When I operated SO2R years ago I had bandswitching filters ahead of
the amps and homemade stubs after. I could operate anywhere except
within 15-20 Khz of the second harmonics.
50 ohm coax is not required for the stubs - I was using free 75.
Jerry W4UK
At 12:21 AM 3/20/2016, Jim W7RY wrote:
George Cutsogeorge, W2VJN's, book is really great for using tuned
stubs (coax cable) for low notching out other bands for SO2R. I use
on on my 80 meter antenna to keep from getting into 40 meters.
Something I cant do with a Dunstar filter between the exciter and amplifier.
73
Jim W7RY
-----Original Message----- From: Bill Turner
Sent: Saturday, March 19, 2016 8:15 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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