FULL SIZE 75M LOOP..

[ve6pg]

HI FROM TIM...I WAS OUT IN THE GARDEN THIS AFTERNOON,AND GOT THINKING ABOUT PUTTING UP A FULL SIZE 75 METRE LOOP.THIS LOOP WOULD BE FED WITH OPEN WIRE,BUT HERE IS MY QUESTION. THIS ANTENNA WOULD LIKELY BE 25-30FT OFF THE GROUND.,AND I WOULD LIKE OPINIONS AS TO THE PROS/CONS OF SUCH AN INSTALLATION. IF YOU HAVE TRIED ONE WITH 4 SUPPORTS THIS CLOSE TO THE GROUND,PLEASE LET ME KNOW...73...TIM...SK..

[Tom WA3KLR]

Hi Tim,

I was on 1885 kHz AM this evening ~ 9:30 pm - 10:30 pm EDST and heard you calling several times.  You were weak and just readable.  I answered you, but with only 24 watts AM from my IC-706.

Earlier in the evening, I was on the Top Band Sideband Net and the net control station for the 2nd call area was WF2H, Francis.  He is in upper NY state, about 330 miles from me.  He had the best signal on the net.  He said he runs a 496' loop at 25' off of the ground.  I was quite surprised.
So in his case, a low 1 wavelength loop was working well.

I just got back on 160 meters with a Zepp at 30 - 60 feet.  I hope to have a full legal limit Class E AM transmitter on by this coming winter.

[K1JJ]

Hi Tim,

The loop will "work" OK.

But you're up in Toronto, so I would think you would want a
lower angle antenna to work out into the states, etc. A full
sized loop at 30' high is designed to be a cloud burner.
Most useful take off angles on 75M are around 50-60 degrees
out to 400 miles. Farther out you need antennas up above
90' high to see <40 degrees and longer haul for highest
performance.

So, with 30' supports, you're limited to higher angles, but
put up a simple 1/2 wave dipole as high and flat as possible
and you cannot do any better.  Even 40'-45' will make a big
difference if it is easier to support a dipole rather than a
bigger 4 cornered loop. If you have a favorite direction, put up
two dipoles spaced 60' apart and feed them 90 degrees out... or
stick a reflector behind the dipole.

There's several articles on East Coast sound covering ideas
on these antennas.

There's many many opinions on antennas. One thing you will
find is that an antenna must be matched to your own
location/terrain for optimization. Experimentation is key.
There IS an antenna and height  that will perform the best
for you, but most of the time it turns out to be a simple, flat
dipole at about 60' high for out to 400-500 miles or so.  

Farther than that, then a Yagi above 90' takes the cake. The best
system is two antennas, one low and one high to cover all the
valuable angles. Vertical takeoff angle is key and the most
important factor.

A 3el Yagi is good for only 5-6 db over a dipole.
BUT, the proper vertical angle selection can mean a 15-20 db
difference at times!

73,
Tom, K1JJ

[ve6pg]

OK TOMS..!
  THE DIPOLE THING WONT FAVOUR THE DIRECTIONS I WANT...I'M NOT INTO WORKING DX ANYMORE,BEEN THEN,WORKED THAT...I ENJOY THE HIGH QUALITY AM QSOs,AND THOSE ARE GENERALLY WITHIN 300 MILES,OR SO...I DO HAVE THE END FED WIRE,THAT REALLY WORKS WELL
AS WELL. SO I THINK I'LL GO WITH IT,THE PROPERTY WILL HANDLE IT..
  AS FAR AS AM ON 1885,I JUST THREW UP A QUARTER WAVE COAX FED WIRE,THAT IS IN PARALLEL TO A HOMEBREW 40M VERTICAL. IT GOES UP VERTICALLY ABOUT 25FT,AND THE REMAINDER 105FT IS ABOUT 20FT OFF THE GROUND,IN THE SHAPE OF THE NUMBER 7..SEEMS TO WORK OK,GOOD BANDWIDTH. NEXT THING WITH IT IS TO RAISE IT UP HIGHER,BUT I DONT WANT THIS THING TO HAVE TOO MUCH VERTICAL POLARIZATION...I WILL BE TESTING ON 1885 A FEW NIGHTS PER WEEK,TESTING WITH AL,VE3AJM. AL USES A TMC TRANSMITTER,1KW INPUT TO A FULL SIZE LOOP. MY TRANSMITTER IS A VIKING 2,WITH ABT 105 WATTS CARRIER...OK TOMS..THANKS FER THE INPUT...TIM..SK..

[wavebourn]

Guys, I don't understand what means "Full size". Why a magnetic antenna should be of some sort of corellation with a wavelength?

[WA1GFZ]

I've tried a number of 75 meter loop configutations close to the ground.

Results
1. H loop at 45 feet put RF all over the house and only good for local contacts
2. Vertical square with 1 side 6 feet above ground. A dummy load with a wip on it might be better.
3 best configuration was triangle loop with 1 corner point 6 feet above ground and feed point at a corner at 1/2 height with third corner at 80 feet in vertical plane. This worked the best and was fed with open wire line. A dipole at 75 feet was still about 6 dB better.

I also ran a quad for 20 years which was a great antenna for 20 meters.
conclusion is a loop needs to be away from the ground to get the real performance possible.

[K1JJ]

Yes, agreed, Frank!

Loops are no different than dipoles, ONCE they are up
high.  I have nothing against using them. In fact, I have
up two, 2el quads at 190' on 75M for Europe and S.
America on 40' aluminim booms.. fixed.  Each is  the
equivalent of a 3el Yagi. BUT, they are erected with
their apex up high so that the AVERAGE height is
what a dipole or Yagi should be at.  Apex at 190' =
average height at 140', so performs like a Yagi at 140'.

The advantage is that only one high support is needed if
a boom is used. For a wire Yagi, two supports are needed
to keep it flat.

I've found that the average height of a loop needs to be up
about 20' higher than a dipole to have the same vertical take
off angle.

I realize this may not apply to the average ham looking
for local 75M contacts,  but the concept stills points to using
a simple FLAT dipole at 50' -90' high for best all around
performance and minimum problems.

73,
T

[WA1GFZ]

Tom,
Do you find the loop quieter than a dipole or did I get the impression because it was close to the ground and suffered high loss?

[K1JJ]

Franz,

No, I didn't find the quad loops quieter for receiving. I believe
that is ham folk lore. [And I hear it often as you do too]

It may just be a matter of a low loop having little low angle
component compared to a dipole, so that the static from horizon
power lines or far away T-storms are cut back. I beleieve the same
effect could be achieved with a very low dipole.

Indeed, for high power transmission, a closed loop will not
have corona like on the ends of a dipole, but for receiving
I could not, and still do not see any difference between my loops
and dipoles for noise/static reduction.

The question I would have to axe is:  How would a quad/loop
KNOW the difference between noise and a desired radio signal
anyway? Same as a dipole.

As for receive - static discharge noise before or during
thunderstorms, they BOTH still pop.  It's the same
debate about using insulated elements on Yagis vs:
grounded elements.  All the same for noise.  So, I
ground [plumber's delight] all my Yagi elements to
the boom. So much easier.

Yes, perhaps your loop was quieter because it was
closer to the ground and more deaf to low angle, dunno.

I know some guys believe loops are quieter than dipoles,
but I'd like to hear the technical reason WHY this would be so.

The only antenna which appears to exhibit a better signal
to noise ratio when listening thru static is a beverage. I'm
really not sure why except that when I listen on bad T-storm
static nights to Europe on 75M, I can hear stations on the beverage
thru the static crashes that are covered up when listening on
the high quads. When there is no static, they are close to equal
or the 2el Quad may have a slight edge. So, normally I use them
BOTH in dual diversity receive... a FB system.

Perhaps the answer is as simple as the beverage having a cleaner
and sharper pattern into Eur and attenuating the T-storms off the
sides better. I would be hard pressed to believe that if the T-storm
was directly in front, to the NE, neither would hear better. The only
other variable is vertical takeoff angle, and modeling shows the 2el
quad and beverage to be quite similar.

73,
T

[nq5t]

Loops are no different than dipoles, ONCE they are up
high.  I have nothing against using them. In fact, I have
up two, 2el quads at 190' on 75M for Europe and S.
America on 40' aluminim booms.. fixed.  Each is  the
equivalent of a 3el Yagi. BUT, they are erected with
their apex up high so that the AVERAGE height is
what a dipole or Yagi should be at.  Apex at 190' =
average height at 140', so performs like a Yagi at 140'.

So should those of us on a typical suburban lot with a 30' height restriction and struggling to get ANYTHING that works just go ahead and bite down on the cyanide capsule now? I mean I'd like to have something up 190', too, but not everyone is so fortunate  :shock:

[WA1GFZ]

I would tend to try a smaller vertical loop with copper pipe as a conductor
if I couldn't get a dipole up. Under sized dipole with large conductor open wire feed is also an option.

Tom you would be interested in some of the observations in the EMI world using different antennas. Near field is full of interesting readings

[WB3JOK]

I would tend to try a smaller vertical loop with copper pipe as a conductor if I couldn't get a dipole up.

I agree, small loops work great for me to Europe from northern Maine. Although 40m has been really crappy this week, I fired up the 20m loop (only 4 feet in diameter, inexpensive 1/2" copper tubing) and was able to work Serbia with the HW-101 barefoot, and even a pileup to Italy with the SB200 on!

My larger loop (8 ft. rectangle of 1" tubing) also works on 75m but loses a few db compared to 40m because it is so electrically short for 75 (1/8 wavelength in circumference) and the loss resistance becomes larger than the radiation resistance. If you have room for a square 10' on a side it'll be even better. Or even a triangle that will fit in your attic, assuming you don't have metal siding or roof. Silverplating the tubing would help too. Incidentally these small vertical loops have a sharp null, perpendicular to the plane of the loop.

-Charles

[K1JJ]

Loops are no different than dipoles, ONCE they are up
high.  I have nothing against using them. In fact, I have
up two, 2el quads at 190' on 75M for Europe and S.
America on 40' aluminim booms.. fixed.  Each is  the
equivalent of a 3el Yagi. BUT, they are erected with
their apex up high so that the AVERAGE height is
what a dipole or Yagi should be at.  Apex at 190' =
average height at 140', so performs like a Yagi at 140'.

So should those of us on a typical suburban lot with a 30'
height restriction and struggling to get ANYTHING that works
just go ahead and bite down on the cyanide capsule now? I
mean I'd like to have something up 190', too, but not everyone
is so fortunate  :shock:

I'm just saying what works and what doesn't.

You can bite down on a cyanide capsule if you'd like, but it
ain't gonna improve your signal if you're disatisfied with it..... :lol:

You think I didn't have to spend 20+ years too, living on frick'in
postage stamps, frustrated?  I also lived in a trailer for 10 years
with antenna restrictions. Had to sneak antennas up and even
got evicted from an apartment for RFI to the other 12 occupants.  
I've been there, OM.

But when you finally get some towers up the difference in
hearing ability can be appreciated, rather than starting out
that way. I've worked for 10 years here putting up towers
and building all kinds of antennas to experiment and find
what works and what doesn't. Biggest project of my life,
I'd say. It's not a matter of "fortunate"... it's a matter of
hard work and ham radio functions like capatalism rather
than like the internet where everyone is the same strength...

73,
T

[K1JJ]

Tom you would be interested in some of the
 observations in the EMI world using different antennas. Near field
is full of interesting readings

Sure would. What have you got and at what frequency were
the tests run?

T

[Glenn K2KL]

I've had excellent results in the past with full wave vertical triangle loops. I disagree with master Vu, at my last location (only a few miles from my present QTH) The triangle loop was consistantly quiter than a 1/2 wave dipole. (same plane)  The quad vs dipole (full wave loop vs 1/2wave dipole) debate seems to be as old as ham radio shunny. Triangle loops are nice because you only need one support, like an inverted vee. I found that height above ground was less critical with the full mave vertical loop antenna than with the 1/2 wave dipole antenna, maybe because the loop is an "H" field antenna? When I get to my new QTH down in NC, I'm going to try a 2 element, vertical triangle, driven array. Master Vu talked me out of attempting a parasitic array at less than optimum heights. With 8 acres I'll be like a kid in a candy store!... I too spent many years paying my dues operating on postage stamp sized lots...I'm looking forward to experimenting with different wire antennas!    

[K1JJ]

I've had excellent results in the past
with full wave vertical triangle loops. I disagree with master Vu,
at my last location (only a few miles from my present QTH)
The triangle loop was consistantly quiter than a 1/2 wave dipole.
(same plane)  The quad vs dipole (full wave loop vs 1/2wave
dipole) debate seems to be as old as ham radio shunny.

Hi Glenn,

Yes, it IS an old debate...  

I'm curious as to what kind of noise you felt the triangle
loop [delta loop?] was quieter for.  Power line noise,
atmospheric ambient noise, T-storm noise, etc?

And, what would you attribute this to?  ie, how does the loop
know the difference between a signal or noise...OR do you
feel  the dipole might generate it's own additional noise by
having higher impedance ends, or some other reason?


T

[Glenn K2KL]

Yes, locally generated noise, power line noise, etc.. I believe the reason for this was probably due to the fact the the loop is DC grounded where the dipole as you mentioned, has high impedance open ends. Both antennas were horizontally polorized so that wasn't a factor. Very interesting discussion!

Hi Glenn,

Yes, it IS an old debate...  

I'm curious as to what kind of noise you felt the triangle
loop [delta loop?] was quieter for.  Power line noise,
atmospheric ambient noise, T-storm noise, etc?

And, what would you attribute this to?  ie, how does the loop
know the difference between a signal or noise...OR do you
feel  the dipole might generate it's own additional noise by
having higher impedance ends, or some other reason?


T

[WA1GFZ]

Tom below 30 mHz we use a 41 inch rod antenna with a FET in the base
30 MHz to 200 MHz we use a biconical dipole a meter long with cage elements. This on a tripod so we test H and V mode. above that we can go to 40 GHz with various horn antennas.
The biconical range is the most interesting. I would love to try a large biconical dipole. There is a balun at the feed point.

We have an amplifier with a couple dozen 4CX250s for strap tests.
You stay away when that baby is running and we use radiation detectors
for safety.  200 volts per meter field can cook you

You would be amazed by how hard we can make a system.
Then there is lightning. 600 amps is quite typical on a cable.

[K1JJ]

Yes, locally generated noise, power line noise, etc.. I believe the reason for this was probably due to the fact the the loop is DC grounded where the dipole as you mentioned, has high impedance open ends. Both antennas were horizontally polorized so that wasn't a factor. Very interesting discussion!

OK, Glenn...

But I'm still cornfused..  

A signal at 3.8mhz has to propagate to the DC grounded loop
just like any other signal to a dipole. How does the power line
signal (at 3.8 mhz) know that it shud bypass itself to DC ground
whereas the 3.8 WA1HLR signal knows to stay away ?  I'm
acting stupid here, but you get my question, right?  

T

[Glenn K2KL]

...I'm going to go out on a limb here and if I'm blowin smoke then someone please step in and stuff a spicy tuna roll down my pie hole...

It is my understanding that the closed,  DC grounded loop is an H field  type antenna, where the dipole or vertical is an E field antenna. Locally generated noises are in the E field so the loop is not as sensitive to E field noise....

Like I said, I may be blowing smoke... in fact I kinda getting hungry for some rolls.. :lol:  :lol:
 

Yes, locally generated noise, power line noise, etc.. I believe the reason for this was probably due to the fact the the loop is DC grounded where the dipole as you mentioned, has high impedance open ends. Both antennas were horizontally polorized so that wasn't a factor. Very interesting discussion!

OK, Glenn...

But I'm still cornfused..  

A signal at 3.8mhz has to propagate to the DC grounded loop
just like any other signal to a dipole. How does the power line
signal (at 3.8 mhz) know that it shud bypass itself to DC ground
whereas the 3.8 WA1HLR signal knows to stay away ?  I'm
acting stupid here, but you get my question, right?  

T

[K1JJ]

OK, I see what you're saying, Glenn...

So it's more that your loop was vertically polarized, thus less
suceptible to horizonatally polarized power line noise... and
probably not due to the fact that it is DC grounded.  I mean
you could make a horizontally polarized loop DC grounded too.

I guess what I'm trying to figure out here is that just cuz a
loop [or any antenna for that matter] is at DC ground doesn't
make it less susceptable to ANY kind of noise.

But, I'm hoping some antenna guru will come in here and set me
straight, too... :-0

73,
T

[Glenn K2KL]

E field = voltage, H field = current. not polarization. I know I'm not explaining this very well, I'll try and dig up more information (in between packing boxes for my move to 4-land)

The loop is DC grounded regardless of polarization (fed from the bottom or side)

OK, I see what you're saying, Glenn...

So it's more that your loop was vertically polarized, thus less
suceptible to horizonatally polarized power line noise... and
probably not due to the fact that it is DC grounded.  I mean
you could make a horizontally polarized loop DC grounded too.

I guess what I'm trying to figure out here is that just cuz a
loop [or any antenna for that matter] is at DC ground doesn't
make it less susceptable to ANY kind of noise.

But, I'm hoping some antenna guru will come in here and set me
straight, too... :-0

73,
T

[W3SLK]

Tom said,

I guess what I'm trying to figure out here is that just cuz a
loop [or any antenna for that matter] is at DC ground doesn't
make it less susceptable to ANY kind of noise.

Except snow/winter static that is typical of dipoles. Since it is a "closed" loop, the conductor, (or wire in my case) is at ground potential. Preventing those nasty static arcs that one hears during the dark of winter.  At least that's my take on it. It is a DC short, (with the exception of ohms/100' of wire).

[K1JJ]

Hi Glenn,

Yes, dig out that info when ya get a chance after the move...  
I didn't realize you were going so soon down south.

BTW, when I look at plots on my antenna modeling
program, "H" field shows the vertical pattern and "E" field  
shows the horizontal pattern of a horizontal antenna.  So, I
thought that was what you meant and the reason for the
attenuation to the "E" power  line noise.  99% of my modeling
is with horizontally polarized antennas, thus the cornfusion on
my part.

So, my question is: Would a simple ground mounted vertical
have similar characteristics to the loop you described regarding
better power line noise rejection? The verts I've tried have always
been noisy for atmospheric noise, but I have no power line noise
on 75M to test with here.

Mike: I know what ya mean about the snow static. Though
I hear popping on all of my antennas usually. The loops
sound as loud as the dipoles when it snows, BUT, it could
simply be that they are all coupling to one another... ie,
when the dipole pops it gets picked up on the loop when
I'm listening on the loop -  Even though they are all separated
by at least 150' apart.

Though the idea of a closed loop, lower impedance system
makes sense vs: a dipole with end barrier boundaries
approaching the breakdown voltage of air.

T

[Glenn K2KL]

Hi Tom;

Yea, our original plans were a few years down the road but with the local real estate market at an all time high, and prices down south going up, we decided to strike while the iron is hot   We've been flying down every weekend looking at houses.

When you hear the static pop on your loop, I'd try grounding the dipole to see if it makes a difference.

Hi Glenn,

Yes, dig out that info when ya get a chance after the move...  
I didn't realize you were going so soon down south.

BTW, when I look at plots on my antenna modeling
program, "H" field shows the vertical pattern and "E" field  
shows the horizontal pattern of a horizontal antenna.  So, I
thought that was what you meant and the reason for the
attenuation to the "E" power  line noise.  99% of my modeling is with
horizontally polarized antennas, thus the cornfusion on my
part.

So, my question is: Would a vertical have similar characteristics
to the loop you described regarding better power line noise
rejection? The ones I've tried have always been noisy for
atmospheric noise, but I have no power line noise on 75M to
test with here.

Mike: I know what ya mean about the snow static. Though
I hear popping on all of my antennas usually. The loops
sound as loud as the dipoles when it snows, BUT, it could
simply be that they are all coupling to one another... ie,
when the dipole pops it gets picked up on the loop when
I'm listening on the loop -  Even though they are all separated
by at least 150' apart.

Though the idea of a closed loop, lower impedance system
makes sense vs: a dipole with end barrier boundaries
approaching the breakdown voltage of air.

T