[RTTY] bandpass filters

[Bill Turner]

Bandpass filters at the 1500 watt level are quite expensive - around
$400 for each band. Do the math.  

If you want to save some money, you can build your own.  Accompanying
each ARRL Handbook is a CD which contains design software for high
pass and low pass filters. By choosing the cutoff frequencies
carefully and putting them in series, you could save a considerable
amount of money. 

This particular software is especially useful because it uses standard
value components. In fact that is the name of the program: SVC Filter
Designer.  Here's a hint: Each filter segment can be looked at as a
parallel resonant circuit, i.e. a coil paralleled by two capacitors in
series. You can use a grid dip meter to carefully adjust the coil to
resonate at the frequency given by the standard equations for
resonance. Do each filter segment separately, then connect them
together. You can check the final result by sweeping it with an SWR
meter while terminated into a dummy load or a real antenna. 

It is also available at this website:  http://tonnesoftware.com/
along with other filter design software and there may be others as
well. It is well worth browsing around. 

73, Bill W6WRT