[TowerTalk] CMC-230-5K

[Jim Thomson]

Date: Tue, 19 Apr 2016 10:06:02 -0700
From: Jim Brown <jim at audiosystemsgroup.com>
To: towertalk at 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