Back in the loop

My main project for at least the last 12 months has been building a solid magnetic loop antenna and its companion automatic loop controller. I’ve been roughly tracking its progress at my magnetic loop antenna project page on this blog.

As usual, life has got in the way, but I want to get back on track and complete the project. To start pumping some RF current through it again, over the weekend I spent a short time playing with the loop on WSPR on 40, 30 & 20m. The tests were too brief but they certainly confirm that the loop is capable of transmitting a signal in spite of the fact the loop is only half a metre above ground and surrounded by metal garden furniture, a steel framed awning and gutters.

I used the WSPR Beacon android app to control my transmitter. There was some discrepancy (tens of Hz) between the actual output frequencies on the app and those shown on WSPRnet. I also found that tuning the loop to each WSPR frequency using the iP30 antenna analyzer was easy and the KX2 gave lower SWR figures.

The brief test became an exercise in understanding theWSPRnet results taking into account propagation and loop orientation which was aligned north-south.

This map view combines all 20 spots of the 1W VK2RH transmissions from grid square QF56oc. The first test was logged at 2017-05-07 01:36 UTC. (I’ve trimmed repeated info from the chart below to improve its fit on the page.)

Time MHz SNR Drift Reporter RGrid km az
 05:24  14.097001  -15  1  VK4ALR  QG56fk  1151  356
 05:24  14.097016  -26  0  VK4TDI  QG62lm  733  14
 04:48  10.140109  -22  0  VK4TDI  QG62lm  733  14
 04:48  10.140094  -23  0  VK7TW  QE37pc  1057  198
 04:48  10.140091  -17  0  VK6XT  OF86td  3086  261
 04:40  10.140095  -27  0  VK7TW  QE37pc  1057  198
 04:40  10.140090  -4  0  VK3WE  QF32se  547  216
 04:40  10.140090  -22  0  ZL1RS  RF64vs  2069  101
 04:40  10.140092  -15  0  VK6XT  OF86td  3086  261
 04:40  10.140091  -16  0  ZL3GA  RE66ho  2130  126
 03:18  7.040121  -24  0  VK3BAL  QF22mc  711  230
 03:18  7.040134  -7  0  VK3AXF  QF33fn  516  235
 03:18  7.040135  -18  0  VK4MOB  QG62ol  734  16
 03:18  7.040130  -18  0  VK3DXE  QF21nv  720  228
 03:18  7.040128  -12  0  VK2TPM  QF56of  14  0
 03:18  7.040129  -14  0  VK7DIK  QE38cu  918  207
 01:36  7.040183  -16  -1  VK3AXF  QF33fn  516  235
 01:36  7.040177  -16  -1  VK2TPM  QF56of  14  0
 01:36  7.040184  -24  -1  VK4MOB  QG62ol  734  16
 01:36  7.040179  -21  0  VK3DXE  QF21nv  720  228

40 metres favoured north-south, while 30 metres was literally an all-rounder and 20 metres was too brief. These results probably say more about propagation than the loop, not to mention the heavy lifting done by all the reporter stations extracting my down to -26 or -27 dB signals from the noise! Impressive all round!

I wonder how many people are using the Sotabeams WSPRlite antenna tester device. Certainly looks tempting, especially for longer term antenna evaluation.

In any case, the main purpose of today’s exercise was to re-start the loop project. The To Do list includes

  • building & installing the SWR bridge into the loop controller,
  • deciding on the best way to couple the stepper motor shaft to the tuning capacitor shaft,
  • and wiring it all together with appropriate coax and control cables.

3 Responses to “Back in the loop”

  • Lowell KM4QEG:

    Re item two on the “To Do.”

    There are dozens of types of nylon and plastic tubing that will do a great job of this. They allow and compensate for shaft mis-alignment, are dilectric by nature, and the stiffer varieties will have minimal backlash.

    They can be softened with heat to allow fitting to different shaft sizes and are easily anchored with small compression rings typically used for gas/vacuum tubing on small engines.

    Lowell Haney
    Rome GA USA

  • Charles Kollett:

    Nice article and very professional construction. I am an aerospace design engineer and this is the kind of quality not seen that often. I am also very interested in loop antennas and have been wanting to build one which will tune 80-10 meters. Curious, did you use a mandrel to bend the aluminum tubing?

    Very best
    Charles Kollett
    W7CRK
    Queen Creek, AZ. USA

  • richard g3cwi:

    I use my WSPRlites a lot. But that’s not surprising really! There is a good Facebook group where you can ask questions:

    https://www.facebook.com/groups/607517072784534/

Leave a Comment

Subscribe FREE to AmateurRadio.com's
Amateur Radio Newsletter
News, Opinion, Giveaways & More!

E-mail 
Join over 7,000 subscribers!
We never share your e-mail address.



Also available via RSS feed, Twitter, and Facebook.


Subscribe FREE to AmateurRadio.com's
Amateur Radio Newsletter

 
We never share your e-mail address.

Please support our generous sponsors who make AmateurRadio.com possible:

KB3IFH QSL Cards

Hip Ham Shirts

Georgia Copper

Ham-Cram
Expert Linears

morseDX

Ni4L Antennas

N3ZN Keys

West Mountain
R&L Electronics


Do you like to write?
Interesting project to share?
Helpful tips and ideas for other hams?

Submit an article and we will review it for publication on AmateurRadio.com!

Have a ham radio product or service?
Consider advertising on our site.

Are you a reporter covering ham radio?
Find ham radio experts for your story.

How to Set Up a Ham Radio Blog
Get started in less than 15 minutes!


  • Matt W1MST, Managing Editor




Sign up for our free
Amateur Radio Newsletter

Enter your e-mail address: