Ah I have been misled by my latin teacher
so must now clarify I guess
--
Caveat Lector - Reader Beware



"Richard Clark" wrote in message
news
On Mon, 31 Jan 2005 10:54:43 -0500, Buck wrote:

(Caveat emptor means buyer beware, what does caveat lector mean?)

Hi Buck,

You got the Caveat part down, but I'm not sure if ***** is being coy,
or has taken the wrong translation. His intent may be (if read
literally) that "reader beware." However, this is not the same as the
meaning of lector, where the meaning would offer "beware reader." It
is a subtle distinction at best leading to the same caution, but
Lector is one who reads (imparts information) to others (instead of
being a silent reader, such as anyone "reading" this post).

73's
Richard Clark, KB7QHC

The formula for a DIPOLE is 468/freq in Mhz = length in ft.....the formula
234/freq is for one leg OR usually quoted for a 1/4wave vertical but the
standard dipole formula is 1/2 wave (just to clarify that).

As for a good FM omni antenna, he should build a simple 1/4 ground plane or
coaxial sleeve antenna.....OR a turnstile (cross dipoles)..

FM stations USUALLY use Circular Polarization.....(similar to horiz and
vertical at the same time...)
so an antenna set for horiz or vertical will work (but lose 3db of signal
compared to a CP antenna!)

Chris
WB5ITT

"Buck" wrote in message
...
On 30 Jan 2005 17:14:42 -0800, wrote:

I don't know why you want FAT. It will give you lower gain. However,
you might consider building a dipole out of 1/2 copper tubing. A
piece of PVC T connector and two elements about 2.4 feet long each can
be connected to the coax, painted (if desired) and mounted inside the
attic or outside if desired.

The formula for a dipole is 234/frequency in Mhz = 1 leg of a dipole
or 1/4 wave length approximately. (Each dipole needs two legs.)

the copper pipe will give plenty of band width and do as well or
better than three inches.

You don't have to be worried about perfect dimensions as you aren't
worried about SWR so the elements I showed you will work very well.

Someone correct me, but don't FM stations transmit both vertical and
horizontal?

I hope this helps.


--
73 for now
Buck
N4PGW

"CWB" wrote
FM stations USUALLY use Circular Polarization.....
(similar to horiz and vertical at the same time...)
so an antenna set for horiz or vertical will work
(but lose 3db of signal compared to a CP antenna!)
________________

FM broadcast stations in the US _must_ radiate their licensed h-pol ERP
regardless of the ERP they radiate in other polarization planes. However
for most omni FM stations, v-pol RMS ERP cannot (legally) exceed h-pol RMS
ERP.

The gain of a true c-pol transmit antenna is 3dB lower than for the same
configuration of linearly polarized radiators. However in FM broadcast, the
transmitter power is increased by 3dB to make up for that, and h-pol ERP is
the same for either antenna configuration. Therefore the h-pol field
strength produced by either transmit antenna over the same path should be
the same.

Using a c-pol antenna to receive a c-pol FM station would add 3dB to the
signal seen by rx (over a free space path), as well as reduce the
self-interference caused by multipath.

RF

Visit http://rfry.org for FM transmission system papers.

Brad wrote:
"I want to build a fat dipole for FM listening for my brother-in-law,
who refuses to get a rotor."

A twin-lead dipole may be fat enough. These are sold at Radio Shack and
other outlets for just a few dollars and can be used to determine if
such an approach is satisfactory. You can still build an "improved
antenna" if the bought antenna works on site.

Best regards, Richard Harrison, KB5WZI

Thanks for the overload of info guys. I may have resolved his issue by
purchasing a Marantz ST-17 tuner, which has provision for two antennas.
The ST-2 that he has is fine for all stations he listens to except
one. I'll have him get the Radio Shack Yagi abd some good coax and aim
it for best reception on that station.

However, I need to make a good omnidirectional antenna to go in my
attic. I did not get an answer on if the ARRL handbook has the
directions for makinng the fat dipole.

I live outside of Atlanta, GA (hilly) and cannot have an outside
antenna, and have very little room horizonally in attic - a directional
is out, but do have an area for a tal vertical antenna.
What would be your recommendations?

What suggestions

On 2 Feb 2005 16:09:02 -0800, wrote:

but do have an area for a tal vertical antenna.
What would be your recommendations?

Hi Brad,

Go back to radio shack and buy their discone antenna.

73's
Richard Clark, KB7QHC

Brad wrote:
"What would be your recommendations?"
Brad also wrote:
"---but do have an area for a tall vertical antenna."

There are often obstructions in an otherwise line-of-sight path. Antenna
gain is usually not enough to overcome an obstructed path. Antenna
height can overcome the obstruction.

Flagpoles are usually acceptable where antennas are banned. In Terman`s
1955 edition of "Electronis and Radio Engineering" on page 902 are found
"Flagpole Antennas". These are balanced vertical dipoles, transformed to
a coax feed through the bottom of the dipole.

If the flagpole is tall enough, you receive FM broadcasts.

Q = f/BW means your dipoe needs a Q of less than 4.8 to span 88 MHz to
108 MHz. The antenna would center upon 97.5 MHz, the geometric mean or
center of the band.

Such a bandwidth is likely impractical. You can settle for less or
center the response on the part of the band you would most use.

Multiply the lowest frequency of high interest by the highest frequency
of high interest and take the square root of the product to find the
frequency the dipole should be cut for. The fatter the dipole is, the
lower its Q will be, and the more even its frequency response will be.
You can probably do quite well with uneven response in your antenna is
high enough.

Best regards, Richard Harrison, KB5WZI