Date: Thu, 21 Apr 2016 09:36:53 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] CMC-230-5K
On Thu,4/21/2016 6:42 AM, Jim Thomson wrote:
> Date: Thu, 21 Apr 2016 03:28:00 -0400
> From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] CMC-230-5K
>
> I don't have any antennas that cover 3-30 MHz so why would I need a
> choke that covers that range? A quickly wound choke for the specific
> antenna is more than sufficient. Only if you want a choke for all the
> HF antennas you "might" put up would that bandwidth be justified. I do
> have two chokes in series on 75/80.
>
> ### I only have ONE feedline going up the tower. The remote switch box is
> at the
> top of the tower. For this application, for experimental purposes, I want to
> be able
> to quickly move the CMC from one ant to another to another, so it has to
> cover at least from
> 160-15m.
Your plan is wrong. A choke is most effective at the feedpoint, not some
fraction of a wavelength from the feedpoint, as it would be at a switch.
&&&& U misunderstood me. The CMC-230-5k will be at the feedpoint....
since in this case, I can get to the feedpoint of both the 3 el 40m yagi..and
also the
80m rotary dipole, plus some other ants. I want to try it with one, then
both CMCs
in series.
> I also want to evaluate the effects of cascading both boxes in series, on
> each of the
> 160-15m ants. For this series of tests, it will only see a max of 1200w pep
> out on ssb..and flat
> swr across each band. So Im not concerned about heating.
Again, don't believe advertising claims about power handling, especially
from a new vendor with little experience in the application of his product.
&&& say what ? Folks are not overheating them with a OM-3500, nor
anything that alpha, emtron or any other brand of amp can throw at it.
Throw your venom at Mosley, Hy-gain /mfj, w2au baluns, BN-86, and everything
else out there. Ive literally melted all of em, and set 2 of em on fire. I
took one look
at the internal xfmr inside the stepir, and was not about to get into another
gong show.
&& In the case of your 40m vertical dipole, using
a CMC as the bottom insulator, that is a unique, one off situation, that
will stress any CMC. Didn’t yours overheat, burn up, then get replaced with
2 of em in series ? 5K was not enough, so 10K RS was required. Again that
is an extreme one off case. Cut the guy some slack here. If a bunch of
contesters
in Eu, all running > limit cant blow it up, I’d say he has a sound product.
&& The way you deal with heat is...don’t generate as much of it in the 1st
place.
His CMC 230-5k is 8.5k to 12k. How much do you actually need? hes already
way more than your 5 k goal. If it runs too warm, I will put the 2nd one in
series with it,
which is part of the overall experiment.
> I also want to try one then both of em
> on the output of the 1200 w amps.
WHY? There's no common mode at the output of an amp or in your shack
unless you haven't grounded the coax shield at the entrance. You have
done that for lightning protection, right?
&&& coax shield is bonded to SPG plate, just inside basement. SPG consist
of a large piece of 1/4 inch thick AL plate on the inside basement wall....
which is
bonded via 2 ga insulated wire to an 8 ft grnd rod, just outside basement.
My 200A panel is now also bonded to the same SPG..... since my incoming 3/4 inch
Copper water pipe has now been replaced with 1 inch PEX plastic pipe. So I
lost my
copper water line ground.
&&& 2 ga bare cu run a few inches below the dirt for aprx 40 ft, along side
the house...to the base of the
tower, where 3 x more grnd rods are located. 1 rod per leg, and all
cadwelded at all 4 x rods.
&& station is 20-25 ft away from SPG in next room. Dunno if the single 8 ft
rod outside basement
constitutes a good RF grnd, probably not. Good enough for lightning. RFI
vanishes when a CMC is placed
directly on the output of the amp. I know several folks with same or similar
setups, and a CMC on the linear
solved all the issues. I know others who have well grnded towers... that are
mere feet away from their homes, same
deal, CMC on back of amp solved the rfi. The filters they were using on the
DSL etc, were not having any effect.
After the CMC installed on the amp, problems vanished...and dsl filters
removed...along with filters on a lot
of other gear in the home. This bead type cmc on back of amp has now
been used on 160-6m. If my 4 grnd rods and buried 2 ga cu is not good
enough, tough luck. I’m not about to
improve it any time soon. I want to swap the bead cmc for the
cmc-230-5k..then test it.
later... Jim VE7RF
73, Jim K9YC
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