Receiver Review: ICOM IC-R100

IC-R100

Year Introduced: 1990
Power: 13.8 V DC supply (not included)
Size: 150 x 181 x 50 mm
Weight: 1400g
Price: US$700, CAN$1090, ú499
Coverage: 0.1-1856 MHz

Value Rating: star

Table top or mobile scanner with AM, FM, and FM-WIDE modes. No SSB. This set uses a keyboard for direct frequency entry or a tuning control. 121 memories, of which 100 store the frequency, mode, RF attenuator and preamplifier settings. 24 hr clock timer. The receiver is clearly designed for broadcast listening below 50 MHz. Only signals in the AM mode can be demodulated, so if you want to listen to radio amateurs using SSB or teletype signals using Frequency Shift Keying (FSK), then you can immediately reject the R-100. The tuning steps are selectable at either 1, 5, 8, 9, 10, 12.5, 20, or 25 kHz. For shortwave, the 1 kHz step was slightly too coarse. A 100 Hz step would have been better. The IC-R100 does have an Automatic Frequency Control which locks onto VHF/UHF signals and compensates for any slight frequency drift by the radio as a result of temperature changes in the environment. The IC-R100 has 100 memories, plus a further 20 which are used to determine the scanning limits, and one channel which is used for a priority frequency. Although the memories store useful info like the mode of the signal, they are not arranged in "banks". Scanning 100 channels takes far too much time. The ICR-100 is sensitive enough on shortwave, figures are around 1.5 ÁV (10 dB s+n/n, measured with 1 kHz tone, 60% modulation, into 50 Ohms). Above 50 MHz, where the atmospheric noise is much lower, sensitivity becomes more important. The IC-R100 is also more than adequate in this region too. The pre-amplifier on the set, however, is not much use at all. The manufacturer's specifications state that a 6 kHz filter is used for AM, and a 15 kHz filter for FM narrow reception. But this doesn't say much about the shape of the chosen filters. It is more interesting to look at how well strong signals in the same part of the band are rejected in favour of the signal you are trying to listen to. The so-called RF- protection ratio says a lot, and the IC-R100 doesn't score too well. There are several reasons for this, not least the rather high synthesizer noise generated internally by the receiver. This leads to reciprocal mixing, seriously affecting the dynamic selectivity. Also there may be some signal leakage around the ceramic filters. Whatever the cause, long wire antennas present so much signal to the input circuitry that the receiver can't cope. In a car the efficiency of the antenna is lower, but since the signals are weaker you are again faced with the basic fact that, below 50 MHz, the IC-R100 is only really designed to pick up the stronger shortwave broadcast stations. The same story applies to VHF. The dynamic selectivity of this radio is well below what one would expect from a scanner in this price class.


Radio Netherlands Receiver Test Laboratory: Full Review

This review was compiled independently. The Medium Wave Circle and Radio Netherlands has no financial connection with Icom, the manufacturer of this receiver.

 

Introduction

The requirements for a good shortwave communications receiver are very different to those of a good scanner. The R-100 was introduced in 1991 and covers 100 kHz to 1856 MHz without a break, but we have divided our comments to performance above and below 30 MHz. ICOM has packed a receiver with 100 memories, and three modes (AM, FM (narrow) and FM (wide) into a box just 150 x 50 x 181 mm. The set comes with a suitable mounting bracket for use in a car or a boat. The radio's speaker is mounted on the bottom of the cabinet, so if you use it at home on a table then four rubber feet (supplied) have to be attached to allow sound out from underneath the case.

The R-100 runs off a car battery or a 13.8 volt (3 amp) DC power supply, available as an optional extra. The low voltage power cord can be bolted to the case (preventing it from coming loose), but the colour coding of the supplied cable could have been clearer.

The number of function keys on the R-100 has been reduced to a minimum with the result that many keys have two or even three functions. This takes some getting use to, but the instruction manual has been clearly written in this regard, and the receiver's software is very intelligent. The radio has a multi- functional back-lit liquid crystal display (LCD) which includes information on the chosen mode, the size of the tuning step, whether or not the attenuator is activated, and, of course, the frequency.

The rear of the set has no less than 3 antenna inputs, but this is needed because, of course, no single antenna can cover 100 kHz - 1800 MHz. The lower frequency portion (100 kHz - 50 MHz) has a SO 239 connector, an N connector for 50-905 MHz and another N connector for 905 - 1800 MHz. Because of the band activity, the changeover at 905 MHz is not as handy in Europe as in Japan. But the set has provision to power an external relay to switch one antenna across either one of the N connectors. The handbook does not tell you that the potential coming out of the receiver is +10 volts between 100 kHz - 50 MHz, 0 volts between 50-905 MHz, and +10 volts again between 905 - 1800 MHz. The middle pin is positive.

 

VHF/UHF Characteristics Different

The required specifications for a good shortwave receiver are very different from a VHF/UHF receiver. For instance, sensitivity below 1 microvolt on a shortwave set is not really desirable. With the high powers used by international broadcasters, even simple antennas are capable of delivering signals between 10 and 100 millivolt to the receiver's front end circuitry. The radio's delicate tuning circuits have to be able to pick out the weak signals whilst rejecting this enormous unwanted energy. On VHF/UHF the sensitivity becomes far more important. The limiting factor is not the atmospheric noise, but the internally generated noise from the front end! But in the busy communications bands (e.g. around 118 MHz) it is also important that strong signals on nearby channels do not desensitize (or "block") the weaker signals you want to listen to.

 

Performance Below 50 MHz

The R-100 is clearly designed for broadcast listening below 50 MHz. Only signals in the AM mode can be demodulated, so if you want to listen to radio amateurs using SSB or teletype signals using Frequency Shift Keying (FSK), then you can immediately reject the R-100. The tuning steps are selectable at either 1, 5, 8, 9, 10, 12.5, 20, or 25 kHz. For shortwave, the 1 kHz step was slightly too coarse... 100 Hz would have been better. The R-100 does have an Automatic Frequency Control which locks onto VHF/UHF signals and compensates for any slight frequency drift by the radio as a result of temperature changes in the listening room.

The R-100 has 100 memories, plus a further 20 which are used to determine the scanning limits, and one channel which is used for a priority frequency. Although the memories store useful info like the mode of the signal, they are not arranged in "banks". Scanning 100 channels takes far too much time. Whilst it is true that empty channels are skipped, in practice 40-50 important channels are possible when listening in a city area. When you only want to listen to a limited number of channels this means you have to programme a skip marker in all the other unwanted channels! This is very time consuming.

Other sets offer a method to "bank" frequencies (say all aeronautical channels) together in one group. The R-100 offers no less than 9 different methods of scanning the memories, skipping or only selecting certain modes, as well as automatically scanning the dial and storing active frequencies in up to 20 channels of the memory. But this flexibility is marred by a practical problem. When the receiver scans the dial it stops as soon as it hears a signal. Scanning resumes when the signal goes off the air... quite common on VHF/UHF communications. However if the set stops scanning because it has hit an internally generated birdy, or a transmitter that is on continuously, the scan is suspended. Most scanners allow you to jump over this problem with the manual tuning knob or the UP/DOWN buttons. If you try this on the R-100 you jump out of the scanning mode. If you then switch to the scanning mode again, the radio restarts at the pre-programmed start frequency. There are ways round the problem by programming unwanted frequencies into the memory for the radio to skip, or scanning in the pause mode, but both solutions are clumsy.

The R-100 has several timing functions similar to a video-recorder, but no way to remotely control a tape-recorder. The only solution is a cassette deck that starts when an audio signal is applied to the input (often termed VOX control).

 

Sensitivity

The ICR-100 is sensitive enough on shortwave, figures are around 1.5 ÁV (10 dB s+n/n, measured with 1 kHz tone, 60% modulation, into 50 Ohms). Above 50 MHz, where the atmospheric noise is much lower, sensitivity becomes more important. The R-100 is also more than adequate in this region too. The pre-amplifier on the set, however, is not much use at all. Ideally such a pre-amplifier should be in the antenna mast to be most effective. The pre-amplifer on the R-100 on works in the 50 - 905 MHz region, whereas it would have been most effective above 905 MHz where the sensitivity of the front end drops off. The problem is that pre-amplifier not only amplify the incoming signal, they add noise to the signal too. Pre-amplifiers designed for a small specific frequency range can achieve very low noise levels, but wide-band pre-amplifiers are much noiser. Between 50 and 144 MHz the preamp does not help in the reception of weaker signals because it generates the same noise as the front-end RF amplifer.

Between 144 and 174 MHz, the sensitivity is even slightly worse with the pre-amp switched in. Above 220 MHz the pre-amplifier starts to show results, but because the dynamic range of the radio is quite low, overloading is quite possible. Leave the pre-amplifier switched off, and check whether the attenuator helps. Often switching in the 20 dB of attenuation results is a signal that's easier to understand!

 

Squelch

The squelch is useful on VHF/UHF to silence the set when no signal is being received. The receiver will only start to scan when the squelch is active, so it is important that it works well. If the R-100 is mounted in the car, or there is fading on shortwave signals, the received signal can vary enormously. Some squelch designs has a so-called "hysterisis" effect. Once the squelch opens for a reasonably strong signal, it will shut again at a much lower signal level, thus compensating for fading. The IC-R100 doesn't do this, so signals on the edge of the set squelch level cause an annoying "chuffing" effect. The upper signal limit of the squelch is fine for shortwave, and the AM/FM WIDE modes on VHF. But we found the lower limit is too high.

 

Selectivity

The manufacturer's specifications state that a 6 kHz filter is used for AM, and a 15 kHz filter for FM narrow reception. But this doesn't say much about the shape of the chosen filters. It is more interesting to look at how well strong signals in the same part of the band are rejected in favour of the signal you are trying to listen to. The so-called RF-protection ratio says a lot, and the R-100 doesn't score too well. There are several reasons for this, not least the rather high synthesizer noise generated internally by the R-100. This leads to reciprocal mixing, seriously affecting the dynamic selectivity. Also there may be some signal leakage around the ceramic filters. Whatever the cause, long wire antennas present so much signal to the input circuitry that the receiver can't cope. In a car the efficiency of the antenna is lower, but since the signals are weaker you are again faced with the basic fact that, below 50 MHz, the R-100 is only really designed to pick up the stronger shortwave broadcast stations. The same story applies to VHF... the dynamic selectivity of this radio is well below what one would expect from a scanner in this price class.

The blocking level of the receiver on VHF is just 41 microvolts... signals stronger than this totally de-sensitize the receiver even if they are up to 5 MHz away from the frequency being listened to. That will no doubt cause problems if you use the set in the vicinity of a FM broadcast station or a mobile telephone repeater. The figures for 3rd order intermodulation products was also somewhat disappointing too. The radio has an intermodulation free dynamic range of just 69 dB!

 

Conclusions

We could go further, but the bottom line is that this receiver is an example of a very large compromise. The price in Europe is, for which you get a shortwave radio with performance similar to receivers costing half the price the price. The same is true of the VHF/UHF section. If big frequency coverage is important, then this radio provides it. If you want to search for weak stations then you'd be better off deciding whether your needs lie either on shortwave or VHF/UHF, and buy a shortwave receiver or VHF/UHF scanner to do the job. The radio still seems to be available worldwide, with the exception of North America. The price in Europe is around ú499.

This review first appeared on the Radio Netherlands website.