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Looking for ideas on a AM antenna for broadcast band

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WP4CPR, Mar 7, 2009.

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  1. WP4CPR

    WP4CPR Ham Member QRZ Page

    Just want to make a loop, L, or whatever for the AM broadcast band. i'm trying to receive local stations maybe 40 to 60 miles from my home but just cant receive them with a normal home radio. so i'm going to try put up an antenna and receive them on my HF. any thing gose but would like something that is directional.
     
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    If you do not have an external antenna connection on the receiver you are going to have to couple any external antenna to the receiver. One trick is to put up as much wire as you can and then wind a number of "loops" on something like a piece of cardboard. Connect one end of this coil to the antenna and the other end to ground. Place the AM receiver so that the internal ferrite loop antenna is as close to the coil as possible. This will usually give enough coupling to greatly improve the reception.

    Glen, K9STH
     
  3. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Yes...this is how the "SELECT-A-TENNA" works. The radio station I worked for sold HUNDREDS of these to listeners out in the bush. :)

    eric
     
  4. AE5JU

    AE5JU Ham Member QRZ Page

    For the AM Broadcast Band (aka MW) there is nothing that works as well as a loop. And a loop is a comparatively small antenna, indoors. It is not necessary for the antenna to be outdoors or up high. I have a friend who uses a loop I made for him in his basement. Another uses a loop I made for him at work in a metal building.

    There are two kinds of loops you can make, simple untuned loops, which are rather broadband, or the more sensitive tuned loops.

    http://members.cox.net/rwagoner/columns/am_antenna.html

    For an untuned loop, four turns of 22 ga insulated hookup wire, and it does not really make any difference if stranded or solid, around a wooden form measuring 12" on a side (or 17" diagonally) will work fine. I have an untuned loop that I use with my livingroom and bedroom stereo systems that are simple cross shaped forms, with brass "shoulder hooks" on each corner, that work very well. All hardware should be brass (non inductive).

    Hookup to the stereo systems tuner (or receiver) can be just a simple twisted pair of hookup wire, or 300 ohm twinlead. It really makes no difference. Connect to the AM Antenna terminal and the Ground terminal (or chassis ground) on the tuner or receiver.

    Next, a tuned loop:

    http://www.mtmscientific.com/loop.html

    This is the classic "sports fan's loop". I built mine (which you can see if you click the link that says "Photos and Reviews from Customers") from the plans kit, which consists of plans, tuning capacitor, and nothing else. It would have been easier to just purchase the full kit, but I had fun building it. Also, I added a "pickup loop", one turn, just inside of the main windings, and that loop goes to the two speaker binding posts you see in the photo mounted on the crossbar.

    If your radio has a build in ferrite stick for AM, simply place the radio next to the tuned loop and dial it in. If you have a stereo system tuner or receiver that has no built in antenna, you would use connection to the pickup loop to feed the tuner/receiver. Again, twisted pair of hookup wire or 300 ohm twinlead will suffice.

    Tuning covers the entire 540-1700 khz range, and actually a little extra on each end. Mine will actually cover the 160 meter band, too.

    Tuning is so sharp that I can easily tune in a station on 860 khz despite a strong local on 870 khz.

    Long wires, random wires, etc, are all a waste of time for this band. A quarter wave at 1000 khz is 234' or 78 yards. And double that for a halfwave dipole. And that will work no better than a tuned loop.

    Loops, whether tuned or untuned, are quite directional.

    In daytime, I easily receive a 5000 watt station that is 180 miles away. At night I receive stations as far as 1000 miles with no problem.

    Paul
    AE5JU
     
    Last edited: Mar 8, 2009
  5. WP4CPR

    WP4CPR Ham Member QRZ Page

    Thanks AE5JU this is more then enough info. im going to try the untuned and see how much it will improve my signal. IF id dose't inprove much then i'll try the tuned loop. thanks to all that posted.
     
  6. AE5JU

    AE5JU Ham Member QRZ Page

    For connection to your HF radio, you can also use coax going to a PL-259. Just hook the shield to one terminal from the pickup loop, and the center conductor to the other terminal.
     
  7. WP4CPR

    WP4CPR Ham Member QRZ Page

    it never seems to amaze me how something so simple works so well. i built the non tuned loop with some #14 wire that was laying around just to see if anything hapend and the thing works 100+ better than i was expecting. tomorow i will get the #22 wire and build it as was on the DIY link. Thanks again 73's
     
  8. VE4CY

    VE4CY XML Subscriber QRZ Page

    You aren't mentioning which radios you are using or when you are listening for these stations.

    A general coverage amateur radio with a modest antenna should have no trouble picking up AM broadcast band stations 60 miles away. I have an old Yaesu FT-890.. Using my 6 meter dipole, during the day, I can pick up just about every AM radio station within 250 miles of me.

    Note that day and night propagation on the AM band is as different as night and day :) At night AM signals travel much further. Because of this, it's possible for stations 60 miles away to be drowned out by stronger signals from more distant stations. This is especially true if your 'local' station broadcasts at low power (Less than 1000 Watts).

    For example, KFYR at 550 Khz in Bismarck ND transmits at 5000 Watts and is 270 miles from me. I can hear it any time I want during the day.. But, when the sun sets, it's usually gone and I hear the more distant stations on that frequency.
     
  9. W8HDU

    W8HDU Ham Member QRZ Page

    Check out the National Radio Club's web site, www.nrcdxas.org, and look in publications.

    They have a book on making Loop Antennas which is very good.

    I made a loop for listening at home, and also made one for work that will allow us to monitor WOWO-1190 when they drop to night pattern. (EAS)

    Both work like a champ.

    Besides an air core loop, don't bypass a ferrite core loop. Get the material from Amidon. I use a 12" long, 1" diameter, with a 1.25" coil over the ferrite with 33 turns of #26 lintz wire. With a small FET amp, you can get about 12 dB gain, plus null offending signals.

    The nulls can be deep on these antennas if positioned carefully. Here in my home QTH I have a 1kW non-directional station about 4.6 miles from me. In the daytime I can knock them down by as much as 20dB by careful positioning.

    The trick with loops is making something that holds the turns solid, and allows you to position the whole coil az/el in numerous positions.

    Good listening!!
     
  10. AE5JU

    AE5JU Ham Member QRZ Page

    Wood frames, a little sanding, a quick wipe with some stain, let dry overnight.

    Then a couple of coats of Minwax Polyacrylic Spray Varnish (in the blue spray can). Those coats dry in about 20 minutes. You can spray both sides with two coats, and two or three cups of coffee later you can assemble.

    Remember, brass hardware.

    73
    Paul
    AE5JU
     
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