I want to build a fat dipole antenna for FM listening for my
brother-in-law, who refuses to get an antenna rotator.

He is located with antenna's all around him but not on top of him.

I would of course orient it vertically and use 75 ohm coax from where
it is mounted to his tuner.

Does the ARRL Antenna Handbook have directions on building one of
these?

I would be using 8 inches as the diameter. Is the math to figure out
the length gonna get me - I've been out of college for 30 years and
have only done business math since....

Thanks,

Brad

On 30 Jan 2005 17:14:42 -0800, wrote:
I would be using 8 inches as the diameter.

Hi Brad,

Well, you sure pegged it down for being Fat. However, this is not
particularly useful for just the FM Band. A fat antenna has useful
properties as being wide banded (which means you suffer nothing from
it being obese), and this would roughly equate to many times as wide
as the FM band. (Another)However, receive antennas are not
particularly demanding as long as they are high enough to see the
antenna that is transmitting. In that regard, and as a rule of thumb,
your antenna can see as far in miles as the square root of twice its
height in feet (hope that is not too alien from business math). If
you figure how high the other (transmitting) antenna is, you can add
those two mileages to compute your listening range.

Example: your Fat vertical antenna is 25 feet high (above the ground -
on the peak of your roof for instance) and the transmitter antenna is
on a hill 250 feet high. That computes to your antenna being able to
see about 7 miles and the transmitter being able to see 22 miles.
Hence you would be able to hear that program being broadcast from as
far as 29 miles out (barring obstructions like mountains in the way).

73's
Richard Clark, KB7QHC

On 30 Jan 2005 17:14:42 -0800, wrote:

I want to build a fat dipole antenna for FM listening for my
brother-in-law, who refuses to get an antenna rotator.

He is located with antenna's all around him but not on top of him.

I would of course orient it vertically and use 75 ohm coax from where
it is mounted to his tuner.

Does the ARRL Antenna Handbook have directions on building one of
these?

I would be using 8 inches as the diameter. Is the math to figure out
the length gonna get me - I've been out of college for 30 years and
have only done business math since....

Thanks,

Brad


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

On Mon, 31 Jan 2005 02:35:51 -0500, Buck wrote:

I don't know why you want FAT. It will give you lower gain.

Hi Buck,

No such thing.

73's
Richard Clark, KB7QHC

On Mon, 31 Jan 2005 00:24:03 -0800, Richard Clark
wrote:

On Mon, 31 Jan 2005 02:35:51 -0500, Buck wrote:

I don't know why you want FAT. It will give you lower gain.

Hi Buck,

No such thing.

73's
Richard Clark, KB7QHC


No such thing as 'fat' or 'gain'?


--
73 for now
Buck
N4PGW

Buck wrote:

I don't know why you want FAT. It will give you lower gain. . .

That's interesting. How much lower? Why?

Roy Lewallen, W7EL

On Mon, 31 Jan 2005 02:21:24 -0800, Roy Lewallen
wrote:

It will give you lower gain. . .

What were you thinking?

My apologies to the OP and others.....

I don't know why I said 'lower gain'. (make a note to myself, don't
answer usenet when I should be asleep.)

The fatter dipole will offer a broader bandwidth and a reduced length.
However for the FM broadcast band reception, bandwidth isn't a
problem.

Thanks Roy and Richard. My apologies to you Brad.


--
73 for now
Buck
N4PGW

Roy, W7EL wrote:
"That`s interesting.(I don`t know why you want fat. It will give you
lower gain.) How much lower? Why?"

It`s a fact. Fat antennas have more bandwidth, and that is inversely
proportional to Q. Teducing antenna Q, by fattening the antenna, reduces
the antenna potential by about the same factor.

Best regards, Richard Harrison, KB5WZI

Fat antennas have more bandwidth, and that is inversely
proportional to Q. Teducing antenna Q, by fattening the antenna, reduces
the antenna potential by about the same factor.

Best regards, Richard Harrison, KB5WZI

===========================
Richard, If you got this off Terman and Kraus then Terman and Kraus are a
couple of the oldest of old wives.
---
Reg

On Mon, 31 Jan 2005 16:55:03 +0000 (UTC), "Reg Edwards"
wrote:

If you got this off Terman and Kraus then Terman and Kraus are a
couple of the oldest of old wives.

Reggie,

This has got to be the height of your boredom to force your nemesis
into the thread to then complain about them. Sounds unmistakably like
the envy of a hausfrau.

73's
Richard Clark, KB7QHC