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Icom, Osaka

IC - R70

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überarbeitet am 19.10.2010

After Icom got a good reputation for their amateur radio equipment, they presented their first communications receiver with continuous coverage up to 30 MHz in 1982 - a set with excellent reception performance but a slightly difficult operation scheme.

Triple / Quadruple conversion superhet, I.F. 70,4515 MHz, 9,0115 MHz, 455 kHz

Digital display accuracy 100 Hz, 10 Hz markings on the tuning knob, coverage 200 kHz - 30 MHz

AM, CW, USB/LSB, FM (optional)

Sensitivity AM <0,5 uV, CW/SSB <0,15 uV, FM < 0,3 uV

Selektivity(-6/-60 dB) AM 6/18 kHz, SSB 2,3/4,2 kHz, CW 0,5/1,5 kHz (0,25 opt.), FM 15/25 kHz

S Meter, RF Gain, two speed AGC, PBT, HF Notch, 2 VFO/ Memories

Icom's IC-R70 is a quite compact tabletop communications receiver, it's dimensions are 28,6 x 11,1 x 27,6 cm and it's weight 7,4 kg. There is an optional external speaker in similar sign and grey - blue - black colour, the sound quality is much better then the one with the internal auxiliary speaker.
The set can be powered from different mains voltages, You have to make sure that the corresponding wire bridges are soldered in, a special 12 V DC kit allows You to run the receiver from a car battery.

Many of the IC-R70's controls are quite small and difficult to operate with hefty fingers.
The mains switch is found at the left of the front panel, the controls just above it are used to control the volume when monitoring Your signal if the set is used connected to a transmitter, to select the AGC speed and to switch the noise blanker. The noise blanker technology developed from Icom was one of the best remedies against "Woody Woodpecker", the noise of the pulsed Russian over the horinzon - rader.
The signal strength meter has a pleasant yellow illumination and gives You S readings and dB over S9 as usually found in amateur radio equipment. Next to tiny LEDs to indicate muting and activated RIT, You find the blue - green fluorescent display. The first digit is in fact a letter, it will takee some time until You get used to read it: A stands for AM, U and L for upper and lower sideband, C for CW, r for radioteletype and F for FM. The letter "a" or "b" next to it indicates, which of the two VFO settings is in use. The frequency ist displayed in 100 Hz steps, lines on the main tuning knob of the R-70 indicate 10 Hz gradation as the IC-R70 tunes in 10 Hz steps.
Below the S meter and to the right of the power switch, You find more controls: In the top rows the pushbuttons to select the reception modes, a FUNCtion key, a sliding switch for the preamp / attenuator and two keys to select the two independent VFOs and to copy the content from one VFO into the other.
The switching of the modes in the Icom IC-R70 is a bit qirky: CW-W selects the standard CW filter, in case, a special narrow CW filter is installed, press FUNC and CW to activate it. In a similar way, the receiver selects in single sideband mode the standard sideband used by the radio amateurs (i.e. LSB for frequencies below 10 MHz and USB for frequencies higher then 10 MHz, to select the other sideband (to select LSB on a frequency above 10 MHz), You have to press FUNC and SSB.
Two concentric controls act as volume / AF gain and RF gain controls and as TONE ans Squelch control, when the squelch is open, the green signal lamp is lit.

The big main tuning knob is spinning easily, use a small screw to adjust it's resistance. The upmost of the four pushbuttons at the left of the main tuning knobs dims the S meter illumination. With the button HAM/GEN, You select the mode of operation of the UP/DOWN buttons just below: in position GENeral, You jump from one to the next 1 MHz segment, in HAM mode to the next amateur radio band.
The pushbuttons at the right set the tuning speed, the stes are 1 kHz, 100 and 10 Hz and tuning can be locked completely.
You tune within 1 MHz segments, when You tune higher and higher from 5990 kHz, the set will jump back to 5005 kHz when You get passed the complete MHz position, but be careful, in the range x.000 to x.001.4 the reception frequency is 1000 kHz higher then the one displayed (e.g. the R-70 is receiving 5001 kHz when 4001 is displayed, when You turn it higher, above 4001,5 kHz, the frequency displayed is actually the one, the set is tuned to.

At the right, below the internal monitor speaker, You find another two rotary controls. The RIT (receiver incremental tuning) will shift the reception frequency a certain amount higher or lower then the frequency displayed, You can use this feature when receiving a RTTY signal with a decoder. The concentric knobs of the other control operate the excellent notch filter (active on the R.F. level) and the PBT. In contrast to the passband tuning as found in classic Drake receivers, the IF filter passband can be narrowed up to 500 Hz from either edge of the passband, this will give You the capability to select the less disturbed sideband of a signal in case of interference from a carrier on an adjacent frequency. When the set comes from factory, the PBT tuning width is small, so this feature is only useful for CW reception. My set has been modified for a wider passband shift, so I can use is for SSB and even AM reception - I have never had such an efficient passband tuning control on any receiver I owned.
At the rear face of the receiver, You find all sorts of sockets like in a semiprofessional receiver: SO239 antenna connector, HF converter (for a 2m or 6m amateur band converter), a panoramic display adaptor, external speaker, muting and a multiconnector socket for different signals and control voltages.

The Icom IC-R70 was one of the receivers, in which modifications could even improve the results. The replacement of the PBT ceramic for a quartz filter is one of these modifications, to set the preamplifier to be active also on mediumwaves for the avid mediumwave Dxer is another one.
As I have written above, operating the Icom R-70 might be a bit "tricky", the reception performance of this set on shortwaves is excellent, the lack of independantly selectable I.F. filters and reception modes is a minor drawback. To listen to AM signals under very crowded band conditions, it's worth using the SSB mode and selecting the less disturbed sideband, alas the receiver has no automated ECSS mode.

From time to time, Icom's IC-R70 can be found very reasonably priced on the used market - it's worth to think about it. The successor, the Icom R-71 featured a direct frequency entry keypad, so it was much more popular amongst the BC DXers. But it suffers from the RAM failure problem: when the internal RAM backup battery fails, not only all memories are erased, but the content with informations to control the radios internal microprocessor is lost also, so the IC-R71 can become completely inoperative and has to be sent in to Icom or has to be equipped with a modified EPROM replacement board to "resusscitate" the radio again.
This is no problem with the IC-R70 which came without such a microprocessor, so no memories, but no trouble with RAM backup failure.

weitere Lektüre:
e: the Icom IC-R70 - a DXers review, technical description and modifications, Kevin Atkins, John Tow, Jerry Strawman, fine tunings proceedings
e: Icom IC-R70, WRTH 1983, receiver review
d/e: model page at www.radiomuseum.org

© Martin Bösch 4.7.2010