Posted by
Bill Coleman-2 on
May 08, 2005; 3:25am
URL: http://elecraft.85.s1.nabble.com/Setting-up-Filters-with-a-modern-Macintosh-tp378053.html
I know many of you out there set up your filters using Spectrogram on a
Windows PC, but some of us only have (or simply prefer to use)
Macintosh computers.
I recently had to completely reconfigure my filters, as I added the
RTTY mode. In order to accommodate my chosen center frequency of 1500
Hz for AFSK RTTY, I had to modify the BFO to get sufficient range. I
had already added 47 and 100 pf caps across C174 and C173, respectively
when I made the A->B mods and the BFO stability mod. I changed these to
56 and 120 pf, but this did not move the BFO frequencies much at all.
Then I added a 3 pf cap from X3/X4 junction to ground. This moved the
lower frequency about 800 Hz without affecting the upper frequency.
Of course, this meant my filter settings were now incorrect. I had
previously used an ancient MacOS 9 computer and MacCRO to set up my
filters. I recently went searching for software that could be used from
MacOS X. I ended up using two different programs.
First, I used CocoaModem (
http://homepage.mac.com/chen) by Kok Chen.
This is an excellent piece of software -- a RTTY and PSK modem
implementation. Chen started it a bit over a year ago, and has made
great progress. CocoaModem was the reason I was adding the RTTY mode.
CocoaModem has a number of features, including a spectrum analyzer in
the RTTY Monitor window, and also in the Config window. The spectrum
analyzer doesn't have any averaging -- so it is a bit difficult to
determine the final shape of the filter. It's certainly good enough to
adjust the filters. By entering in mark and space frequencies on the
main RTTY window, you can place markers in the spectrum analyzer
window. For adjusting OP1, I used 400 and 2400 Hz. This worked out well
for my "1.9" kHz filter. If you only need one marker, just enter the
same frequency for both mark and space.
To help line up the filters between modes (CW and CW-R, LSB and USB,
RTTY and RTTY-R), I used a second piece of software.
For this, I used iSpectrum
(
http://www.dogparksoftware.com/iSpectrum.html) by Dog Park Software.
While it isn't as adjustable as Spectrogram, it features limited
averaging, a marker, and a waterfall.
After I had done the initial alignment with CocoaModem, I used
iSpectrum to check the symmetry between the filters in opposite modes.
What I did was to let the audio play for about 10 seconds, then switch
modes for another 10 seconds. I could easily spot discrepancies in the
waterfall view. A few small adjustments to the BFO frequencies and now
the complementary modes offer little, if any, change in noise "color"
when you switch between them (using the CW REV key).
In the end, this was a much easier filter alignment than I had done
previously using MacCRO. I recommend this software to anyone trying to
align the K2 filters with a Mac.
Bill Coleman, AA4LR, PP-ASEL Mail:
[hidden email]
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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