Greetings To All !
I have recently decided to do a little research and attempt to find out what the proper method was to identify 'mystery' ferrite toroids and snap-on ferrite cable 'beads' or 'sleeves'. I have a box of a small assortment that I managed to salvage from some cables that I discovered in the trash bin of a local company. Since the 'snap-on' split core ferrite 'sleeves' are quite pricey from most vendors and the fact that I had 60 or so snap-on split core sleeves in my stash with an inner diameter of .505 inch, I thought it would be prudent to finally try to determine their 'MIX' type in order to determine their usefulness around my amateur radio (Ham) shack. I was particularly interested in determining the 'mix' for these in particular since their inner diameter is .505 inch size which fits perfectly on RG-8/U, RG-9913 and LMR400 coaxial cables, the exact type of feedline cables that I use for my ham radio gear.
Upon doing a bit of research I was intrigued by what I discovered, and just how simple of a process it is if you are fortunate enough to have the luxury of owning or borrowing an
'Antenna Analyzer' such as the
MFJ Model 269C or 259C, or similar antenna analyzer,
http://www.dxengineering.com/parts/...zRUSbfOgCwPrMiHiInnRockFqAHc1fn8aAozsEALw_wcB
Fortunately for me it was easy to get access to using one of the MFJ analyzers since two very nearby fellow ham radio friends has one each, one a MFJ unit, the other, I can't recall the make or model presently, but a good quality commercial analyzer nonetheless. I was thrilled to discover that I had ready access to one of these two gems since they are a bit pricey for my casual use.
For the sake of about a half-hour of work, I cobbled together the required 'test jig' using a 50 ohm coaxial cable jumper about a foot long with PL-259 connectors at each end and a single type SO-239 RF connector, an alligator clip and a 6 inch piece of copper hookup wire, it doesn't get much easier, or cheaper, than that !
For the benefit of those seeking to ascertain the same, I came across this simple 'test fixture' and explanation of how to use it to determine, once and for all, what 'MIX Type' those mystery ferrites are, whether you have scavenged them from old cables like me, or have seen them at electronic flea markets or 'hamfests' or on EBay ! In fact, if you are lucky enough to own an antenna analyzer of your own, it is just portable enough to carry along at hamfests for electronic flea markets and determine the MIX type before buying, to ensure you are, in fact, getting what you are paying for ! Once you become accustomed to the test procedure, you can easily determine the mix type in less than a minute or two ! The process is quite simple, as you shall read from the information I gleaned online and have thoroughly tested, for accuracy. See the procedure and information below:
TEST SETUP (Test Jig)
All that is required in order to evaluate ferrite cores, beads, sleeves or snap-on's, is a short length of RG-58/U or other 50 Ohm impedance coaxial cable, about a foot or so long, length is not critical, with PL-259 RF connectors at each end, a Type SO-239 RF connector and of course, your antenna analyzer of choice similar to the MFJ Model 259C or 269C.
The 'test jig' consists of the following: Solder a short length of copper hookup wire, around 22 or 20 gauge or similar, again, not critical, to the center connection of the SO-239 connector. Strip off the insulation at the free end of this wire. Connect a short length of the same type of hookup wire to the ground side of the SO-239 RF connector. You may either solder the wire to the ground side of the connector or fasten it using a machine screw and nut. Solder a small alligator clip to either of the two 'loose' ends of the hookup wire affixed to the SO-239 connector. This method makes for a quick and easy method for quickly swapping out ferrite toroids or sleeves to be measured.
TEST PROCEDURE
Simply connect your antenna analyzer, using the short length of coaxial cable, to the SO-239 connector. Insert your ferrite product to be measured into the 'open' loop and simply attach the alligator clip to the other loose wire on the SO-239 connector and you are ready to roll !
You've seen a big box of cheap ferrites at the surplus place. What kind of ferrite are they? What's their properties? This question comes up all the time, so here's some info on identification.
First, the statistical approach... Most all of the shielding ferrites you see are Fair-Rite Type 43, or the equivalent. The permeability is around 1000 for lowish RF frequencies (<1MHz), and they become mostly resistive.
Measuring using an Antenna Analyzer (as long as it reads both R and X)
(Suggested by Scott Townley) Loop a single wire through the core. Run the frequency up until R=X. The mix is identified by the following:
Mix 33 - around 10 MHz
Mix 43 - around 20-25 MHz
Mix 61 - around 50-70 MHz
(Additional mix values listed below)
The FairRite Catalog (http://www.fair-rite.com/) has actual tables showing impedance vs frequency for a one turn loop. You'll have to measure your particular ferrite and find one with matching specifications.
Chuck Counselman cautions that measuring the inductance at too high a frequency can perturb your measurements, because all these materials start to become quite lossy at higher frequencies, the frequency at which this occurs being dependent on the material (which is how Townley's scheme works, really).
A bit of reading of the Fair-Rite catalog will greatly repay you. The URL (as of 13 May 2018) is http://www.fair-rite.com/files1/Fair-Rite_Catalog_17th_Edition.pdf
Amidon Associates also has data **broken link removed**but it's a bit harder to find.
Additionally, you will also find a wealth of useful, very informative information on the Palomar Engineers website at: http://palomar-engineers.com
Identifying ferrite materials
Note that ferrite materials are subject to manufacturing tolerances and variation with temperature, so do not expect 1% accuracy in applying datasheets to real cores.
Table 1: Selected Fair-rite data
Mix Frequency where R=X (MHz) µi
31 3.6 1500
33 4.5 600
43 14 800
52 30 250
61 43 125
73 2.3 2500
77 1.7 2000
Table 1 shows the cross over frequency and µi for some common Fair-rite materials. It can be seen that although #33 and #43 have similar µi, their RF performance is quite different, due in part to the fact that #33 is MnZn ferrite and #43 is NiZn ferrite. If one was to classify an unknown core of type #43 or #33 based on µi alone, allowing for manufacturing tolerances, temperature and measurement error, it would be very easy to wrongly classify it.
Likewise, other manufacturers may have cores of fairly similar materials, and measuring µi alone gives no indication of the RF performance, or a valid comparison with a known core.
***NOTE --- If I have regurgitated information already presented here in the past, I apologize, my goal was to outline the procedure for those who may be exploring these fascinating ferrite products for the first time, hopefully providing a shortcut, to my hors of research on the subject.
If you would like to comment or make suggestions you may reach me at:
highmountainradio@gmail.com
73, Mark, Amateur Radio Station, WN3SIX
