[CQ-Contest] Stubs - they are not mysterious

[Jim Brown]

On 1/24/2020 7:28 AM, Jukka Klemola wrote:
> K3NA dual stub design is not placement sensitive 

WRONG! ANY stub design intended to suppress harmonics IS sensitive to 
placement if the antenna with which it is used is NOT resonant at the 
harmonic.
The use of double stubs insures that at least one of the stubs will be 
effective, but the ADDITIONAL effectiveness of the second stub is 
entirely dependent on its location with respect to the antenna. Putting 
some numbers to it, double stubs in the "wrong place" with respect to 
the antenna provide 25-30 dB suppression; in the "right place" they 
provide an additional 25-30 dB of suppression.

Placement of stubs with respect to the antenna is NOT sensitive ONLY if 
the antenna is resonant at the harmonic.

> and supports both Pi and
> PiL output circuit amplifiers.

ANY stub system is sensitive to placement with respect to the power amp.

My analysis of this was peer reviewed at the time of publication in NCJ 
several years ago. Those who don't have access to it can download it 
from my website. k9yc.com/publish.htm  There is both the text of the NCJ 
piece and a slide deck for talks I've done about it.

My work included measurements in my lab of stub effectiveness as 
placement between the power amp and the stub nearest to it was varied, 
and was done separately with power amps having both an inductor as the 
output element (Pi-L, a ten Tec Titan 425) and a capacitor output 
(Elecraft KPA500). The difference between "right" and "wrong" was on the 
order of 15-18 dB.

On 1/24/2020 8:45 AM, Jim George wrote:
 > you can buy professional caliber stubs from W2VJN (Top Ten Devices).

This discussion has NOTHING to do with construction of the stubs, which 
is as simple as choosing high quality, low loss coax, cutting them to 
length, tweaking that length with instrumentation as simple as an 
MFJ-259, and using high quality connectors, properly installed.

A year or so prior to my piece in NCJ, George published a piece in NCJ 
addressing stub placement, noting that stub systems he'd built were not 
effective. It got halfway there. My analysis was more thorough, and 
looked separately at location with respect to both the power amp and the 
antenna.

73, Jim K9YC