On 6/15/2012 2:23 PM, Boomer wrote:


I have used a 75 meter loop antenna here where I live for the past 5
years. It works very well. I live right in town on a lot surrounded by
other homes. I started with a dipole but was advised that a loop would
hear less noise. It turned out to be quite true. I am now a convert to
the loop antenna. Have no idea of the physics of how it works, but it
sure does work well on bands between 75 and 20 meters. It actually seems
to work best on 40 meters.

It is not true. Only in the cases of corona buildup, etc, on the
elements would that be the case.
If you hear less noise with the loop, vs the dipole, it's due to
the change in pattern. Not due to any qualities of the loop itself.
Noise is RF the same as any other signal, and follows all the same
rules. It's no different than an actual signal.
If what you/they say is true, and the loop received less noise, it would
also receive less "desired" signals. Or in other words, everything
would be down vs the dipole.
The most likely explanation is the change in pattern less favored
the direction the noise is coming from. Either that, or the noise is
local to your shack, and for some reason the loop's feed line is better
decoupled than the one feeding the dipole.
If I had to bet, I'd say it's the change in pattern.
There are no magical anti noise properties with loops.

On Friday, June 15, 2012 4:06:25 PM UTC-5, NM5K wrote:
Only in the cases of corona buildup, etc, on the
elements would that be the case.

He may be talking about precipitation static which was considerably reduced for me in the AZ desert when I converted my dipole to a folded dipole. My problem was dust storms even on a sunny day.

http://www.its.bldrdoc.gov/fs-1037/dir-028/_4096.htm

P-static is unrelated to the reception of EM RF far-field signals. It is a static charge transferred from charged particles in the air directly to an antenna. It was so bad in AZ that arcing occurred at my coax connector. I have actually seen the p-static envelope on my IC-756PRO's display.

The problem with a dipole is that one element of the dipole normally does not have a DC path to ground. When the p-static discharge takes place, it may be through the series capacitor in the receiver. With a loop antenna, including a folded dipole, the p-static usually has a path directly to ground from any point in the antenna system. It's not the only path but it certainly reduces the p-static noise although not completely eliminating it.

Of course, it is possible to reduce the p-static problems on a dipole with a parallel resistor/choke, a 4:1 voltage balun, or heavily insulated wires. Hams who live in low p-static areas of the country will invariably say that there is no such thing because they have never seen it. But hams who have lived in the AZ desert know better.
--
73, Cecil, w5dxp.com

On 6/15/2012 6:03 PM, W5DXP wrote:
On Friday, June 15, 2012 4:06:25 PM UTC-5, NM5K wrote:
Only in the cases of corona buildup, etc, on the
elements would that be the case.

He may be talking about precipitation static which was considerably reduced for me in the AZ desert when I converted my dipole to a folded dipole. My problem was dust storms even on a sunny day.

http://www.its.bldrdoc.gov/fs-1037/dir-028/_4096.htm

P-static is unrelated to the reception of EM RF far-field signals. It is a static charge transferred from charged particles in the air directly to an antenna. It was so bad in AZ that arcing occurred at my coax connector. I have actually seen the p-static envelope on my IC-756PRO's display.

The problem with a dipole is that one element of the dipole normally does not have a DC path to ground. When the p-static discharge takes place, it may be through the series capacitor in the receiver. With a loop antenna, including a folded dipole, the p-static usually has a path directly to ground from any point in the antenna system. It's not the only path but it certainly reduces the p-static noise although not completely eliminating it.

Of course, it is possible to reduce the p-static problems on a dipole with a parallel resistor/choke, a 4:1 voltage balun, or heavily insulated wires. Hams who live in low p-static areas of the country will invariably say that there is no such thing because they have never seen it. But hams who have lived in the AZ desert know better.
--
73, Cecil, w5dxp.com

True, but I mentioned that first thing..
"
Only in the cases of corona buildup, etc, on the
elements would that be the case. "

The "etc" including what you are referring to.. I was
just too lazy to include that in the list. :/

But say here in Houston, with the high humidity, we rarely
ever see the type static you had in AZ.
You can also see that in some snow storms from what I hear.

But I mainly want to vote against the idea that a loop, with
no static problems, has the ability to receive less noise as
far as radiated RF from other sources.
It's one of those myths "as far as I'm concerned" that needs
to be put out of it's misery.
For instance, some will claim a small shielded loop that is
indoors, will receive less noise than an equal size unshielded
loop in the same location. Have never seen that to be the
case here, when comparing them. In fact, both the loops I kept
for permanent use were regular old unshielded diamond loops.
The biggest being the PVC frame loop that is 44 inches per side
as I recall.. I have another one that is a circular loop about
16 inches dia. The large one is 7 turns. The small one I think 12
or so.
I tried using shielded loops, but the performance was the
same. I also tried using shielded loops as the coupling loop
inside the larger unshielded loop. Worked fine, but no better
than an unshielded coupling loop with no balance problems.
I kept the shielded coupling loop for the small loop, but
used plain wire on the large one. It was easier to thread
through the spreaders, and also lighter.

On 6/15/2012 4:06 PM, NM5K wrote:
On 6/15/2012 2:23 PM, Boomer wrote:


I have used a 75 meter loop antenna here where I live for the past 5
years. It works very well. I live right in town on a lot surrounded by
other homes. I started with a dipole but was advised that a loop would
hear less noise. It turned out to be quite true. I am now a convert to
the loop antenna. Have no idea of the physics of how it works, but it
sure does work well on bands between 75 and 20 meters. It actually seems
to work best on 40 meters.

It is not true. Only in the cases of corona buildup, etc, on the
elements would that be the case.
If you hear less noise with the loop, vs the dipole, it's due to
the change in pattern. Not due to any qualities of the loop itself.
Noise is RF the same as any other signal, and follows all the same
rules. It's no different than an actual signal.
If what you/they say is true, and the loop received less noise, it would
also receive less "desired" signals. Or in other words, everything
would be down vs the dipole.
The most likely explanation is the change in pattern less favored
the direction the noise is coming from. Either that, or the noise is
local to your shack, and for some reason the loop's feed line is better
decoupled than the one feeding the dipole.
If I had to bet, I'd say it's the change in pattern.
There are no magical anti noise properties with loops.



I understand that my experience contravenes your theories about how
antennas should work.

I had several local hams suggest that I use a loop after I kept
complaining about noise. I finally put it up. It is more difficult to
erect than a simple dipole. It is at the same height as was my dipole 35
feet.

The receiver noise level dropped dramatically. I was so glad I went to
the trouble to do it. I finally took down my dipole after switching back
and forth for a year just to be sure the dipole was not better in some
circumstance.

The other effect was an immediate increase in the signal received by my
friends who live within about 200 miles. We operate at 3913. I could not
figure this out until I consulted a pdf file about antennas. The 75
meter loop has a 9 dbi gain at the optimum height of 25 feet. Mine is a
bit high but still gets some gain. All my friends reported on this
increase in my output signal. This information can be found at
http://www.hamuniverse.com/n4jaantennabook.html

This configuration is basically a NVIS antenna. It works so much better
than did my dipole. It gets pretty good dx on 40 and 20. I use an Imax
2000 for 15 and 10.

So, I and my friends know that this antenna works better than a dipole
by actually using it for several years. One of the hams in our group has
been using a loop hung from 2 200 foot towers in a vertical position. He
has done extensive experimentation over the last 45 years.

And yes, a 75 meter loop at 35 feet above ground has a different pattern
than a dipole. I don't care why it works better at all. I and others
just know that it works better and with less noise than a dipole.

And no, a loop antenna is not magic. It is different than a dipole.
Different types of antennas behave differently. The worst antenna I hear
on the air comes from people using G5RVs. Their signal is just totally
lame when they use the recommended 80 foot dipole on 75 meters. If they
would just extend that same antenna to 120 feet they would do so much
better.

Sorry my loop works so well.

Michael

In message , Boomer
writes



The worst antenna I hear on the air comes from people using G5RVs.
Their signal is just totally lame when they use the recommended 80 foot
dipole on 75 meters. If they would just extend that same antenna to 120
feet they would do so much better.

The full-size G5RV is 102' (not 80'), and works pretty well as a
shortish halfwave on 80m. The half-size is 51', and is intended for 40m
and above. However, although maybe not the antenna of choice, with a
tuner and 450 or 600 ohm twin feeder it should be possible to make even
an 80' dipole work fairly effectively on 80m.

One amateur (local to me), who I believe has limited space, reckons that
a straight, short dipole works better than a squeezed-in, dog-legged
full-size dipole. I think his is 85', and it certainly works well on
80m.




--
Ian

On 6/16/2012 2:19 PM, Ian Jackson wrote:
In message , Boomer
writes



The worst antenna I hear on the air comes from people using G5RVs.
Their signal is just totally lame when they use the recommended 80
foot dipole on 75 meters. If they would just extend that same antenna
to 120 feet they would do so much better.

The full-size G5RV is 102' (not 80'), and works pretty well as a
shortish halfwave on 80m. The half-size is 51', and is intended for 40m
and above. However, although maybe not the antenna of choice, with a
tuner and 450 or 600 ohm twin feeder it should be possible to make even
an 80' dipole work fairly effectively on 80m.

One amateur (local to me), who I believe has limited space, reckons that
a straight, short dipole works better than a squeezed-in, dog-legged
full-size dipole. I think his is 85', and it certainly works well on 80m.





On 160m, I had better luck using a full size "Z" dipole than
I did shorter dipoles that were loaded with high Q coils.

I sort of agree with him about the G5RV, but it's the feed that
is the problem, not the length of the radiator. Generally too much
feedline loss with the way most people run them. Same problem with
many of the various commercial Windoms that they sell.

I prefer the full length dipoles because it's easy to feed them in
a low loss manner. On the low bands, it's very hard to beat a dipole
fed with coax for overall system efficiency. Maybe nearly impossible,
being as I've never found anything more efficient so far.
I suppose a tuned feeder of ladder line would be as good, "IE: the Cecil
method" but not nearly as convenient.
I never could match coax performance using ladder line and a tuner.
Close, but not quite.. No matter how careful setting the tuner using
the very minimum of inductance.

I guess that's why I'm such a coax fan... May not be good for multi-
band use with a single dipole, but for single or limited band use, very
hard to beat.

I remember one year I got stuck using some kind of Windom for 80 and 40
at field day.
It was terrible... I swore never, ever again..
But sure nuff.. The next year they tried to stick me on a windom again.
But I was ready.. I brought everything I needed to make a dipole
on site. Which I did. I then whipped out a coax switch so I could
A/B the two antennas, just to prove I wasn't barking at the moon.
When you switched to the coax fed dipole, *everything* jumped up
at least full 2 S units on his rig. His eyes got big as saucers.
He never really suspected he was losing that much.
Needless to say, I stayed on the coax fed dipole.
The RF mayhem of field day is no time to be using lossy compromise
antennas.. I never could see that, when you have enough room to
use just about anything.

On Saturday, June 16, 2012 2:48:21 PM UTC-5, NM5K wrote:
I guess that's why I'm such a coax fan... May not be good for multi-
band use with a single dipole, but for single or limited band use, very
hard to beat.

Here's one that will beat most RG-8x fed dipoles.

http://www.w5dxp.com/notuner.htm
--
73, Cecil, w5dxp

On 6/16/2012 3:21 PM, W5DXP wrote:
On Saturday, June 16, 2012 2:48:21 PM UTC-5, NM5K wrote:
I guess that's why I'm such a coax fan... May not be good for multi-
band use with a single dipole, but for single or limited band use, very
hard to beat.

Here's one that will beat most RG-8x fed dipoles.

http://www.w5dxp.com/notuner.htm
--
73, Cecil, w5dxp

I use 213 though... Your method is about the only other one
I can think of that should be as good. On paper, slightly less
loss than the coax, but being I've never compared them side by
side, I couldn't say if your method is actually superior enough
to see a difference on a meter.. I've never tried your method of
feeding. The physical aspects are not too convenient for me most
of the time.
In the case of the ladder line/tuner vs coax, the difference was
small, but enough to notice a bit of difference on an S meter.
Of course, I'm using received signals to judge. Things should be
reciprocal, so I usually don't bother trying to do transmit tests
as I consider it less reliable than quick A/B comparisons and my
eyes on a meter.
Good ladder line is generally less loss than good coax, but on the
low bands, the loss per foot of good coax is pretty low.
I would think the advantage to your system would increase as you
rise in frequency. IE: at 50 Mhz, might be quite worthwhile.. Or if
long runs are involved. When I ran ATV on 70 cm, I preferred TV twin
lead over coax for the UHF TV antenna I used for receive.
It had less loss than coax to a 4:1 TV balun. As long as it was dry..
Wet? Nearly useless...

On 6/15/2012 4:06 PM, NM5K wrote:
On 6/15/2012 2:23 PM, Boomer wrote:


I have used a 75 meter loop antenna here where I live for the past 5
years. It works very well. I live right in town on a lot surrounded by
other homes. I started with a dipole but was advised that a loop would
hear less noise. It turned out to be quite true. I am now a convert to
the loop antenna. Have no idea of the physics of how it works, but it
sure does work well on bands between 75 and 20 meters. It actually seems
to work best on 40 meters.

It is not true. Only in the cases of corona buildup, etc, on the
elements would that be the case.
If you hear less noise with the loop, vs the dipole, it's due to
the change in pattern. Not due to any qualities of the loop itself.
Noise is RF the same as any other signal, and follows all the same
rules. It's no different than an actual signal.
If what you/they say is true, and the loop received less noise, it would
also receive less "desired" signals. Or in other words, everything
would be down vs the dipole.
The most likely explanation is the change in pattern less favored
the direction the noise is coming from. Either that, or the noise is
local to your shack, and for some reason the loop's feed line is better
decoupled than the one feeding the dipole.
If I had to bet, I'd say it's the change in pattern.
There are no magical anti noise properties with loops.




Here is quote from N4JA's informative antenna book.

......XIV. ONE-WAVELENGTH SINGLE LOOP ANTENNAS


1. The Horizontally Oriented Loop


To calculate the length in feet of any one-wavelength loop, divide 1005
by the frequency in MHz. Horizontally oriented one-wavelength loop
antennas have become very popular on 160, 80, and 40 meters and it is
one type of NVIS antenna. (NVIS stands for "near vertical incidence
skywave" because of its high angle radiation pattern.) It is claimed by
its users that the loop antenna is quieter than other antennas. This is
because it doesnt pick up the noise from power lines, thunderstorms,
etc., coming in at low angles. These antennas radiate on their
fundamental frequencies with a broad pattern straight up to put a strong
signal for nearby contacts. Recently published articles on this type of
antenna have called them "cloud warmers." There are other types of
antennas called NVIS antennas other than loops. They are dipoles at low
heights or dipoles with parasitic reflectors placed under them to cause
the signal to radiate mostly straight up. The NVIS antennas have an
advantage in working nearby stations because you dont get the static
noise and interference from far distances. They are definitely not DX
antennas. An article on NVIS antennas appears in the December 2005 QST......

On 6/15/2012 7:23 PM, Boomer wrote:

If I had to bet, I'd say it's the change in pattern.

An article on NVIS antennas appears in the December 2005
QST......



I guess my hunch on the difference being pattern related
panned out..
I've used horizontal loops on the low bands. But I came to the
conclusion they were generally not worth the extra trouble, vs
a dipole. I could barely see any difference here from the usual
dipoles I ran. And if the signal is stronger at one angle or direction,
vs another antenna, it's weaker in another. So it's all a compromise.

On the low bands, I came to the conclusion my favorite antenna for
mostly NVIS and medium path work was the turnstile.
Which are crossed dipoles. You can feed them in or out of phase
for either dipole patterns, or with them 90 degrees out of phase,
for a fairly round omnidirectional pattern.
I like to do well to the close in stations, but also the ones
farther off too.. So even if I used a loop, I would generally
try to get it as high as possible.
Which I also do using dipoles, or turnstiles.