Transceiver prefix to the R-250 receiver. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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The proposed version of the transceiver based on the R-250 receiver does not require much intervention in the design of the receiver.

In addition, in this design, an amateur can use the transmitter he already has, and the frequencies of the quartz used in it are not critical and may differ from the calculated values.

The block diagram of the transceiver is shown in the figure. The frequency of the smooth local oscillator of the receiver Fget is mixed with the frequency of the transmitter's crystal oscillator Fkv, then the total signal is mixed with the frequency of the already existing SSB signal of the FSSB transmitter.

The calculated frequency of quartz Fkv for high-frequency ranges (28, 21 and 14 MHz) is equal to:

Fkv \uXNUMXd Fd-Fhet-FSSB,

and for low frequency ranges -

Fq=Fd-Fget+FSSB

(Fd is the frequency of the amateur band).

Since SSB transmitters usually have a smooth master oscillator covering the 500 kHz range, the quartz frequency Fkv may differ from the calculated one, as indicated above, by +/-250 kHz.

The local oscillator frequencies Corresponding to the low-frequency boundaries of the amateur bands, in the version of the receiver available to the author, turned out to be as follows: for 3,5 MHz - 1665 kHz, for 7 MHz - 3215 kHz, for 14 MHz - 2215 kHz, for 21 MHz - 3215 kHz , for 28 MHz - 1715 kHz. The 28-29,7 MHz range was obtained by rebuilding one of the receiver bands not used in amateur practice. In this case, quartz with a frequency of 26,5 MHz was used.

A radio amateur, having the same receiver and radio transmitter with an SSB signal frequency that varies, for example, from 3000 to 3500 kHz, can use quartz 14-14000-2215 = 3250 ± 8535 kHz for the 250 MHz band. Thus, any quartz with a frequency from 8285 to 7185 kHz will do.

The table shows the frequencies of the crystal oscillator for the most common SSB signal frequencies. The frequencies for the 3,5 MHz band are indicated with a smaller spread, since it is impossible to use the SSB signal in the range from 3,2 to 3,8 MHz due to the impossibility of filtering it.

Structurally, the alteration of the receiver and the existing transmitter is as follows. In the free space of the receiver, for example, in the gap between the front panel and the block, variable capacitors, a cathode follower lamp (type 6Zh1P, 6Zh2P, etc.) is installed above the gain control potentiometer at the intermediate frequency. In the compartment in which the parts of the smooth local oscillator of the receiver are mounted, a relay is installed (for example, of the RES-10 type), which, during transmission, disconnects the RF local oscillator voltage from the anode of the L6 lamp and connects it to the cathode follower. The output of the RF voltage from the receiver (using a coaxial cable) can be done through the little used antenna socket A2 or through the adapter block II.

An additional mixer is installed in the transmitter, for example, on a 6Zh2P lamp or (better) a balanced mixer, for example, described in "Radio", 1970, No. 8. In order to be able to rebuild the receiver separately from the transmitter, another one relay (you can type RES-10) and a tuning capacitor. The trimmer capacitor control knob is brought out through a drilled hole on the front panel. To ensure smooth tuning, the author used a vernier device from the RBM radio station. This control is located below the IF gain control (40mm lower). At the same time, the quartz of the quartz calibrator had to be replaced by a smaller one.

To prevent the transmitter signal from deafening the operator, when transmitting, a blocking voltage of 24 V is supplied to the control grids of the receiver lamps through a relay installed in the upper unit.

The transceiver set-top box has been operated at the radio station since 1969 and has shown good results.

When choosing the conversion frequencies, it is imperative to check whether the combination frequencies do not lie near the frequencies used. How to do this is described, for example, in the article "Nomogram for determining combination frequencies" ("Radio", 1968 No. 10, p. 48).

Author: V.Potseluev (UA9VX), Novokuznetsk, Kemerovo Region; Publication: N. Bolshakov, rf.atnn.ru

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