Original source:
Active Ferrite Rod Antenna for HF, 08.10.2005 OH7SV
Active Ferrite Rod Antenna OH2NLT
The ferrite rod made by Pramet Sumperk during the Iron Curtain era may be sourced cheaply from
http://ferity.cz/e-shop/en/ferity/548-n2101x144-0000000038430.html
The rod is not as good as the Amidon 61 material counterpart, namely the Pramet N2 material has 2x higher permeability than the Amidon 61 material and it has lower Q and higher losses on HF than the Amidon material. But you cannot beat the price, the rod is about $1.50. If there is enough interest, I may organize a group buy. I may also source the boxes and pieces of the PVC tube.
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| Tuning control, power off switch, power indicator LED and BNC output on the front side. The ferrite rod is fixed in the PVC tube by injecting hot melt glue at both sides. |
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| Old Russian made polyvaricon placed above the ferrite rod, because the box standoffs would stay in way if the rod was positioned at the top. The box has a convenient 9V battery compartment. |
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| Tiny amplifier board made on a double sided blank board by cutting traces with a needle file. Using two BFR93 low noise transistors as OH2NLT. The output is coupled to the BNC connector by a voltage balun wound on a tiny Amidon 43 material binocular core. |
2 comments:
Dear I saw that you put the coils spaced from the primary and 3 turns of secundariio in the center of the ferrite. Take me these questions: how many loops used to cover 80 to 20m and capacity of the variable capacitor.
Now appreciate the information.
sds
alcineu
Hello Alcineu.
Unfortunately the coil is hidden inside the tube, I cannot count the primary windings. It was not much, likely around 15. The secondary is just 2 turns. Lowering the number of secondary turns increases Q of the antenna.
The variable capacitor is 2x 5-285pF russian made. I connected the two sections in parallel. The value is not critical.
Vojtech
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