Bob wrote:
"There`s a 99 FM xmtr a couple of miles to the SE of me, lower in
elevation, right in the path of all the other stations - & right smack
in the middle of the FM band."

Bob seems to be lucky that the elevation of the interferring station is
enough lower that keeping the receiving antenna low hides it. That seems
to be what`s going on with the car radio and the built-in antenna on his
stationary radio.

Further suppression can come from a parallel-resonant trap in the middle
of his FM antenna element(s). This should make the elements an open
circuit at 99 MHz. Bob`s other stations aren`t on 99 MHz.

For higher Q in the parallel-resonant trap, it might be wise to use
1/4-wave short-circuit stubs. Impedance should be high for 99 Mhz and
lower for other frequencies. For a folded dipole, you might try to use
one, 1/4-wave short-circuit stub and locate it in the middle of the side
of the dipole opposite the feedpoint. This can all be made of 300-ohm TV
twinlead if desired. This may not be as effective as stubs in each side
of the 1/2-wave dipole. Folded dipoles are really loops. Frequently
loops have similar characteristics, open-circuit or short-circuit.
Placed in the middle of each side of the driven element of the folded
dipole, its resonance will be disturbed at the frequency of the 1/4-wave
short-circuit stubs.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote:
For higher Q in the parallel-resonant trap, it might be wise to use
1/4-wave short-circuit stubs. Impedance should be high for 99 Mhz and
lower for other frequencies. For a folded dipole, you might try to use
one, 1/4-wave short-circuit stub and locate it in the middle of the side
of the dipole opposite the feedpoint.
__________

A 1/4 wave at what freq? If 99 MHz, that stub configuration will have ~
zero loss at 99 MHz, and greatest loss centered on the 2nd harmonic (not
what he needs).

RF

On Fri, 10 Jun 2005 08:28:02 -0500, "Richard Fry"
wrote:

An option would be to install a notch filter tuned for the local FM at the
input to the problem receiver. It will attenuate that local signal (and
others close to it in frequency, to some extent). A "5KFM" type notch
filter from Microwave Filter Company may do the job, for about $25 as I
recall. Here is a link: http://www.microwavefilter.com/

That's the perfect answer, but you may be able to achieve satisfactory
results by - surprisingly - adding an attenuator (a 6db 300-ohm pad
made from resistors would be a good start) in line with the antenna
lead. RF overload characteristics are proportional to the square of
the incoming signal, so the interference will be reduced more than the
desired signals. Also, a three-element FM antenna won't be nearly as
selective as a larger yagi of the type shown he

http://www.starkelectronic.com/fm.htm

Putting one of these on a rotator will normally run rings around any
cable company unless you have interference from the new IBOC digital
radio signals.

Dave B.

Richard, an open 1/4 in parallel with the feed point would do the trick.
Your shorted quarter will not be seen at Fo.
A shorted 1/2 wave would.

"Richard Harrison" wrote in message
...
1/4-wave short-circuit stubs. Impedance should be high for 99 Mhz and
lower for other frequencies. For a folded dipole, you might try to use
one, 1/4-wave short-circuit stub and locate it in the middle of the side
of the dipole opposite the feedpoint. This can all be made of 300-ohm TV
twinlead if desired.