Changes between Version 12 and Version 13 of HardwarePage


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Timestamp:
12/02/09 03:34:32 (8 years ago)
Author:
max
Comment:

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  • HardwarePage

    v12 v13  
    3333 
    3434For soundcard use, generally the signal must be attenuated (volume lowered) before transmission,  accomplished using the -f flag.  Some transmitters also require a polarity reversal (-v).  For test purposes, the input signal can be replayed over and over (-r).  Example: 
     35{{{ 
    3536  ./audio_p25_tx.py -v -r -i base.packed.dat -f 0.04 
     37}}} 
     38The sound card's transmit level (volume control setting) also affects this, and is usually controlled by a slider in your mixer app.  The mixer volume setting and the -f flag (above) combine to set the overall the signal transmit level, which must be set within tight limits to insure proper reception, and carefully checked to insure standards compliance and proper (and legal) RF signal emission.  The error rate is somewhat improved when the -f value and the mixer volume setting are properly set; these two adjustments interact, and are inversely proportional. 
    3639 
    37 The sound card's transmit level (volume control setting) also affects this, and is usually controlled by a slider in your mixer app.  The mixer volume setting and the -f flag (above) combine to set the overall the signal transmit level, which must be set within tight limits to insure proper reception, and carefully checked to insure standards compliance and proper (and legal) RF signal emission.  The error rate is somewhat improved when the -f value and the mixer volume setting are properly set; these two adjustments interact, and are inversely proportional. 
     40A newer TX program is also available. 
     41{{{ 
     42./op25_audio_tx.py -n 1 -G 0.8 
     43}}} 
     44It takes audio in at 8000, encodes it and outputs an audio signal at 48000. YMMV, but it requires either a full duplex-capable sound card without any bleedthrough, or two separate sound cards with input to one and output from the second.  This example shows one channel with mono operation at the sound card.  To use two independent audio channels, specify the {{{-n 2}}} option. 
     45 
     46C4FM audio levels must be carefully set. Here's one method: 
     47 * Start the audio_p25_rx. py program and tune to a known-good P25 station. Select the "Datascope" tab. 
     48 * Calibrate the audio level as shown on the Hardware page (-3/-1/+1/+3) 
     49 * With the proper audio gain setting now known and calibrated, tune the receiver to the test TX station. 
     50 * *Without adjusting* the RX gain, now adjust 
     51 * a) TX gain [-G option] 
     52 * b) the "speaker volume" gain slider(s) in your audio mixer app which governs the output soundcard channel(s) 
     53 * c) the "FM deviation pot" in the radio transmitter (if applicable). 
     54You should adjust these gains to obtain precisely the same C4FM deviation as shown in the RX datascope for the known-good station. 
     55 
     56The output gain (-G) option should probably not be set much higher than 1.0, but could be set lower. The -G interacts with the speaker volume slider in the mixer and they're inversely proportional. There is probably one or a range of "best" settings. 
     57 
     58Also remember- 
     59 * A professional [C4]FM deviation meter may be used to set the proper deviation value. 
     60 * The transmitter output should be verified for proper spectral purity using a spectrum analyzer. 
    3861 
    3962=== Sound Card Sampling ===