AM Attenna solution

Discussion in 'Wireless & RF Design' started by dbsoccer, May 28, 2014.

  1. dbsoccer

    Thread Starter New Member

    May 28, 2014
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    My AM radio reception for my current configuration is terrible. The radio is part of a surround sound amplifier. The provided loop attenna is housed within some cabinets that contain other electronics including a flat screen TV. There is a lot of building (walls, wiring, appliances, etc) between the loop and the outside. I've tried repositioning the loop but without much luck.

    During a remodel I provided a two runs of coaxial cable into the cabinet with this amplifier, TV, etc. I am using one of these cables for the TV. I am wondering if I can use the other cable to provide a means to get a better AM signal to the receiver. The other end of this cable terminates at central panel with many cables. I can tie the end of this cable to another unused coax cable. This second cable terminates in a higher point in the house that is on an outside wall. Could I attached an AM attenna at the end of this second piece of coax? The FM signal is better than the AM but if I could improve both, that would be a bonus.

    Any help would be appreciated.
     
  2. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    I have not yet experimented with antennas as much as I plan to, but I'm sure that running coax up to an antenna on the roof is the best way to go. As you pointed out there are AM antennas and then there are FM antennas. They have different characteristics and so your radios need to see what they are looking for, so to speak.

    I plan to do the same thing as you seem to be planning and so I'm interested in how you deal with the problem and the results. Using a single coaxial cable for everything is the way I want to go and this seems to necessitate a three-resistor mixer in your house at the point where your TV, AM radio and FM radio take off to the antenna. But this may not be possible in that one antenna may interfere with the other.

    At this point, my idea is to test this possibility of multiplexing a single coaxial cable by hooking up all three antennas in series. My hope is that the two unsuitable antennas will not interfere with the one that is suitable. I'm sure others posting here will set us straight on this. ;)
     
    Last edited: May 28, 2014
  3. dbsoccer

    Thread Starter New Member

    May 28, 2014
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    I just realized my TV attenna, which is in the attic, has a secondary collector for the FM signals, as I recall. This may be an easy fix for my FM issue. As I understand I can put a splitter on the TV end of the coax running from the antenna and route one split to the TV and the other to the FM input on the receiver/radio.

    I recall using quad shield RG6 Coax. Are there any issues with impendence matching? I think RG6 is 75 Ohm.
     
  4. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    Impedance matching is probably a matter of 75 ohm cable for your TV. But then look up the specs for your FM radio. If it is 75 ohms, you're good to go. Otherwise you need an impedance transformer in order to optimize your reception.

    Now don't take my word for it. I am a novice at radio. Hopefully someone who knows will answer your question.
     
  5. bertus

    Administrator

    Apr 5, 2008
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    WillS_70 likes this.
  6. dbsoccer

    Thread Starter New Member

    May 28, 2014
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    The FM side of this issue is now seemingly fixed. I inserted a splitter on my line coming from the TV antenna in the attic and routed one lead to the TV and other to the FM receiver. The FM reception is now outstanding and with little effort or cost.

    My focus is now on the AM side. My quesiton is still can I some how use the unused coax cable to pull a signal from an antenna located in a more ideal location in my house and, if yes, what sort of antenna would be most suitable? I could always put the current loop antenna at then end of my coax (which would be in an upper level and on an outside wall) or I could look into the attenna idea from Bertus.

    Fundamentally, is the coax a suitable conductor for an AM signal? I can simply strip back the insulation layers and use one of the shield layers as one conductor and the center lead for the second conductor.
     
  7. Art

    Distinguished Member

    Sep 10, 2007
    785
    61
    If your original radio AM antenna was this:
    [​IMG]

    It's difficult to make a loop antenna for AM broadcast that is tuned right across the band.
    Even something like this:
    [​IMG]

    Usually doesn't tune the antenna across the whole band unless there are also a bunch of taps in the coil that have to be changed at intervals as you sweep the dial across the band.
    The AM broadcast band varies greatly in wavelength from one end of the band to the other.

    If you have an old AM radio that can be junked you might try pulling the ferrite loop
    and tuning capacitor out of that, connecting them in parallel, and connecting each end of that somewhere semi-remotely from the unit, and not resting on any metal surface, across the two terminals that were connected to the first antenna.
    That's worth a try if you have a radio to junk.
     
  8. dbsoccer

    Thread Starter New Member

    May 28, 2014
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    Thank Art,

    I may be able to find an old radio but electronics is not a strength area for me. I believe I know what the ferrite loop is and I understand a parallal versus series connection but after that you lost me. What is the tuning capacitor? That sound like the 'dial' on the radio. For me remote would be on a different floor of the house and on the inside surface of an outside wall. I have two leads coming from the 'radio' now. If I understand you want to connect the loop and cap in parallel and then connect my two antenna leads to the ends of this parallel connection.

    Does it matter how big the ferrite loop is? I may have an old clock radio around somewhere. Would that suffice? Or should I find something bigger?

    Thanks again.
     
  9. Art

    Distinguished Member

    Sep 10, 2007
    785
    61
    I wouldn't suggest smashing something good just for a try, unless it really is junk,
    but yes I do mean the part that turns with the tuning dial.

    I've still found in my location at least if it's a choice between a tuned antenna,
    and just getting an antenna outside, the tuned antenna wins.
     
  10. BR-549

    Well-Known Member

    Sep 22, 2013
    1,995
    388
    Am broadcast ferrite loop are notorious for picking up line noise. Orientation is the biggest factor. I am assuming you can't move your RX around. I would suggest you either buy or build an am rx. Then you can feed your surround sound system.
     
  11. JMW

    Member

    Nov 21, 2011
    88
    8
    I have the same issue, and am trying to decide the easiest and cheapest options. if you have the room you might want to try a "bottle antenna" Google it and see if that suits your needs. The other option is a cheap car radio. Mount an after market auto antenna on your satellite dish and go from there.
    I haven't tried the bottle option yet, I've had a major roof leak and haven't wanted to interfere with the contractors.
     
  12. dbsoccer51

    New Member

    Jun 10, 2015
    3
    0
    Well after a year of having other projects to work I'm back at my AM reception issue. The antenna I'm using looks almost identical to the one Art posted above (the store bought one). Last night I used the AM radio in a Walkman as a tester. If I placed the Walkman near where this antenna is at and the static was awful. The antenna is on a shelf directly above a 36" flat screen TV. If I moved the Walkman away from this area the reception became almost static free particularly if a changed the orientation a bit. This area in our kitchen and was under canned light fixtures, etc.

    I have a fairly long lead wire on the surround sound antenna and was able to move it a distance similar to where I got the best reception with the Walkman but the reception was never as good. There was always an element of static no matter how I oriented the antenna. Again the antenna looks like the one pictured above.

    I figured could go to my local ARC store and see is I can find an old AM radio. BR-549 had this comment: "I am assuming you can't move your RX around. I would suggest you either buy or build an am rx. Then you can feed your surround sound system." I'm not sure what an RX is. Can someone decode?

    If I were to build something (RX??) using parts from an old AM radio, I was hoping I could get some sort of a simple schematic. I understand series and parallel circuits but having a drawing would remove any assumption you might have of my electronic savvy.

    Thank you all in advance.
     
  13. BR-549

    Well-Known Member

    Sep 22, 2013
    1,995
    388
    RX means receiver. TX means transmitter.

    Disregard my first post, it will not apply to you.

    Do you still have the spare tv coax going up to the attic?

    How much room in attic?
     
  14. PRFGADGET

    Active Member

    Aug 8, 2011
    51
    7
    Alright, just for the sake of sticking my foot in my mouth !
    Do a web search for "160 meter loop antennas" , the 160 meter ham band is just above the AM broadcast band and most on -line calculators you will find will handle what ever "prime" frequency you have of interest, for general purposes pick one in the middle or low end of the AM broadcast band.
    Keep in mind, a full-wave loop at those frequency's is going to involve between 500 and 600 feet of wire (you can divide your result by 2, 4, 6, or 8 to work with "fractions" of a wave-length).
    In order to use 75 ohm TV coax to feed a receiver with screw terminal antenna connections you will need a "BALUN" transformer like what used to be supplied with TV sets and most "LOG PERIODIC" TV antennas (or make your own) to get the impedance value's to match (or near) at each end of the coax run.
    One thought I will offer is to keep such an antenna disconnected from the radio when not in use (during storm season) since they make good "lightening catchers".
    I would also suggest keeping a few extra BALUN'S on hand for such needs.

    73 and good luck, John
     
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