Manufactured by Icom, Osaka.
After the Japanese company Icom already had built up a good reputation with its amateur radio equipment, the company introduced their first communications receiver with a continuous frequency coverage up to 30 MHz in 1982, it prepared the way for other successful receivers due to its good reception performance, but its operation scheme was not entirely straightforward.
Icom's IC-R70 is a quite compact tabletop receiver, with its dimensions of 28.6 x 11.1 x 27.6 cm and a weight of 7.4 kg, it is a few centimetres smaller than JRC's tabletop sets. An optional external loudspeaker in the same colour scheme and design is available; its sound quality far exceeds that of the built-in front monitor speaker.
Internally, the receiver can be set to different operating voltages from 100 - 235 Volts by changing solder bridges. Operation on a 12 V car battery is only possible with a special DC power kit.
The power switch is located on the left of the front panel, the controls above it are small and can only be operated with pointed fingers. The „Monitor“ control is used to adjust the monitoring volume when the receiver is unsed together with a separate transmitter; next to it you find the switch for the fast & slow AGC speed and for turning it completely off. Below that are the pushbuttons for the noise limier, whose width can be selected. In the early 1980s, this Noise blanker circuit, developed by Icom, was one of the most effective means to eliminate the crackling noise of the Russian over-the-horizon radar known as the „Woodpecker“. The analog S-meter to the right of these switches is backlit in yellow and, as it's standard with ham equipment, indicates the signal strength not only in steps of 0-5 but also in S units.
Next to small LED indicators for mute and RIT control, the blue-green fluorescent display is lacted. The first digit U, L, C, A, r(tty) and F is not easy to decipher, it indicates the Operation mode, a symbolic a or b next to it gives you the information, which of the two VFO's/ memory locations is currently active. The digital frequency display indicates the operation frequency with an accuracy of 100 Hz. The smallest tuning steps of the IC-R70 are 10 Hz, but they are not displayed, but line marks on the edge of the main tuning knob let you calculate the 10 Hz digit of the frequency.
Below the S-meter to the right of the mains switch are two rows of push-buttons, the upper ones select the Operation modes. The FUNCtion key in the row belos gives you access to alternative functions: One quirk of the R70 is the selection of the SSB Operation mode. By default, the SSB key activates the one of the two sidebands, that is used as standard in the respective amateur radio band range. Below 10 MHz, the key will call up LSB (lower sideband), on frequencies higher then 10 MHz, it will call up USB (upper side band). To receive the reverse sideband (e.g. LSB on frequencies higher then 10 MHz) FUNC-SSB must be pressed. An optional second narrow CW filter must also be selected with FUNC-CW.
In the second row of knobs, you find also two buttons for actions between the two VFOs, that can be used like two memories and the memory contents can be transferred from one memory location to the other. A tiny switch selects between a 10 dB preamplifier, the normal position, and a 20 dB attenuator. Below this are two dual controls, the left inner control adjusts the volume, the outer ring adjusts the RF gain, the right inner control adjusts the squelch, the outer ring adjusts the tone.
The large tuning knob is equipped with a finger recess, the fact that the smooth operation can be adjusted with a brake screw is a feature usually found only in the world of commercial receivers. The buttons on the left are used to dim the illumination. The HAM/GEN switch below it determines whether the UP/DOWN keys below it are used to change the reception frequency in 1 MHz steps or to jump directly to the next amateur radio band, each time the BAND UP /DOWN button is pressed. The right row of keys selects the tuning step or the tuning speed. If you tune upwards from 5990 kHz, the set jumps back to 5005 kHz or the low corner frequency of the actual 1 MHz range. The fact that when tuning up, in the range between x.000 and x.001.4 the radio receives 1000 kHz higher then what you read on the display (when 5.000 kHz is shown on the display, the R70 receives in fact 6.000 kHz; only when you tune further up, after you reach 5001.5, the receiver „jumps down“ and the correct operating frequency is displayed, this is another quirk of the receiver that you need getting used to. On the far right below the speaker are two rotary controls, the RIT control for a selectable frequency offset and another double control, it's outer ring operates the excellent HF notch filter, the inner ring the passband tuning.
On the rear you will find all the connectors typically found on semi-professional receivers, from the SO-239 antenna socket, an HF converter socket, panorama display, the external speaker & mute jacks to a special socket for various signals and control voltages. Additional switching elements are located under a cover to optimally adapt the receiver to the operating situation. These options, such as the installation of optional accessories (FM board, optional IF filters) are well documented in the manual; a number of modifications are available in the DX literature.
Above all, replacement of the ceramic filter used in the PBT is recommended. After replacing it with a quartz filter, adjacent signals can be separated razor-sharp from a wanted signal with my R70. Incidentally, the PBT, which is active in all Operation modes, does not work like the standard by shifting the whole IF passband curve but as a variable narrowing of the passband curve. With another simple modification, the preamplifier can also be activated in the MW and VLF range.
The operation of the Icom IC-R70 is „tricky“, as partly mentioned. With the appropriate knowledge, the R70 is an excellent performer, apart from a modest selection of the standard IF filters. The most delicate signals can be separated from unwanted interference from adjacent channels thanks to the post-processing options. Lacking the memory capabilities of more modern microprocessor controlled receivers, the R70 is less suitable for quickly scanning many frequencies from a frequency, like a programme listener does, than for intensive DX in a (tropical) band with low signal strengths, for amateur radio or radio teletype reception. Thanks to the narrow SSB filter, ECSS operation can be used for receiving disturbed radio stations; an AM synchronous detector is missing.
As a second-hand set, the R70 can be purchased at a much lower price than its successors, which are equipped with numerous memories, etc., and could, for example, serve as a second set for tricky reception situations in addition to an inexpensive set for programme listening - however, a second-hand R70 cannot be found very often. Just as a side note, the R70, unlike its successor the R71, does not suffer memory loss when the memory battery is exhausted, so no need to send the set to Icom for reprogramming.
After a JFET-equipped switchable RF amplifier stage, the RF signal is fed to a double balance mixer and converted to the high first IF of 70.4515 MHz, resulting in a high mirror frequency stability. In a ring mixer, it is converted to the second IF of 9.0115 MHz. The repeated conversion to 455 kHz and back to 9.0115 MHz is used to realise passband tuning by shifting the passbands of the two intermediate frequencies against each other to suppress interfering signals.
The frequency synthesizer is a PLL circuit, and a 4-bit microcomputer controls the frequency divider circuit on the basis of the pulses from the optocoupler of the tuning wheel.
The set is equipped with semiconductors.