NASWA Journal Columns · Equipment Reviews, November 1999

Alan Johnson, N4LUS • 2490 Sharon Way • Reno, NV 89509 alanjohnson◊gbis.com

Equipment Reviews, November 1999

The Icom IC-R75 Communications Receiver

The IC-R75 is Icom’s re-entry to the HF-only desktop communications receiver market after the R71A was discontinued. Yes, there was the R-72, but this receiver was poorly received by the SWL community. This leaves Icom as one of the few Japanese ham radio equipment manufacturers that hasn’t written off the SWL market. The R75 is a definite step-up from the R72 and rated specifications are closely equivalent to the R-71A. The R75 is a triple-conversion digitally synthesized radio, but signal processing and filtering are analog in nature. There is provision for adding a DSP audio processing unit for noise reduction and automatic notch filtering. The R75 has a list price of $950, but the street price is very attractive at less than $800, making it a competitor to the Drake SW8. For a receiver in this price class, there is a high degree of flexibility in configuring the various operating parameters of the receiver.

The R75 is not completely HF-only, as it has coverage up to 60 MHz to permit reception of the amateur 6 meter band and the low VHF public service band. All reception modes are supported (including FM for ham and public service transmissions) and it comes standard with two IF filter bandwidths, 6 and 2.4 kHz. There is a dual passband shift control to vary the recevier’s selectivity. There are sockets for additional filters, one in the 9 MHz IF chain and another in the 455 kHz IF. Double sideband AM synchronous detection is provided. It has 99 memory channels, as well as two channels to set the limits for frequency scanning. It is a compact 9.5 x 4.0 x 9.5 inches (WxHxD). Icom must consider the radio compact enough for mobile use, since they offer the IC-MB5 mobile mounting bracket as an option. The radio requires 12 volts DC and an AC adapter is provided. The receiver’s portability can be enhanced by adding the optional MB23 carrying handle kit.

The front panel

The front panel is dominated by a 1.5 by 3.4 inch LCD display with attractive orange backlight–the illumination level is adjustable through the “Set Mode” menu. The orange display provides a pleasant contrast to the receiver’s black front panel and case. The display shows the tuned frequency to either the nearest 10 or one hertz. The display can be toggled between frequency or time by pressing the “CLK” button. There are only a few knobs on the front panel but a plethora of pushbuttons. The knobs include concentric volume and RF gain/squelch (choosing between the latter two is another Set Mode menu), the PBT controls and a 1.75 inch rubber rimmed tuning knob. The friction on the tuning knob can adjusted by a small lever beneath the knob. Tuning steps can be can be quickly switched between 10 hertz, one kilohertz or one megahertz by pressing the “TS” button. Holding the TS button for two seconds puts the radio into tuning step programming mode, where the tuning step can be set to 0.1, 1, 5, 6.25, 9, 10, 12.5, 20, 25 or 100 kHz. The radio can also be directly tuned via the front panel keypad with frequency entry in MHz format, i.e. entering frequencies below one megahertz requires pressing “0” and the decimal point. The keypad also doubles as an alphanumeric keypad for labelling the memory channels.

There are too many pushbuttons to list, since most of the buttons control a single function, unlike the menu style interface of the AOR 7030. Many of the buttons have dual functions depending on whether the pushbutton is momentarily pressed or held for two seconds. Most of the secondary functions are “set and forget” configuration options, so once the radio is setup, operation is quick and straight forward. Reference to the manual is definitely required for the initial configuration, however.

There is a small speaker mounted behind the left-hand side of the front panel. The sound produced is crisp, but adequate. Below the speaker is a 1/4-inch headphone jack. The internal audio amplifier produces two watts of output power.

The back panel

The most appealing feature of the jacks provided on the back panel is actually located on the front panel. That is the button to toggle between the two antenna imputs, either a 50-75 coaxial socket or a terminal for a 500 ohm wire antenna. The back panel has provisions for two types of computer control–a DB9 connnector for a RS-232 interface or a 1/8-inch jack for Icom’s CI-V remote control. There are also jacks for line level output to a recorder and recorder remote control via a relay driven by the R75’s timer, which is a single event on-off timer.

The RF chain

Once the desired antenna has been selected the signal can be routed through a pre-amp (there are two selections: preamp 1 and 2–the manual doesn’t make the difference between the two clear, but preamp1 seems to give 10 dB of amplification and preamp2 20 dB), through a 20 dB attenuator or straight to the first mixer. The signal is then upconverted to the first IF of 69.01 MHz and then downconverted to the second IF of approximately 9.01 MHz (actual center frequency depends on mode). The first selectable filtering occurs at the 9 MHz IF with the stock filters being 15 kHz and 2.4 kHz. One optional filter can be added to the 9 MHz stage, with available bandwidths being 2.8, 1.9, 0.5, 0.35 and 0.25 kHz. These filters can be individually selected for each mode through the filter set menu. The signal is then converted to the third IF of 455 kHz (450 kHz in AM/FM modes). The stock bandwidths in this stage are 15, 6 and 2.4 kHz. One optional filter can be added in the 455 kHz IF, with available values being 3.3, 2.8, 1.8, 0.5 and 0.25 kHz. The available optional filter bandwidths reflect Icom’s emphasis on the ham, rather than SWL market. Icom also makes a 6 Khz bandwidth filter for use in the 9 MHz IF in some of their transceivers (the FL-102), but according to Icom America, this filter cannot be used since it is not supported by the R75’s filter selection menu. This is a shame, as it would help tighten the overall IF selectivity.

There are three available bandwidths for each mode: Wide, Normal and Narrow. The desired filters are chosen in the “Filter Set Mode” menu. For example, in AM mode the two 15 kHz filters can be chosen for “Wide”, “Normal” can be set to use the 15 kHz filter in the 9 MHz IF and the 6 kHz filter in the 455 kHz IF and “Narrow” can be set to use both 2.4 kHz filters. The review unit had the 3.3 kHz 455 Khz optional filter, so I set the “Narrow” filter setting for 15 kHz/3.3 kHz.

The concentric-knob twin passband tuning control can be used to “slide” the filter bandwidth windows relative to the received signal. If both controls are turned in the same direction, the control acts as an IF shift, which can be used to emphasize the higher frequencies in a signal. If the controls are turned in opposite directions, the effective filter passband is narrowed, serving to increase selectivity. The range of adjustment varies with the filter in use: either ±1.29 kHz in 15 Hz steps with the wider filters and ±258 kHz in 3 Hz steps with the narrower filters. I did not find the Twin PBT to be very effective with the AM filters. I’m not sure if this was due to poor skirt selectivity of the filters themselves or the limited range of passband adjustment relative to the width of the filters. The Twin PBT worked well with the narrower SSB and CW filters, however.

The AF chain

After the signal has been filtered in the IF stages, it goes to the detector stage. For SSB/CW signals a standard product detector is used. AM signals can be detected by a standard detector or by a synchronous detector. This sync detector does not allow for selection of either sideband and, what’s worse, I couldn’t tell any difference in signal distortion or fading when the synchronous detector was engaged.

The most interesting part of the audio chain in the R75 is the optional UT-106 audio frequency digital signal processing unit. This is a small PC board which mounts on the receiver’s main circuit board. The UT-106 provides two functions: a noise reduction system that is effective in reducing static, hiss and hum and an automatic notch filter that slices out multiple single tone signals. The noise reduction level can be set in 15 steps–level “5” worked the best for me. I found the DSP noise reduction filter to be very useful at reducing the background “wash” of noise without significantly reducing signal intelligibility. There was a slight reduction in the high frequency content of audio signals when the noise reduction was engaged, but the benefits of the noise reduction was a worthwhile trade-off. The manual states that the noise reduction and notch filter are not available in AM mode, but it seemed to work fine in this mode in the review unit. I E-mailed Icom America about this, but they were unable to clarify this discrepancy.

I found the R75 to be very pleasant to listen to for long periods, especially when the DSP noise reduction was used. The internal front-mounted speaker produces a crisp, but not tinny, sound. The headphone out audio was rather bassy for my tastes, but this may reflect the headphones I used. There was plenty of power to drive an outboard speaker and I thought the audio with an external 8 inch speaker was rich and full.

What about value?

The street price of the R75 puts it head-to-head with the Drake SW-8 and the JRC NRD-345. The Drake is more portable, since it has provisions for internal batteries, a built-in whip antenna and a carrying handle. The Drake also has a narrow (4 kHz) AM filter and covers the FM broadcast band. The Icom has more features than the NRD-345 and is smaller than the SW-8. What does have to be factored into the R75’s price, however, is the additional cost of the DSP unit at $139.95 and the cost of the FL-257 3.3 kHz filter ($159.95) if a narrow AM filter is desired. Icom America is providing a free UT-106 DSP units with R75’s puchased by December 31, 1999. This offer makes the R75 an outstanding value for listeners looking for a quality table-top radio, especially those who are interested in a receiver for utility listening as well as receiving SW broadcasters. The R75 is attractive, easy to use (once configured) and a good performer. Thanks to fellow NASWAn John Wagner for providing the “full-dress” R75 for review.

Read more Equipment Reviews columns.

Comments are closed.

Quick Information

Solar Conditions

At 2017 Mar 25, 1800 UTC

  • Solar Flux: 72
  • A-index: 6
  • K-index: 1

Full Report from NOAA

Search