Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Scrapyard loop

The AM Forum
November 27, 2022, 02:52:08 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
Author Topic: Scrapyard loop  (Read 307 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline

Posts: 417

« on: November 21, 2022, 04:50:33 PM »

Well, here is first try at a loop antenna.  I was at the local metals scrapyard a week or so ago and found this 5' diameter SS hoop (3$ a pound)....  have been interested in making a hoop to experiment with and picture is what I came up with.... the small hoop is foot in diameter and the large is 5 feet.  The material is stainless steel and is 1 inch in diameter. 

I cut the hoop at the weld and inserted a variable cap at the top.... then at the bottom I robbed the wife's plastic container lid as a support for the lower loop made from coax.

At first I was concerned that the stainless steel might not be the best conductor but wow does it work! 

Initial tests show it to be very sharp in SWR and very sensitive to variable capacitor adjustment (touchy)....  however, the settings are very stable after adjustment and don't seem to fluctuate with my old body approaching the hoop.

So far I am happy to report the 40 meter band seems to be near the center of tuning range though 10 megahertz WWV signal is almost as good.  We have a noon time net on 7284 which seems as good as my other antennas but with significantly less background noise.

It is the drop in background noise that is the most impressive result.

I am a little fearful of transmitting yet but will give it a try soon.

* Loop Antenna.jpg (119.27 KB, 483x644 - viewed 113 times.)

Offline Offline

Posts: 66

« Reply #1 on: November 21, 2022, 08:26:44 PM »

That SS loop is a great find.
Offline Offline

Posts: 76

« Reply #2 on: November 22, 2022, 10:42:08 PM »

Please be wary of fire potential...with Q factor like that monsterous voltages appear on the cap, and
arcing can happen. Yes, as your body approaches it will have little effect: at proximity, you are in the magnetic field of the antenna, and at 7 MHz the electric field has not yet been developed at that distance. Your body is mainly an electric device, therefore "Invisible" to the antenna. Try putting 10 watts into it and approach it with a fluorescent bulb! A similar 20m version with 50 watts into it and the bulb would light full brilliance just a couple of feet away. (in  retrospect, not sure why--electric field emanating from the tuning cap??)

I did a fascinating experiment at 2 GHz or so: two loop antennas, broadside to each other spaced maybe 20 inches apart. I took an electrically-lossy piece of sheet material, held it orthogonal to the propagation path, and moved it from one loop to the other. When the sheet material was within about 1/4 wave of either loop, little path loss was observed (still in the magnetic-field-only region). Further away and the path loss became immediately and profoundly obvious.
Pages: [1]   Go Up
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.05 seconds with 18 queries.