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.
Normally you only need the cores. Just run the feed line through the
required number of cores, the required number of turns and add the coax
connector. That's it. I stocked up on cores and that's normally all I need
Normally there is no need for a box, Teflon coax with double silver
braid, and those special connectors. Actually, they are just SO239s
with a tapered shield added.
Rarely is there a need for anything other than a chassis mount SO239 at
HF, if you must use a box. The impedance bump is so slight on HF that
the power to the antenna will likely never notice, so you really don't
need the fancy connectors. It's like the power loss we see for UHF
connectors. Even when you add a bunch the loss on HF is still small.
I do have the a box of cores and a coil of the expensive coax, but have
not found much need for that expensive coax,
I have used it to redo the matching networks on commercial antennas
because of space limitations.
73
Roger (K8RI)
On 4/20/2016 Wednesday 9:29 AM, Jim Thomson wrote:
Date: Tue, 19 Apr 2016 10:06:02 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] CMC-230-5K
There's something I don't understand here. In 2007, I published the
research upon which all of this is built, with measured data for a broad
range of chokes for the ham bands, and with full instructions for buying
the cores at very good prices, and a "cookbook" for the various ham
bands. Why in hell would you want to pay someone 3x the cost of doing it
yourself, when all you have to do to do it yourself is wind turns of
coax through ferrite cores?
AND -- l would not trust any published power ratings for ANY chokes
without understanding the common mode voltage that they will see in any
given installation. To do that, you've got to put them in an NEC model
that approximates YOUR installation. Simply putting one of these chokes
in a sealed enclosure greatly reduces its power handling because it
greatly reduces air flow around the choke.
73, Jim K9YC
### By the time I buy 4 x torroids from one vendor PLUS shipping, then a pair
of
those special one off SO-239s he uses, no Z bumps, silver /teflon
/gold...PLUS shipping,
then double shielded teflon coax, with silver braids + silver center
conductor...PLUS shipping,
then a UV /water proof enclosure... PLUS shipping, then 4 of the one off nylon
tie downs, that
are machine screwed down...PLUS shipping....and assuming I have the SS hardware
on hand
plus the required gear to silver solder and terminate the ends, I decided I
will save next to nothing.
In fact, I would save nothing.
## sometimes mucking about, dealing with in this case, at least FIVE
different vendors, and shipping
on all FIVE, assuming no screw ups, and hoping it all arrives intact, I spend
more time rounding this stuff
up vs building it. Shipping from USA to canada is not cheap.
## I don’t see any plug and play cook book designs by anyone, that covers
the 2-30 mhz
spectrum, with a sky high 8-12k Z, that fits into a very compact 6 long x
4.375 wide x 2 tall box,
that weighs exactly 1.8 lbs.
## he offered FREE shipping to Canada on a completed, plug and play unit. It
was here real fast.
I wish I had the megabuck worth of test gear to do my own experimentation on
CMC chokes.
Nobody has managed to overheat a CMC-230-5k....yet. You will literally melt
the traps in any
Mosely pro-96 yagi long b4 the cmc heats up. Ditto with the xfmr inside the
stepir yagi.
## I hb all sorts of stuff, but sometimes I don’t have the patience, nor time
for some items, and
not right now with 6 other projects on the go. I was going to HB the henry
radio 10 kw CCS LP filter
a few years back. The 8 x HT-57 NPO caps alone are $40 each, so $320 worth
of caps, then the huge
anodized box, and a pair of 7-16 dins, plus the huge 1/4 inch OD silver
plated coils inside. They were
selling it for $295.00 No way could I HB it for that. Plus I didn’t have the
test gear to verify the finished
product.
## Why do folks pay $10K for a 1.5 kw linear amp....when they could hb a 12
kw amp for $7k ?
## To increase power handling capability of a CMC, there is a few ways to do
it, and that depends on
how much spectrum it has to cover. More cores + less turns is one technique.
Cascaded CMCs is
another technique.... or a combo of both techniques. Sky high Z + RS is
another concept.
## That small teflon coax is slick, he manages to easily get 10 turns onto the
torroids,
and 6 turns on the 2nd stack. Most you can get with 213-U or 393 is just 7
turns..and
you cant wind em tight either.
Jim VE7RF
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73
Roger (K8RI)
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