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Author Topic: Proper Air Wound Choke Method?  (Read 17383 times)
G3TXQ
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Posts: 1464




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« Reply #15 on: September 09, 2013, 10:11:47 AM »

Guy,

One on top of the other, so it forms one toroid of twice the height. It still looks like a single letter "O".

Hope that's clear,
Steve G3TXQ
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VA3GUY
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Posts: 172




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« Reply #16 on: September 09, 2013, 12:28:27 PM »

Steve,

Thank you for your patience and info.  I checked the Fair-Rite website to see about purchasing said cores and here is what they say on one of their pages:

Fair-Rite Products Corp 52 material is best for 1 to 5 MHz, the 61 material from 1- 25 MHz, the 67 material from 10 – 50 MHz and 68 material from 50 – 100 MHz.

Your suggestion is to use type 52 but according to Fair-Rite, type 67 or 68 seems to be a better choice.  Or is it because you are doubling up the cores that something changes and type 52 becomes a better mix?  Also, if I am looking at 40 & possibly 60 meter activity, could/should I add another type 61 core(s)?

Thanks much...
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G3TXQ
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Posts: 1464




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« Reply #17 on: September 09, 2013, 12:49:24 PM »

The frequency ranges quoted by Fair-Rite are "guides" and will vary considerably depending on the application. For example they list Type 52 as <20MHz for some applications, and 200MHz-1000MHz for others!

I already assumed you wanted 40m coverage because in your original posting you said "(10, 15 & 20 with 40 add-on)". The choke I recommended is good for 40m and more than adequate for 60m when feeding a reasonably well-matched antenna.

Steve G3TXQ
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VA3GUY
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Posts: 172




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« Reply #18 on: September 09, 2013, 12:54:34 PM »

Thank you very much Steve.  All your help is greatly appreciated.

Best 73,

- Guy
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VA3GUY
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Posts: 172




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« Reply #19 on: September 10, 2013, 07:22:55 AM »

One last question (I hope) Steve.  I have some M17/60-RG142 coax available.  I am not positive but it looks like this might be more for VHF use or could it be used in lieu of RG400?

tu de Guy
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G3TXQ
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Posts: 1464




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« Reply #20 on: September 10, 2013, 07:36:13 AM »

RG142 should be fine - just a little more difficult to wind through the toroids because it has a single centre conductor rather than the multiple strands of RG400.

Steve G3TXQ
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VA3GUY
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Posts: 172




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« Reply #21 on: September 13, 2013, 06:29:52 AM »

Steve,

I have been searching for FT240-52 ferrite toroids but can not find any.  I have been able to find T200-52 and T300-52 iron powder toroids though.  Are these the ones you were referring to?  If not, where would one buy some FT240-52 ferrite toroids?

Thank you...
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G3TXQ
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Posts: 1464




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« Reply #22 on: September 13, 2013, 07:03:58 AM »

The manufacturer's (FairRite) part number is 5952003801.

I bought my last ones from Mouser; their part number is 623-5952003801

73,
Steve G3TXQ
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VA3GUY
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Posts: 172




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« Reply #23 on: September 14, 2013, 07:29:11 AM »

Steve,

I sincerely appreciate your patience and assistance as I pick your brain!  I have ordered my FT240-52 toroids and am looking at getting some RG400.  Now my question is, obviously, there is a proper way of winding the cores.  On this website  (http://translate.google.com/translate?sl=auto&tl=en&js=n&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Ff5ad.free.fr%2FANT-QSP_F5AD_Baluns.htm)  down approx just past half way, there is a picture of a Hy-Gain BN86 balun and just above that on the right hand side, is a hand made drawing in blue, of a toroid with a winding going 1/2 way around and then crossing over to the other side of the toroid and continuing the winding in the opposite direction.  Is that what I should be doing?  I hope this all makes sense!

Thank you...

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W6RMK
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Posts: 649




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« Reply #24 on: September 14, 2013, 08:09:47 AM »

I'm not familiar with the BN-86, so can't really comment on the results you have had with it.

11 turns on two stacked FT240-52 cores makes an excellent choke for 40m through 10m. If you wind with RG400 instead of RG58, it will handle your 1kW easily.

73,
Steve G3TXQ


I'd use the newer #31 mix, which has better wideband properties in this application.

See Jim K9YC's excellent primer on building chokes (including lots of measurements on a VNA)  http://www.audiosystemsgroup.com/RFI-Ham.pdf  He has all the curves from the Fair-Rite catalog and discusses why some mixes work well and some less so well.
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G3TXQ
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Posts: 1464




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« Reply #25 on: September 14, 2013, 08:41:24 AM »

Now my question is, obviously, there is a proper way of winding the cores.

Take a look at a commercial version here:
http://www.balundesigns.com/servlet/the-32/balun-designs-baluns-1-cln-1/Detail

The 4th photo shows some winding detail. That particular design also has 11 turns - you count the number of times the coax passes through the centre of the toroid.

The "cross over" half way round is not important electrically, but it's a neat way of arranging that the coax exits the toroid at opposite sides, rather than on adjacent turns. And that makes it a neater fit in the box!

73,
Steve G3TXQ
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G3TXQ
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Posts: 1464




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« Reply #26 on: September 14, 2013, 08:45:53 AM »

I'd use the newer #31 mix, which has better wideband properties in this application.

The Fair-Rite #52 mix is more recent than the #31 - it was a replacement for the old #K mix. It is excellent for the upper HF bands.

If you want 160m thru 10m performance #31 is a better choice; but the OP wants 40m thru 10m, and you can wind a better choke for that range on #52.

Take a look at my charts here and compare the #31 designs with the #52 design:
http://www.karinya.net/g3txq/chokes/

73,
Steve G3TXQ
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VA3GUY
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Posts: 172




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« Reply #27 on: September 15, 2013, 08:04:02 PM »

Thanks much Steve.  I am on my way to making my choke!

73,

- Guy
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VA3GUY
Member

Posts: 172




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« Reply #28 on: September 21, 2013, 06:36:03 AM »

At one time, I had a COMTEK (W2FMI) 1:1 Balun (model COM-BAL-11130T) by DX Engineering (http://www.dxengineering.com/parts/com-bal-11130t).  I seem to recall that when I tried it on my Hy-Gain TH3MK3, it raised the SWR on all bands.  That got me wondering, just what exactly is the difference between a 1:1 balun and a common mode choke?

Thank you...
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G3TXQ
Member

Posts: 1464




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« Reply #29 on: September 22, 2013, 08:53:51 AM »

If it's a 1:1 Current balun, and we're talking about a choke which impedes CM current, they're the same thing!

Steve G3TXQ
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