D L 4 X A V - jo 43 xn - h a m b u r g

this is the filter.
both stubs are 1/4 lambda * V. the line between the stubs is 1/4 lambda * V. if the stubs are open at the bottom one will have a sharp notch filter for an unwanted frequency (band). if one connect the inner lead and the shield at the bottom of each stub, its a band pass filter for a wide frequency band.

a notch filter of this design cuts also Freq.*3, F*5, F*7 ...
(3, 5 , 7 ...* 1/4 lambda).
it has a bandpass characteristic for F*2, F*4, F*6 ...
because the stubs come in 1/2, 1, 1 1/2, ... lambda resonance.

a bandpass filter (closed at the bottom) let also pass F*3, F*5 F*7 ... and has notch characteristic for F*2, F*4, F*6 ... because the stubs come in 1/2, 1, 1 1/2, ... lambda resonance.

use good coax for your feed line. make the stubs with the same cable type !
you must know the velosety factor " V " of the cable. RG213, as shown here, has V = 0.66 . that means that the stubs are only 66% of 1/4 lambda. other coax cables have different velosety factors.

step 1

step 2

step 3

step 4

step 5

step 6

there are several posebilitys to use this filters.

i use this as a notch filter at my 2m sat transmitter to cut off the 3rd harmonic spur more than 40 dB.
so i have full sensivety with my 70cm sat receivers preamp

one single bandpass stub is good to cut static electricity to ground ( if its propper grounded ). that saves the radio frontend and pa.

how to feed a preamp / relay with a coax bandpass filter

its also possible to feed a preamp via the coax line
the capacitors must handle the transmitter power.

you can NOT use a 2m notch filter stub at the 70cm radio,
it also cuts the 3rd harmonic ( 145 MHz * 3 = 435 MHz ).
most of the signal will be cut off. the receiver will survive but the transmitter will see realy BAD swr.

Notch Freq.	Notch ATT	low Freq. -3 dB	low Freq -6 dB	hi Freq. -6 dB	hi Freq -3 dB
28.5 MHz	-28.3 dB	20.7 MHz	23.8 MHz	33.1 MHz	36.8 MHz
29.5 MHz	-28.3 dB	21.15 MHz	24.4 MHz	34.5 MHz	38.3 MHz
51 MHz	-31 dB	34.8 MHz	42.15 MHz	61.45 MHz	69.75 MHz
88 MHz	-31.4 dB	61.6 MHz	72.0 MHz	103.2 MHz	114.4 MHz
108 MHz	-32.3 dB	74.0 MHz	89.0 MHz	126.2 MHz	140.4 MHz
145 MHz	-32.8 dB	94.3 MHz	118.6 MHz	172.2 MHz	192.7 MHz
165 MHz	-33.4 dB	108 MHz	138.1 MHz	196.0 MHz	223.2 MHz
300 MHz	-32.2 dB	209.4 MHz	246.8 MHz	357.8 MHz	420 MHz
435 MHz	-29.4 dB	272.6 MHz	333.4 MHz	554.2 MHz	607.4 MHz

how to make a coax notch or bandpass filter

COAX NOTCH FILTER - SINGLE STUB - RG 58

COAX BANDPASSFILTER ????