Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Ferrite toroid cores  (Read 2392 times)
VA3GUY
Member

Posts: 172




Ignore
« on: January 10, 2013, 10:52:58 AM »

These may be stupid questions but here goes anyway.

1)  In all of my reading about these toroids, it seems that type 31 is best suited for 2-10MHz and type 43 is best for 20MHz and up.  Based on those numbers (if, in fact, the stats are correct), what type is best for 10-20MHz?

2)  Is there any harm/advantage to putting a type 31 AND type 43 toroid together in the the same line?

Thank you...
Logged
KD0REQ
Member

Posts: 848




Ignore
« Reply #1 on: January 10, 2013, 11:42:12 AM »

I don't see 31 mix ferrite in the Amidon spec sheets... I do see 43 listed up to 15 MHz primary range, with discussion up to 40 MHz.

curves for these mixes don't drop off like a crystal filter, but wander about a bit on the slope to -60 dB.  if you have multiple stages, you can stagger-tune them for flat response with a little extra amplification in a strip amplifier.  if this is for oscillator service, you shouldn't squeeg and stop at 19.2, but might have a little reduced output.  nothing critical unless you are building for Uncle Sam and there are 10 stages of rejection in the purchasing process.

43 ought to do you proud.  but I grew up using iron powder toroids, and the #2 mix is high-Q from 2 to 30 MHz.  it should be flatter.
Logged
N6GND
Member

Posts: 331




Ignore
« Reply #2 on: January 10, 2013, 11:44:46 AM »

For making common mode feedline chokes there is useful information here:

http://www.karinya.net/g3txq/chokes/
Logged
W0BTU
Member

Posts: 1559


WWW

Ignore
« Reply #3 on: January 10, 2013, 02:43:45 PM »

 it seems that type 31 is best suited for 2-10MHz and type 43 is best for 20MHz and up.  Based on those numbers (if, in fact, the stats are correct), what type is best for 10-20MHz?

The short answer is that those two ferrite mixes overlap. Download, read the pertinent sections, and study the applicable graphs in http://audiosystemsgroup.com/RFI-Ham.pdf and it'll all become clear. :-)

There's more info at http://audiosystemsgroup.com/publish.htm
Logged

G8JNJ
Member

Posts: 473


WWW

Ignore
« Reply #4 on: January 11, 2013, 01:11:48 AM »

Hi,

On re-reading your question, I'm not quite sure what you wish to use the cores for.

If you wish to construct inductors for use in tuned circuits then Iron Powder cores of Mix 2 (Dark Red coating) for Low HF frequencies and Mix 6 (Yellow coating) for the Higher HF and lower VHF frequencies are generally the norm. As they introduce a very small resistive component and so are suitable for the construction of high Q circuits. Type 61 Mix ferrite can also be used for this purpose. If a greater amount of inductance is required for a given number of turns. However none of these materials are particularly suitable for the construction of 'current' baluns. As they do not provide a sufficiently high enough value of resistive choking impedance.

Ferrite core materials are much better suited for the construction of baluns. However the material needs to be chosen to best suit the required operating frequency. Which is where Steve, G3TXQ's charts come in handy.

As a 'finger in the air' rule I'd say:-

Type 73, 75 & 77 Materials are best for the LF bands 500KHz, 1.8MHz & 3.5MHz
Type 31 for 3.5MHz, 7.1MHz & 10MHz
Type 43 & 52 for 7.1MHz through to 24MHz
Type 61 for 14.0MHz through to 54MHz

However this is only for guidance. The actual choice really depends upon the use it is being put to, and the number of turns required for a given value of common mode choking impedance. There are lots of factors that have to be taken into account, in order to produce a satisfactory design. There are a LOTS of poor and misleading construction articles for Baluns and Ununs on the web. Particularly those using powdered Iron cores.

Also beware of unmarked or unknown ring cores !!!!

Many of the types being sold (particularly on the internet or at ham table top sales), were intended for use as storage inductors in switched mode power supplies. They are not at all suited for the construction of Baluns or Ununs.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com



Logged
W5DXP
Member

Posts: 3540


WWW

Ignore
« Reply #5 on: January 11, 2013, 05:07:35 AM »

#2 mix is high-Q from 2 to 30 MHz.

I use #2 powdered-iron for conventional RF transformers. But a $75 store-bought 4:1 voltage balun based on a large Sevick #2 toroidal design was the worst balun I have ever seen for 10m operation. I had the factory measure the common mode impedance on 10m and it appeared to be approaching series resonance.
Logged

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.
G8JNJ
Member

Posts: 473


WWW

Ignore
« Reply #6 on: January 11, 2013, 11:51:32 AM »

Hi,

Cecil has brought up a valid point.

Type 2 Iron powder does not provide enough inductance for Baluns and Ununs to operate correctly on HF and LF frequencies.

Because so many turns are required the winding length becomes problematic, and the inter-winding capacitance causes self-resonances to occur.

They don't really work that well at suppressing common mode current, so they don't tend to absorb any power and overheat. For this reason folks like using them because they are difficult to destroy when used in ATU's (as an attempt to produce a balanced output from an unbalanced source). or when they are attached to an unsuitable load.

However transformers constructed on Iron powder cores, are inherently narrow band devices and in my opinion really shouldn't be called Baluns or Ununs.

You can read more about this at:-

http://g8jnj.webs.com/Balun%20construction.pdf

Regards,

Martin - G8JNJ

www.g8jnj.webs.com

Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!