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

"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

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

On Mon, 23 Jan 2006 15:29:13 GMT, "Eric"
wrote:

1. Can one antenna feed both tuners by being hooked up in parallell? Is
there a signal loss?

Hi Eric,

Yes/Yes. Does the loss matter at a distance of 18 miles? Probably
not. However, this question is rather hazy given the ones that follow
seem to ask the same thing again.

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.

Again, the presumption of loss is exaggerated. Your problem, as you
describe it, is noise. However, the transformers are probably more
suited for FM than AM. On further consideration, that may not matter
either as it is the shielding action of the coax that may in fact
offer more payback in noise reduction for the AM operation than any
issue over the expected transformer loss.

To take this one step further, at the AM antenna end of the coax,
simply coil the coax around an empty liter coke bottle with a dozen or
so turns. This is more to help isolate from noise than anything else.

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?

Another hazy question. Run separate lines for AM and FM. You can
combine them, and split them out at each end so that there is only one
long run of coax (which is commendable). However, as you are
approaching this with a known problem, it is in your best interest to
keep the bands/antennas/lines separate.

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).

Another hazy question. Through all this haze, it seems you are quite
set upon combining things. With such a wide separation in frequency,
you would tend to end up with a single solution that poorly serves two
purposes. It raises the complexity factor, and any problem compounds
that further.

This simply means that, yes, you can; but it would not seem likely you
are actually doing yourself a favor.

73's
Richard Clark, KB7QHC

Richard,
Thanks for your detailed answer.
I am not really set upon combining. I am glad to run another wire. I gather
from your response I am better off with the coax and two transformer setup
than with using 300 ohm twin wire for the strictly AM radio purpose.
Thanks,
Eric

"Richard Clark" wrote in message
...
On Mon, 23 Jan 2006 15:29:13 GMT, "Eric"
wrote:

1. Can one antenna feed both tuners by being hooked up in parallell? Is
there a signal loss?

Hi Eric,

Yes/Yes. Does the loss matter at a distance of 18 miles? Probably
not. However, this question is rather hazy given the ones that follow
seem to ask the same thing again.

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.

Again, the presumption of loss is exaggerated. Your problem, as you
describe it, is noise. However, the transformers are probably more
suited for FM than AM. On further consideration, that may not matter
either as it is the shielding action of the coax that may in fact
offer more payback in noise reduction for the AM operation than any
issue over the expected transformer loss.

To take this one step further, at the AM antenna end of the coax,
simply coil the coax around an empty liter coke bottle with a dozen or
so turns. This is more to help isolate from noise than anything else.

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?

Another hazy question. Run separate lines for AM and FM. You can
combine them, and split them out at each end so that there is only one
long run of coax (which is commendable). However, as you are
approaching this with a known problem, it is in your best interest to
keep the bands/antennas/lines separate.

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).

Another hazy question. Through all this haze, it seems you are quite
set upon combining things. With such a wide separation in frequency,
you would tend to end up with a single solution that poorly serves two
purposes. It raises the complexity factor, and any problem compounds
that further.

This simply means that, yes, you can; but it would not seem likely you
are actually doing yourself a favor.

73's
Richard Clark, KB7QHC

Hi Eric

I certainly welcome your question, amateur radio related or not!

Most effort in amateur radio circles on MF is associated with matching a
transmitter and antenna. The next most important step is to increase the
desired signal to noise ratio into the receiver (by using antenna
directivity, type and orientation etc) Since atmospheric noise is far
stronger than that contributed by the receiver device, actual signal
loss over the feedline length isnt normally an issue. The actual signal
level isnt important provided it is greater than the noise.

1. Under perfect conditions assuming known source, load and feedline
impedences, yes the power going to each receiver will be cut by half
(3dB). Purist may argue that a simple "in parallel" configuration is a
bad thing. For AM MF I dont think you'll even notice it...

2. I doubt the balun to RG6 would be useful. I'd also suspect they will
be hard to find given the operating frequency. (Cheapo TV baluns
probably wont work well much below 40MHz) One of the problems you will
encounter coax or ribbon is that if the antenna isnt symmetrical you
will receive noise from along the length of the feedline itself. Not a
good thing if it runs past a fluro or light dimmer (or wiring).

I also doubt that the input Z at the antenna input terminal truly is 300
ohms. I mean it works over a 3:1 frequency range as well..

One of the downsides of using ribbon is possible interactions with
nearby metalwork. I'd suggest in your case that it wont be an issue. In
fact using the supplied loop antenna may be no better than using a
random length of wire (dipole arrangement) attached to the ends of the
ribbon in the attic. The line loss is not so much an issue than the
signal received at the antenna itself.

I'd suggest you use the random wire approach with the ribbon in parallel
to both tuners and see what the signal is like. If it is still noisy
play with the antenna polarity (vert vs horiz or at least diagonal) I
suggest that trying to match impedence and getting the same signal power
in each line/RX isnt important at all. If one wanted a perfect
configuration (ie for transmitting) the difficulty is major given the
frequency range the thing has to work over.

Tell us how you fair

Cheers Bob W5/VK2YQA East Texas


Eric wrote:
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.

"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

On Mon, 23 Jan 2006 19:37:34 GMT, "Eric"
wrote:

Richard,
Thanks for your detailed answer.
I am not really set upon combining. I am glad to run another wire. I gather
from your response I am better off with the coax and two transformer setup
than with using 300 ohm twin wire for the strictly AM radio purpose.
Thanks,

Hi Eric,

Why you would use 300 Ohm twin wire for AM antennas is odd, but not
prohibited. However, it does demand all the attention to keeping the
line balanced (like I said, move away from coax, and problems become
compounded). If there are 300 Ohm issues both at the antenna and at
the radio, you must preserve them through transformers if you do
migrate to coax.

Balanced goes by many requirements, none of which can be ignored. An
unbalanced condition is a tacit allowance for the intrusion of noise.
As you describe a problem with noise - well, you see where this leads,
an absolute exercise in driving out the imbalance.

Where does it occur? How do you find it? The problems are stacking
up already. It happens at the antenna itself when it is mounted near
conductive materials. This observation only leads to more questions,
what might be conductive that is nearby, and how near is nearby? The
same problem exists with coax feeds, but you can solve those easier
with the coiled lead at the end (you probably could do the same with
twin lead - and winding either lead 4 or 5 times through a ferrite
core could be equivalent fixes). However, this is only at the antenna
end, and that may not be the source of the imbalance. For twin leads,
it could be as easily that the lead traces up against metal ducting,
or along house wiring.

If you are scrupulous about these kind of details, twin lead may
indeed work fine.

Another method of tackling the problem is to carry a small transistor
radio around the house, and try to locate the noise itself. Killing
the source is a one pound cure for a ten pound problem. If the noise
comes from outside the house, then you have antenna issues, and all
the wishing in the world in trying to avoid a different antenna will
come to naught.

73's
Richard Clark, KB7QHC

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