[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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