I confess, I am spoiled. I have access to a plethora of RF devices such as
network and impedance analyzers so I wouldn't have to make do with making this
measurement with a rigged up setup.
BUT, if I found myself stranded on a desert island with Ginger and Mary-Anne
and they had some ferrite that they wanted me to characterize for them I could
probably do it with my trusty MFJ Antenna Analyzer as a signal source and a
receiver with an S-meter. Two things most hams have. I might not be able to
characterize it too accurately but I could probably sort out the 850u from the
125u material as well as figure out if I had enough turns to generate the
desired choking impedance and build Mary-Anne the balun of her dreams. I would
just use the analyzer and receiver as a makeshift impedance analyzer and
measure the signal attenuation through the ferrite at several frequencies and
maybe with a couple of different number of turns configurations.
Comparing it to known materials of the same size and shape would tell you what
it was for sure.
Earl
N8SS
----------------------------------------------------------------------
On 4/10/14 5:34 AM, Patrick Greenlee wrote:
>
> Just about everyone using a tower in Ham radio also uses ferrites, often
> on the coax to/from the tower. OK hi-tek guys what is a good
> experimental lash-up for testing ferrites? Typically the mix is not
> labeled on the part and how do you know it is labeled right if it is? A
> lot of kinds and sizes of ferrites available at all kinds of prices
> typically not labeled. Even if you get what you pay for then a few
> months later when they are mixed with some previous ferrite bargains
> which is which?
What sort of test equipment do you presume having?
A couple turns though the core and a way to measure Z at RF frequencies
is a pretty good way to sort them out.
It's pretty idiosyncratic (everyone has a different style of winding,
etc, and the parasitics on your analyzer are different than someone
else's)..
But, if you have something like a MFJ, you can measure Z at 2 or 3
frequencies at something like 1-2 MHz, 10-20 MHz and 100 MHz and get a
feel for what the different mixes are like (with some knowns to check with).
the different mixes have VERY different mu, so the Z at a given
frequency will be radically different (for the same size core). And the
other thing is whether it's a powdered metal or ferrite core and whether
it has high loss or just high inductance.
I have a little chart in the box with my old MFJ 259, a PL259 to
cliplead adapter and 12" of wire. Mostly, I just measure when I know
what it is, write it down, and then in the future, compare.
>
> I don't think identifying the mix is an important goal although you may
> be able to make an educated guess after measuring performance attributes
> of your ferrites. What would be good to know and would constitute
> success would be to get a measure of their characteristics at various
> frequencies. The preferred method of testing should not require a bunch
> of lab gear not typically found in a modest shack. A minimal set of gear
> would include your station's primary equipment, such things as your
> transmitter, coax jumpers, dummy load,SWR meter, volt meter and watt
> meter.
That would be tough.. you're going to have to do a lot of recabling.
What you really want is something like a RF bridge (e.g. a MFJ antenna
analyzer or equivalent).
The test may require putting a toroid on a length of coax and
> then installing a connector (maybe repetitively.) Tests may require
> winding an insulated conductor around/through a ferrite core.
Almost certainly.
>
> Perhaps an antenna analyzer would be available for a different test
> schema. Maybe there are other pieces of equipment that would be useful
> and likely to be available. To be accessible to more hams the tests
> should not be limited to only those requiring more sophisticated gear
> such as my HP 8753D Network Analyzer with accompanying HP 85041 S
> parameter accessory for testing from 300 Hz to 3 GHz.
>
One could probably build a "ferrite checker" for hamfest/junkbox use
with something like a canned crystal oscillator (e.g. used in
computers), a diode and a voltmeter. It's mostly a matter of calibration.
It's all about measuring the Z of the thing at a couple or three
frequencies. For "categorization" the Z measurement doesn't have to be
all that accurate.
>
> How about it guys? What about a quick and dirty GOOD ENOUGH test to
> select ferrites based on their in-shack measured performance?
>
> Patrick NJ5G
>
> _______________________________________________
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|