[CQ-Contest] Dual stubs

[Kenny K2KW]

>Please explain stagger tuning.
>Do you tune the other stub to CW and the other to SSB 
>part
>of the band, and in between a mid-band quarter wave 
>line to
>provide at least 25+dB over a broader range of 
>frequencies?

A single stub (RG213 type coax) will give you +/- 30 
dB attenuation on the targeted 2nd harmonic.  (notch 
depth and width vary based on frequency).  If you use 
smaller coax like RG-8X, the notch may only reach 25 
dB attenuation on the 2nd harmonic.

If you use a dual stub, cut one stub for the SSB 
portion of the 2nd harmonic band, and the 2nd stub for 
the CW portion of the 2nd harmonic band.  Then 
separate the stubs by 1/4 wavelenght on the 2nd 
harmonic you are trying to notch (center of band is 
OK, and not critical).

So, if your 40m station's 2nd harmonic is causing 
problems to your 20m station, here's an example of the 
stub for the back of the 40m TX to minimize the 20m 
harmonic:  (I didn't keep notes on the exact 
frequencies I cut them to...)

Cut first 1/4 wave stub for 14050
Cut spacing coax to 14150
Cut 2nd 1/4 stub for 14225

If you use RG213 type coax for the stubs, your 
resulting attenuation will be about 50-60 dB across 
most of 20m.  If you have access to a network 
analyzer, you can experiment on the best frequencies 
for the 1/4 stubs.  The spacing coax length is not 
very sensitive to the band segment.  

I hope that helps.

Kenny K2KW