For the maximum oscillator frequency of 955 kHz required, frequency drift over a 20 degrees change is therefore only 360 Hz. This device can be operated at frequencies up to 1 MHz and for an R-C tuned oscillator, has the excellent temperature stability of 20 parts per million per degree Celsius. The low level of local oscillator signal in the output assists in achieving operation with the oscillator frequency close to the intermediate frequency, as is needed when tuning at signal frequencies down to 10 kHz.ДЇor a tunable oscillator, precision oscillator package type XR2209 was selected so that variable resistance tuning could be applied.

The low level of third order intermodulation products adds up to a low order of nuisance intermodulation beats or 'birdies'.

Level of signal at the output, equal in frequency to the local oscillator frequency: 53 dB below the level of the oscillator at the mixer input.

Level of signal at the output, equal in frequency to the input signal: 33 dB below the level at the input.

Even at 1 volt input, the third order products are 55 dB below signal level at 455 kHz.

Third order intermodulation products: At input levels below 70 microvolts, products are below the noise floor.

Equivalent noise level at input: 10 microvolts in a 1 kHz band.

Conversion gain (Ratio of output level at 455 kHz to input level at 200 kHz): minus 6 dB.

Performance tests at an input 'frequency of 200 kHz and an intermediate frequency (IF) of 455 kHz have produced the following results: This device is suitable for use at frequendes up to 8 MHz, and as a mixer at low frequencies its performance is outstandng.

The mixing is carried out by an operational multiplier package type XR2208.

The circuit diagram of the receiver is shown in figure 1 and the following discussion refers to elements in that diagram.ДЇigure 1 VK5BR VLF-LF receiver circuit diagram (Refer also to fig 4 for BFO) The mixer stage All inductive elements are provided by stock lines of miniature RF chokes.Д«ecause of the low frequencies involved, it has been possible to use a number of excellent integrated circuit packages which would be unsuitable on the HF bands. The RF end is untuned and the receiver bandwidth is set by two inexpensive ceramic filters in the IF channel. Tuning is carried out by a potentiometer, the resistance of which sets the frequency of the heterodyne oscillator. It has no variable capacitors or inductors except for one preset trimmer in a trap circuit. The receiver design is a little different from the usual form. The VLF and LF bands have their own unique useful characteristics and these will be discussed further on. It has been designated a VLF-LF receiver, because it tunes the VLF-LF range from 10 to 300 kHz, but it also tunes part of the MF spectrum from 300 to 500 kHz.

The superheterodyne receiver described is the result. Likewise, the writer had no receiver which could tune these frequencies and set out to design a simple receiver for just that purpose. Home - Techniek - Electronica - Radiotechniek - Radio amateur bladen - Amateur Radio - A VLF-LF receiver - 10kHz to 500 kHz with resistance tuningДЇew communications receivers tune to frequencies below 500 kHz and because of this, many radio enthusiasts are unfamiliar with this section of the radio frequency spectrum which supports numerous radio services.

Vlf receiver experimental audio