In article ,
"HankG" no_one@invalid wrote:

"Telamon" wrote in
message

gy.com.. .
In article ,
"HankG" no_one@invalid wrote:

"Telamon" wrote in
message


gy.com..
.
In article ,
"HankG" no_one@invalid wrote:

My primary antenna is a 33 ft folded dipole made from 300 ohm
twin lead and is mounted in my roof. It is coupled by a 300
to 75 ohm tv transformer to 75 ohm coax. The antenna is
described in message 2471 of the Yahoo Rx-320 group and works
fairly well.

Recently, I acquired 3 rolls (40 ft each) of indoor 300 ohm
coax, a closeout at Radio Shack. On checking my house
diagram (drawing), I determined that I could run another
antenna which could run about 100 feet if I include my
garage. This is measured from left rear roof, through a
wall, diagonally to front right garage (plus a 20 ft wrap on
each end).

I'd welcome any suggestions from the group on an antenna
configuration such as dipole, folded dipole, twinlead
converted to long wire (doubled back on itself), etc. This
would be for SW reception, but MW would be a plus. Thanks.

You could take two of those 40 foot pieces and make a 80 foot
folded dipole antenna.

Yes. The resonant frequency of an (un)folded dipole of 80 ft
would be about 5.85 Mhz. My current antenna (resonant at 14.18
Mhz) uses a twinlead stub which supposedly confers a broader
bandwidth. I have used it to monitor 160 meters and works fairly
well in the single digits. Is there a formula for calculating
stub length to give this 80 footer greater bandwidth?

According to a Joe Carr antenna book I have this:
In meters
A - 141.8 / F MHz - Over all length or distance between outer shorts
B - 122 / F MHz - distance between inner shorts

In addition you could leave the outer shorts open then it would be:
A - 142 / F MHz - Over all length or distance between outer ends
B - 122 / F MHz - distance between inner shorts

Example for 9.75 MHz is
A = 14.56 meters
B = 12.51 meters

Some of the Radio Shack 300 / 75 ohm transformers are not much
good below 10MHz.

Interestingly, I acquired the transformers (2 on a card) at the
local dollar store. Works fine.

Well, it depends on which one you got your hands on. On some the
S21 falls off below 10MHz and you were talking about a lower
frequency antenna so just watch out for that.


What is meant by inner and outer 'shorts'?

If you use 300 ohm line to make the folded dipole then you "short" the
two conductors on the ends.

There are two designs above I wrote about. The first is a folded dipole
so the ends are shorted and in order to make it more broadband you add
two more shorts between the conductors a specific distance from the
center.

The second design only has the shorts placed at the "B" distance and the
ends are left open.

--
Telamon
Ventura, California