Date: Thu, 21 Apr 2016 00:50:05 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] CMC-230-5K
On Wed,4/20/2016 6:29 AM, Jim Thomson wrote:
> ### 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.
You would save a lot if you did what I recommended about 8 years ago --
get together a group purchase and buy in quantity. I've been part of at
least half a dozen, two of which I've organized. Appendix One of my
tutorial lists Fair-Rite part numbers of some useful parts and lists
several good industrial vendors who sell in quantity at great discounts.
Remember - we need these parts not only for feedline chokes, but also to
kill the many RFI sources that most of us have in our homes, and that
are in the homes of our neighbors.
&&&& Points well taken. Trying to initiate a group buy in this town of 400
hams is
like pulling teeth, whether its type 31 cores or entire spools of heliax, or
anything else.
Too bad. I gave up trying a while back.
>
> ## 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've also organized several group purchases of Amphenol 83-1SPs, and
assorted audio connectors of the type we use around the shack. I'd be
very surprised if there are no distributors of Fair-Rite and Amphenol in
Canada.
&&& There are distributors in canada, with the usual...price is double or
triple the US price,
plus you must buy qty, pay shipping from VE3 land to the west coast, and wait
4-8 months,
then cross ur fingers. I rarely buy electronics up here, except for audio
connectors, like
Neutrik XLRs, of which I use quite a few, and local store has exactly what I
want.
I don’t buy car parts or gun stuff here in canada either, nor specialized
tools.
>
> ## 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.
Don't you recognize an advertising claim when you see one? I'm not
trying to sell you anything, I publish measured data on the chokes, AND
tell you exactly what's in them and how I measured them. Do you see ANY
of that in the magic boxes you're buying?
&&& No offence, but hes using the same HP gear + more, as you are using to
measure
them. If you doubt his Z / RS claims, then measure one for yourself. Im sure
that can easily
be arranged. Then you can verify his claims one way or another.
>
>
> ## 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.
It's a brand new product, Jim! And you really believe a mfr is going to
tell you about his failures?
&&&& Its sitting in several contest stations already. Nobody has blown one
up...yet.
I could take the cover off of one of em, and use the Fluke IR pointed in
there..and measure the
temp rise, and also surface temp of the torroids, with different power levels,
and on different freqs.
Or leave the cover on, and use a small probe to the inside, to measure internal
box temps. How hot
is too hot, I have no clue. 150F or less would be a guestimate.
> 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.
>
>
> ## 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.
WRONG!
&&& Did u try it ? IF you can achieve similar RS, (on one band), the choke
with more cores
has more thermal mass. But that’s difficult to achieve similar RS on a given
single band. There are
several different combos not listed on your Fig-41 graph. Like 6 turns on 7
cores. Or all the various
combos of 8-9-10 core stacks. If you use a binoc config, you can increase in
half turn increments,
which allows for finer tweaking. With a single stack, you have to use full
turn increments.
&&& Those 2.4 inch torroids are only 118 grams each. The big beads that slide
over 213-U are 55 grams
each. I suspect that the reason that the string of beads never heats up, is
because of the total greater mass
of the beads. 5 x torroids = 10.72 beads. Typ, if beads are used, 15-40
are used. The most I have seen used is 7’.
&&& each application is different. We can only estimate CM voltage, then go
from there. A lot of variables
in play. Like is the ant really balanced, or slightly off balance. Is the
shield of the coax bonded to the top of the tower?
What is the length of the coax from yagi feedpoint.....to top of tower? If
its .25 or .75 wavelength, things typ get better,
at least on one band, if a multiband yagi used, but then u have to factor in C
from braid to boom. Then factor in height
of tower, and how well tower is grounded at its base, etc.
&&& measuring core temps, when they are way out on a boom is no easy feat. Not
an issue on a 3 el 40m yagi, with
its DE next to the tower.
Jim VE7RF
> Cascaded CMCs is another technique.... or a combo of both techniques. Sky
> high Z + RS is another concept.
I published my take on this 6 years ago, and what I wrote about it was
not smoke and mirrors. I also have written about specific single core
chokes that failed at high power.
73, Jim K9YC
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