Yaesu FRG - 7

Manufactured by Yaesu Musen Company Ltd., Tokyo.

After having developed several amateur radio receivers, the Japanese company Yaesu launched the FRG-7 as its first general coverage receiver. As a transistorised solid state set with high stability, good frequency reading accuracy and above-average reception characteristics, it quickly became very popular, even if the front panel design did not not meet everybodys esthetic expectations. It was known as the „Frog“ or Frog-7„.

Yaesu / Sommerkamp FRG-7

Technical data

Power supply


  • 340 x 153 x 285 mm, weight 7 kg


Yaesu / Sommerkamp FRG-7


The tabletop receiver with its 34 x 15.3 x 28.5 cm and a weight just below 7 kg was sold as Yaesu FRG - 7 and also under the Sommerkamp brand. It has has a grey metal cabinet, the front panel is in dark grey colour. With an optional battery holder for 8 large UM-1 batteries or with external 12 V DC from a car battery, the receiver can be operated independent from the mains and it's power consumption is quite low compared to receivers with digital frequency display. In most cases it is powered from mains, to adapt to the lower mains voltages used in the USA, wire jumpers next to the transformer had to be soldered in different positions. The FRG - 7 is fully transistorised and therefore immediately ready for operation after switching on, a loudspeaker is integrated in the front panel.

Under the 10 x 7 cm loudspeaker grill, on the far right of the front panel, are the jacks for headphones and tape output, next to them the bright red mains switch and the dial illumination switch. The mode switch next to it is used to select one of the two sidebands in SSB reception, AM and it also activates the noise limiter.

At the top left of the front panel, the dial of the preselector is located: the entire shortwave band is divided into 4 ranges, which are selected with the band selector switch below. The preselector has to be operated manually with great care and tuned to maximum signal. It prevents unwanted large-signal effects by letting only a narrow range of the entire AM spectrum pass to the first mixer. The MHz band must be tuned on the staircase-shaped dial right next to it; when the circuit locks into the selected MHz band, the red LED marked LOCK goes out, indicating that the Wadley loop is locked and the frequency display is correct. A drum dial with markings every 10 kHz and, thanks to the Wadley Loop technique, an absolutely linear frequency response, allows a frequency reading accuracy of 5 kHz. The frequency mark can be shifted with a knob to correct the frequency display after an exact frequency announcement is received. The S-meter above the frequency dial is calibrated in S units up to S+40 dB. The main tuning knob is easy to grip and without backlash, for SSB reception the frequency can be optimally adjusted with the fine tuning knob.

To the left below the tuning knob is the attenuator switch marked ATT, the most sensitive position is the normal position in the middle. The TONE switch activates an LF filter that cuts the frequency response, especially in the high range, and the volume control is found on the right below the tuning knob.

You need some experience to get used to the operation scheme due to the combination of a Wadley loop circuit and passive preselector. First, the MHz digit of the desired frequency is tuned: in the desired range, the MHz knob is turned very slowly until the red LOCK lamp goes out. With the main tuning knob, the receiving frequency is set, e.g. 150 - I - 160. The band switch is set to the position corresponding to the frequency, in our case C (4.0 - 11.0), and the preselector is peaked to the signal maximum slightly above the 6 MHz mark with the help of the small preselector dial. Now you should hear Radio Oesterreich International on 6155 kHz. The frequency can be adjusted slightly with the Fine Tuning control. The described procedure may seem complicated at first, but a frequency change is done within seconds. However, due to the tuning scheme, the FRG - 7 is more suitable for search reception within a band than for quickly checking frequencies in different bands out of a frequency list.

Yaesu / Sommerkamp FRG-7The combination of the Wadley - Loop principle and the excellent preselector help the FRG - 7 to an superior large signal response, rarely found in early transistor receivers. With this, thanks to the high sensitivity and the rather narrow IF filter, the FRG - 7 also is a good performer on the tropical bands. For this set, which was widely used by DXers, several IF filter modifications were offered. Occasionally, the set can be found second-hand at amateur radio flea markets for a good price, and it still can perform well on the bands.

Technical principle

After the attenuator and the preselector, the radio frequency signal has to pass through a first HF amplifier stage and is converted to the first intermediate frequency of 55.5-54.4 MHz in the first mixer. In a special circuit, the various harmonics of the 1 MHz reference oscillator, which are 1 MHz apart, can be tuned between 55.5 and 84.5 MHz; the corresponding harmonic is amplified and fed into the first mixer. After passing through a 55 MHz bandpass filter, the signal is, by help of a 52.5 MHz oscillator signal, converted to the second intermediate frequency of 3 - 2 MHz in the second mixer. After an IF amplifier stage, the signal is converted to the third intermediate frequency of 455 kHz in the third mixer by adding the VFO signal, which is linearly tunable from 2.455 - 3.455 MHz. This technically demanding procedure, which could be realised with simple electronic components, helps the receiver to achieve a linear tuning with excellent stability - the frequency accuracy depends only on the quality of the VFO. This technique was first developed by T.L.Wadley for receivers of the English company Racal and was used in several general coverage receivers in the seventies. After passing through the ceramic 3 kHz filter, the signal is feed to the AM or SSB demodulator, to the latter, the BFO signal is added. After the noise limiter and the AF filter stage, the audio signal is feed to the loudspeaker.


The set is solid state.

Technical documentation


Further information

en/frg-7.txt · Zuletzt geändert: 2024/03/25 07:23 von mb