User manual

For ﬁne tuning, push a screwdriver between two turns to bend them apart a lit-

tle. When the lower band threshold is perfectly adjusted, you can also adjust the

upper threshold of 108 MHz. The frequency depends on battery voltage, how-

ever. If you ﬁnd in current operation that the upper-most station can no longer

be set, replace the batteries.

Reception Practice

During station tuning, the receiver’s AFC (Automatic Frequency Control) will lock

on the precise frequency. The station is then audible in a certain range of the fre-

quency controller. Set this control as precisely to the centre of this range as pos-

sible. If the battery voltage drops considerably in operation, the frequency may

change. Then you have to re-set the transmitter. Depending on station modula-

tion, sound distortions may occur from over-modulation of the radio end ampli-

ﬁer. In this case, turn the volume control back a little. The FM retro radio with its

moderate volume is ideally suitable for relaxed listening to the radio in the evening.

With the telescopic aerial extended all the way, the radio is sufﬁciently sensitive

for all strong local stations. If you connect a longer aerial wire, you will also be

able to listen to weaker stations (e.g. local stations of the adjacent towns). For

even higher reception performance, additionally connect a second aerial wire to

the GND connection.

You are then using a dipole aerial. The perfect length is 75 cm per wire. Careful

alignment of both wires can improve reception of a weak station.

Explanations on the Circuit Diagram

Most VHF superhet receivers use an intermediate frequency of 10.7 MHz. The re-

ception frequency is ﬁrst transposed to the intermediate frequency, then ﬁltered,

ampliﬁed and demodulated. The VHF

retro radio also is a superhet and transposes the signal it receives to an interme-

diate frequency. However, the intermediate frequency is much lower at 70 kHz.

This makes it possible for the intermediate frequency ﬁlters to do without bal-

anced coils. The FM demodulator becomes simpler and much more distortion-

proof. All essential stages ﬁt in a single SMD-IC, the TDA7088 with 16

connections. Instead of a rotary capacitator as in older receivers, the radio uses

the capacity diode D1. The higher the voltage at the diode, the lower its capacity