ADF NDB beacon antenna change seeking comments
 

We are going to drop using the shunt feed tower no matter how hard we
work on it we don't think it's going to work any better that it does
right now.

We have two choices :

We have two towers spaced 250 feet apart the towers are 95 feet
high. We could install a 'flat top' wire run it from tower to tower.

The horizontal run tower to tower would be 250 feet : The vertical
drop to the ground would be 90 feet or so.

The vertical wire would be connected to the flat top wire dead
center

We could series feed it against a good ground; 8 to 15 radials 500
feet long


Choice two:

We have two towers spaced about 140 feet they are 150 feet high The
'flat top' wire would run 140 feet horizontal tower to tower The
vertical drop would be 150 feet. same as above vertical wire
connected dead center of flat top.

series feed working against 8 to 15 500 foot ground radials.


My question to the group:

Is it better to have more (150 feet) vertical wire in the air with
LESS (140 feet) flat top wire or :

LESS vertical wire in the air (90 feet) but MORE flat top wire 250
feet??????


The flat top wire is insulated from the towers using power line
fiberglass rods

NDB freq is 529 KC

P.S.

Would their be a big difference if the 'flat top' has two runs of
3/8 aluminum cable side by side spaced about 30 inches ?? or
would one 3/8 cable do the job???

Thank you for your input

Dave WA4SZE

ADF NDB beacon antenna change seeking comments
 

wrote
We are going to drop using the shunt feed tower no matter how hard we
work on it we don't think it's going to work any better that it does
right now.

We have two choices : etc
________________

A quick look with NEC shows the tee with the 90 ft vertical section to
have -5 dBi h-plane gain, and the tee with the 150 ft vertical section to
have -2.1 dBi gain, when both using a 2 ohm coil resistance and a 25 ohm r-f
ground. So other things equal, the taller vertical with the shorter
horizontal wire will give better performance.

Adding wires in parallel will improve r-f bandwidth, but will not change the
gains significantly.

BUT if the supporting towers are good conductors they will act as
parasitics, and the azimuth patterns will not be truly omnidirectional, nor
will a deep null exist toward the zenith. These may be factors to consider
for this application.

RF

ADF NDB beacon antenna change seeking comments
 

On Jul 5, 6:20 pm, wrote:


Would their be a big difference if the 'flat top' has two runs of
3/8 aluminum cable side by side spaced about 30 inches ?? or
would one 3/8 cable do the job???

Thank you for your input

Dave WA4SZE

The combined "resonant length" is almost the same with the two.
Appx 215 feet total radiator for the short one, vs appx 220 ft total
for the tall one.. I would go for the tall version myself.
Either one will still need more coil loading to tune.
MK

ADF NDB beacon antenna change seeking comments
 

On 6 jul, 01:20, wrote:
We are going to drop using the shunt feed tower no matter how hard we
work on it we don't think it's going to work any better that it does
right now.

We have two choices :

We have two towers spaced 250 feet apart the towers are 95 feet
high. We could install a 'flat top' wire run it from tower to tower.

The horizontal run tower to tower would be 250 feet : The vertical
drop to the ground would be 90 feet or so.

The vertical wire would be connected to the flat top wire dead
center

We could series feed it against a good ground; 8 to 15 radials 500
feet long

Choice two:

We have two towers spaced about 140 feet they are 150 feet high The
'flat top' wire would run 140 feet horizontal tower to tower The
vertical drop would be 150 feet. same as above vertical wire
connected dead center of flat top.

series feed working against 8 to 15 500 foot ground radials.

My question to the group:

Is it better to have more (150 feet) vertical wire in the air with
LESS (140 feet) flat top wire or :

LESS vertical wire in the air (90 feet) but MORE flat top wire 250
feet??????

The flat top wire is insulated from the towers using power line
fiberglass rods

NDB freq is 529 KC

P.S.

Would their be a big difference if the 'flat top' has two runs of
3/8 aluminum cable side by side spaced about 30 inches ?? or
would one 3/8 cable do the job???

Thank you for your input

Dave WA4SZE

Hi Dave,

I would go (if mechanically feasible) for the longer vertical run
(150ft). The resultant radiation resistance will be higher; hence the
losses in the ground will be less.

Yes it helps using two separated wires for the horizontal sections. It
increases the top capacitance. This will result in an easier match
(smaller series inductor) and you will get more current into the top
of the vertical wire. More current in the top of the vertical wire
increases the radiation resistance.

Higher radiation resistance will improve the radiation efficiency.

Best regards,

Wim
PA3DJS
www.tetech.nl

ADF NDB beacon antenna change seeking comments
 

wrote in message
oups.com...
We are going to drop using the shunt feed tower no matter how hard we
work on it we don't think it's going to work any better that it does
right now.

We have two choices :

We have two towers spaced 250 feet apart the towers are 95 feet
high. We could install a 'flat top' wire run it from tower to tower.

The horizontal run tower to tower would be 250 feet : The vertical
drop to the ground would be 90 feet or so.

The vertical wire would be connected to the flat top wire dead
center

We could series feed it against a good ground; 8 to 15 radials 500
feet long


Choice two:

We have two towers spaced about 140 feet they are 150 feet high The
'flat top' wire would run 140 feet horizontal tower to tower The
vertical drop would be 150 feet. same as above vertical wire
connected dead center of flat top.

series feed working against 8 to 15 500 foot ground radials.


My question to the group:

Is it better to have more (150 feet) vertical wire in the air with
LESS (140 feet) flat top wire or :

LESS vertical wire in the air (90 feet) but MORE flat top wire 250
feet??????


The flat top wire is insulated from the towers using power line
fiberglass rods

NDB freq is 529 KC

P.S.

Would their be a big difference if the 'flat top' has two runs of
3/8 aluminum cable side by side spaced about 30 inches ?? or
would one 3/8 cable do the job???

Thank you for your input

Dave WA4SZE


The secret is in having a good ground, the FAA systems I have seen use
buried grounds about 10 meters long. The only type of antenna I am familar
with them using is a flattop that is about 10 meter tall with the horizontal
portion about twice this. Nav aids aint my thing I was just suppling grunt
duty at the time.


Jimmie

ADF NDB beacon antenna change seeking comments
 

wrote in message
oups.com...
We are going to drop using the shunt feed tower no matter how hard we
work on it we don't think it's going to work any better that it does
right now.

We have two choices :

We have two towers spaced 250 feet apart the towers are 95 feet
high. We could install a 'flat top' wire run it from tower to tower.

The horizontal run tower to tower would be 250 feet : The vertical
drop to the ground would be 90 feet or so.

The vertical wire would be connected to the flat top wire dead
center

We could series feed it against a good ground; 8 to 15 radials 500
feet long


Choice two:

We have two towers spaced about 140 feet they are 150 feet high The
'flat top' wire would run 140 feet horizontal tower to tower The
vertical drop would be 150 feet. same as above vertical wire
connected dead center of flat top.

series feed working against 8 to 15 500 foot ground radials.


My question to the group:

Is it better to have more (150 feet) vertical wire in the air with
LESS (140 feet) flat top wire or :

LESS vertical wire in the air (90 feet) but MORE flat top wire 250
feet??????


The flat top wire is insulated from the towers using power line
fiberglass rods

NDB freq is 529 KC

P.S.

Would their be a big difference if the 'flat top' has two runs of
3/8 aluminum cable side by side spaced about 30 inches ?? or
would one 3/8 cable do the job???

Thank you for your input

Dave WA4SZE


You may want to check with the MIKE MARONEY AERONAUTICAL ACADAMEY in OKC.
This is The FAA tech school and engineering support.

ADF NDB beacon antenna change seeking comments
 

"Jimmie D" wrote in message
...

wrote in message
oups.com...
We are going to drop using the shunt feed tower no matter how hard we
work on it we don't think it's going to work any better that it does
right now.

We have two choices :

We have two towers spaced 250 feet apart the towers are 95 feet
high. We could install a 'flat top' wire run it from tower to tower.

The horizontal run tower to tower would be 250 feet : The vertical
drop to the ground would be 90 feet or so.

The vertical wire would be connected to the flat top wire dead
center

We could series feed it against a good ground; 8 to 15 radials 500
feet long


Choice two:

We have two towers spaced about 140 feet they are 150 feet high The
'flat top' wire would run 140 feet horizontal tower to tower The
vertical drop would be 150 feet. same as above vertical wire
connected dead center of flat top.

series feed working against 8 to 15 500 foot ground radials.


My question to the group:

Is it better to have more (150 feet) vertical wire in the air with
LESS (140 feet) flat top wire or :

LESS vertical wire in the air (90 feet) but MORE flat top wire 250
feet??????


The flat top wire is insulated from the towers using power line
fiberglass rods

NDB freq is 529 KC

P.S.

Would their be a big difference if the 'flat top' has two runs of
3/8 aluminum cable side by side spaced about 30 inches ?? or
would one 3/8 cable do the job???

Thank you for your input

Dave WA4SZE


You may want to check with the MIKE MARONEY AERONAUTICAL ACADAMEY in OKC.
This is The FAA tech school and engineering support.


BTW are you aware NDBs are being phased out. I think they are all supposed
to be gone by 2012. They arent needed with GPS

Jimmie

ADF NDB beacon antenna change seeking comments
 

WA4SZE wrote:
"We are going to drop using the shunt feed tower no matter how hard we
work on it we don`t think it`s going to work any better than it does
right now."

Shunt feed is a valid means to excite a grounded radiator. Its
disadvantage is difficulty in predicting the best place to tap into the
radiator to feed it if you want a particular impedance.

Bill Orr wrote: "The
performance of a shunt-fed antenna is substantially the same as one with
conventional series feed, provided the resistance of the ground return
path is low.

Unloaded vertical antennas as short as 0.15 wavelength may be shunt-fed.
Below this length, the tap point of the feed wire may be higher than the
physical height of the antenna."
See "Vertical Antennas" Radio Publications, Inc., ISBN 0-933616-09-0,
1986.

E.A. Laport has extensive information on low-frequency and medium
frequency antennas in "Radio Antenna Engineering".

Any unbalanced antenna must work against some sort of ground system. The
shorter the antenna is with respect to respnant length, the more
critical its grounding is because its radiation resistance is similarly
lowered, thus even a very small ground resistance can make it
inefficient.

The T antenna needs a good ground too, but the capacitive top loading
provided by the horizontal section brings the antenna closer to
resonance and raises its radiation resistance which improves its
efficiency. Balanced currents in opposite directions of the horizontal
section eliminate its radiation. The vertical section of the T is its
radiator.

Advantage of the shunt-fed tower is its near lossless capacitor needed
to tune the loop which feeds it. A series-fed short tower needs a large
inductance to bring it to resonance and it is usually lossy.

WA4SZE`s problem can be fixed by simply adding ground radials to to the
tower until he hits the point of diminishing returns.

Best regards, Richard Harrison, KB5WZI

ADF NDB beacon antenna change seeking comments
 

BTW are you aware NDBs are being phased out. I think they are all supposed
to be gone by 2012. They arent needed with GPS

Jimmie

I know my experience is out of date, but I recall a lot of times in
General Aviation when I was shooting a NDB approach while the techs
were busy on the ground trying to restore more complex Nav Aids and
Radar after a Thunder Storm. I don't believe the GPS system can
survive a serious attack any more than the World Trade Center.

I would like to be wrong on this point...

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"

ADF NDB beacon antenna change seeking comments
 

On Mon, 09 Jul 2007 12:44:24 GMT, John Ferrell
wrote:

I don't believe the GPS system can
survive a serious attack any more than the World Trade Center.

I would like to be wrong on this point...

Hi John,

Well, perhaps not wrong currently. Military systems and the future of
the Web is migrating towards what is called Network Programming (in
distinct contrast to prime time TV programming) where content is
massively parallel and noise (an attack) is rejected.

73's
Richard Clark, KB7QHC