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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