There are 1, 2, or 3 stubs as described below between the amp and the antenna. I like to keep them as close to the amp as possible, usually just a ‘T’ connector on the amp output or at the SWR meter.
The lengths below are for solid dielectric coax with a velocity factor of .66. I use RG-8, but you could also use RG-213 or RG-11. If you want to use a foam coax most of them have a velocity factor of .80. On the high bands (10, 15, 20) I use CATV hardline that has a velocity factor of between .81 and .83. The basic formula for a shorted 1/4 wave stub is 246*V/f. Where V is the velocity factor of the cable and f is the frequency in MHz.
Band by Band these are K2TR’s stub plans. The copy of the article I have I think was from an old YCCC Scuttlebutt.
10 Meters. 2 Stubs
11′ 6″ OPEN nulls 20m
23′ OPEN nulls 40m and 15m
15 Meters. 1 stub
23′ SHORTED nulls 10m and 20m
20 Meters. 2 stubs
23′ OPEN nulls 40m and 15m
11’6″ SHORTED nulls 10m
40 Meters. 3 stubs
23′ SHORTED nulls 20m and 10m
15’3″ SHORTED nulls 15m
7’8″ OPEN compensates for reactance from 15’3″ stub. This pair of stubs works out to a 1/4 wave on 40m that is tapped at a point that results in a 1/2 shorted stub on 15m.
80 Meters. 1 stub
46′ SHORTED nulls 40m, 20m, 15m, 10m
160 Meters. 1 stub
92′ SHORTED nulls 80m, 40m, 20m, 15m, 10m
For more detailed analysis of stubs and pairs of stubs see my other notes:
Single Coax Stub Analysis
Coax Stub Pair Analysis
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Info from K1TTT
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