How many people have noticed that the latest firmware update for the ICOM 7610 includes a new Digital Pre-Distortion feature?
YAESU's AMC
Many experienced amateur radio operators using Yaesu FTDX series equipment have observed that when transmitting on SSB, the entire building can hear the signal, but the "power meter" still doesn't indicate a strong signal. In this case, you may need to adjust your antenna matching unit (AMU).
AMC, Automatic Microphone Gain Control, is a new feature on the FTDX series of radios. It doesn't actually control microphone gain; it's a parameter that can affect the gain of the transmitted signal. The purpose is to prevent the transmitted signal from being distorted or producing unwanted spurious signals. There's an internet joke that says: "If you see an SSB signal at 8KHz, chances are you're using a YAESU."
AMC needs to be coordinated with ALC. Generally, the observed ALC reading is around 75, and the AMC parameters are set around 55. This configuration allows for relatively optimal transmission of signals and power. However, this only reflects my own observations and does not guarantee that others will receive a clean signal. Therefore, combining these two sets of parameters becomes somewhat arbitrary. Why is this the case?
- Today, an increasing number of mail sorting machines are using digital technology, which results in a steadily rising overall noise level across the entire circuit.
- Most machines use solid-state MOSFET amplifiers, which have lower linearity than vacuum tubes.
- In a typical RF architecture, where signals and amplifiers are combined, it is inevitable to experience intermodulation and harmonic distortion, which results in non-linear distortion of the transmitted signal.
The resulting distortion, if not properly controlled, leads to various signals "spilling out," over-saturation modulation, unwanted scattering, and ghosting effects. More importantly, due to the distortion of the transmitted signal, the actual transmission power is also reduced. For example, if a design specifies a 3dB gain, the output may only be 1dB, with the lost power being dissipated as heat.
Have you played Fish Wash? Does it feel a bit similar?
Regarding digital pre-distortion
In theory, this type of distortion is a weakness for SDRs with high levels of digitization. However, SDRs have an inherent advantage in addressing this: by adding an algorithm to the FPGA and calculating the distortion, they can then compensate the amplifier to transmit a perfect "pure signal."
This is what's known as "Digital Pre-Distortion". (DPD)", Some places also refer to it as "Adaptive Digital Predistortion," or ADP.
The DPD signal not only has excellent purity, but also allows for amplification with almost 100% of its power. The signal gain is at least several dB higher.
The image above shows the DPD effect of the ICOM-7610. The "skirt" effect of the signal waveform is significantly reduced.
The ARRL's Clean Signal Initiative（CSI）
Today, in professional radio fields such as cellular networks, 5G, and Wi-Fi, DPD is already commonplace. However, it is still relatively rare in the amateur radio field.
DPD technology is a concept that exists only within the realm of "pure software-defined radios." Previously, it was primarily used in ANAN's Apache, and now ICOM 7610 has just followed suit. FlexRadio mentioned ADP earlier, but it seems to have been repeatedly delayed. These are all devices that handle both transmission and reception using SDR technology.
After all, traditional Chinese doctors are more concerned with the receiving performance of the equipment, and few people pay attention to the transmitting performance – because the "receiving" experience is more direct and intuitive, while the effect of transmission is not easily perceived.
Therefore, ARRL believes that improving signal purity is an opportunity in the era of Software-Defined Radio (SDR). In 2023, they launched the "Clean Signal Initiative".（CSI）。
On one hand, CSI encourages enthusiasts to focus on tuning launch parameters. On the other hand, CSI also promotes manufacturers to correct their launch metrics and characteristics through measures such as increasing signal purity testing.
Honest reviews of YAESU
For amateur radio enthusiasts, we've all encountered issues like over-modulation, excessive distortion, and out-of-band interference. This isn't just a problem in SSB mode; it can also occur in FT8, RTTY, FM, and even CW modes. The primary solutions involve adjusting the gain and AGC parameters of various audio channels, while closely monitoring the ALC (Automatic Level Control) table.
After the introduction of YAESU's AMC function, there were many discussions and reviews online, and the performance of the FTDX series transmitters had also improved significantly. We also want to support YAESU, as I am personally using the FTDX-10.
In the simulated world, YAESU takes signal purity to an extreme level.
Oh? This means that the FTDX only uses SDR for receiving, but uses a simulated transmitter.
Tube amplifiers are a great thing.
References
ICOM 7610 website
https://www.icomjapan.com/lineup/products/IC-7610/
ARRL Clean Signal Initiative
https://www.arrl.org/files/file/QST/This%20Month%20in%20QST/2023/06%20june%2023/0623%20article%20Ritz.pdf
Digital pre-distortion for RF communication: From equations to implementation schemes
https://www.analog.com/cn/resources/analog-dialogue/articles/digital-predistortion-for-rf-communication.html
How to implement a practical and effective digital pre-distortion solution
https://www.analog.com/cn/resources/analog-dialogue/articles/how-to-make-a-digital-predistortion-solution-practical-and-relevant.html
Exploring the audio microphone gain, AMC (Automatic Mic Control), processing, EQ (equalization), splatter suppression, and distortion hardening features of the Yaesu FTDX101D in relation to the FTDX101, FTDX10, and FT-710.
https://www.wirelessgirl.net/Projects/FTDX101D_AudioSetup.html
The original article was published on my WeChat public account, BG6LH.
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