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	Ferrite beads for current baluns
	In antenna systems very often baluns are needed. Current baluns are popular because they are easy to make.
	A few ferrite beads are just put on the feeding coax cable. I have mostly used ferrites made by Amidon.
	In order to avoid measuring their impedance for every antenna project again I made this memo.
	I had three different materials in my inventory. My goal was to measure the additional impedance a ferrite generates when on a coax.
	My measurement instrument was AIM 4170. Calibration was made such a way that influence of the measurement cable was eliminated.
	Below is the summary of the measurements on HF. One shall recognize that there is some 10-20% spread in performance of ferrites.
	Samples were selected from small population (<20) and therefore one shall read these results accordingly.
	Bead type	One turn generates impedance:					Number of beads needed for				Number of beads needed for
		F/ MHz	R /ohm	X /ohm	Z /ohm		R=500	X=500	Z=500		R=250	X=250	Z=250
	FB77-1024	1.8	68	-4	68		7	125	7		4	63	4
		3.5	40	-13	42		13	38	12		6	19	6
		7	29	-11	31		17	45	16		9	23	8
		14	23	-6	24		22	83	21		11	42	10
		28	22	-4	23		23	125	22		11	63	11
	FB43-1020	1.8	5	29	29		100	17	17		50	9	9
		3.5	23	46	52		22	11	10		11	5	5
		7	47	61	77		11	8	6		5	4	3
		14	80	75	110		6	7	5		3	3	2
		28	119	83	145		4	6	3		2	3	2
	FB31-1020	1.8	21	35	41		24	14	12		12	7	6
		3.5	39	43	58		13	12	9		6	6	4
		7	54	52	75		9	10	7		5	5	3
		14	74	75	105		7	7	5		3	3	2
		28	113	103	152		4	5	3		2	2	2
	Number of beads needed for 500 ohm or 250 ohm is also calculated above. Calculation is made separately for
	resistive part, reactance and total impedance. In different circumstances criteria what is important  may vary.
	I will not discuss here when to use voltage balun and when current balun, or, what impedance is suitable for each applications.
	This is just a measurement memo
	Measurements in more details are here:
		FB77-1024				https://www.amidoncorp.com/categories/9
		FB43-1020
		FB31-1020
		Test-jig
	Pekka, OH1TV
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																22.11.2011