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[TowerTalk] RG-304 for CMC ?

To: <towertalk@contesting.com>
Subject: [TowerTalk] RG-304 for CMC ?
From: "Jim Thomson" <jim.thom@telus.net>
Date: Tue, 26 Apr 2016 06:50:56 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Date: Sun, 24 Apr 2016 22:44:40 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] RG-304 for CMC ?

On Sun,4/24/2016 9:35 PM, Jim Thomson wrote:
> ##  Bunched up loops  lowers  res freq.
Right.

>    Depending on choke  config, it can narrow the range of the choke,

Not if the core material is #31 or #43.


> to the point where it covers 80m  with high  5-6 k RS... but not 40m.
> Lousy on 40m, like 650 ohms.    This appears to be the case  when  Binoc
> config is used in some cases.   With binoc config, with torroids at the 9 +
> 3  oclock positions, the turns all end up bunched  together for the entire 
> loops.
> Bad news  if  LMR-400 /213-U /393  coax used.   A LOT more C  between turns
> with the .405 OD cables...vs  58-U / 303 etc.

This is nonsense.

>
> ##  One  advantage to binoc config, is you can then wind in 1/2 turn 
> increments, like
> 4 -  4.5 ? 5  - 5.5  etc.

This is also nonsense. Chokes wound for the HF bands using #31 and #43 
material have VERY low circuit Q, typically on the order of 0.4. This 
makes them broad as a barndoor!  Their tuning is NOT critical.

>
> ## 12 inch diam loops is a trick to maintain spacing between each loop.   
> With loops
> equally spaced around the cores, now you end up with a mess that is almost 2 
> foot in diameter,
> which is exactly what I dont want for a cmc...esp on a 80m rotary dipole, 
> mounted 10 ft up
> the mast.     8.5 K in a little box, on 80m, with the CMC-230-5K is a more 
> elegant solution.
>
> ## 12 inch diam loop = 3 ft in circumference.  7 turns = 21 ft of  
> LMR-400..which is a lotta
> weight,bulk,windload, etc.  But it does provide outstanding high Z / RS  
> across 80+ 40m..and
> 160m.

I don't know where you get this stuff, but it's nonsense.

73, Jim K9YC

&&   Which part  of  12 inches + 12 inches  doesnt = 24 inches.... is  nonsense 
?     Simple grade schools maths. 
The 8 x cores used for the  latest binoc experiment are all  type 31...and all 
are the 2.4 inch OD variety.

This just in from Danny, who is doing some experiments for me using binoc 
config +  393 coax. 
..........................................................................................................................................................................

I have spent some time playing with RG393 and binocular Balun made of 8   x   
type 31,  2.4 inch OD cores.
I was right, 5 turns went down below 3Mhz and 5.5 turns narrows the choke so 
much that it becomes very reactive just a  few hundred KHz from Fres.

With 4.5 turns there is Fres at ~3Mhz and pretty good at 3.5 and 3.8MHz as you 
can see in the image I attached. 

Binocular style with more turns easily become very narrow and it is very hard 
to get the "sweet spot". I have tested many binocular Chokes
and it is easier to make it with thinner coax due to less interwinding 
capacitance unlike with larger size coax cables like RG3939 or LMR400.

...........................................................................................................................................................................................................
Ok, here is the results   when 4.5  turns   of  RG-393 used  with 8 x cores,  4 
per side.    RG-393 is aprx  .390 to.392  inch OD

1.80 mhz     Z= 3703.91 ohms         RS = 1410.57  ohms      XS=  3424.61 ohms 

3.03 mhz     Z= 7016.74 ohms         RS=  7015.71  ohms       XS=  20.91   ohms

3.55 mhz     Z= 6232.08 ohms         RS=  5660.31  ohms        XS=   -  2606.91 
  ohms

3.80 mhz     Z= 5730.50 ohms         RS=  4776.18  ohms        XS=   -  3166.34 
 ohms

7.00 mhz     Z= 2235.04 ohms          RS=   670.78  ohms        XS=   -  
2132.01  ohms

.................................................................................................................................................................................................
As you can see in the above chart I made up  from the graph,  the choke peaks 
at 3 mhz,  works good across the 80m band,
then goes all to hell  on 40m band....and ditto with 160m band.   The initial 
idea was to make a  binoc cmc, using 393, that
would work on both 80+ 40m.      4 turns  and also  3.5 turns  and also 3 turns 
 will be tried, but maybe too much of a compromise,
we shall see.    Teflon   RG-304  with its .280 inch  OD  and 14.5 gauge center 
conductor might just be the ticket, offering less
inter winding C vs  393, but higher voltage and current rating  vs  303 /400  
coax.  These CM chokes are not as simple as folks
make them out to believe. 

Jim   VE7RF




 
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