From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jonathan Lassoff Subject: Re: Soundmodem Not Decoding Real Packets Date: Fri, 1 Jul 2005 23:56:54 +0000 (UTC) Message-ID: References: <20050701184203.2013.qmail@radagast.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: Sender: linux-hams-owner@vger.kernel.org List-Id: Content-Type: text/plain; charset="us-ascii" To: linux-hams@vger.kernel.org Dave Platt radagast.org> writes: > In my experience, the user-mode soundmodem code does a very fine job of > decoding AX.25 packets, and it does so even if the radio is operated > "open squelch". In fact, in many areas it is a preferred practice for > packet nodes to be run with the receive squelch open - this allows > the TNC or other modem to synchronize very rapidly at the beginning > of each packet, without a long wait for the radio to detect carrier > energy and open its squelch. This, then, allows the nodes in the > area to use a shorter beginning-of-packet synchronization burst, and > increase the useful data throughput of the packet channel. > [...] > In your situation, I'd look at several things: > > - Audio levels, as you suggest. Take a look at the audio coming > out of your radio when it's receiving a clean packet - use > an oscilloscope. Check for clipping (a "flat-top" appearance) > in the waveform. If you see it, turn the radio's audio-output > control down until it goes away. > [...] > Also, check the quality of the signal from the sending station. It's > not unusual for TNCs or soundmodems or audio interfaces or radios to > be misadjusted, causing any of several problems: > [...] > My own guess is that that Thomas Sailer's soundmodem code is not > the cause of your problem. I've found it to be quite good indeed > at receiving packet. I did find out that the audio output from my radio was a bit high. I don't have an oscilloscope to play with, so I just used audacity to see the audio while recording it. I trimmed it down so that everything is there. I'm still having the same problem though. I have also been trying to decode packets off of APRS here in California on 144.390 to no avail. I also tried the decoding process with squelch open. I'm not really sure what is going on here. I also tried twiddling with the audio levels on my input channel in a mixer program. Any crafty diagnostic ideas? Jonathan (KG6THI)