[TowerTalk] CMC-230-5K

[Jim Brown]

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