[RTTY] bandpass filters

[Al Kozakiewicz]

Since the highest power transceivers are 200 watts, why would you need filters rated for 1500? There is no technical reason I can think of why they can't go between the xcvr and amp.

Al
AB2ZY

-----Original Message-----
From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of Bill Turner
Sent: Saturday, March 19, 2016 11:15 PM
To: RTTY Reflector
Subject: Re: [RTTY] bandpass filters

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
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