Shunt feed tower for Aircraft NDB beacon Help
 

"Walter Maxwell"
Richard, I just now tried to access your link above, but it says the file
is no longer available. Do you have any other source of this data? I
worked with BL&E, so I'm kinda partial to having all the data from their
1936 experiment that I can find. I have their 1937 IRE paper.
_________

Walt -

I showed the working link in another post I made in followup, which should
work for you.

The link (again) is

http://i62.photobucket.com/albums/h8...ndERadials.gif

But if you have their 1937 paper, you already have the figures I referred
to.

RF

Shunt feed tower for Aircraft NDB beacon Help
 

Richard Fry wrote:
"So it`s not just the number of radials that is important, but also
their length."

True. I don`t have B.L. and E`s work to refer to but do recall an
observation that to get the best ground connection for the least copper
it might be wise to cut the radials in half so that their number might
be doubled.

The FCC standard is 120 radials, each 1/4-wavelength long, which may
seem extreme but it produces a near perfect ground connection.

Fortunately, the length of radials does not need to be increased in
direct proportion to wavelength below the broadcast band as skin effect
varies with the square root of the frequency so as we go lower in
frequency we need to increase length of the radials by the square root
of the wavelength to keep the resistance of our contact constant.

Best Regards, Richard Harrison, KB5WZI

Shunt feed tower for Aircraft NDB beacon Help
 

Shunt feed tower for Aircraft NDB beacon Help
 

"Richard Harrison" wrote
Fortunately, the length of radials does not need to be increased in
direct proportion to wavelength below the broadcast band as skin effect
varies with the square root of the frequency so as we go lower in
frequency we need to increase length of the radials by the square root
of the wavelength to keep the resistance of our contact constant.
____________

Here is a quote about this from RADIO ANTENNA ENGINEERING
by Edmund Laport:

"The distance from the antenna at which returning ground currents are of
such a low value as to be negligible is of the order of 0.5 wavelength."

At least across the AM broadcast band 530-1700 kHz, Laport, Terman, Kraus,
and Balanis show _no_ dependence of the lengths of buried radials with
frequency -- except, of course, that radials used with lower frequency
systems need to be physically longer to reach the desired radius from the
monopole, in free-space wavelengths.

The FCC uses a computer program (linked below) to calculate the groundwave
inverse distance field at 1 km and 1 mile from a MW monopole, based on the
radiator height and the number/length of buried radials.

On-line users of this program can enter their own system parameters to see
their effects on the radiated field. The program does restrict entries to
the minimum values acceptable to the FCC for commercial AM broadcast
stations.

== NOTE: The FCC program applet has no entry block for frequency.

Here is the link. The applet starts at the bottom of that web page.

http://www.fcc.gov/mb/audio/bickel/figure8.html

RF

Clarification
 

== NOTE: The FCC program applet has no entry block for frequency.
_________

Yes it does (sorry), but ...

== NOTE: The FCC program results are essentially the same regardless of
frequency for all systems of a given radiator height and radial length (in
wavelengths), when using the same number of radials.

RF

Shunt feed tower for Aircraft NDB beacon Help
 

wrote in message
oups.com...
I have installed a FAA approved NDB beacon here at our private
airport located in Manchester,TN .

The Beacon is transmitting on 529 KHZ Carrier power is 50 watts the
facility Id is : LYQ

I have shunt feed a 120 foot high Rhon 25G tower. The tap wire (3/8
dia aluminum 'power line' cable) is at the 90 foot level runs down
the face of the tower with 24 inch spacing to the matching network.

I am using the 'Gamma' match network : the SWR is down to 1.2 or so.

The top of the tower has 4 ten foot radials

The base of the tower has 8 200 foot 3/ 8 inch aluminum cable
radials we plan to add more.

The tower has a 3/8 'power line' type cable from the top to the base
to ensure bonding of each section.

When I fly the Company's Jetstar from 1000 to 41,000 feet, I get
solid points on the RMI indicator:

when I pass right over the beacon tower the RMI needle swings to the
tail indicating positive station passage.

The problem is the range of the LYQ beacon it seems to work 10 miles
or less??? The airplane has dual ADF systems that work perfect.

As an aside, 10 miles away, is another ADF beacon on 332 KHZ 25
watts! using the traditional three strand 'flat top' suspended
between two telephone poles. The vertical radiator for this beacon is
less than 60 feet high : I can track the beacon out to 70 miles or so!

Is a shunt feed tower lossy??? poor radiator??? comments???

I am a Ham op WA4SZE : by the way, we will QSL the beacon when we
get it commissioned.

Thanks!!


The one that works is probably an FAA facility and has a better ground
system. The one I helped install had 96 buried radials. I was surprised that
they werent that long. Same length as the flat top , Guessing 30 ft. I do
know the antenna was 10 meters tall tophat and radials were probably close
to being the same.

Jimmie