Thanks to Tom, Dave and the rest of you that answered my question so
quickly.

I thought I should give a little more pertinent info on this project. A
elderly ham friend of mine is putting together a 70cm fast scan TV
station. He chose the quad because of its wide band characteristics. His
tower is Rohn 45 at 73 feet. It has a Glen Martin "Voyager" trolley/tram
system. The steel mast is above the bearing plate about 14 feet. Out the
top of the steel mast is 6 feet of thick wall fiberglass tubing. The two
70cm quads will be on a fiberglass cantilever arm that is approximately
48" long. It slips over the fiberglass mast and bolts into place. (arm
required to clear the tower when cranking antenna system down) This arm
will have two, 1 1/4" diameter post sticking up vertically to mount the
quads. Here is where the question arose about how far apart the quads
should be.

I don't think I could/should push the cantilever arm out any further.
The system, all together, could probably withstand a little longer arm
if required. ?? Three 1/2 wavelengths would be ~39 inches.

The quads are 7 1/2 feet long with 12 elements each and weigh 3.5 pounds.

We have no modeling software, just a desire to do it right the first time.

Thanks again & 73,

Steve
ab5mm

sounds like a lot of joints that could slip. i wouldn't expect a lashup
like that to survive very long up here in ice and wind country. i would
get rid of the '1 1/4" posts sticking up' and mount the quads right to the
cross arm. and unless that extra 6' really is necessary i would mount the
crossarm directly to the steel mast. which way are these going to be
polarized, horizontal or vertical?? even if vertically polarized they
should be ok being 2' out from the steel mast i would think.

"ab5mm" wrote in message
...
Thanks to Tom, Dave and the rest of you that answered my question so
quickly.

I thought I should give a little more pertinent info on this project. A
elderly ham friend of mine is putting together a 70cm fast scan TV
station. He chose the quad because of its wide band characteristics. His
tower is Rohn 45 at 73 feet. It has a Glen Martin "Voyager" trolley/tram
system. The steel mast is above the bearing plate about 14 feet. Out the
top of the steel mast is 6 feet of thick wall fiberglass tubing. The two
70cm quads will be on a fiberglass cantilever arm that is approximately
48" long. It slips over the fiberglass mast and bolts into place. (arm
required to clear the tower when cranking antenna system down) This arm
will have two, 1 1/4" diameter post sticking up vertically to mount the
quads. Here is where the question arose about how far apart the quads
should be.

I don't think I could/should push the cantilever arm out any further.
The system, all together, could probably withstand a little longer arm
if required. ?? Three 1/2 wavelengths would be ~39 inches.

The quads are 7 1/2 feet long with 12 elements each and weigh 3.5 pounds.

We have no modeling software, just a desire to do it right the first time.

Thanks again & 73,

Steve
ab5mm

A well designed yagi would have had plenty of bandwidth, but that's moot
now, I guess.

I would say 1.17m H plane, or 1.06m E plane would be pretty close.
That's based on an estimate of your gain. You could email me the plans,
and I would find where the 3dB points really are.

tom
K0TAR

ab5mm wrote:

Thanks to Tom, Dave and the rest of you that answered my question so
quickly.

I thought I should give a little more pertinent info on this project. A
elderly ham friend of mine is putting together a 70cm fast scan TV
station. He chose the quad because of its wide band characteristics. His
tower is Rohn 45 at 73 feet. It has a Glen Martin "Voyager" trolley/tram
system. The steel mast is above the bearing plate about 14 feet. Out the
top of the steel mast is 6 feet of thick wall fiberglass tubing. The two
70cm quads will be on a fiberglass cantilever arm that is approximately
48" long. It slips over the fiberglass mast and bolts into place. (arm
required to clear the tower when cranking antenna system down) This arm
will have two, 1 1/4" diameter post sticking up vertically to mount the
quads. Here is where the question arose about how far apart the quads
should be.

I don't think I could/should push the cantilever arm out any further.
The system, all together, could probably withstand a little longer arm
if required. ?? Three 1/2 wavelengths would be ~39 inches.

The quads are 7 1/2 feet long with 12 elements each and weigh 3.5 pounds.

We have no modeling software, just a desire to do it right the first time.

Thanks again & 73,

Steve
ab5mm

Why stack them horizontally rather than vertically?

jw
K9RZZ

"ab5mm" wrote in message
...
Thanks to Tom, Dave and the rest of you that answered my question so
quickly.

I thought I should give a little more pertinent info on this project. A
elderly ham friend of mine is putting together a 70cm fast scan TV
station. He chose the quad because of its wide band characteristics. His
tower is Rohn 45 at 73 feet. It has a Glen Martin "Voyager" trolley/tram
system. The steel mast is above the bearing plate about 14 feet. Out the
top of the steel mast is 6 feet of thick wall fiberglass tubing. The two
70cm quads will be on a fiberglass cantilever arm that is approximately
48" long. It slips over the fiberglass mast and bolts into place. (arm
required to clear the tower when cranking antenna system down) This arm
will have two, 1 1/4" diameter post sticking up vertically to mount the
quads. Here is where the question arose about how far apart the quads
should be.

I don't think I could/should push the cantilever arm out any further.
The system, all together, could probably withstand a little longer arm
if required. ?? Three 1/2 wavelengths would be ~39 inches.

The quads are 7 1/2 feet long with 12 elements each and weigh 3.5 pounds.

We have no modeling software, just a desire to do it right the first time.

Thanks again & 73,

Steve
ab5mm


Several years ago some friends and I tried mking some gain measurements on
quads. Found that more than about six elements did not help the gain of the
antenna to any useful degree. I would go with quads with fewer elements but
more antennas in your array.

"Jimmy" wrote in message
m...

"ab5mm" wrote in message
...
Thanks to Tom, Dave and the rest of you that answered my question so
quickly.

I thought I should give a little more pertinent info on this project. A
elderly ham friend of mine is putting together a 70cm fast scan TV
station. He chose the quad because of its wide band characteristics. His
tower is Rohn 45 at 73 feet. It has a Glen Martin "Voyager" trolley/tram
system. The steel mast is above the bearing plate about 14 feet. Out the
top of the steel mast is 6 feet of thick wall fiberglass tubing. The two
70cm quads will be on a fiberglass cantilever arm that is approximately
48" long. It slips over the fiberglass mast and bolts into place. (arm
required to clear the tower when cranking antenna system down) This arm
will have two, 1 1/4" diameter post sticking up vertically to mount the
quads. Here is where the question arose about how far apart the quads
should be.

I don't think I could/should push the cantilever arm out any further.
The system, all together, could probably withstand a little longer arm
if required. ?? Three 1/2 wavelengths would be ~39 inches.

The quads are 7 1/2 feet long with 12 elements each and weigh 3.5
pounds.

We have no modeling software, just a desire to do it right the first
time.

Thanks again & 73,

Steve
ab5mm


Several years ago some friends and I tried mking some gain measurements on
quads. Found that more than about six elements did not help the gain of
the
antenna to any useful degree. I would go with quads with fewer elements
but
more antennas in your array.


This tends to give me doubts about the ethics of those who manufactor the
long quads.

Jimmy wrote:
Several years ago some friends and I tried mking some gain measurements on
quads. Found that more than about six elements did not help the gain of
the
antenna to any useful degree.


This tends to give me doubts about the ethics of those who manufactor
the long quads.


I'm sorry that you and your friends weren't successful... but that
doesn't prove it can't be done.

Microwave operators regularly use long quads (loop yagis) with 20, 30
and even more elements. Range measurements *prove* that they work, about
the same as conventional yagis of the same boom length, but the loop
elements do have some constructional advantages for the low microwave
bands.

As with any yagi-type antenna, you need to add significant numbers of
extra elements and boom length in order to see a significant increase in
gain. If you do it right, the gain will come.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

I think one other factor not factored in (sorry, I just had to do that,
it's friday), is that no one has written a good optimizer for loop/quad
yagis.

I wonder if one could craft a converter that makes equivalent loops out
of regular dipole elements, then you could convert optimized yagis to
loops yagis. That assumes a lot, of course, like spacing between the 2
types works the same. Probably won't work at all, but if it's possible
to do it, I bet I have the way. Same one I gave to Brian to do scaling
in YO.

tom
K0TAR

Ian White, G3SEK wrote:

I'm sorry that you and your friends weren't successful... but that
doesn't prove it can't be done.

Microwave operators regularly use long quads (loop yagis) with 20, 30
and even more elements. Range measurements *prove* that they work, about
the same as conventional yagis of the same boom length, but the loop
elements do have some constructional advantages for the low microwave
bands.

As with any yagi-type antenna, you need to add significant numbers of
extra elements and boom length in order to see a significant increase in
gain. If you do it right, the gain will come.

Tom Ring wrote:

Microwave operators regularly use long quads (loop yagis) with 20,
30 and even more elements. Range measurements *prove* that they work,
about the same as conventional yagis of the same boom length, but the
loop elements do have some constructional advantages for the low
microwave bands.
As with any yagi-type antenna, you need to add significant numbers
of extra elements and boom length in order to see a significant
increase in gain. If you do it right, the gain will come.

I think one other factor not factored in (sorry, I just had to do that,
it's friday), is that no one has written a good optimizer for loop/quad
yagis.

I wonder if one could craft a converter that makes equivalent loops out
of regular dipole elements, then you could convert optimized yagis to
loops yagis.

The practical advantages of loop yagis lie in their element
construction, which is a circle rolled from flat strip. Unfortunately,
that is a very difficult shape to model with any software I'm aware of.

That assumes a lot, of course, like spacing between the 2 types works
the same.

Which it doesn't, because parallel-spaced loops are very obviously
different from parallel-spaced rods, and are going to interact in a
different way. The general rules for building yagis are the same -
progressively shorter loop lengths along the boom; progressively
increase the spacing until you reach a certain limit, and then keep it
constant - but the details are definitely going to be different. And
it's those small details that make the difference between a good,
average or poor yagi.

Probably won't work at all, but if it's possible to do it, I bet I have
the way. Same one I gave to Brian to do scaling in YO.

It would certainly be very difficult, but I doubt if it will ever be
done. Existing loop yagi designs are already quite close to the
theoretical optimum for the boom-length, so the limited rewards wouldn't
justify the effort.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek