Chuck,
Thank you for your detailed reply.
I have to use this tuner as it is part of a whole house audio system that is
remote controlled. As such, I can't simply swap it out with another set.
All of the stations I need are in the same place, New York City, so I won't
need to reorient the loop once it is set. All I am looking to do is place
the same antenna in the attic, and I need some advice on the connections.
Thanks,
Eric

"Chuck Olson" wrote in message
. ..

"Eric" wrote in message
news:dD6Bf.4214$qG3.2011@trndny04...
This is a series of questions about AM broadcast antenna and lead-in
problems I have, it is not a strictly "amateur radio" question, so I
hope
you forgive the intrusion but I thought this group to be the best for
the
question.
I have purchased a Russound ST2 dual tuner for medium wave (AM
broadcast)
and FM for my whole house audio system. I have hooked up a Radio Shack
FM
Stereo Antenna in the attic and it works well for FM. The AM antenna
input
is 300 ohm. Two loop antennas (about 5" diameter) are supplied but do
not
work well in the room I have the tuner as there is lots of noise and
weak
signal. I would like to mount the supplied loop antenna(s) in the
attic.
I
am 18 miles from New York and only want to recieve local broadcasts (no
DX).
It is not practical for me to put up a 200 foot longwire. I have to make
some decisions:
1. Can one antenna feed both tuners by being hooked up in parallell? Is
there a signal loss?
2. Am I better off using 300 ohm flat TV type cable or should I use two
300/75 transformers (one at the reciever and one at the loop antenna)
with
RG-6 quad shield? I am wondering if the transformer loss is worth the
possible noise reduction from the coax.
3. Should I be able to use 1 loop for the two tuners and the coax, is it
best to split the 75 ohm coax and use independent 300 ohm transformers
or
to
split the 300 ohm feed from one tuner to the other?
4. Is it possible to use the FM antenna for the AM and how would it be
best
to split that up? (I would have to feed two FM and two AM tuners but
only
two could be used at once).

Thanks,
Eric


Most AM radios use a ferrite loopstick antenna. But that is part of the
input high-Q tuned circuit. Just connecting a loopstick to the 300 ohm
input
of your receiver would probably not work well, but if you could put a
"source-follower" (a special transistor circuit that has a very high input
impedance and low output impedance) between a remote loopstick tuned
circuit
and your set, and somehow using a voltage-variable capacitor to remotely
tune it, the result could be quite good.

A loopstick is very directional, and if pointed the wrong way, will
partially null out the signal you want. However the null is directionally
fairly sharp, so most loopstick antennas turn out to be adequate. In any
event, AM broadcast in any but a high signal strength area with the
equipment you describe is going to be "iffy", and at worst, a bother
having
to re-tune a remote antenna each time you change stations.

What's your experience with regular AM transistor radios around the house?
Do they work okay? If they do, it suggests the signal strengths on the
stations you like are probably high enough, but your choice of a radio
that
doesn't have a tuned loopstick antenna is somewhat ill advised. If you can
take it back or sell it - - and get a better radio that has enough front
end
gain to use the 5" diameter loops or that has a large ferrite rod antenna
on
the outside that you can see - - that might be best.

Always listen to a radio before buying it, and make sure you can take it
back if it doesn't work out in your system.

Good luck,

Chuck

"Eric" wrote in message
news:ev9Bf.1021$0n4.381@trndny05...
Chuck,
Thank you for your detailed reply.
I have to use this tuner as it is part of a whole house audio system that
is
remote controlled. As such, I can't simply swap it out with another set.
All of the stations I need are in the same place, New York City, so I
won't
need to reorient the loop once it is set. All I am looking to do is place
the same antenna in the attic, and I need some advice on the connections.
Thanks,
Eric

"Chuck Olson" wrote in message
. ..

"Eric" wrote in message
news:dD6Bf.4214$qG3.2011@trndny04...
This is a series of questions about AM broadcast antenna and lead-in
problems I have, it is not a strictly "amateur radio" question, so I
hope
you forgive the intrusion but I thought this group to be the best for
the
question.
I have purchased a Russound ST2 dual tuner for medium wave (AM
broadcast)
and FM for my whole house audio system. I have hooked up a Radio Shack
FM
Stereo Antenna in the attic and it works well for FM. The AM antenna
input
is 300 ohm. Two loop antennas (about 5" diameter) are supplied but do
not
work well in the room I have the tuner as there is lots of noise and
weak
signal. I would like to mount the supplied loop antenna(s) in the
attic.
I
am 18 miles from New York and only want to recieve local broadcasts
(no
DX).
It is not practical for me to put up a 200 foot longwire. I have to
make
some decisions:
1. Can one antenna feed both tuners by being hooked up in parallell?
Is
there a signal loss?
2. Am I better off using 300 ohm flat TV type cable or should I use
two
300/75 transformers (one at the reciever and one at the loop antenna)
with
RG-6 quad shield? I am wondering if the transformer loss is worth the
possible noise reduction from the coax.
3. Should I be able to use 1 loop for the two tuners and the coax, is
it
best to split the 75 ohm coax and use independent 300 ohm transformers
or
to
split the 300 ohm feed from one tuner to the other?
4. Is it possible to use the FM antenna for the AM and how would it be
best
to split that up? (I would have to feed two FM and two AM tuners but
only
two could be used at once).

Thanks,
Eric


Most AM radios use a ferrite loopstick antenna. But that is part of the
input high-Q tuned circuit. Just connecting a loopstick to the 300 ohm
input
of your receiver would probably not work well, but if you could put a
"source-follower" (a special transistor circuit that has a very high
input
impedance and low output impedance) between a remote loopstick tuned
circuit
and your set, and somehow using a voltage-variable capacitor to remotely
tune it, the result could be quite good.

A loopstick is very directional, and if pointed the wrong way, will
partially null out the signal you want. However the null is
directionally
fairly sharp, so most loopstick antennas turn out to be adequate. In any
event, AM broadcast in any but a high signal strength area with the
equipment you describe is going to be "iffy", and at worst, a bother
having
to re-tune a remote antenna each time you change stations.

What's your experience with regular AM transistor radios around the
house?
Do they work okay? If they do, it suggests the signal strengths on the
stations you like are probably high enough, but your choice of a radio
that
doesn't have a tuned loopstick antenna is somewhat ill advised. If you
can
take it back or sell it - - and get a better radio that has enough front
end
gain to use the 5" diameter loops or that has a large ferrite rod
antenna
on
the outside that you can see - - that might be best.

Always listen to a radio before buying it, and make sure you can take it
back if it doesn't work out in your system.

Good luck,

Chuck





Hi, Eric,

I was just looking at the specs of the Russound ST2, and it doesn't look too
good for AM reception. 55dBu sensitivity is really, really poor - - that's
562 microvolts to reach 20dB signal/noise ratio - - no wonder the loops
don't work well on stations 18 miles away. Typical AM broadcast sensitivity
of Ham Radio gear runs around 13 microvolts. I think you can forget about AM
broadcast, especially if you have one with XM radio, since XM will most
likely occupy more of your listening time. It looks to me like the
manufacturer is just not serious about providing any decent AM reception.
The 3 KHz response on AM is also not very inspiring - - maybe okay for news
or talk radio, but not much more. If anything can improve the outlook on AM
reception with this radio, here's a website that may help:
http://www.mindspring.com/~loop_antenna/

Good luck,

Chuck

Whoever authored "AM Loop Antennas" attached to Chuck Olson`s posting
wrote:
"A spiral loop is least sensitive to signals received in its plane."

Nonsense. Spiral, edgewound, or whatever, any loop antenna which is
small in terms of wavelength is sensitive to signals within its plane,
and insensitive to signals broadside to its plane.

My authority is Kraus` 1950 edition of "Antennas", page 160, Fig. 6-6.

The plane wave arriving broadside to the small loop tends to generate
currents in the same direction in all sides of the loop. The sides of a
turn in the loop are connected in series. So, the currents in opposite
sides of the loop tend to add to zero when the wave sweeps the loop from
broadside.Time of arrival and phase are the same on both sides of the
loop from broadside.

Best regards, Richard Harrison, KB5WZI

Richard, you are correct - - thanks for spotting that - - the edge-on view
of the loop in red should be in line with the "node" direction rather than
in line with the "null" direction. I hadn't looked very carefully at the
text since I was more interested in the links section at the end, which I
felt might be a good resource for Eric.

Chuck W6PKP

"Richard Harrison" wrote in message
...
Whoever authored "AM Loop Antennas" attached to Chuck Olson`s posting
wrote:
"A spiral loop is least sensitive to signals received in its plane."

Nonsense. Spiral, edgewound, or whatever, any loop antenna which is
small in terms of wavelength is sensitive to signals within its plane,
and insensitive to signals broadside to its plane.

My authority is Kraus` 1950 edition of "Antennas", page 160, Fig. 6-6.

The plane wave arriving broadside to the small loop tends to generate
currents in the same direction in all sides of the loop. The sides of a
turn in the loop are connected in series. So, the currents in opposite
sides of the loop tend to add to zero when the wave sweeps the loop from
broadside.Time of arrival and phase are the same on both sides of the
loop from broadside.

Best regards, Richard Harrison, KB5WZI