On Fri,4/22/2016 8:40 AM, Jim Thomson wrote:
### 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....
Are you saying that the coax between the switch and the antennas is ZERO
length? Somehow I doubt that. :) It has some electrical length, and
that length between the antenna and the choke is in the common mode
circuit -- that is, it is part of the antenna.
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.
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
I have no "venom," only skepticism based on what I have learned through
lots of research and experience. :) Also, my "Cookbook" has been
published for 8 years now, with millions of downloads, and, so far, no
one has emailed me that they have blown up any of my recommended
chokes. I've blown up only two -- one as the end insulator on that 40M
dipole that was an intentional test of power handling, and one of the
single-core bifilar chokes under high duty cycle use.
&& 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.
Again, it depends entirely on the common mode circuit into which they
are connected.
&& 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.
Go ahead with your experiment. But don't assume that it applies to all
conditions.
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 suspect that some of those stations, including yours, may not have all
their chassis bonded together with short, fat copper, and to all ground
electrodes in your home, including power, CATV, telco, etc. This
includes computer, rig, accessories, etc.
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.
The only "bead type" choke that is effective on the HF bands is one that
uses the #73 beads that W2DU selected for his original design, the
largest #73 beads fit only small diameter coax, and you would need 200
of them.
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.
Grounding is more than a connection to earth -- it must be combined with
proper bonding. I've shown this in http://k9yc.com/GroundingAndAudio.pdf
73, Jim K9YC
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