Marc Double Conversion NR-52F1 manufactured by a Japanese manufacturer.
The multi-band receiver NR-52F1 with numerous AM and VHF ranges was sold under various names as a so-called export set, at radio fairs, you come across sets with the designation „Marc Double Conversion „ or “Tokyo Skylark„ quite regularly.
- 400 x 275 x 125 mm, weight 5.17 kg
The NR-52F1 is a multiband receiver in analogue technology, covering not only the AM ranges from longwave to shortwave and the FM broadcast band, but also VHF ranges. For this reason, only possession of the receiver, but not operation on the unauthorised band ranges was permitted in Switzerland; in Germany, possession of such an „export device“ was also prohibited. For a long time, an air of the forbidden and secret surrounded such sets; the reception performance were praised more highly than they proved to be in reality.
The front of the portable receiver is dominated by the large frequency scale and the tuning knob, which is equipped with a mechanical fine drive. Below, at the right to the speaker, a panel with the several controls is located, five rotary controls at the bottom and five toggle switches above.
If you open the lid, on the inside of the lid you find a time zone calculator in form of a metal disc; the button row of the band range selectors becomes accessible, on the far left the round push-button for the dial illumination.
The antennas for the AM and VHF ranges are located on the top face, and connections for an external antenna are located on the right face. The set also has two ferrite antennas, probably for long and mediumwave.
For (mains) operation the set is switched on with the POWER switch set to „ON“, the mode switch must be in AC operation, and of course the set must be set to RADIO mode and not to tape playback (TAPE).
For reception in the AM ranges, the range switch must be set to „AM“. Use the push-buttons at the top right to select the corresponding band range; the 49 m band is in the middle of the range „SW1“, where you can now hunt for stations; a desired station can be peaked for maximum signal strength with the fine tuning control. With the rotary control „RF GAIN“ in the zero position or at the left stop, the automatic RF gain control (AGC) is activated; in overload situations, for example, when an external antenna is connected, the RF gain can be adjusted manually with the RF gain control knob.
To receive a CW or SSB amateur radio station, a BFO can be activated with the corresponding rotary control. It can be carefully adjusted for optimum speech intelligibility of SSB transmissions. However, SSB reception with the Tokyo Skylark with its coarse frequency dial and the BFO is only rudimentary.
For FM reception, the corresponding toggle switch has to be set to „VHF“; for broadcast reception, the left-hand switch VHF DOUBLE CONV must be set to „OFF“. Only for narrowband reception the switch is set to „ON“, for FM broadcast band stations there will be severe distortions; with a little luck you can hear a few radio amateurs in the 2m band around 144 MHz or in the UHF range in the 70 cm ham band.
Apparently the set is a double conversion set, unfortunately I don't have the schematic or the technical manual.
The set is semi-conductor equipped.
To remove the rear panel, three screws are removed at the top and three at the bottom. The rear panel can then be rotated away to the left, and the antenna connections are fixed with copper clips. On my set, the push-button units and the crackling toggle switches needed a thorough cleaning with Ballistol.
Unfortunately, I do not have the schematic or the technical manual.
The set was made in Japan, the manufacturer's name could not yet be definitively determined. The set was sold as Tokyo Skylark, MARC or Shebro NR-52F1; also by the Swiss company Globe Electronic as Globephone ICF-2003DX.
- Circuit diagram still wanted!