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Zelscope is a Windows software that converts your PC into a dual-trace storage oscilloscope and spectrum analyzer. It uses your computer's sound card as analog-to-digital converter, presenting a real-time waveform or spectrum of the signal - which can be music, speech, or output from an electronic circuit.

Voice Shaper is a freeware windows speech pre-processor for SSB transceivers. It receives the voice signal from the microphone connected to the soundcard, and sends the processed audio back to the soundcard in real time by Alex Shovkoplyas, VE3NEA

The FreeDV project offers a suite of digital voice modes for HF radio, with its flagship mode being the Radio Autoencoder (RADE). This free GUI application for Windows, Linux, and macOS allows any SSB radio to be used for high-quality digital voice communications. The technology, including the Codec 2 speech codec, is 100% open source under the GNU Lesser Public License v2.1 and two-clause BSD license, fostering experimentation and innovation in amateur radio digital voice. Development is managed by a six-person Project Leadership Team and funded by an ARDC grant, with Software Freedom Conservancy as the financial sponsor. Controlled testing indicates that RADE technology performs comparably to SSB on both high and low SNR channels. The resource lists various FreeDV nets and activities, including a worldwide activity day, and specific nets in Argentina (7.045 MHz LSB), Australia (7.197 MHz LSB), the UK (3.640 MHz LSB, 5.3685 MHz USB), and the USA (7.181.5 MHz LSB, 7.177 MHz LSB). Support resources include a mailing list, Discord channels, and a Zoom channel. Documentation such as the FreeDV GUI User Manual and the SM1000 Manual are provided, alongside access to source code for RADE, FreeDV GUI, and Codec 2.

Presents Telstar Electronics as a manufacturer specializing in amateur radio accessories, detailing its history since 1995 and highlighting key product offerings. The resource specifically mentions the _VoiceMax Transceiver Speech Processor_, designed to enhance audio fidelity and punch for SSB transmissions, and the _SkyWaveDX350_, indicating a focus on signal processing and reception improvement for DX operations. The company's product categories span ham radio accessories, microphones, and RF amplifiers, catering to various aspects of a station setup. The site implies a direct-to-consumer model for these specialized components, providing technical solutions for Icom, Yaesu, and Kenwood transceivers, and supporting homebrew enthusiasts with components and technical references.

An open source software decode various xMBE based modes. It support decoding QPSK, C4FM modes such as P25 Phase 2 (TDMA), MotoTRBO, NexEDGE, ProVoice and others more.

When one operates at low power on SSB, speech processing becomes almost essential to get through the QRM. The circuit is a low cost speech processor that will perform well with a minimum of construction effort.

RF Speech Clipper into Yaesu's MH-31 Standard Microphone

Yaesu FT-817 and MFJ-616 speech intelligibility enhancer product review & short takes columns from QST Magazine

Codec2, an open-source speech codec, targets low bit rate voice communication, specifically designed for digital radio applications operating within constrained bandwidths. The project focuses on achieving intelligible speech quality at data rates around 2400 bits per second, a critical parameter for efficient spectrum utilization in amateur radio. Its development addresses the need for robust voice transmission over channels where higher bit rate codecs would be impractical or inefficient. The resource details the technical specifications and implementation aspects of Codec2, including its underlying algorithms and performance characteristics. It provides insights into how the codec processes speech to achieve its low bit rate, outlining the various coding schemes and their impact on voice fidelity and error resilience. The information presented allows radio amateurs and developers to understand the codec's operational principles and its suitability for integration into custom digital communication systems. Applications for Codec2 extend to digital voice modes on HF and VHF bands, enabling more users to share limited spectrum resources. The project's open-source nature facilitates community contributions and widespread adoption, fostering innovation in digital amateur radio. It represents a significant effort to provide a freely available, high-performance speech coding solution for the amateur radio community.

Small and inexpensive homebrew HF radio 5W Output, CW SSB AM FM, DSP, Speech Processor, Sprectrum Scope, Watefall Display. mcHF is a small, home-brewed amateur radio project. Firmware is released as open source.

Codec2 is an open source low bit rate speech codec designed for communications quality speech at around 2400 bit/s. Applications include low bandwidth HF/VHF digital radio.

The Elecraft K2 transceiver requires specific modifications for optimal soundcard digital mode operation, particularly for PSK31. The original article, circa 2001, details initial challenges with manual PTT and speech compression settings. A key modification involves adding headphone audio and a compression disable signal to the K2's microphone jack, utilizing pins 4 and 5. The **COMP0** signal, active low, is shorted to ground via a non-inverting open collector switch circuit, comprising two resistors and two transistors, mounted on the SSB board near U3. This circuit provides effective control of an analog signal line with good noise immunity. The switchbox itself repurposes a computer COM port switch, using only two of its original connectors and four of the nine poles. It integrates a microphone preamplifier, a PTT circuit built with 'flying leads' construction, and RCA jacks for soundcard connections. A trimpot adjusts the audio drive to the K2. The central DB9 connector links to the K2's mic connector via a shielded RS232 serial cable, ensuring proper grounding and signal routing. An external footswitch PTT jack is also included. Further enhancements include a **noise-canceling microphone** preamp based on a QST December 2000 article, adapted for Heil mic elements. This preamp, built with pseudo-Manhattan style construction, provides a gain of approximately 2 by changing emitter resistors (R9 and R16) from 680 ohms to 330 ohms. A 10-ohm series resistor and 47 µF capacitor on the +5V supply mitigate noise spikes.

MUlti mode digital signal decoder software capable or C4FM D-Star decoding, a guide to compile and install DSD

DSP for FT-817, the Antenna BOSS Motorized Antenna Controller for Yaesu Radios, Speech Compressor and more

Noise eliminating products. Remove unwanted background noise and interference leaving only the speech. Clear communications, listen stress free. Dsp noise cancellation solutions.

Codec2 is an open source low bit rate speech codec designed for communications quality speech at 2400 bit/s and below. Applications include low bandwidth HF/VHF digital radio and VOIP trunking.

For over 20 years, bhi Ltd has specialized in digital signal processing (DSP) technology to mitigate noise and interference across various radio channels. Their product line, including the _ParaPro EQ20 Audio DSP_ units, focuses on enhancing receive audio quality, even for operators without significant noise issues, by offering precise parametric equalization to suit individual hearing preferences. The core offerings are noise-cancelling speakers and in-line modules, specifically engineered for amateur radio applications, but also adapted for commercial, PMR, and marine radio systems. The company provides audio demonstrations, such as a 20m SSB example and a 14MHz band filter comparison, allowing users to hear the effectiveness of their DSP units against common QRM sources like plasma TV interference or diesel engine noise. Located in Burgess Hill, West Sussex, UK, bhi Ltd emphasizes clear voice communications, aiming to remove unwanted noise and leave only intelligible speech.

This app will give you a 16 tone DTMF keypad and the ability to generate custom DTMF sequences, and set the duration and tone to silence ratio. Includes the characters 1234567890*# and the menu tones ABCD. You may enter a custom sequence via the keypad, soft keyboard, or speech if your device already has speech-to-text capability. This is basically a touch tone telephone keypad, which may be of interest to amateur ham radio repeater operators

Sonogram is a highly flexible audio spectrum analyzer for the analysis of sound, music and speech signals in the frequency-domain using different algorithms.

The **HamRacer** voice keyer, a Windows-based application, is showcased in this video, illustrating its utility for radio amateurs participating in SSB contests. It functions as a synthesized PC-based voice keyer, specifically designed for HF and VHF SSB contest operations, allowing operators to transmit pre-recorded or text-to-speech generated messages during rapid-fire exchanges. The demonstration includes actual recorded QSO examples from a contest, featuring contacts with stations such as SP6OWA, S57O, OK1IEI, 9A1DL, OE1PAB, OK1GTH, and 9A1E. These examples highlight the software's practical application in a live contesting environment, demonstrating how it facilitates contest participation for operators who might otherwise face challenges with traditional voice keying. The resource provides a direct look at the software in action, emphasizing its role in promoting inclusivity within the amateur radio contesting community. It details the use of Windows SAPI for speech synthesis, a core component of HamRacer's functionality.

The IC703 features a built-in DSP filter and auto ATU as well as speech processing an a CW keyer with 3 message memories. It is an ideal all-in-one ham station for QRPers.

How to improve performance of your audio using a home made speech processor. In this article the author describes how to make your own speech processor providing a PCB foil pattern and with a 60mm x 60mm board.

This transmitter covers the 160, 80, 40 and 20 metre bands and provides both SSB and properly generated CW. The CW side of this transmitter is not compromised and produces excellent CW. On SSB the audio has been tailored to provide a rising response to 3 KHz, with a sharp drop above that frequency. There is RF speech clipping to both provide more "punch" and to limit the peak output.

This construction project is for anyone wanting to give this popular little radio a voice of its own. This Speech synthesiser reads out the current frequency, mode and menu settings whenever they are changed via the front-panel controls

Designed for the FT-817, this audio speech compressor, centered on the Analog Devices SSM2165, offers a 40 dB compression range, enhancing signal power. Built externally with the SMD version to preserve warranty, the circuit interfaces smoothly with electret microphones. Testing shows a 6 dB average power increase. Adaptable to rigs with electret microphones, it maintains unity gain and 40 dB compression.

The 8m ISM band, a unique frequency range between 10m and 6m, holds potential for amateur radio enthusiasts, yet it remains largely unallocated. This spectrum offers fertile ground for research and self-training. The author's experience with low-power transmissions and WSPR testing highlights the band's capabilities and the need for a narrow, speech-free amateur allocation to encourage experimentation. Discover the world of 8m ISM radio exploration and its future possibilities.

Many low-power SSB rigs and kits lack dedicated speech processor circuitry, although most modern HF rigs include it. Speech processing is crucial for low-power SSB to overcome QRM. This simple, low-cost circuit integrates a microphone element and can be housed in a defunct desk mike. It features a feedback amplifier, audio preamplifier, and adjustable speech compression control

This software connects to a DMR master using the MMDVM protocol, enabling a ChatGPT-powered AI bot for voice interaction. It comprises a main program (a DMR/D-Star client handling audio via AMBEServer) and a Python script for audio processing via APIs. OpenAI Whisper handles speech recognition, while Google Translate powers text-to-speech, supporting multilingual interaction. Clear, polite questions improve recognition. If silent for over one second, the bot provides local weather, with forecasts available on request. English performs best for recognition accuracy.

Demonstrates _FreeDV RADE_, an open-source digital voice mode for HF, which combines machine learning with classical Digital Signal Processing (DSP) to achieve improved speech quality and spectral efficiency. Released in June 2025 by ARDC grantee FreeDV, RADE operates at Signal-to-Noise Ratios (SNRs) as low as -2 dB and occupies approximately 1.5 kHz of bandwidth, half that of a typical SSB signal, while transmitting about 8 kHz of voice audio. The mode also features an optimized Peak-to-Average Power Ratio (PAPR) for efficient power amplifier use, reducing heat and consumption. Users, such as _VK3TPM_, report significantly improved listening ease compared to analog modes, particularly in high HF noise environments, making it easier to conduct nets across various Australian states. The mode's integration into popular radios like the _FlexRadio 6000_ series allows direct operation without external computers. A C library for RADE is available, facilitating broader integration into other radios and SDR programs, with development continuing on FreeDV RADE v2 to further narrow bandwidth below 1 kHz.

Early 20th-century transatlantic wireless communication efforts involved distinct technical approaches by Reginald Fessenden and Guglielmo Marconi. Marconi's systems, operational until approximately 1912, primarily utilized _spark technology_ for wireless telegraphy, facilitating Morse code communication between ships and across oceans. His Poldhu station in December 1901 radiated signals in the MF band around 850 kHz, later evolving to 272 kHz in October 1902, and eventually 45 kHz by late 1907 with increasingly larger antenna structures like the pyramidal monopole and capacitive top-loaded arrays. Fessenden, conversely, focused on _continuous wave transmission_ for wireless telephony, recognizing its necessity for speech. His transatlantic experiments in 1906 employed synchronous rotary-spark-gap transmitters and 420-foot umbrella top-loaded antennas at Brant Rock, MA, and Machrihanish, Scotland, tuned to approximately 80 kHz. Fessenden later utilized the _Alexanderson HF alternator_ at 75 kHz by late 1906 for pure CW transmission, integrating a carbon microphone for amplitude modulation. Receiver technology also differed, with Marconi initially relying on untuned coherer-type detectors, later developing the magnetic detector in 1902, while Fessenden's CW approach necessitated more advanced detection methods.

The Gemini Amplifier Remote Control software operates on Windows 7 and above, facilitating remote management of the Gemini HF-1K and DX-1200 amplifiers. Users connect via Ethernet, configuring the amplifier's IP address through the front panel. The software allows seamless band and antenna selection, saving settings for each band without requiring transmission. Integration with _OmniRig_ from Afreet Software, Inc. enables automatic band adjustments based on the radio's frequency changes. Users can configure serial or virtual serial connections, with tracking options accessible through the ribbon bar. The software supports speech functionality, enhancing accessibility for operators. Firmware updates, such as version 2.5Ee, introduce features like background datalogging and power output control, uploaded via FTP. Version 1.2.0 allows users to offload internal parameter data for support purposes. The firmware upload process requires the amplifier's IP address and port 21, taking approximately 90 seconds. Users are encouraged to upgrade to the latest firmware for improved performance and remote diagnostics.