you are claiming this does not work, then say so rather than
talking about atmospheric noise.

I've already stated two or three times that it's the pattern
that causes what you see. I never said it didn't work.
In fact, I showed in the model that 2 db would be fairly easy to
come by. Maybe more, if you raised the loop to 50 ft.
All you are doing is continuing to show I was correct as far as my
initial guess for the reason. I said it was almost surely the pattern
from the first post. You seem to be intent on proving me right.. :/
OK, I give up. You win. I concede I was right from the first guess.. :|

I know what you are doing works for the noise you are trying to reduce.
But it's working for a different reason that some *others* propose,
usually when discussing small loops.
Like I say, the noise issue I harp on is more often discussed when
talking about small receiving loops, not full size loops.
It's a bit different issue than what you see with a full size
horizontal loop on 75m.



Those of us who live in a suburban area bombarded with local noise know
very well which antenna will be more quiet. At least those who have
tried a loop. I suppose there are some suburban areas without noise. I
have not lived in one.

There are no absolutes.. It depends on the noise source, polarity,
direction, etc.
If I have noise, it's usually line noise from the power lines.
There could be cases where the dipole received less of that noise
if the orientation was just right.


I always prefer empirical evidence over theoretical postulates. Those
who prefer to defer to a theory over evidence are welcome to do so. I
like to use what actually works.

As do I. And I've tried the loops, believe me.. When it comes to 75m,
I've pretty much tried everything trying to get the very last drop of
performance to NVIS paths. 160, 80 and 40 is where I've always spent
most of my time.


There appears to be an anti-loop antenna feeling among some people. I
have no such innate prejudice against most antennas. I have tried
various types of antennas and use what works best where I live. I found
the random wire antenna and the G5RV to be the worst performing of all
antennas I have tried. If I had no room for a loop, I would use a folded
dipole. After that, I would use a simple 1/2 wave dipole. I have tried
the double bazooka but found it only marginally wider in bandwidth than
a dipole and heavier and more difficult to support.

I have no problems with a loop. I just have a problem with saying they
receive less noise for the wrong reasons.
Note the title of this thread. It's mainly about small receiving loops,
and the title infers that they may offer noise suppression if you use a
shielded loop vs an unshielded loop.
I consider that hogwash. All the shielded version offers is a better
chance of it being balanced. But it's quite easy to build an unshielded
loop that is balanced. If both are balanced, both will perform the same
assuming the same size loop.

The double bazooka actually has more loss than a plain wire dipole.
It's the loss that increases the bandwidth.


I do admit that I find the wide spread acceptance of the G5RV by new
hams to be a mistake. I certainly understand why they might originally
chose this antenna. It claims operation from 75 meters to 10 with just a
102 foot length. This is an attractive specification, but comes with a
serious performance cost.

The G5RV can be OK if fed properly. Straight ladder line would
work much better than the usual coax/choke/ladder line that many
use. It's the silly feed systems they use that kill the performance.
It's that coax/choke/ladder line feed config that kills the performance
of most of the commercial windoms also.
If I ran a G5RV, or any other single dipole for multi band use,
I'd feed with ladder line the whole way from the rig to the antenna.

"W5DXP" wrote in message
...
On Tuesday, June 19, 2012 2:59:12 PM UTC-5, Helmut Wabnig wrote:
If you ground your dipole properly, you have less static.

Yes, there are a number of approaches: transorb, resistor, choke, 4:1
voltage balun, convert to a folded-dipole, arrestors, etc. But most hams
don't ground their dipoles properly.
--
73, Cecil, w5dxp.com

I have no idea how to ground a dipole and I don't think I've ever done it
except by accident.

I welcome any direction. (Having just read the foregoing, I have not
searched the Internet, yet.)

"Sal
(KD6VKW)

In message , Boomer
writes




I do admit that I find the wide spread acceptance of the G5RV by new
hams to be a mistake. I certainly understand why they might originally
chose this antenna. It claims operation from 75 meters to 10 with just
a 102 foot length. This is an attractive specification, but comes with
a serious performance cost.

The G5RV is not a miracle antenna. However, those who find that it does
not perform fairly well probably have not bothered to find out why it is
like it is, and where the radiation goes on the various amateur bands.
If they don't want an antenna with a radiation pattern like the G5RV,
then they should choose a different type of antenna.
--
Ian

On Wednesday, June 20, 2012 3:40:40 PM UTC-5, Sal M. O'Nella wrote:
I have no idea how to ground a dipole and I don't think I've ever done it
except by accident.

Apparently, you have never had P-static problems with your dipoles. I, however, had a coax connector start arcing in the middle of the night and it sounded like a machine gun.
--
73, Cecil, w5dxp.com