K1TTT Technical Reference


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K2TR Coax Stub Filters

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

15 Meters. 1 stub

20 Meters. 2 stubs

40 Meters. 3 stubs

80 Meters. 1 stub

160 Meters. 1 stub

For more detailed analysis of stubs and pairs of stubs see my other notes:



David Robbins, K1TTT K1TTT@arrl.net