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Re: AM antenna update [message #25837 is a reply to message #25835] Thu, 11 May 2006 09:00 Go to previous messageGo to next message
colinhester is currently offline  colinhester
Messages: 1349
Registered: May 2009
Location: NE Arkansas
Illuminati (3rd Degree)
Audio magazine, now defunct, had an article in the early 90s on how to build FM antennas. The simplest mod was to cut down the noraml t-type dipole included with reseivers. This consisted of cutting some length off to match 1/4 wavelengh (and a little bit more for transmission factor through the plastic casing) of a particular station. There were other desings for an extended dipole with phasing loops every 1/4 or 1/2 wavelenght.

There was also a DIY on the Sterba curtain. See: http://www.hamuniverse.com/sturba.html This is a fantastic antenna if you have attic space and can string between rafters. VERY high dB gain.

Check out the local libraries and see if you can find this issue. Well worth it

I have a TAB book on HI-FI from the early 80s that details other types (chicken wire if you don't have a HOA )and one made from a bicycle wheel.......Colin



Re: AM antenna update 2 [message #25838 is a reply to message #25836] Sat, 27 May 2006 07:15 Go to previous messageGo to next message
Paul C. is currently offline  Paul C.
Messages: 218
Registered: May 2009
Master
More on AM antennas:

Yesterday I received a new and improved Godar Model 10 AM Antenna after returning the previous Godar 10 to the manufacturer.

http://users.mcleodusa.net/m/mgodar/MDL10.html

The original Godar Model 10 is described as a "Loop" antenna on the website, instruction sheet, and in conversation with Mike at Godar. It is not a loop design. I opened it up. It is at most, a base loaded bent whip. There is no "loop".

This new Godar AM antenna (also labeled Model 10) has a different cable, with the connector removed from one end for connection directly to your receivers AM Ant and Ground posts. New instructions warn not to use a regular cable and transformer (as supplied with the previous version).

The instructions that came with this new Godar 10 describe it as a ferrite loop. While I have not yet opened it, a quick check with my multimeter shows there is no continuity back to ground... so it is NOT a loop.

The new Godar works exactly like the previous one... it doesn't. There is no difference in signal with or without the cable screwed into the Godar antenna. As with the previous Godar antenna, signal increased if I held the antenna, and increased even more if I touched the outside of the connector.

While touching the connector on the end of the cable there was no difference in signal whether plugged into the Godar 10 or not.

This antenna was tested on an Onkyo T-4500 tuner, Onkyo TX-850 receiver, and Onkyo TX-901 receiver, all with the same poor results.

HOWEVER, this tuner and receivers work very well with a true loop, the "Ultimate AM Loop" antenna... which is simply four turns of wire around a simple wood frame.

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

The Ultimate Loop described in my previous post is the superior unit by far, and one I can recommend to everyone. Here is a kit version of the Carver Ultimate loop:

http://cgi.ebay.com/ws/eBayISAPI.dl..._Pr3_PcY_BIN_IT

The photo below is my actual kit built Ultimate. There is also available a finished version and a small finished version.

---

Update: I returned the Godar antenna to the seller, who is giving me a full refund. He stated that these antennas work well for some, and don't work for others, he did not know why.

So, what I have done is sent Mike (Godar) schematics of my tuners so that he can see what might be different about my gear from others for which the Model 10 AM antenna do work with.

All of this has been frustrating, especially since I have a Godar FM1-A in the attic that works quite well. Not as well as a previous outdoor antenna (a Channelmaster, don't remember the model) that was on a mast about 10' above the peak of my roof, but still gives acceptable performance for an indoor antenna.


Godar product alert [message #25841 is a reply to message #25838] Wed, 31 May 2006 11:11 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18786
Registered: January 2001
Illuminati (33rd Degree)

That's embarassing for Godar. With the loop antenna so effective and easy to manufacture and use, Godar has no excuse. They probably should stop selling antennas, 'cause that's pretty bad.


Re: AM antenna update [message #25844 is a reply to message #25826] Mon, 05 June 2006 21:25 Go to previous messageGo to next message
Paul C. is currently offline  Paul C.
Messages: 218
Registered: May 2009
Master
I made one of the small 9" loops... nowhere near as good as the larger version. If you order a kit from Jeff, get the large one.

Re: AM antenna update [message #25845 is a reply to message #25844] Mon, 05 June 2006 22:33 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18786
Registered: January 2001
Illuminati (33rd Degree)

Good info, thanks!

This is a good one to make purely DIY too. A loop antenna is easy to build with a minimum of materials and effort, and it works great!


Re: AM antenna update [message #25846 is a reply to message #25845] Tue, 06 June 2006 21:18 Go to previous message
Paul C. is currently offline  Paul C.
Messages: 218
Registered: May 2009
Master
Materials needed to make your own:

Base- decoupage plaque from a craft store

4 Rubber or plastic bumpers- self adhesive type, for feet, need to be about 1/4" thick

1/2" x 3/4" x 18" long pine- cross arm

1/2" x 3/4" x 20" long pine- upright

#6 x 2 1/2" woodscrew- to secure upright to base

4 brass "shoulder hooks"- to hold wire loop on upright and crossarm

#8 brass machine screw, 2 washers, nut (all must be brass)- to connect the crossarm to the upright

terminal strip

18' of #22 insulated wire, stranded or solid, does not matter

300 ohm twinlead - length as needed to go from terminal strip to your tuner or receiver.

The shoulder hooks are screwd into the ends of the cross arm about 3/8" from the ends. Also on the upright, 3/8" from the top, and one about 2" from the bottom.

A 5/32" hole is drilled in the center of the base (plaque), and another drilled 1/2" in front of it. A third hole is drilled to one side coming out next to the terminal strip.

See photos.

The upright and crossarm are notched (1/4" deep, 3/4" wide) so that they may be assembled and be flush. A hole is drilled through them and the machine screw, washers, and nut are used to hold it together.

Before assembly of wood parts, sand and stain, varnish, or finish as you wish. I used Minwax stain, let dry overnight, then a few coats of spray on water based finish.

A 3/32" hole is drilled in the bottom of the upright. The #6 2 1/2" screw is screwed in from under the base and into the upright to hold it to the base.

6" of wire is pushed down through the hole just in front of the upright, under the base, and out the hole beside the terminal strip and secured to the terminal strip.

Pull out the excess slack from the top by the upright.

Pass the wire over the lowest shoulder hook, then up around one of the crossarm shoulder hooks, up to the top, down to the other side, back down to the bottom shoulder hook, and around again. Total of four loops.

At the bottom loop the wire around the bottom shoulder hook and then down through the hole in the base. Pull it snug. Up through the hole by the terminal strip, and secure to the terminal strip.

Then run 300 ohm twinlead from the terminal strip to your tuner or receiver. Connect to the AM and Ground terminals. Both leads must be connected.

Listen to the AM stations roll in!




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