"Robert Morein" wrote in message
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"Margaret von B." wrote in message
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"Robert Morein" wrote in message
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"Margaret von B." wrote in message
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"Robert Morein" wrote in message
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"ric" wrote in message
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Robert Morein wrote:
Are you familiar with the FM2G-C? It is being strongly
considered.
http://www.fanfare.com/fm-2g-c.html
This is an omnidirectional antenna, which means it will be very
susceptible
to multipath. The fact that it is cut for the educational band
gives
it
a
little more gain, but, as I said, gain is seldom the problem. The
problem is
phase cancellation caused by reception of a signal that is
reflected
by
two
or more different paths. This causes the signal to actually
cancel
100%
at
certain frequencies. More gain on nothing does not result in
something.
The
solution is a directional antenna, which attenuates all but one
of
the
reception paths, eliminating the phase cancellation.
Hmmm...I'm getting a slew of opinions on this, and few of them
reach
the same conclusion. Such as:
http://www.hawaiipublicradio.org/recep.htm
I've tried various dipole antennas, all with similar results. Best
results so far was an RCA powered indoor TV "rabbit ear" type
antenna.
I'm tempted to have an antenna cut specifically for 88.3 MHz, as
that
is
the only FM I listen to. Oh well...
You can do it yourself. Take a look at
http://www.ycars.org/EFRA/Module%20C/AntDip.htm
The wavelength of 88.3 mHz is 66.88 inches. Your dipole should be
1/2
that
length: 33.5. All you need is a piece of twinlead, which is just
junky
antenna lead-in wire. Cut it to 33.5 inches. At each end, twist the
conductors together. At the center, break one conductor. Connect the
loose
ends to your feed wire. It is not essential, but nice, if you can
have
t
the
connections soldered. Protect the wires from bending and breaking by
encasing the joints in some RTV (GE silicone goo).
I do not understand why the station engineer recommended the
Fanfare.
I do. It worked in his location.
This
antenna has 0 dB gain. 0 is a very small number. The only advantage
to
the
Fanfare is for external use, since it is self-supporting. An indoor
dipole,
which can be taped or tacked to any convenient surface, does not
need
mechanical rigidity.
A properly cut dipole has twice the signal strength: 3 dB.
There's more to antennas than theory, especially these "little ones".
As
I
stated before, I don't have any experience of this particular antenna
but
I
have plenty of experience of seemingly similar design, The Magnum
Dynalab
ST-2.
http://www.magnumdynalab.com/x_st2.htm
It has worked admirably well over the years in many urban locations
except
one. NYC RF hell rendered it pretty much useless. However, at the time
I
did
not have the Signal Sleuth that greatly complements the whip albeit at
a
considerable cost.
http://www.magnumdynalab.com/x_sleuth.htm
Based on my "nontechnical" opinion I can say that the whip alone
generally
outperforms the "grocerybagful" of dipoles I've accumulated over the
years
by a comfortable margin. With the Sleuth, it is the ultimate quick and
small
FM antenna solution. One of my favorite tuners has a scope that allows
the
monitoring of multipath signals and contrary to what one might think,
the
ST-2 is not all that easily bothered by it. That said, there are
locations,
such as NYC, where the cheap but nearly unobtainable Dennesen dual
whip
cannot be beat. I suspect that the Dennesen would be an easy DIY
project
for
those so inclined.
But no one should fool themselves into thinking that any of these
products
will succesfully compete with a competent outdoor antenna such as
those
made by APS.
Cheers,
Margaret
Margaret, without contradicting your experience, I think that the
difference
in sound has to do with the placement of the antenna.
That's probably most of it. As I said, "there's more than theory"...
Perhaps the
freestanding whip was placeable in a way that the dipole was not.
The real solution comes from an antenna arrangement with some
directionality. If the multipath signal(s) can be reduced below one
particular strongest signal, then phase cancellation cannot occur. Two
whips
separated by 1/2 wavelength can be directionally oriented by a
combining
phase shift network, which is probably why your Dennesen worked so
well.
It still works, if I can stand to look at it. :-) However, my primary
residence sports a Sniper these days with Yaesu rotor.
A single vertical whip receives equally well from all directions. This
means
that reduction in multipath can be accomplished only by moving the
antenna
about the room. By contrast, a dipole can be rotated through 180
vertically,
and 180 degrees horizontally, while in the same location, provided one
can
find a way to support the floppy wires. Taping it to a dowell stick
would
work.
I hear you, but when using an A/B switch and watching the trace as you
switch antennas, any changes in multipath reception are easily detected.
Using such setup, I can only conclude that the ST-2, generally speaking,
is
not impeded by multipath reception and will deliver a stronger, cleaner
signal to a tuner than a R/S dipole and its cousins.
Cheers,
Margaret
I don't doubt the result. Your reply has forced me to additional thought:
1.Mere inches are significant to multipath.
2. The other thing which is signficant is this: the ST-2 connects to the
receiver by coax, which picks up negligible signal by itself. The twinlead
from a folded dipole is part of the antenna system itself. Therefore, it
picks up more signal, which can cancel with that received by the nominal
antenna. Back in the 60's, people would prewire their houses with twinlead
for a rooftop TV antenna, and the ghosting (visual multipath) was vicious.
Replacing it with coax eliminated the distribution system as a secondary
antenna.
I should append the following note to my original advice to "ric". After
constructing his custom 33.5" folded dipole, he should purchase a balun
transformer from Radio Shack or any other source. He should connect the
pigtails on the balun to the feed of the dipole, and he should run coaxial
cable to his receiver.
That should do it. OTOH, the person who bought my old "nightmare reception"
loft in NYC simply ended up buying a Blaupunkt car stereo with a diversity
tuner and got better results than with any home units at a fraction of the
cost. Of course one still needs to optimize antenna location, but it is
pretty much set and forget. I was stunned how well it worked. In fact, I
should buy one of those Blaupunkts and compare it to my existind tuners for
the fun of it. I believe even the Audio Critic did an article on the
Blaupunkt tuners after they got a whiff of it...
Cheers,
Margaret