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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73
Roger (K8RI)
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