This is a "0.1" version -- it works, on my V2 within IRFZ24N finals.? ?Receive equalization can significantly assist hams with senory-neural high frequency hearing loss without having to purchase expensive add-on hardware.? ?Transmit boost of higher frequencies can make your signal more intelligible but must be approached somewhat more cautiously unless your radio has the GATE PROTECTION on the final mosfets.
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?For those who wish to try out the audio-equalized sBitx software that I've developed, a README.pdf can be found at:
and the zipped software at:
The executable by itself can be found at:
(the executable will probably use your existing data files at /home/pi/sbitx/data? ?
and will need to be made executable by
chmod +x sbitx? ? )
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README.TXT
Gordon Gibby KX4Z
March 15, 2024
Version 3.11 "science fair 2"
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Disclaimer: This is experimental software without any warranty. Use at your own risk. Particularly, before activating the transmitter high frequency pre-emphasis, be certain that your PA MOSFET gates are protected with zener or TVS diodes (as current V3 sBitx's are).
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This version was compiled for the earlier V2's that had IRFZ24N mosfets suitable for up to 40 watts output. In order to adjust the ALC for the lower power IRF510 of the V3, you may wish to reduce the critical ALC trip voltage from 130 down to about 99 for ALC limiting at 25 watts:
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Find these lines in the routine void read_power()
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if (rf_v_p2p > 130 /* && !in_calibration*/ ){
alc_level *= 130 / (1.0 * rf_v_p2p);
printf("ALC tripped, to %d percent\n", (int)(100 * alc_level));
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If you don't use the transmit pre-emphasis features, this will be of no concern to you.
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OVERVIEW
This software is an adjustment of the amazing software created by Ashhar Farhan VU2ESE, to allow for primitive efforts at mitigating sensory-neural high frequency hearing loss. Via typed commands, it is able to create additional emphasis of higher frequency portions of the received audio. For the transmitted audio, it is able to reduce wasted energy in the very low frequency portions of the audio spectrum, and to create a limited amount of additional emphasis in user-chosen higher frequencies of the transmitted audio. It is designed for use with voice transmissions, and in general should not be used with CW or DATA (digital) transmissions.
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CONTROL
In this version, the control is via typed commands preceded by "/" into the sBitx software. (These commands should also be possible via TELNET.)
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# |
Command |
Impact |
Example |
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1 |
/treblerxfreq |
Set the bottom end of the received audio frequencies to be emphasized |
/treblerxfreq 2000 will allow emphasis of frequencies >= 2000 Hz. |
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2 |
/treblerxboost |
Analog voltage multiplier that will be applied (in the frequency domain) to frequencies above the treblerxfreq |
/treblerxboost 8 will multiply signals above the treblerxfreq by 8. ? The dB gain can be calculated by gain = 20 log10(treblerxboost) ? For example: ? treblerxboost dB gain 2 6 dB 4 12 dB 6 15.6 dB 8 18 dB 10 20 dB 15 23.5 dB 20 25 dB ? |
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3 |
/treblerxcut |
DECREASES the received audio above the treblerxfreq. ? This is not intended for hearing deficit mitigation, but instead to simulate a hearing deficit. |
/treblerxcut 10 will create a simulated hearing deficit of 20 dB above treblerxfreq |
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4 |
/basscutfreq |
For transmitting, sets the frequency below which audio will be reduced by 20dB |
/basscutfreq 300 will cut out audio below 300 Hz |
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5 |
/trebletxfreq |
For transmitting, sets the frequency above which the audio can be amplified |
/trebletxfreq 2000 will make it possible to boost transmitted audio frequencies above 2000 Hz. The amount of boost is determined by /trebletxboost |
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6 |
/trebletxboost |
For transmitting, sets the amount of boost applied to transmitted audio spectrum above trebletxfreq |
/trebletxboost 3 will add 9.5 dB to the transmitted audio above /trebletxfreq. ? To mitigate uncontrolled increases in power, the software limits the product of the frequency range affected and the boost to approx 6000 Hz*boost. If this limit kicks in, a warning statement is printed on the console. In general, avoid setting a low trebletxfreq and a high amount of trebletxboost as this increases the entire transmitted audio and does so after the protecting transmit signal clipping in the time domain portion of the software. ? |
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DISCUSSION
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Because upper sideband and lower sideband appear in different portions of the FFT arrays, the code for the different sidebands is somewhat different. However, the overall technique can be recognized by the boost in the upper sideband reception in the rx_process()
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for (i = (int) (treblerxfreq/50); i < 61; i++){
__real__ r->fft_freq[i] = (__real__ r->fft_freq[i] * (float)treblerxboost) /(float)treblerxcut;
__imag__ r->fft_freq[i] = (__imag__ r->fft_freq[i] * (float)treblerxboost) /(float)treblerxcut;
}
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