Here at Palomar we measured different ferrites for impedance using the
Autek RF-1 meter. The results favor 43 material over 77 material for the HF
bands. Here are some results at 7-MHz:
One turn on Radio Shack "snap-on" choke: 16 ohms
One turn on Palomar (Fair-Rite) 1/2" split bead: 68 ohms
One turn on 2.4" toroid 43 Mix: 36 ohms
One turn on 2.4" toroid 77 Mix: 13 ohms
3 turns on 2.4" toroid 43 Mix: 280 ohms
3 turns on 2.4" toroid 77 Mix: 86 ohms
6 turns on 2.4" toroid 43 Mix: 1400 ohms
6 turns on 2.4" toroid 77 Mix: 322 ohms
For a single turn the split beads are best because they are longer (1" vs.
1/2" thickness for the large toroids. But with multiple turns the impedance
goes up as turns squared so for coax the toroids are best. For small cable
such as telephone wiring you can put multiple turns through the split
beads.
Jack, K6NY
--
Submissions: rfi@contesting.com
Administrative requests: rfi-REQUEST@contesting.com
WWW: http://www.contesting.com/rfi-faq.html
Questions: owner-rfi@contesting.com
|