10-31-2013, 03:39 PM
You can make a loop antenna, see my page Loop antenna instructions
"I just made an antenna for a radio I installed into an old bookshelf speaker (not a good one, so don't worry). I made it large to capture more signal out of the air. What to do: Get a spool of wire about a hundred feet long. Select wire without solder coating on it. Skin effect would force most of the RF current thru the solder, which has a higher resistance than copper, and that will kill the Q. Better yet if you have a supply of silver coated wire, usually done with Teflon wire (Teflon does bad things to copper, so the silver plating). Silver is a better conductor than copper, but as silver is much more expensive, everyone uses copper to wire their houses. Or use litz wire for the antenna if you happen to have some. Anyway, get some corrugated cardboard from that box your latest ebay win came in, and make a coil form. Cut an odd number of notches one every 2 inches or so. You will wind the wire in a basket weave pattern. This basket wave pattern needs the odd number of notches or else it won't work out. That reduces stray interwinding capacitance. You have seen this done in older AA5 antennas. I made one about 15 inches by 11 inches. It took about 17 turns. But be prepared to add or remove turns or fractions thereof. Smaller size loops will need more turns. Tune the radio the antenna is for to a weak station near the bottom of the band, like 570KHz. Connect the inner wire of your antenna to the "hot" part of the antenna tuning cap, and the outer wire to the AVC "RF ground". Use a high impedance voltmeter to monitor the AVC voltage. Add or remove turns of wire from your antenna to peak the signal strength of that station selected above. A few solder joints in the antenna won't hurt anything as long as you can't get shorted turns. You can have a few feet of wire between the antenna and AVC line as you're tweaking the antenna. You are actually adjusting the antenna inductance to resonate it to the tuning cap. After you get the peak, tune up to a station around 1500KHz and tweak the antenna trimmer cap. If you did the basket weave pattern, you should be able to get a peak. The radio should be more sensitive now. Check that strong stations are not distorted or causing intermod in the band. Now you're done."
"I just made an antenna for a radio I installed into an old bookshelf speaker (not a good one, so don't worry). I made it large to capture more signal out of the air. What to do: Get a spool of wire about a hundred feet long. Select wire without solder coating on it. Skin effect would force most of the RF current thru the solder, which has a higher resistance than copper, and that will kill the Q. Better yet if you have a supply of silver coated wire, usually done with Teflon wire (Teflon does bad things to copper, so the silver plating). Silver is a better conductor than copper, but as silver is much more expensive, everyone uses copper to wire their houses. Or use litz wire for the antenna if you happen to have some. Anyway, get some corrugated cardboard from that box your latest ebay win came in, and make a coil form. Cut an odd number of notches one every 2 inches or so. You will wind the wire in a basket weave pattern. This basket wave pattern needs the odd number of notches or else it won't work out. That reduces stray interwinding capacitance. You have seen this done in older AA5 antennas. I made one about 15 inches by 11 inches. It took about 17 turns. But be prepared to add or remove turns or fractions thereof. Smaller size loops will need more turns. Tune the radio the antenna is for to a weak station near the bottom of the band, like 570KHz. Connect the inner wire of your antenna to the "hot" part of the antenna tuning cap, and the outer wire to the AVC "RF ground". Use a high impedance voltmeter to monitor the AVC voltage. Add or remove turns of wire from your antenna to peak the signal strength of that station selected above. A few solder joints in the antenna won't hurt anything as long as you can't get shorted turns. You can have a few feet of wire between the antenna and AVC line as you're tweaking the antenna. You are actually adjusting the antenna inductance to resonate it to the tuning cap. After you get the peak, tune up to a station around 1500KHz and tweak the antenna trimmer cap. If you did the basket weave pattern, you should be able to get a peak. The radio should be more sensitive now. Check that strong stations are not distorted or causing intermod in the band. Now you're done."
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