Icom IC-705 Test

Icom IC-705 User Evaluation & Test Report

Icom IC-705 Test – This report describes the evaluation of IC-705 from a user perspective.

Icom IC-705 Test Appendix 1 presents results of an RF lab test suite performed on the radio. I was also able to spend some time with the IC-705 in my ham-shack, and thus had the opportunity to exercise the radio’s principal features and evaluate its on-air behavior.

Physical “feel” of the IC-705:

The IC-705 was conceived as a lightweight portable HF/VHF/UHF transceiver which can be powered from an internal battery pack (BP-272 or BP-307) or from an external 13.8V DC source. RF power output is 5W on battery and 10W on external power. The case dimensions are 200(W) x 83.5(D) x 82(H) mm (excluding projections) and the radio with the BP-272 fitted weighs 1.16 kg.

The IC-705 features a large color touch-screen display similar to that of the IC-7300. This is a new departure in Icom’s “portable” transceiver product line, offering easy band/mode selection and navigation through the radio’s menus. The placement of many control functions on the touch-screen and in the MULTI knob menus has moved many controls off the front panel.

Owners of current Icom IF-DSP transceivers should find the IC-705 quite familiar, and should feel comfortable with it after a little familiarization with the touch-screen. In addition to the display, the front panel has a number of feature keys in location similar to those on other Icom radios as well as two knobs (Twin PBT, AF Gain + RF Gain/Squelch) and MULTI to the left and right of the display respectively.

Pressing the MULTI knob opens a context menu on the right edge of the screen; this menu changes with the previously-selected mode or function, allowing adjustment of appropriate parameters. The learning curve will be minimal for owners of other Icom IF-DSP radios. The Twin PBT and MULTI controls are multi-turn and detented. The main tuning knob is large and has a knurled Neoprene ring and a rotatable finger-dimple; it turns very smoothly with minimal side-play.

The 2.5 mm MIC jack, and the 3.5mm PHONES jack, are on the left edge of the case, behind the front panel. The supplied HM-243 handheld speaker/mic or any other compatible electret or low-impedance dynamic mic can be plugged into the mic jack.

(The +8V electret bias on the mic jack can be turned off when using a dynamic mic.)

The BNC antenna socket and the grounding screw are also on the left side of the case.

The micro-SD card slot for memory storage and loading, recording and firmware upgrade is below the speaker/mic jacks. A screen capture function (enabled via menu) allows capture of the current screen image to the SD card as a PNG or BMP file by briefly pressing the POWER key. The image can also be viewed on the screen via menu.

Three 3.5mm jacks and a Micro-USB socket are located on the right edge of the case, behind the front panel. From the top down, the jacks are SEND/ALC, TUNER and KEY. The SEND line is low-level and bi-directional. The TUNER jack will interface with external tuners such as the AH-4 and compatible third-party units, as well as the planned AH-705 ATU. The KEY jack accepts a paddle, bug or straight key (configurable via menu).

The Micro-USB socket (USB-B) allows PC connectivity via a suitable cable. The concentric +13.8V DC power socket is also on the right side of the case. The battery pack can be charged from the DC power socket or the Micro-USB port (the latter only when the radio is off).

The IC-705 is solidly constructed and superbly finished. Like other Icom radios, it conveys a tight, smooth, and precise overall feel. The ABS plastic case and front panel have a smooth, matte surface. The touch-screen display is the same size as that of the IC-7300. The display can be turned off to conserve battery power.

The battery recess on the rear panel accepts a BP-272 (2 Ah) or BP-307 (3.15 Ah) battery pack. The battery pack has two latches to secure it in the recess.

Icom IC-705 architecture:

Icom is the first Japanese amateur radio manufacturer to offer a family of amateur transceivers embodying direct-sampling/digital up-conversion SDR architecture. In the receiver, the RF signal from the antenna feeds a high-speed 14-bit ADC (analogue/digital converter) via a preselector.

This is a set of bandpass filters which protect the ADC from strong out-of-band signals. The ADC digitizes a portion of the HF range defined by the preselector; the digital output of the converter feeds the Field-Programmable Gate Array (FPGA) which is configured as a digital down-converter (DDC) and delivers a digital baseband, 12 kHz wide and centered on 36 kHz, to the DSP which carries out all signal-processing functions such as selectivity, demodulation etc. A DAC (digital/analog converter) at the DSP output decodes the digital signal back to audio. Figure 2 is a simplified block diagram of the IC-705 receiver below 25 MHz.

Icom IC-705 Test

The FPGA also delivers a 1 MHz-wide digital video signal to the Scope Display Processing, which manages the screen displays, including the fast FFT spectrum scope, waterfall, audio scope and audio FFT (spectrum analyzer) as used in other Icom transceivers (7300 7610, 9700). The spectrum scope has a maximum span of ±500 kHz, adjustable reference level (-20 to 20 dB), video bandwidth and averaging, and minimum RBW < 50 Hz.

A unique “touch-tune” feature allows quick tuning to a signal displayed on the scope by touching the scope or waterfall field to magnify an area, then touching the desired signal within that area.

In the transmitter, the audio codec converts mic audio to a digital baseband, which the DSP then processes further and the digital up-converter in the FPGA then converts to a digital RF signal at the transmit frequency. This signal is converted to analog by the highspeed 12-bit DAC to the RF excitation for the PA Unit.

Above 25 MHz, a heterodyne converter down-converts the RF signal to an IF in the 38.85 MHz range. This IF is then sampled by the ADC.

The touch-screen:

The large (93 x 52 mm) color TFT touch-screen displays a very clear, crisp image, with excellent contrast and color saturation, and an LCD backlight.

The home screen displays the current frequency in the upper field, the bar-graph meter in the middle and the spectrum scope in the lower field. The first two keys below the screen, MENU and FUNCTION, are unique to the IC-705.

The third key, M.SCOPE, moves the spectrum scope to the middle field; a different screen, selected via the MENU key, can be opened in the lower field (e.g. a multi-function meter, RTTY decoder or CW keyer controls, depending on mode). The waterfall is activated via the EXIT/SET key at the bottom right of the home screen; a reduced-height scope and waterfall can be displayed on the home screen via an EXIT/SET menu parameter.

When the Twin PBT knobs are rotated, a bandwidth/shift pop-up appears, and the trapezoidal icon at the top centre of the screen changes, a dot appears to the right of the icon. Pressing the inner PBT knob clears the Twin PBT setting. Pressing the MULTI knob opens a menu with RF PWR, MIC Gain, COMP and MONITOR settings.

A setting is changed by touching its icon and rotating the MULTI knob. The MULTI knob menus are context-sensitive; for example, pressing and holding the NB key activates NB, and displays NB settings when the MULTI knob is pressed. RIT and ATX are adjusted by pressing their respective keys on the top right of the front panel and rotating the MULTI knob without pressing it. In this mode, pressing the MULTI knob clears these functions.

Pressing and holding the Notch, NR and NB keys makes their settings accessible from the MULTI knob. These can be used to select notch width, NR level and NB parameters respectively. When MN is selected, a pop-up displays its width.

TPF (Twin Peak Filter) can be activated via the MULTI menu in RTTY mode.

The menus are somewhat akin to those in other current Icom DSP radios. I found the setup process fairly intuitive after consulting the relevant user-manual sections in cases of doubt. Icom continues the use of a “Smart Menu” system which changes available functions in a context-sensitive manner based on the mode currently in use.

Different screens are selected by pressing the MENU key on the bottom left of the screen. Menu selections with default values can be returned to default by pressing and holding their DEF softkey. Many of the screens have a “Back” arrow key to return to the previous screen.

The MENU screen includes a “SET” icon which opens a list of the 705’s configuration settings arranged in a hierarchy which is easily navigable. The desired line in the onscreen table can be selected via the MULTI knob or up/down arrows.

The FUNCTION key opens a screen with switches for functions such as AGC, COMP, IP+, MONItor, VOX, BK-IN etc. Some of these (NB, NR, Preamp/ATT, NOTCH) duplicate front-panel keys.

The QUICK key opens a context-sensitive Quick Menu for rapid configuration or default setting of various menu functions.

Touching the leading (MHz) digits of the frequency display opens a band-selection screen; the desired band is selected by touching its designator. Mode selection is similar; touching the current mode icon opens the mode-selection screen. Tuning steps for kHz and Hz are set by touch, or by touch/hold, on the respective digit groups.

The filter selection and adjustment procedure is similar to that on other Icom DSP radios. Touch the FIL-(n) icon to toggle between FIL-1, FIL-2 and FIL-3. Touch and hold this icon to adjust the filter bandwidth and select CW/SSB Sharp/Soft shape. All IF filters are continuously adjustable. As in other Icom IF-DSP radios, filters with 500 Hz or narrower bandwidth have the BPF shape factor, but a non-BPF filter can be configured via Twin PBT.

The Time-Out Timer feature limits transmissions to a preset duration (3, 5, 10, 20 or 30 minutes, selectable by menu.) RF PWR can be turned down to 0. This feature is useful when receiving via active antennas or mast-mounted preamplifiers without T/R switching, or to avoid damaging test equipment when conducting receiver measurements.

The AUDIO screen displays an audio FFT spectrum analyzer and oscilloscope very similar to those implemented in the IC-7851, IC-7800 (Firmware V3.00 and higher) and IC-7700 (V2.00 and higher). This feature is very helpful in setting up one’s transmit audio parameters, and also for visual audio assessment of a received signal.

Receiver front end management:

The P.AMP/ATT icon on the FUNCTION screen toggles between Preamps 1 and 2, and a 20 dB RF attenuator. The AF/RF/SQL control functions as an AF Gain control when not pressed; when pressed, it opens a context menu for selection of RF GAIN and SQL functions.

The input level limit for a direct-sampling receiver is the ADC clip level, where the digital output of the ADC is “all ones”. When the ADC clips, the receiver can no longer process signals. Thus, the 705 provides means to prevent this condition from arising.

When the ADC starts clipping, a red OVF (overflow) icon lights at the top left of the screen. At this point, rotating the RF Gain control counter-clockwise will extinguish OVF and restore normal operation. RF Gain should be set just at the point where OVF goes dark, otherwise weak-signal reception will be degraded. If required, ATT can be activated as well.

When OVF lights, the preamp should be turned OFF. (In general, use of the preamp on 7 MHz and below is not recommended, as the band noise is almost always higher than the receiver’s noise floor and the preamp will only boost band noise without improving signal/noise ratio.)

The IC-705 dos not have an IP+ (dither) function.

Being a current IC-7300/IC-7610 owner, I found that the IC-705’s controls and menus fell readily to hand. A user familiar these radios, or with the IC-9700, should find the IC-705 very user-friendly and its learning curve manageable. The IC-705’s default settings are very usable, allowing the radio to be placed in service with minimal initial set-up.

The IC-705 offers a configurable SWR Plot indicator with manual stepping (as in the IC-7300) rather than a sweep function.

An front-panel AUTO TUNE key “tunes in” CW signals rapidly and accurately.

Touching the currently-displayed meter scale toggles between scales. Touching and holding the meter scale opens the multi-function meter, which displays all scales simultaneously.

USB, WLAN & Bluetooth interfaces:

The IC-705 is equipped with a micro-USB “B” port. The radio can be directly connected via the “B” port to a laptop or other PC via the supplied USB cable. This is without doubt one of the IC-705’s strongest features. The USB port transports not only CI-V data, but also TX and RX PCM baseband between the IC-705 and the computer.

As a result, the USB cable is the only radio/PC connection required. Gone forever is the mess of cables, level converters and interface boxes! This feature is now standard on all Icom HF radios released since 2009. An Icom driver is required in the PC; this is downloadable from the Icom Japan World website.

The WLAN interface supports connection to a PC, LAN or Internet router via Wi-Fi, for NTP time synchronization or for remote control via the Icom RS-BA1 V.2 software suite. As the IC-705 has a resident RS-BA1 server, a collocated PC is not required.

The Bluetooth interface supports connection to a compatible Bluetooth headset or Android data device (smartphone or tablet).

Filter selections and Twin PBT:

As do the other Icom DSP transceivers, the IC-705 offers fully-configurable RX IF selectivity filters for all modes. Three default filter selections are available via the touch-screen for each mode, with continuously variable bandwidth via the FILTER menu. In addition, there are selectable Sharp and Soft shape factors for SSB and CW. The BPF filter configuration feature (for filter bandwidths of 500 Hz or less) operates in the same manner as on other Icom IF-DSP radios.

Pressing and holding the Twin PBT knob restores PBT to neutral.

The TPF menu item in the MULTI RTTY context menu selects the Twin Peak Filter (TPF) in RTTY mode. No CW APF (Audio Peak Filter) is provided. However, the CW RX LPF and HPF in the TONE SET menu are a reasonable alternative to the “missing” APF; their ranges are 100 – 2000 and 500 – 2400 Hz respectively. The HPF and LPF can be set to “bracket” the received CW tone in a tight 100 Hz audio bandwidth. The DEF softkey restores these filters to default (off).

BPF vs. non-BPF filters:

As in other Icom IF-DSP radios, the IC-705 allows the user to select two additional shapes for 500 Hz or narrower filters, in addition to SHARP and SOFT. These are BPF (steeper skirts) and non-BPF (softer skirts).

To configure a BPF filter, select a 500 Hz or narrower CW, RTTY or SSB-D filter with Twin PBT neutral. To set up a non-BPF filter, select a filter with BW > 500 Hz, and narrow the filter to 500 Hz or less by rotating the Twin PBT controls. When Twin PBT is displaced from its neutral position, a dot appears to the right of the filter icon at the top of the screen.

Notch filters:

The tunable manual notch filter (MN) is inside the AGC loop, and is extremely effective. The MN has 3 width settings (WIDE, MID and NAR); its stopband attenuation is at least 70 dB. The manual notch suppresses an interfering carrier before it can stimulate AGC action; it thus prevents swamping. To adjust the notch frequency precisely, press and hold the NOTCH icon (FUNCTION screen), then rotate the main tuning knob.

The auto notch filter (AN) is post-AGC. It suppresses single and multiple tones, but strong undesired signals can still cause AGC action and swamp the receiver. MN and AN are mutually exclusive, and AN is inoperative in CW mode. The NOTCH key toggles OFF – AN – MN. Touching and holding the NOTCH icon in MN mode opens the MN context menu next to the MULTI knob. MN position and width can then be adjusted by rotating the MULTI knob.

NR (noise reduction):

The DSP NR is very effective. In SSB mode, the maximum noise reduction occurs at an NR control setting of 10. As NR level is increased, there is a slight loss of “highs” in the received audio; this is as expected. The measured SINAD increase in SSB mode was about 14 dB. For precise NR adjustment, press and hold the NR key, then rotate the MULTI knob.

NB (noise blanker):

The IF-level DSP-based noise blanker is arguably one of the IC-705’s strongest features. I have found it to be extremely effective in suppressing fastrising impulsive RF events before they can stimulate AGC action within the DSP algorithm.

The NB completely blanks noise impulses which would otherwise cause AGC clamping.

I found its performance comparable to that of the IC-7300 NB. The NB menu (threshold, depth and width) is accessed by pressing and holding the NB key. The NB works very effectively in conjunction with NR.

AGC system:

The IC-705 has an in-channel AGC loop. The digital AGC detector for the AGC loop is within the DSP algorithm. Level indications from the detector are processed in the DSP, and control the DC bias on a PIN-diode attenuator at the RF ADC input. This architecture prevents strong adjacent signals from swamping the AGC, and allows full exploitation of the ADC’s dynamic range.

The AGC menu is similar to that of other Icom IF-DSP radios. The Slow, Mid and Fast AGC settings are customizable via menu for each mode, and AGC can be turned OFF via menu.

Receive and transmit audio menus:

The IC-705 TONE SET menu offers the same generous selection of audio configuration parameters as that of the IC-7300 and IC-7600 TBW (low and high cutoff frequencies), RX and TX Bass/Treble EQ, RX HPF and LPF, transmit compression, etc. All audio settings are grouped under the SET/Tone Control menu.

13.    Metering:  The on-screen bar-graph meter displays the S-meter at all times; touching the scale toggles between Po, SWR, ALC and COMP. Touch and hold displays the multi function meter.

14.    TUNER function:  Not tested due to lack of a compatible ATU.

15.    RTTY decoder and memory keyer:  The IC-705 features an on-screen RTTY decoder/display as well as an 8 x 70 chars RTTY memory keyer for transmitting short messages.

16.    VFO/Memory management:  The IC-705 offers the same VFO and memory management features as other current Icom HF+ transceivers: VFO/memory toggle and transfer, memory write/clear, memo-pad, Split, VFO A/B swap [A/B] and equalize [toucl and hold A/B], etc.

Brief “on-air” report:

Upon completing the test suite, I installed the IC-705 in my shack and connected it to multi-band HF/6m vertical antenna and then to my 2m/70cm vertical collinear antenna. Due to extremely poor HF propagation at my location, on-air HF tests were not feasible. Thus, tests with local stations were conducted on 2m and 70cm.

a) SSB: I chatted with a local Ham friend on 2m SSB, using the HM-243 speaker-mic and the IC-705’s default audio settings. At 10W output, signals were 55 to 57, taking polarization loss into account; switching to 5W caused < 1 S-unit drop as expected but with no loss of intelligibility. Audio reports were excellent, and NR at 5 sufficed to reduce the band noise to a comfortable level.

As discussed in 10. above, I found the NR very effective on SSB. Even at 10, NR did not attenuate “highs” excessively. NR is very effective in conjunction with NB, although in this test, NB was not needed.

The preamp (« 10 dB gain) brought weak stations up to very comfortable copy without S/N degradation. The SSB filters and Twin PBT were excellent, as we have come to expect from other Icom DSP radios.

b)    DV: I conducted a test with another local friend on 2m DV simplex with 10W output. Due to the distance between us (17 km), the path was subject to QSB and marginal at times. When copy was solid, signals were approx. 57 and audio quality was excellent. (NR was off, as it degrades DV receive audio quality.) The preamp was required for this test.

c)    FM: I checked in on local 2m and 70cm repeaters, and found the receive audio very good. The distant station also provided a good audio report. The TONE and TSQL features worked very effectively. The preamp was on.

d)    AM: In a quick check of AM reception, I listened to various MF and HF broadcast stations. A local station on 690 kHz and a music broadcast on 5995 kHz sounded good on the IC-705’s internal speaker, but much clearer (as one would expect) on my SP-41 external speaker. I noted that the AM IF filters cut off quite steeply below 200 Hz, as in other Icom DSP radios.

The 9 kHz AM filter offered the best frequency response, but the 6 kHz setting sounded a little “smoother” and 3 kHz cut the “highs” excessively. The IC-705’s Twin PBT is fully functional in this mode. Mid AGC was best for average to good signal conditions, but Fast AGC handled rapid selective fading more effectively. NR was quite effective in improving the S/N ratio of weak AM signals (but at the cos of some high-frequency audio response).

The NR did not distort the recovered audio. NR Level 6 was the “sweet spot”, providing optimum noise reduction with minimal attenuation of highs. Higher NR settings cut the highs excessively. Above 10, the NR control had no further effect. (Note that the AM bass and treble EQ settings were both 0 dB, with HPF off.)

AN was effective in suppressing interfering tones and heterodynes, but MN caused some distortion when tuned across the signal. The reason for this is that MN suppresses the carrier in a manner similar to selective fading.

Slight hiss was evident when receiving weak AM signals, but NR largely suppressed it.

e)    RTTY: I tuned in some 40m RTTY signals and was able to tune them accurately with the FFT tuning aid and decode them reliably using the internal decoder.

USB AF Output Level Check:

During receiver testing, I checked the receive AF levels at the USB port using a level-meter program. All levels were well within specifications.

USB MOD Input Level Check:

During transmitter testing, I also checked the AF input levels at the USB port using a tone-generator program, for 10W PEP output. All levels were well within specifications. To use the USB port, I installed the IC-705 Icom USB drivers (downloadable from the Icom Japan world-wide support site).

Case temperature:

The radio showed no signs of excessive heating even after lengthy “key-down” phase noise testing at full output. The rear of the case was warm to the touch (temperature indicator at mid-range, 2 orange bars).

Concerns: Only two minor items were flagged:

•    An “RF tail” when unkeying in QSK-CW mode. The duration of the tail is

0.5 to 1.5 ms at the preset power output plus the decay time of the code element (determined by the CW rise time setting). The initial steady-state portion is shorter at higher rise time settings.

•    A 2.5 dB initial ALC overshoot during the white noise overshoot test (Tes 20, p. 27). No significant overshoot was observed in SSB voice testing.

Conclusion:

After a few days’ “cockpit time” on the IC-705, I am very favorably impressed by its solid, refined construction, clear and informative display, easy familiarization experience, smooth operating “feel”, impressive array of features and excellent on-air performance. This radio is unique in that it is a true, stand-alone* direct-sampling/digital up-conversion SDR in an attractive, compact package. Yet again, Icom has a winner with the SDR performance, intuitive touch-screen and the straightforward USB computer interface. This is certainly a lot of radio for its price category.

Acknowledgements:

I would like to thank Ray Novak N9JA at Icom America, and Paul Veel VE7PVL and Jim Backeland VE7JMB at Icom Canada for making an IC-705 available to me for testing and evaluation.

*Stand-alone SDR: self-contained, not requiring a computer as a prerequisite for operation.

Copyright © 2020 A. Farson VA7OJ/AB4OJ. All rights reserved.

FULL DOCUMENT:

error: Content is protected !!