[Elecraft] KPA1500 in the IARU Contest Last weekend

[Jim Brown]

On 7/15/2020 1:36 PM, CUTTER DAVID wrote:
> It's all about size.  Bigger core helps, 

Dave,

No, it is NOT about size. It is about design of the entire antenna 
system, including the antenna, the feedline, and other parts needed to 
make the SYSTEM work. The principal characteristic of a common mode 
choke is the resistive component of its common mode impedance at the 
operating frequency(ies) where it will be used. Further, dissipation in 
the choke occurs at least as much in the WIRE that is wound around the 
core as in the core itself.

There is another fundamental error in many antenna systems that ONLY 
looks at matching to the transmitter at the transmitter, ignoring the 
match between the antenna and the transmission line, using high 
impedance, parallel wire line, and using a random center-fed or 
off-center fed horizontal wire on all bands. Yes, the transmitter can be 
made to supply power to the feedline, yes, it will get to the antenna, 
and yes, it will radiate. But it may not receive all that well due to 
common mode current on the line from noise sources in our own homes and 
those of our neighbors. THAT is the problem with using a decades-old 
design for a world where there was 20 dB less noise than most of us face 
today.

so a core that is OK for ssb
> and cw might be undersized for AM or some data modes. Just like linear 
> amplifiers.

So it is NOT the size of the core, it's the design of the antenna 
system. HFTA author and retired ARRL Antenna Book and Handbook editor 
Dean Straw, N6BV, published an excellent piece in QST 6-8 years ago 
called "Don't Blow Up Your Balun," in which he pointed out the 
differential mode dissipation in chokes, which can be extremely high if 
the choke is at a very high current point in a mismatched line. When he 
passed it to me for review, I noted that these losses were in addition 
to the common mode dissipation, and he revised the piece to reflect that.

  you can't
> label something poorly designed because it doesn't pass the BOK test.

BOK?

73, Jim K9YC