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Author Topic: Toroid Values  (Read 1019 times)
VA3GUY
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Posts: 172




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« on: January 28, 2013, 11:01:17 AM »

I have a bunch of assorted toroids that I seem to have collected over the years.  Not one of them has any markings on them.  Is there any way of identifying their properties...with only a multimeter?  If not, what would be required and what would be the procedure?

73,

- Guy
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KA4POL
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Posts: 1901




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« Reply #1 on: January 28, 2013, 11:12:06 AM »

Colors have a meaning. Check the Amidon website.
A multimeter will only do if you can measure L with it.
Else a dipmeter or a RF generator would be really helpful.
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VA3GUY
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Posts: 172




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« Reply #2 on: January 28, 2013, 11:18:19 AM »

There are no colors on any of them.  There are absolutely no markings at all.  Unfortunately, I only have a multimeter so I guess maybe I am SOL?  Shocked
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W5DXP
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« Reply #3 on: January 28, 2013, 11:22:17 AM »

If not, what would be required and what would be the procedure?

An antenna analyzer, like an MFJ-259B, can test toroids. I put a couple of turns on them and then measure the impedance which gives a clue to the material.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
WB6BYU
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« Reply #4 on: January 28, 2013, 11:39:32 AM »

The approach I've used for grouping them (even if I can't make an exact measurement)
uses an SWR bridge and a dummy load.

Wind a sample coil on the core, put it in parallel with the dummy load, and measure
the SWR on one or more bands.  Generally, the higher the impedance for the same
number of turns, the lower the SWR will be, so the higher the permeability.

To adapt this to various core sizes you can pull up the Amidon datasheets here:

http://www.amidoncorp.com/specs/

and compare the permeability of a specific type (perhaps 43 for ferrite and 6 for
powdered iron) to see how it changes with the core dimensions.  So if, say, your
standard is 5 turns on a half inch core, you can then determine the equivalent
number of turns to try on other core sizes.

You can calculate the expected SWR for a given inductor in parallel with a resistor
for a specific frequency, and from that estimate the inductance.

It isn't a perfect approach, but by measuring at both 80m and 10m (and perhaps
VHF) you should be able to roughly group the cores by permeability.
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VA3GUY
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Posts: 172




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« Reply #5 on: January 28, 2013, 11:45:28 AM »

Thank you Dale.  I do have an SWR bridge and dummy load so I will give it a shot.  I may be able to use some of these after all.

73
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KA4POL
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Posts: 1901




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« Reply #6 on: January 28, 2013, 09:45:48 PM »

Do not apply to much power, the lower the better.
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G8JNJ
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« Reply #7 on: January 29, 2013, 04:33:13 AM »

Hi,

If the cores you have are not coated with a coloured epoxy paint. There is a good chance they will be ferrite, most likely type 43 or 46 mix (which tends to be the most common for EMI suppression purposes). Unless they are small domestic clip-on types which may be possibly be type 61 or some other mix. Which has been optimised for suppression at VHF / UHF frequencies.

The quickest way to work through your collection is to borrow an antenna analyser, and use the guidelines found on this page.

http://vk1od.net/balun/concept/cf.htm

You will notice a bit of variation from the suggested figures. Depending on who originally manufactured the material and how it was 'cooked' to form the final shape.

However a few hours spend grading and bagging or labelling cores, saves a lot of heartache with construction projects later.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com



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AC2EU
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« Reply #8 on: January 29, 2013, 08:29:49 AM »

If you want to get a bit more accuracy on the cheap, you might consider one of these LCR meters.

http://electronics.mcmelectronics.com/search?w=lcr%20meter

If you want to test/grade junk box parts, this is a good tool to have around.
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W6EM
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Posts: 708




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« Reply #9 on: January 29, 2013, 06:46:30 PM »

Colors have a meaning. Check the Amidon website.
A multimeter will only do if you can measure L with it.
Else a dipmeter or a RF generator would be really helpful.
Colors can be deceiving.  i.e., I have some yellow iron powder cores and some yellow "unknown" cores that are high permeability ferrite from switching supply mfg.  So, not just as simple as looking up colors in the Amidon literature.

As for a dip meter, pretty hard to magnetically couple a dip meter coil to a toroidal inductor as the flux is confined to the core pretty well.  Unlike an air-core or old slug-tuned coil.  I guess one could build a coupling loop of a few windings around the test core to another couple of turns to couple to the dip meter.  Of course you'd have to wind a number of turns around the core and shunt them with a capacitor of known value to create an anti-resonant tuned circuit.  I'm getting exhausted just thinking about it.

I like Cecil's suggestion the best.  Grab that "poor man's" RF impedance bridge (MFJ-259B) and measure the inductance of the turns wrapped around the core..... and you're there.

You could then look up the size and estimate the type of mix from the Amidon data.
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