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Hello all,
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I was "encouraged" to post this here.
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Back in the idyllic times of 2016, I noticed that Packet Test CD Track 2
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doesn't sound right, so I did some objective measuring. Track 2 is
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supposed to be the 'de-emphasized' version of Track 1. I extracted the
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same section of inter-packet noise on Track 1 and Track 2, and used
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Audacity to produce spectrum graphs of both. (if anyone doesn't
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understand this technique, email me off-list and I'll explain).
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Track 1 (discriminator output) response is what you'd expect for an NBFM
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channel, flat-ish out to a few kHz, then IF BW limited:
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https://drive.google.com/open?id=0B6J9M7BemghDMU9QdWJuQk9kNm8
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Track 2 (de-emphasized) has an unexpected -15dB notch at ~3100Hz,
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but don't left that distract from the real problem - it has a -12dB/octave
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response from 300Hz to the onset of the notch:
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<br>
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https://drive.google.com/open?id=0B6J9M7BemghDYlB1QVFZdWRUUms
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It's easy to miss that it's -12dB instead of -6dB if you don't look at the
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Y-axis scale. Track 2 doesn't represent any kind of real-world scenario,
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and should simply be deleted. In discussing this Stephen on the phone,
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we lamented that Track 2 was too well-established to correct it now.
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Stephen has documented well the use of Adobe Audition (IIRC) that
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just didn't do what it said it was doing.
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I don't use Track 2 and disregard any test results reported using Track 2,
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and would encourage others to do the same.
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For comparison sake, here's my own de-emphasized Track 1 produced
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using Audacity ( -6dB/octave 300Hz LPF, and a high-pass CTCSS cut
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filter because that's what real radios do):
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https://drive.google.com/open?id=0B6J9M7BemghDV0JKaTdmaHdRUWs
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<br>
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A real-world example, this is the response of a TM-D700A 1200-baud data
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output:
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https://drive.google.com/open?id=0B6J9M7BemghDNjM3dXFWS2VzRzA
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It has the CTCSS cut HPF at 400Hz.
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Here's another real-world example, a proper Batwing Motorola Maxtrac 300:
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https://drive.google.com/open?id=1Oks8g-tJABNML3Ky6cB8ZGe1B2DKMm5R
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<br>
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Forgive me for using a wider X-axis scale here, I took this measurement at a
<br>different time.
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<br>
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73,
<br>Dana K6JQ
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