ICOM IC-756PROII HF/50MHz ALL Mode Transceiver
The IC-756PROII is the high performance HF transceiver of choice for today's discriminating amateur radio operator. Icom's engineers took cutting-edge digital technology and paired it with Icom's extensive experience with analog technology. The result is a major advancement of Icom's original digital IF filter which, in the earlier IC-756PRO model, enjoyed a great reputation around the world.
The IC-756PROII uses the same 32-bit floating point DSP and a 24-bit A/D-D/A converter as the IC-756PRO. It is now possible to execute the digital IF filter, noise reduction and the digital IF filter in the AGC loop processing, and to select the soft/sharp filter shapes. The IC-756PROII employs exclusive DSP/analog circuit matching to further improve receiver performance.
Icom's engineers analyzed the influence of the AGC loop upon the received audio, matching it to an analog circuit suitable for the dynamic range of the A/D converter and the other parts used, and also re-examined the core stage of the receiver (ranging from RF top to mixer circuit), to distribute the mixer levels properly. As a result, the matching of digital and analog technology has attained a level never before achieved.
This technical report does not explain in depth all the digital engineering with its many calculations and formulas. Instead, it focuses on the DSP engineering in an easy-to-understand manner. This report also explains why the 32-bit floating point DSP and 24-bit A/D-D/A converter are included. The dynamic range of the 32-bit floating point DSP and the 24-bit A/D-D/A converter may seem to be an over specification for amateur radio. But this is not the case. This technical report helps clarify these points.
It is Icom's hope that in providing you with this report you will discover the IC-756PROII's many digital advantages. Enjoy!
32-bit floating point DSP and 24-bit A/D-D/A converter
The adoption of a 32-bit floating point DSP and 24-bit A/D-D/A converter in the IF stage (36kHz) was originally developed by Icom. It enables various digital functions which amateur radio operator's desire.
■ 51 types of digital IF filtering
The digital IF filter has superior filtering performance and a distinguished shaping factor that demonstrates the power of 32-bit floating point DSP. The digital filter is completely free from deterioration due to deviations in band characteristics, temperature change, or mechanical vibration, all of which have been observed in analog filters. It also provides excellent ripple characteristics that have never been available with analog filters. The passband (50Hz-3.6kHz) of the digital IF filters used for IC-756PROII come in 51 types. This function allows 3 of these 51 types to be pre-set for each mode and to be changed instantaneously by using the filter button, depending on the situation.
■ 2 types of filter shape (Sharp/Soft)
Changing the IF filter shape is a feature that is not available with analog radios. Select the filter shape from two types, Sharp and Soft, depending on the purpose, operating band, band conditions, etc. It is possible to set CW and SSB filter characteristics independently and also select the filter shape while actually receiving a signal.
■ Digital IF filter in AGC loop
The digital IF filter, manual notch filter, etc. are located in the AGC loop, using DSP, which completely eliminates interference from adjacent strong signals. This allows the AGC to be operated only on the selected frequency. It is also possible to pre-set the operation of AGC in each mode in accordance with 13 types of time constants.
■ Digital twin PBT
The IC-756PROII is equipped with DSP based twin PBT filtering. It provides excellent performance on a completely different level than analog filters. Set the frequency, and then adjust the passband width of the received signal in steps of 50Hz using the dedicated two-position knob. The passband width and direction of shift may be graphically displayed on the LCD, if the operator chooses.
■ High-accuracy digital modulation and demodulation in all modes
The DSP unit allows you to increase transmit/receive audio levels, modulation, and demodulation — even while decoding RTTY. This makes it possible to set the passband width of the IF filter for SSB transmit to 3 different stages. The DSP unit also provides a demodulation level suitable for high-grade HF performance and high-fidelity sound.
■ Manual notch with superior attenuation level
The IC-756PROII's manual notch filter has extremely sharp characteristics for processing in the DSP and provides tremendous performance for attenuation levels >70dB. Analog notch circuits are susceptible to fluctuations in attenuation or changes in temperature. The DSP-based manual notch provides stable performance and is not susceptible to such changes. Also, the DSP signal processing executed within the AGC loop completely shuts off undesirable signals, even with the AGC set to high speed. An automatic notch is included to further enhance receiver performance.
■ Demodulator/decoder for RTTY
This transceiver is equipped with a demodulator and a decoder for BAUDOT RTTY as a standard feature. On-air station calls may be recognized instantaneously by reading the received RTTY message directly on the IC-756PROII's LCD - no personal computer or external components are required. The transceiver is fitted with an on-screen tuning indicator that allows the RTTY to be fine tuned with
ease. A DSP based twin-peak audio filter further improves the S/N ratio. This filter will reduce interference that appears between each tone (mark and space), which cannot be removed by conventional analog filters. This twin-peak audio filter works to capture noise-level signals accurately and to significantly reduce the generation of noise distortion.
■ New-generation speech compressor
The DSP based speech compressor enhances the readability of your transmitted signal at a receiving station without any distortion, even when the compression is set to a high level. The gradation of voice processing is extremely close to the original sound. This assures superior sound quality at all compression levels.
■ Microphone equalizer (enables 121 different settings)
The IC-756PROII is equipped with a microphone equalizer that makes it possible to set the frequency characteristics of the transmitted signal in 11 different stages for both the high-tone range and the low-tone range. Considering all permutations, this provides for a total of 121 different settings. With this flexibility of DSP based waveform shaping, it is possible to adjust transmit audio quality depending on the application. For example, it is possible to set the dynamic sound quality for "Pileup" or to set pleasant sound for "Ragchewing".
■ Variable level type noise reduction
The 32-bit floating point DSP has excellent calculation performance, which processes complex and sophisticated algorithms. This allows the DSP to attenuate noise without delay and extracts noise-level signals. It is possible to vary the suppression level in 16 stages.
■ CW keying waveform shaping function
DSP controls the rise and fall of the CW transmit waveform. The result is a proper CW waveform. The rise/fall timing is selectable to 4 stages of 2ms, 4ms, 6ms and 8ms. This makes it possible to set a "Soft" or "Hard" CW signal, depending on your preference.
■ Advanced receive functions
The RF stage's front-end receive mixer is designed in a 4-element configuration. In the IC-756PROII, this configuration is used in the BPF stage at the RF top. Each element is examined to tune the circuit after RF stage to mixer, which makes it possible to enhance the receive performance. This significantly reduces 3rd and other order distortion and provides a wide dynamic range. This means the IC-756PROII will accurately capture weak signals that analog type radios cannot hear, even in low bands with high noise levels.
■ Real-time spectrum scope
A real-time spectrum scope is recognized as indispensable for DX hunting. The IC-756PROII's spectrum scope uses two colors to display all RF signal activity within a user-selectable bandwidth. One color indicates real-time RF signal activity, while the other color provides peak hold indication. The spectrum scope may be used for sophisticated applications such as identifying the band conditions, quick discovery of stations, and confirmation of interval or call-back frequency. Additionally, you may monitor normal band conditions, while you display sub readout or transmit markers. In case of highband noise, the IC-756PROII is equipped with an attenuator (10/20/30dB) dedicated to the spectrum scope, which allows a reduction of total signal level at the band scope without affecting the received signal.
■ Exceptionally clear SSB transmit signal
Using Icom's advanced digital PSN modulation, the IC-756PROII emits high-quality signals, which makes its transmitter suitable for use as the exciter of a linear amplifier. Unwanted sidebands and carrier leaks are almost completely eliminated. Further, the transmitter employs a wide band power amplifier that incorporates highly reliable bipolar transistors (2SC5125 x 2). The linearity and IMD characteristics achieve superior signal quality never before seen in any amateur redio transceiver. This makes it possible to transmit RF signals with significantly reduced distortion.
■ Built-in high-stability reference crystall oscillator
The IC-756PRON's transceiver exhibits excellent frequency stability of < 0.5ppm. This assures stable communication even for RTTY and SSTV modes for which particularly high frequency stability is required.
The best in operating convenience and features
Dual-watch enables simultaneous two-frequency receive in the same band, providing identical band and filter configurations in both receive systems. This makes it possible to receive two signals simultaneously as if two separate receivers are being used. This greatly enhances split frequency operation; enjoy enhanced DX-operation by searching for pickup frequencies while watching the transmit frequency of a DX station experiencing pile-up. Or have a QSO while simultaneously monitoring a DX net.
■ Triple band stacking register
With the push of a band button, get quick memory recall of three preferred operating settings (including antenna port) per band. Band or mode hopping has never been easier. It's the ultimate in multimode flexibility.
■ Digital Voice Recorder (DVR)
The DVR feature is an indispensable function for DX hunting and contests. The IC-756PROII is equipped with a DVR with 4 channels for transmit and 4 channels for receive, for a total of 8 channels. High quality digital mapping of the transmitted or received analog signal provides high quality audio reproduction, resulting in a natural sounding voice without any noticeable degradation. It is also possible to use these 4 communication channels by allotting them freely with a total recording time of 90 seconds. Each of the 4 channels for receive has a recording time of 15 seconds, or 60 seconds total. Press the key once in any TFT display mode and it becomes possible to not only record or reproduce voice but also to record for up to 30 minutes
continuously. The receive audio may be reproduced for the most recent 15 seconds back to an interruption in recording. By constructing the simplified control unit (page 26) and connecting it to the microphone connector, digital voice recorder function may also be operated.
■ Full-scale electronic keyer
Plug a CW, iambic paddle into the electronic keyer jack on the front panel. Especially handy during long hours of operation, it is possible to set the CW speed between 7 and 56WPM. The discriminating operator may also set the dot/dash keying ratio (2.8:1 to 4.5:1) and polarity, depending on preference. The keyer may also be set for either right or left hand use. For the CW operator who prefers not to use the IC-756PROII's built-in electronic keyer, an ordinary key jack is available on the rear panel, for bug or straight key and is fully compatible with external keyers or PC keying.
■ Multi-function memory keyer
Enhance your contest operations. The IC-756PROII is fully equipped with a convenient memory keyer, offering features such as memory content editing function, auto-repeat function, serial contest number automatic count-up function, contest number abbreviating function, and more. These features will reduce effort when repeating a formatted contents for calling CQ, continuous transmission of call sign, or contests. Since it is possible to confirm the contents of memory on the display, transmission mistakes are eliminated. Construct the simplified control unit (page 26) and connect it to the microphone connector to enhance operation of these memory keyer functions.
■ Quick split function
When the split button is pressed and held, the frequency of the sub-VFO is adjusted to the frequency in the main VFO. Using the split function, it is also possible to control the following:
1. Vary the transmit frequency via the main dial.
2. Direct entry of the designated frequency.
3. Direct entry of the shift frequency.
You are now ready to "bag the DX" while other operators are still tuning up.
■ Preamplifier and attenuator
The IC-756PROII incorporates two types of receive preamplifiers: Preamplifier 1 (10dB) emphasizes modulation across all bands, and preamplifier 2 (16dB) emphasizes sensitivity especially for high bands. The attenuator is selectable in three stages, 6, 12 and 18dB. When there is a strong signal from a local commercial station it becomes possible to control the generation of distortion at the RF stage of the receiver. It is also possible to retain the preamplifier and attenuator settings for each band.
■ Variable noise blanker
The transceiver uses a new noise blanker design that provides significant reduction of pulse-type noise. The noise blanker also greatly enhances weak signal copy, allowing the operator to change the sensitivity in 100 stages in accordance with the noise level without distorting the target signal.
■ Frequency shift function for change from/to SSB to/from CW
A frequency shift function automatically adjusts the CW carrier point when selecting from SSB mode, or vice versa. You may select "Shift function off" whereby the frequency remains the same (by moving the carrier point), or "Shift function on" in which the frequency is shifted without moving the carrier point. Using CW-R mode it is possible to set the carrier point to USB.
Enhanced TFT color display
■ High visibility
A high visibility 5-inch TFT color display has been integrated into the IC-756PROII to provide ease of use and clear indication of the radio's many features. Various function settings such as frequency, memory frequency, comment, filter setting status, RTTY tuning indicator, and more are displayed in the upper portion of the display, The lower portion of the display gives voice memory, characters of received RTTY, and the real-time spectrum scope information. The display color may be selected from 8 types, from vivid color to muted grays. 7 different font types may also be selected. These settings may be made in any combination - customize your display to best suit your personality or favored operating set-up.
■ Memory channel/memory list
The transceiver is equipped with 99 regular memory channels and 2 scan edges, totaling 101 channels. It is possible to enter text of up to 10 characters in each memory channel. It is also possible to display a list of up to 13 memories at a time.
■ Simplified set mode
The IC-756PROII has a list display that allows the status of each set mode item to be seen at a glance. Each function is divided into 4 setting groups and multiple items are listed or displayed to allow quick access to the desired item. This allows the many functions of the radio to be used with ease.
■ Digital meter simultaneously displays 4 transmit level indicators
With the digital meter (including peak-hold), it is possible to confirm the output power, ALC, SWR, and COMP, all at the same time while transmitting. The signal strength is also displayed while receiving.
■ Antenna system
- High-speed built-in auto antenna tuner covering up to the 50MHz band
- 2-piece antenna terminal (incorporated with auto antenna selector)
- Dedicated receive antenna connector
■ Receive system
- General coverage receive (30kHz to 60MHz)
- Control of RF gain and squelch with one knob
■ Transmit system
- IF Monitor function allows the transmissions of your station to be listened to locally
- Built-in 50 frequencies of tone encoder/decoder
- VOX function allows the automatic selection of transmit and receive for "hands free" operation
- All-mode power control function
■ CW system
- CW pitch control function allows the CW receive tone to be set to a desired frequency (300 to 900Hz continuously)
- Double key jack allows 2 types of keys to be connected simultaneously
- Full break-in function allows receive during a break while keying
■ Operation system
- 5-channel memo pad saves frequency and mode (It is also possible to change the 5-channel memo pad to a 10-channel type.)
- RIT and TX variable up to ± 9.999kHz
- 1Hz pitch tuning
- Optional frequency speech allows the S-meter level to be announced
- High visibility needle type white-tone analog meter
- Various scanning functions (program, memory, select memory)
- Auto Tuning Step
- Split frequency lock
- Torque adjustment mechanism for main dial
- Band edge beep function
- CI-V terminal allows control from a personal computer
- Clock/timer function
- AH-4 control circuit
Front and rear panel
What is DSP in radio communication?
IC-756PROII Circuit description
- ACC Sockets
- HF/50MHZ, 1kW linear amplifier
- Interface for digital mode
- External control unit for voice memory keyer
- Installation of UT-102 optional Voice Synthesizer Unit
- CI-V control
- Data format of CI-V