[TowerTalk] [Bulk] Re: CMC-230-5K

Grant Saviers grants2 at pacbell.net
Thu Apr 21 10:50:37 EDT 2016


RG400 and RG142 are same od, same double Ag plated shields, both 0.195" 
od.  RG142 is solid center Ag plated and RG400 is stranded Ag plated.  I 
mount the choke in a J-box so there should be no flexing, so I use 142.  
1.9kv for 400/142, and rated about 1.6kw at 50Mhz. Short lengths of 142 
are on ebay for about $2.60/ft.

The hard one to find is the next size up, RG304 which has a 3kv rating 
and 0.27" od, all Ag plated and small enough diameter for enough turns 
in 240 size cores.  I've searched for a 304 supplier but never found 
one.  Also known as M17/112, the current Mil spec designation.

Grant KZ1W


On 4/20/2016 21:32 PM, Roger (K8RI) on TT wrote:
> Two questions.  Why are they (ARRL) calling common mode chokes, "the 
> best kept secret" when they have been in the arsenal of many of us for 
> some years. The photo looks like an 11 turn 2 core in series with a 7 
> turn, 2 core choke.  Get the RG-400 (e-bay), 4 cores, two connectors 
> and the box for less than $30.
> The RG-400 is expensive compared to LMR 400, but you won't get more 
> than 7 turns in a 2.4" core.
>
> I did have about 50 feet of RG-400, but am down to about 30 now.
>
> It is a very neat construction, but a do it yourselfer could save a 
> lot of money.  I use a similar set up on 75, but mine is open to the 
> elements and uses LMR400.
>
> They are also about 50 feet apart and "hang" from a center fed sloping 
> dipole. I use a single 7T, 5 core for 40 meters. The cores are on the 
> feed line so support is not an issue.    The idea behind the CMC 230 
> 5K is nothing new (two different chokes in series), but its in a very 
> nice package and very handy for the non do-it-your-self ham.
>
> 73,
>
> Roger  (K8RI)
>
> On 4/19/2016 Tuesday 6:30 AM, Jim Thomson wrote:
>> I just received a pair of  CMC-230-5K common mode chokes...from 
>> MyAntennas.com to experiment with.
>> They are configured as a  line isolator, with  silver-teflon SO-239s  
>> on each side.  They can also be configured as
>> a balun, with a pair of standoffs on the balanced ant side if you 
>> like.   Extremely well designed and built, better
>> than I expected.   He does a beautiful job of terminating the coax.  
>> I will try some different placement configurations,
>> including both in series, also in different locations.
>> 2-30 mhz rated, 7k - 12.2k Z...with RS slightly less, 5.4K – 11.3k   
>> 5 kw icas.
>> If this doesn’t do it, I give up, esp with 2 of em in series. Rated 
>> for 40db of common mode attenuation...per  unit.
>> Should be 80db  for a pair of em in series.   They are heavier than I 
>> thought, and UV proof.
>> This will be an interesting experiment.  If I can dump some noise on 
>> RX, I will be happy.   Stay tuned.
>> http://myantennas.com/wp/product/cmc-230-5k/
>>
>> Jim  VE7RF
>> _______________________________________________
>>
>>
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>



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