AM antenna problems
 

I am trying to receive an am signal well below ground level in a metal server room, there is a coax feed up to the roof which I used and attached the standard wire loop that was supplied with the tuner, however when I attempted to tune into some stations I could only pick up a couple of local stations and wasn't able to receive the ones I was hoping for. when I dialed in the desired frequencies, all I was receiving was a tone, the tone changed in frequency/pitch depending on the tuners frequency. To check that I could receive the stations I took the tuner to the roof and attached the antenna directly and sure enough I could pick up the desired stations. My thoughts are that the coax is affecting the signal in some way, perhaps picking up electrical noise? any advise would be appreciated.

AM antenna problems
 

On Fri, 7 Sep 2012 13:58:38 +0000, ULLS
wrote:


I am trying to receive an am signal well below ground level in a metal
server room, there is a coax feed up to the roof which I used and
attached the standard wire loop that was supplied with the tuner,
however when I attempted to tune into some stations I could only pick up
a couple of local stations and wasn't able to receive the ones I was
hoping for. when I dialed in the desired frequencies, all I was
receiving was a tone, the tone changed in frequency/pitch depending on
the tuners frequency. To check that I could receive the stations I took
the tuner to the roof and attached the antenna directly and sure enough
I could pick up the desired stations. My thoughts are that the coax is
affecting the signal in some way, perhaps picking up electrical noise?
any advise would be appreciated.

Rent a room directly under the roof.


w.

AM antenna problems
 

On Fri, 7 Sep 2012 13:58:38 +0000, ULLS
wrote:

I am trying to receive an am signal well below ground level in a metal
server room, there is a coax feed up to the roof which I used and
attached the standard wire loop that was supplied with the tuner,

Numbers please...
What make and model tuner?
What loop antenna?
What type of coax cable?
How many feet of coax?

The loop antenna that comes with most home hi-fi receivers is resonant
in the BCB (broadcast band). If you add coax cable or twinlead to the
loop, it becomes detuned and starts looking more like a short circuit.
The barrier strip BCB connections on the back of the hi-fi are
intended for a "long wire" antenna, and a decent ground connection.
The required BCB antenna impedance is probably much higher than your
coax cable, which means you'll need to build a matching network if you
plan to use coax cable to the roof. You might do better with just the
longest wire you can find that makes it up to the roof and beyond, if
it doesn't pickup RFI/EMI from the servers.

If you're plugged into the "F" connector found on the back of some
hi-fi's, that's for FM band reception, not BCB.

however when I attempted to tune into some stations I could only pick up
a couple of local stations and wasn't able to receive the ones I was
hoping for.

That's because the loop antenna is acting more like a short than an
antenna.

when I dialed in the desired frequencies,

Why would you want to hear BCB AM radio inside a server room?

all I was
receiving was a tone, the tone changed in frequency/pitch depending on
the tuners frequency.

If it's anything like the server farms that I occasionally visit, the
RFI/EMI from the high power switchers, servers, and thousands of clock
oscillators is sufficiently high that I couldn't even get a pair of
cheap FRS/GMRS radios to communicate across the building. I suggest
you consider streaming audio as a better alternative.

To check that I could receive the stations I took
the tuner to the roof and attached the antenna directly and sure enough
I could pick up the desired stations.

Yep. You probably connected the loop directly to the unspecified
model radio. Try it again with an approximate length of unspecified
coax cable and it should fail similarly to your indoor test. Also
note that you're now outside what I suspect is a shielded room, which
should improve reception. For entertainment value, try making a cell
phone call from insider the server room.

My thoughts are that the coax is
affecting the signal in some way, perhaps picking up electrical noise?

Yes to both questions.

any advise would be appreciated.

Long wire antenna or switch to streaming audio.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

AM antenna problems
 

On Fri, 07 Sep 2012 19:35:42 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote:

Rent a room directly under the roof.
w.

Or, get an outdoor or marine AM/FM receiver and mount it on the roof
in a weatherproof NEMA box.
http://www.ticcorp.com/outdoor_amplifiers_amp10pic.htm
CAT5 should be sufficient to run the audio and DC power down the pipe
to the server cave.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

AM antenna problems
 

In message , Jeff Liebermann
writes
On Fri, 07 Sep 2012 19:35:42 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote:

Rent a room directly under the roof.
w.

Or, get an outdoor or marine AM/FM receiver and mount it on the roof
in a weatherproof NEMA box.
http://www.ticcorp.com/outdoor_amplifiers_amp10pic.htm
CAT5 should be sufficient to run the audio and DC power down the pipe
to the server cave.

I think a Google on 'active antenna' might give you a lot more general
information. Start he
http://en.wikipedia.org/wiki/Active_antenna

They typically untuned (and hence fairly wideband).

An active antenna often consists of a short whip antenna, which
functions as a high-impedance RF voltage probe. This is connected to the
input of an amplifier which has a very high input impedance. The
amplifier provides gain, and also converts the high impedance of the
whip to a low impedance, which is suitable for connecting to 50 or 75
ohm coax feeder.

Of course, the amplifier has to be powered, and typically this is
provided by a DC power unit located at the receiver end, which sends the
necessary power back up the coax.

Note that one thing an active antenna must do is not to be overloaded by
strong signals (which can be a problem if you have a local transmitter
or two in your area).

But as I say, have a Google, and see what information it brings you.
--
Ian

AM antenna problems
 

On Friday, September 7, 2012 8:58:38 AM UTC-5, ULLS wrote:
I am trying to receive an am signal well below ground level in a metal
server room,

This twin coil ferrite antenna is supposed to work with coax.

http://www.ccrane.com/antennas/am-antennas/

AM antenna problems
 

On Fri, 7 Sep 2012 13:58:38 +0000, ULLS
wrote:

I am trying to receive an am signal well below ground level in a metal
server room,...I could only pick up a couple of local stations and
wasn't able to receive the ones I was hoping for.

Server room? Internet access? Many (most?) of the AM stations in my
area are now available through live streaming. Might check for the
stations you want.

AM antenna problems
 

On 9/7/2012 6:58 AM, ULLS wrote:
I am trying to receive an am signal well below ground level in a metal
server room, there is a coax feed up to the roof which I used and
attached the standard wire loop that was supplied with the tuner,
however when I attempted to tune into some stations I could only pick up
a couple of local stations and wasn't able to receive the ones I was
hoping for. when I dialed in the desired frequencies, all I was
receiving was a tone, the tone changed in frequency/pitch depending on
the tuners frequency. To check that I could receive the stations I took
the tuner to the roof and attached the antenna directly and sure enough
I could pick up the desired stations. My thoughts are that the coax is
affecting the signal in some way, perhaps picking up electrical noise?
any advise would be appreciated.




I am sure you are too young to remember placing an AM radio on top of a
CPU and running certain programs to produce music. Waltzing Matilda was
one. I recall my 2 meter FM mobile rig, driving up to the building,
hearing the noise from 20 ma. current loop to terminals. You are in the
middle of a vast sea of digital noise! All your AC power wiring is
conducting it everywhere.

I am not surprised at you hearing tones.

First, you need to have a battery powered radio so the AC wiring is a
little further away from the receiver.

Second, you might want to try RG-6 coax. It's cheap and as I recall,
double shielded. You will want to find a place to ground one end, only,
of the coax to a building ground, not an AC outlet ground wire.

How close is your current coax to other signal carrying cables? Keep the
coax as far away as possible. Never running parallel, if possible. And
if crossing, cross at right angles.

Finally, does anyone else working there have a radio that is receiving
properly?

IF nothing else will work, there is always FM.

Paul, KD7HB

AM antenna problems
 

On Friday, September 7, 2012 6:58:38 AM UTC-7, ULLS wrote:
I am trying to receive an am signal well below ground level in a metal

server room, there is a coax feed up to the roof which I used and

attached the standard wire loop that was supplied with the tuner,

however when I attempted to tune into some stations I could only pick up

a couple of local stations and wasn't able to receive the ones I was

hoping for. when I dialed in the desired frequencies, all I was

receiving was a tone, the tone changed in frequency/pitch depending on

the tuners frequency. To check that I could receive the stations I took

the tuner to the roof and attached the antenna directly and sure enough

I could pick up the desired stations. My thoughts are that the coax is

affecting the signal in some way, perhaps picking up electrical noise?

any advice would be appreciated.

Two approaches possible: (1) Disconnect the wire loop from the tuner and attach
the coax to the connection points formerly used for the loop.

(2) wrap about fifteen turns of lightweight insulated wire around the loop that came with the tuner. Attach one end of this wire to the coax shield and the other end to the coax center conductor. (It's an RF transformer.)

Thanks for all your responses!

First off, I am attempting to auto switch/scan between two frequencies on AM. I have FM and internet streams sorted. The tuner is a Cambridge Audio hifi tuner with an RS232 interface for scanning. I don't recall the exact model number. The tuner can't be relocated as the server is controlling the frequency scan.

Obviously I didn't attach it to the FM coax input! I do have a small amount of common sense.

The coax cable was already installed, I assume it's standard CT100 75Ohm.

the loop was just one of those cheap plastic things they bundle with tuners.


somebody mentioned impedance matching, Thanks! I'm going to look into this if I can't already find a ready made 50-75Ohm antenna.

somebody else mentioned overloading with an active antenna....this is central London so there are all kinds of local AM stations....what kind of damage can be done??

again thanks for your input, you have given me something to work with. :)

AM antenna problems
 

In message , ULLS
writes


somebody else mentioned overloading with an active antenna....this is
central London so there are all kinds of local AM stations....what kind
of damage can be done??

In London, I think the only two main medium wave transmitter sites are
Brookmans Park and Crystal Palace (although I do see a 200 watt 'London
Turkish Radio' in Lea Bridge Road - and there may be one or two others).
http://www.mediumwaveradio.com/uk.php
However, with luck, you are unlikely to find a MW transmitter next door
to your house - and certainly not a really high-powered one.

Adverts for commercial remote active antennas seem few and far between
on Google. However, you might find these of interest. The Wellbrook loop
seems promising. The nulls might be useful, but for all-round coverage,
you'll need to rotate it.

http://www.wellbrook.uk.com/ALA1530.html
http://www.wellbrook.uk.com/reviews/mediumwave.html
[Enjoy the blue text on a blue background!]
http://www.eham.net/reviews/detail/2706
http://www.northcountryradio.com/Kitpages/actant.htm
[What IS it with these active antenna people! Blue on black this time.]





--
Ian

AM antenna problems
 

On Mon, 10 Sep 2012 10:35:34 +0000, ULLS
wrote:

First off, I am attempting to auto switch/scan between two frequencies
on AM. I have FM and internet streams sorted. The tuner is a Cambridge
Audio hifi tuner with an RS232 interface for scanning. I don't recall
the exact model number.

If it's not too much trouble, could you make an effort to determine
the exact model number? I couldn't find a model on their site that
has an RS-232 port for frequency control. Once the model number is
determined, we can then look at the rear panel to see what you're
working with.

While you're at it, it might be useful if you describe the path that
the antenna coax is expected to take on its way to the roof. Is it
metal conduit? Plastic conduit? Random run? Diameter? Numbers?

The tuner can't be relocated as the server is
controlling the frequency scan.

I beg to differ. RS-232 will go about 150ft at 9600 baud without
difficulties.

Obviously I didn't attach it to the FM coax input! I do have a small
amount of common sense.

Assumption, the mother of all screwups.
That which is most obviously correct, beyond any need of checking, is
usually the problem.

The coax cable was already installed, I assume it's standard CT100
75Ohm.

Assumption, the mother of all screwups again. Look at the coax and
get the numbers. Also, what kind of connector.

the loop was just one of those cheap plastic things they bundle with
tuners.

Yep, that's what I figured. They're resonant in the AM band and do
not work with extension wires on the leads. If you're ambitious, you
could tear the plastic loop antenna open, replace the fixed tuning
capacitor with a variable, and experiment with different parallel
transmission line lengths. However, I don't think it will work very
well.

somebody mentioned impedance matching, Thanks! I'm going to look into
this if I can't already find a ready made 50-75Ohm antenna.

Hopefully, you mean 50 to 75 ohms, not 750 ohms. To get the antenna
in this range, you need a 1/2 wave dipole. At 1MHz, that's 468ft
long. You can shrink the antenna with loading coils, but the usable
bandwidth will decrease to the point of uselessness. An active
antenna might work.

However, I suspect all this design effort is a waste of time. The
receiver should be able to hear stations with a minimal antenna. All
you have to do is figure out where someone else went wrong.

somebody else mentioned overloading with an active antenna....this is
central London so there are all kinds of local AM stations....what kind
of damage can be done??

No damage. The effect is called "blocking" where the front end
transistors or FET's rectify the incoming signal and change the bias
point to where the device no longer amplifies. Unless you have an AM
broadcast station literally next door, it's not going to happen. Your
antenna is too small and the field strengths involved are insufficient
to cause problems.

again thanks for your input, you have given me something to work with.

Exact model number please.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

AM antenna problems
 

On Mon, 10 Sep 2012 08:48:38 -0700, Jeff Liebermann
wrote:

somebody mentioned impedance matching, Thanks! I'm going to look into
this if I can't already find a ready made 50-75Ohm antenna.

Hopefully, you mean 50 to 75 ohms, not 750 ohms.

Oops... When I put on my reading glasses, it became 75Ohms.
My apologies.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

AM antenna problems
 

On 9/10/2012 5:35 AM, ULLS wrote:
Thanks for all your responses!

First off, I am attempting to auto switch/scan between two frequencies
on AM. I have FM and internet streams sorted. The tuner is a Cambridge
Audio hifi tuner with an RS232 interface for scanning. I don't recall
the exact model number. The tuner can't be relocated as the server is
controlling the frequency scan.

Obviously I didn't attach it to the FM coax input! I do have a small
amount of common sense.

The coax cable was already installed, I assume it's standard CT100
75Ohm.

the loop was just one of those cheap plastic things they bundle with
tuners.


somebody mentioned impedance matching, Thanks! I'm going to look into
this if I can't already find a ready made 50-75Ohm antenna.

somebody else mentioned overloading with an active antenna....this is
central London so there are all kinds of local AM stations....what kind
of damage can be done??

again thanks for your input, you have given me something to work with.
:)




Without knowing what model you have, I looked at the AZAR 651 series.
http://www.cambridgeaudio.com/assets...-01English.pdf

All I see is 300 ohm connection for a loop AM antenna.
So, if you use an antenna on the roof, and 75 ohm coax coming down,
then a 75 to 300 ohm transformer into the receiver. I may even shorten
the leads on the 300 ohm side just to limit ingress.
Does the receiver make all the tones if you short the AM input with a
very short wire?
Mikek

Thanks! it is the Azur range, I don't go to London often so I can't check the exact model right now....thanks for spotting the 300 Ohm in, the white text on the unit was worn away. when I shorted the input the tone was not present. I'm going to go back in a couple of weeks and get this sorted. Thanks!