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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