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Re: How to find the right ferrite toroid for a receiving antenna balun?
Unfortunately, what you all are describing is a transformer and not a balun. The primary purpose of baluns and ununs is to attenuate common mode currents. This cannot be done on a single core other than 1:1. And even then, the discussion should be centered on the rejection of common mode current in your particular implementation.
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Dale W4OP -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Gert Gremmen Sent: Monday, January 13, 2020 7:04 AM To: [email protected] Subject: Re: [nanovna-users] How to find the right ferrite toroid for a receiving antenna balun? What you are looking for is a minimum loss situation. All ferrites are the same but for Al value (always freq dependent) and hysteresis losses. Any low loss ferrite will do for your balun once the optimum wire thickness and winding number is achieved. Low loss characterization would be easiest when doing a simple 1:1 transformer as all impedances remain (the same) 50 Ohm. Than just characterize at your frequency of interest, the transfer value as a skalar (no need here for complex measurements) Then make a 9:1 balun (arbitrary N windings) and use a 400 ohm serial resistor (to make sure it is loaded by 450 Ohm) to the input of the nanoVNA (400 +50(input nano) = 450) to verify you were looking for. Alternately you can reverse the measurement by inputting into the "9" side + 400 and loading the "1" side. (Losses shall essentially be the same, if not, set up problem) Then connect the "1"side of the balun to your receiver (without 400 Ohm) and characterize the "9" side for SWR and having a 450 Ohm real input. (you might characterize the 400 ohm resistor first (to be non-inductive) so as to make sure it does not spoil the measurement, and allowing you to measure the transfer losses created by the resistor) Once you found best ferrite you may experiment with winding numbers (to cope for the specific Al value of your ferrite) and optimize the transfer to your receiver. Experiments may be bifilar winding, other geometries of the ferrite, (though you will find a correlation between ferrite volume and losses,so keep it small) and winding variations and interconnections. The last parts are the fun in this hobby. If you do a good job, your balun may function from 300-30000 kHz. It is difficult to have more than 1:100 in frequency range for a non tuneable balun, due to non-symmetries in windings and interconnects. My 1 cents..... Gert On 13-1-2020 12:06, ptapon@... wrote: Hello everyone,-- |
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