[TowerTalk] CMC-230-5K

Thu Apr 21 03:28:00 EDT 2016

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 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
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk

-- 

73

Roger (K8RI)

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus