In the spirit of trying to get something going on the subject of
antennas, and away from all the off topic posts......

Are you doing anything interesting with antennas? Putting anything up
new for the contest season? Learn something new that the rest of us
might benefit from hearing about, even if it isn't patentable?

For me, I have become interested in rhombics and am currently building
one. It was based on the one featured in the ARRL Antenna Book, which
is 377 feet long (right down the middle) and 210 feet on each side.
210 feet is 3 wavelengths on 20 meters. So far I have learned a
little about the rhombic. It can be built as a terminated rhombic or
a "resonant" rhombic. In the case of a terminated rhombic, you
install a 600 ohm resistor at the far end, and that absorbs the power
that would otherwise be radiated off the back, making the antenna
uni-directional. Another advantage is, the feedpoint Z is
approximately flat and equal to 600 ohms across a huge frequency
range. So the antenna has gain and lots of it, at least over the
range of 20-10 meters and everything in between! If you don't
terminate it, it works the same way in the forward direction but has
no front to back. And the impedance varies all over the place. But
does anyone have a 600 ohm resistor they could supply me with? 300
watts or so? Noninductive.

So getting down to practical details, here's some of my experiences so
far. Copper wire has gotten very expensive. #14 stranded down at the
local Depot store is now 8 cents a foot, #12 is 14 cents. That adds
up fast when you need 840 feet of the stuff. So I managed to find a
roll at 900 ft on eBay for about 60% of that and got it. Now the
problem with #14 is it sags. Well maybe not, maybe it is the rope
holding the end up, it is very hard to pull up 200 feet of wire and
get it to where it doesn't look like the suspension cables on the
Verrazano bridge.

Ok so now how to get the rope up high enough in the oak to make it
useful? Bought a slingshot. For-get-it. I tried bolts, nuts,
fishing weights, etc, can't get the damn thing with fishing line to
get over 16 feet and most of the time it tangled the line and
sometimes actually ended up behind me. Crosman Slignshot for sale,
$25 shipped to your door. Here's what works for 25 feet.... get xyl
to climb a ladder in the back of the pickup parked beside the tree.
She takes a tennis ball with light dacron rope taped to it and throws
over the branch while I shout encouragement from below. It works.
(oh, by the way, xyl is KC2PRW). That's the good news, the bad news
is 25 feet ain't high enough, with the sag problem mentioned above.
Next, get bow and arrow from neighbor, yeahhhhh !! that works. Now
got line over 35 feet, that's decent. Same success on 2nd tree. Now
got the feedpoint tree and one of the corner trees with nice lines up
35 feet. Now pull up the wire and notice that the smallest little
friggin branch in the oak trees will snag the #14, so get the ladder
and trim off dozens of those little suckers. So that's where we are
at the moment. I figure about 50% done. Now the question is, will it
work?

I found (google can find anything) a great circle bearing program that
told me to point it 47 degrees which, from New Jersey puts me right
over London and down into central Germany. Look out DLs. According
to my antenna modeling program it will have 14 dbi gain and a 3 db
beamwidth of 20 degrees. Man that is sharp, much sharper than any 3
element beam. What's with these dbi's ? For comparison, a 3 ele beam
at 70 ft will have 12 dbi gain. The rhombic at 30 ft has its main
beam at about 22-25 degrees elevation. I sure wish I could get it up
to 70 ft, but there's no chance.

So now I have to get two more trees rigged with ropes and then get
down to the business of feeding the monster. I will be using balanced
ladder line to a homebrew tuner which I haven't built yet.

If I get any positive feedback on this post I will continue with my
progress and maybe even provide some on-air results in a week or so.

So that's my story. What are you working on?

Rick K2XT

Rick wrote:
In the spirit of trying to get something going on the subject of
antennas, and away from all the off topic posts......

Are you doing anything interesting with antennas? Putting anything up
new for the contest season? Learn something new that the rest of us
might benefit from hearing about, even if it isn't patentable?

For me, I have become interested in rhombics and am currently building
one. It was based on the one featured in the ARRL Antenna Book, which
is 377 feet long (right down the middle) and 210 feet on each side.
210 feet is 3 wavelengths on 20 meters. So far I have learned a
little about the rhombic. It can be built as a terminated rhombic or
a "resonant" rhombic. In the case of a terminated rhombic, you
install a 600 ohm resistor at the far end, and that absorbs the power
that would otherwise be radiated off the back, making the antenna
uni-directional. Another advantage is, the feedpoint Z is
approximately flat and equal to 600 ohms across a huge frequency
range. So the antenna has gain and lots of it, at least over the
range of 20-10 meters and everything in between! If you don't
terminate it, it works the same way in the forward direction but has
no front to back. And the impedance varies all over the place. But
does anyone have a 600 ohm resistor they could supply me with? 300
watts or so? Noninductive.

So getting down to practical details, here's some of my experiences so
far. Copper wire has gotten very expensive. #14 stranded down at the
local Depot store is now 8 cents a foot, #12 is 14 cents. That adds
up fast when you need 840 feet of the stuff. So I managed to find a
roll at 900 ft on eBay for about 60% of that and got it. Now the
problem with #14 is it sags. Well maybe not, maybe it is the rope
holding the end up, it is very hard to pull up 200 feet of wire and
get it to where it doesn't look like the suspension cables on the
Verrazano bridge.

Ok so now how to get the rope up high enough in the oak to make it
useful? Bought a slingshot. For-get-it. I tried bolts, nuts,
fishing weights, etc, can't get the damn thing with fishing line to
get over 16 feet and most of the time it tangled the line and
sometimes actually ended up behind me. Crosman Slignshot for sale,
$25 shipped to your door. Here's what works for 25 feet.... get xyl
to climb a ladder in the back of the pickup parked beside the tree.
She takes a tennis ball with light dacron rope taped to it and throws
over the branch while I shout encouragement from below. It works.
(oh, by the way, xyl is KC2PRW). That's the good news, the bad news
is 25 feet ain't high enough, with the sag problem mentioned above.
Next, get bow and arrow from neighbor, yeahhhhh !! that works. Now
got line over 35 feet, that's decent. Same success on 2nd tree. Now
got the feedpoint tree and one of the corner trees with nice lines up
35 feet. Now pull up the wire and notice that the smallest little
friggin branch in the oak trees will snag the #14, so get the ladder
and trim off dozens of those little suckers. So that's where we are
at the moment. I figure about 50% done. Now the question is, will it
work?

I found (google can find anything) a great circle bearing program that
told me to point it 47 degrees which, from New Jersey puts me right
over London and down into central Germany. Look out DLs. According
to my antenna modeling program it will have 14 dbi gain and a 3 db
beamwidth of 20 degrees. Man that is sharp, much sharper than any 3
element beam. What's with these dbi's ? For comparison, a 3 ele beam
at 70 ft will have 12 dbi gain. The rhombic at 30 ft has its main
beam at about 22-25 degrees elevation. I sure wish I could get it up
to 70 ft, but there's no chance.

So now I have to get two more trees rigged with ropes and then get
down to the business of feeding the monster. I will be using balanced
ladder line to a homebrew tuner which I haven't built yet.

If I get any positive feedback on this post I will continue with my
progress and maybe even provide some on-air results in a week or so.

So that's my story. What are you working on?

Rick K2XT

You can build a load out of 2 watt resistors if you are careful with
your design. Design the load as a string of attenuators with each
section dissipating about 50 watts or so. I ve done this with 50 ohm
unbalanced design but never with a balanced line. Also consider making
a lossy transmission line, perhaps using some nichrome wire.

On 27 Oct 2006 14:15:43 -0700, "JIMMIE"
wrote:

Also consider making
a lossy transmission line, perhaps using some nichrome wire.

Hi All,

I've found one excellent source for high resistance wire can be found
at the thrift sto 5$ Toasters. Each element is curiously close to
50 Ohms.

73's
Richard Clark, KB7QHC

I've found one excellent source for high resistance wire can be found
at the thrift sto 5$ Toasters.

At the former AT&T High Seas site at Ocean Gate NJ that I am
associated with they terminated rhombics with some kind of wire (looks
like shiny aluminum wire) in the form of an open wire transmission
line. It comes down the pole and then runs back toward the feed point
near the ground, then turns and comes back the whole length of the
rhombic, and does this 2 or three times - a lossy transmission line I
guess.

Rick

"Rick" wrote in message
...
In the spirit of trying to get something going on the subject of
antennas, and away from all the off topic posts......

Are you doing anything interesting with antennas? Putting anything up
new for the contest season? Learn something new that the rest of us
might benefit from hearing about, even if it isn't patentable?

For me, I have become interested in rhombics and am currently building
one. It was based on the one featured in the ARRL Antenna Book, which
is 377 feet long (right down the middle) and 210 feet on each side.
210 feet is 3 wavelengths on 20 meters. So far I have learned a
little about the rhombic. It can be built as a terminated rhombic or
a "resonant" rhombic. In the case of a terminated rhombic, you
install a 600 ohm resistor at the far end, and that absorbs the power
that would otherwise be radiated off the back, making the antenna
uni-directional. Another advantage is, the feedpoint Z is
approximately flat and equal to 600 ohms across a huge frequency
range. So the antenna has gain and lots of it, at least over the
range of 20-10 meters and everything in between! If you don't
terminate it, it works the same way in the forward direction but has
no front to back. And the impedance varies all over the place. But
does anyone have a 600 ohm resistor they could supply me with? 300
watts or so? Noninductive.

So getting down to practical details, here's some of my experiences so
far. Copper wire has gotten very expensive. #14 stranded down at the
local Depot store is now 8 cents a foot, #12 is 14 cents. That adds
up fast when you need 840 feet of the stuff. So I managed to find a
roll at 900 ft on eBay for about 60% of that and got it. Now the
problem with #14 is it sags. Well maybe not, maybe it is the rope
holding the end up, it is very hard to pull up 200 feet of wire and
get it to where it doesn't look like the suspension cables on the
Verrazano bridge.

Ok so now how to get the rope up high enough in the oak to make it
useful? Bought a slingshot. For-get-it. I tried bolts, nuts,
fishing weights, etc, can't get the damn thing with fishing line to
get over 16 feet and most of the time it tangled the line and
sometimes actually ended up behind me. Crosman Slignshot for sale,
$25 shipped to your door. Here's what works for 25 feet.... get xyl
to climb a ladder in the back of the pickup parked beside the tree.
She takes a tennis ball with light dacron rope taped to it and throws
over the branch while I shout encouragement from below. It works.
(oh, by the way, xyl is KC2PRW). That's the good news, the bad news
is 25 feet ain't high enough, with the sag problem mentioned above.
Next, get bow and arrow from neighbor, yeahhhhh !! that works. Now
got line over 35 feet, that's decent. Same success on 2nd tree. Now
got the feedpoint tree and one of the corner trees with nice lines up
35 feet. Now pull up the wire and notice that the smallest little
friggin branch in the oak trees will snag the #14, so get the ladder
and trim off dozens of those little suckers. So that's where we are
at the moment. I figure about 50% done. Now the question is, will it
work?

I found (google can find anything) a great circle bearing program that
told me to point it 47 degrees which, from New Jersey puts me right
over London and down into central Germany. Look out DLs. According
to my antenna modeling program it will have 14 dbi gain and a 3 db
beamwidth of 20 degrees. Man that is sharp, much sharper than any 3
element beam. What's with these dbi's ? For comparison, a 3 ele beam
at 70 ft will have 12 dbi gain. The rhombic at 30 ft has its main
beam at about 22-25 degrees elevation. I sure wish I could get it up
to 70 ft, but there's no chance.

So now I have to get two more trees rigged with ropes and then get
down to the business of feeding the monster. I will be using balanced
ladder line to a homebrew tuner which I haven't built yet.

If I get any positive feedback on this post I will continue with my
progress and maybe even provide some on-air results in a week or so.

So that's my story. What are you working on?

Rick K2XT

I'm not working on anything at the moment, Rick. But, your post is the best
I've seen in quite a while and it makes me want to get up off my butt and do
something. Thanks for that!

I look forward to more info on your project.
73,
John

I have modified my Hustler 5-BTV by adding 12m and 17M - all homebrew for
about $10 1 antenna = 7 bands

1. http://www.ad5th.com/5-BTV-WARC.html

--

73,Charlie-AD5TH
www.ad5th.com


"John - KD5YI" wrote in message
news:9QQ0h.2381$Wy6.1803@trnddc01...
"Rick" wrote in message
...
In the spirit of trying to get something going on the subject of
antennas, and away from all the off topic posts......

Are you doing anything interesting with antennas? Putting anything up
new for the contest season? Learn something new that the rest of us
might benefit from hearing about, even if it isn't patentable?

For me, I have become interested in rhombics and am currently building
one. It was based on the one featured in the ARRL Antenna Book, which
is 377 feet long (right down the middle) and 210 feet on each side.
210 feet is 3 wavelengths on 20 meters. So far I have learned a
little about the rhombic. It can be built as a terminated rhombic or
a "resonant" rhombic. In the case of a terminated rhombic, you
install a 600 ohm resistor at the far end, and that absorbs the power
that would otherwise be radiated off the back, making the antenna
uni-directional. Another advantage is, the feedpoint Z is
approximately flat and equal to 600 ohms across a huge frequency
range. So the antenna has gain and lots of it, at least over the
range of 20-10 meters and everything in between! If you don't
terminate it, it works the same way in the forward direction but has
no front to back. And the impedance varies all over the place. But
does anyone have a 600 ohm resistor they could supply me with? 300
watts or so? Noninductive.

So getting down to practical details, here's some of my experiences so
far. Copper wire has gotten very expensive. #14 stranded down at the
local Depot store is now 8 cents a foot, #12 is 14 cents. That adds
up fast when you need 840 feet of the stuff. So I managed to find a
roll at 900 ft on eBay for about 60% of that and got it. Now the
problem with #14 is it sags. Well maybe not, maybe it is the rope
holding the end up, it is very hard to pull up 200 feet of wire and
get it to where it doesn't look like the suspension cables on the
Verrazano bridge.

Ok so now how to get the rope up high enough in the oak to make it
useful? Bought a slingshot. For-get-it. I tried bolts, nuts,
fishing weights, etc, can't get the damn thing with fishing line to
get over 16 feet and most of the time it tangled the line and
sometimes actually ended up behind me. Crosman Slignshot for sale,
$25 shipped to your door. Here's what works for 25 feet.... get xyl
to climb a ladder in the back of the pickup parked beside the tree.
She takes a tennis ball with light dacron rope taped to it and throws
over the branch while I shout encouragement from below. It works.
(oh, by the way, xyl is KC2PRW). That's the good news, the bad news
is 25 feet ain't high enough, with the sag problem mentioned above.
Next, get bow and arrow from neighbor, yeahhhhh !! that works. Now
got line over 35 feet, that's decent. Same success on 2nd tree. Now
got the feedpoint tree and one of the corner trees with nice lines up
35 feet. Now pull up the wire and notice that the smallest little
friggin branch in the oak trees will snag the #14, so get the ladder
and trim off dozens of those little suckers. So that's where we are
at the moment. I figure about 50% done. Now the question is, will it
work?

I found (google can find anything) a great circle bearing program that
told me to point it 47 degrees which, from New Jersey puts me right
over London and down into central Germany. Look out DLs. According
to my antenna modeling program it will have 14 dbi gain and a 3 db
beamwidth of 20 degrees. Man that is sharp, much sharper than any 3
element beam. What's with these dbi's ? For comparison, a 3 ele beam
at 70 ft will have 12 dbi gain. The rhombic at 30 ft has its main
beam at about 22-25 degrees elevation. I sure wish I could get it up
to 70 ft, but there's no chance.

So now I have to get two more trees rigged with ropes and then get
down to the business of feeding the monster. I will be using balanced
ladder line to a homebrew tuner which I haven't built yet.

If I get any positive feedback on this post I will continue with my
progress and maybe even provide some on-air results in a week or so.

So that's my story. What are you working on?

Rick K2XT

I'm not working on anything at the moment, Rick. But, your post is the
best I've seen in quite a while and it makes me want to get up off my butt
and do something. Thanks for that!

I look forward to more info on your project.
73,
John

"Rick" wrote in message
...
In the spirit of trying to get something going on the subject of
antennas, and away from all the off topic posts......

Are you doing anything interesting with antennas?
For me, I have become interested in rhombics and am currently building
one.

As a no-code, I am my club's sole source of FD points for UHF/VHF. I have
beams for 2m & 70 cm, but maybe rhombics are better. From San Diego, most
of my DX FD contacts are in the same place: Los Angeles. I don't really
need a steerable antenna.

Impedance matching to a 700 ohm antenna seems to be a daunting task. If I
used a 4:1 balun could I connect two or three independently terminated
rhombics (one over the other) in parallel to the balanced side?

I also want to try a rhombic for UHF TV. True, this is not a ham project,
but hamming isn't my sole electronics interest. (Probably the same with
most of us.)

I also have a project for TV DX, which requires canceling out a co-channel
interference source. The QRM is 11 degrees off-axis at Channel 53. This
calls for yoking two antennas about 43 inches apart to create a deep null in
the direction of the QRM. I did one for Channel 36 at 90-degrees off-axis
and it works like a charm.

Sal M. Onella wrote:
I am my club's sole source of FD points for UHF/VHF. I have beams for
2m & 70 cm, but maybe rhombics are better. From San Diego, most of my
DX FD contacts are in the same place: Los Angeles. I don't really
need a steerable antenna.

Well, OK... but it takes a LOT of on-site work before a large rhombic
can show any advantage over one or two decent long yagis. You'd need to
put up four masts in precisely surveyed locations, with enough guy
strength to keep four long spans of wire taut, and then terminate and
match the thing.

BTDT, and succeeded, but it takes far more work than you imagine. When
your club is trying to set up several stations all at the same time, you
may find you don't have enough effort to do it. There's a severe risk of
winding up with no VHF/UHF antennas at all. BTDT too...

And after having spent all that effort on a fixed beam, are you really
prepared to risk a sporadic-E opening in a completely unanticipated
direction?

Impedance matching to a 700 ohm antenna seems to be a daunting task.
If I used a 4:1 balun

That is actually the easy bit. You use the 4:1 balun with an
old-fashioned device called a "universal stub": a half-wave section of
parallel line made from a pair of old yagi elements. One end of the stub
is connected to the antenna, and two clips make a moveable tapping point
for the balun. Towards the far end of the stub, two more clips make a
moveable shorting bar.

Detailed dimensions don't matter at all, because you're going to slide
the shorting bar and the balun along the stub until you find the
combination that gives minimum SWR. It takes all of five minutes.

That was the easy bit... but it's probably the ONLY easy bit of the
whole project.

could I connect two or three independently terminated rhombics (one
over the other) in parallel to the balanced side?

Two stacked rhombics are easy to feed - connect the feedpoints by a
length of open-wire, and then connect the universal stub at the
mid-point. The counter-intuitive thing is that a pair of antennas that
could be hundreds of feet long need to be stacked only a few feet above
each other. But attempting to stack two rhombics will multiply your
rigging problems by a factor MUCH larger than 2!

Having experienced a large rhombic for VHF, I'd stay with yagis.


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

On Sun, 29 Oct 2006 08:23:18 +0000, Ian White GM3SEK
wrote:


BTDT, and succeeded,

Ian, What is BTDT please?

Sal M. Onella wrote:
"Rick" wrote in message
...

In the spirit of trying to get something going on the subject of
antennas, and away from all the off topic posts......

Are you doing anything interesting with antennas?
For me, I have become interested in rhombics and am currently building
one.



I am considering Roy W7EL's FD Special, published in QST in 1984. For
20M, it is about 32 feet long and has two elements separated with about
8 feet lengths of PVC tubing on each end. The elements are 300 ohm twin
lead.
It is a directional antenna. I wonder how difficult it would be to
reverse directionality?

I am considering re-configuring it for 17 meters.
What do you think...given the nadir of the sunspot cycle. Which is the
better band? (I am aiming this one approx NW from Ohio.)

And, yes, Father Owen, I'll consider velocity, etc. this time

John
AB8O

PS
The G5RV I recently built has Z= 86 + j22 at 7270 KHz and Z = 82 -j41 at
14000 KHz. SWR is a little higher than expected but OK.
Aren't antenna bridges cool?