I was out for a walk in my city when I found this old 26" bicycle rim in the brushwood close to the rail tracks. I removed all the crusty stuff and added a  variable capacitor with around 15-120 pF.

Some time later I was able to work RA3BL in Moscow 2.200 km way on 30m. The efficiency on 10 MHz is only 5% on such a small loop but it worked. I later worked LA9NKA on 12m, K8JDC on 17m, DK3KUD on 60m and highlight was VP8LP in Falkland Islands on 17m who was 12.700 km (7.900 mi) away. Unbelievable.

I like this antenna a lot and can highly recommend it. I try to source some old 24" and 28" rims to compare them. 28" should be the best option there performance-wise but you need a capacitor with a low starting capacity, otherwise you probably lose 10m.

Check out my other, big loop on which I worked hundreds of stations already: Magnetic Loop (Magnetantenne) selber bauen

To calculate your loop you can use a calculator like the one from 66pacific: http://www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx

The diameter of conductor for such a bicycle rim is around 33 mm, which is a lot compared to RG-213/214 with only around 10mm. With this value known you can calculate the perfect capacitance for your desired frequency.

Here I calculated the values for a 26 inch rim. The metric dimensions are: 55cm diameter = 1,72m antenna circumference.

 MHz     
Tuning Capacitance  
Antenna efficiency
3.573   1,014 pF  4% (-14.3 dB below 100%)
5.357  451 pF 14% (-8.6 dB below 100%)
7.074  259 pF 30% (-5.3 dB below 100%)
10.136  126 pF 60% (-2.2 dB below 100%)
14.074  65 pF  83% (-0.8 dB below 100%)
18.100  40 pF 92% (-0.4 dB below 100%)
21.074  29 pF 95% (-0.2 dB below 100%)
24.915  21 pF 97% (-0.1 dB below 100%)
28.074  16 pF 98% (-0.1 dB below 100%)
50.313   5 pF 100% (0.0 dB below 100%)

 

  • IMG_20181223_161316831_BURST000_COVER_TOP_01
  • IMG_20181223_180411413_01
  • IMG_20181223_230651613_01
  • IMG_20181223_234850083_01
  • IMG_20181224_005934046_01
  • IMG_20181226_140425762_HDR_01
  • IMG_20181226_140438436_HDR_01
  • IMG_20181226_144231851_01
  • IMG_20181226_144249632_01
  • IMG_20181226_154348972_HDR_01
  • IMG_20181226_154358881_HDR_01
  • VP8LP_40W_bicycle_rim_2018-12-27


Kommentar schreiben