This is a builder friendly design with several advantages over earlier versions of direct conversion projects for those wanting to work CW. The parts are now laid out with more space making it much easier to build. It is a single band rig, normally for 80m (see below), which uses a ceramic resonator for the VFO and gives coverage of most of the CW section of that band. It has a direct conversion RX with narrow 750 Hz bandpass audio filtering as well as a humped 750 Hz low pass filter. The output can drive 8R loudspeakers or 'Walkman' type 32R headphones. It has a small PCB front panel with full sized potentiometers for the AFG and Fine/RIT controls, the main PolyVaricon tuning capacitor, a toggle switch for the RIT, and sockets for the LS and key. The Fine tuning control doubles as the receiver incremental tuning which is automatically removed during transmission, or by the RIT switch. The keying operation is semi-break in, with relay change over of the aerial circuits. The rig includes receiver muting during transmission and a sidetone oscillator, with a separate preset for its level in the LS. There are double tuned receiver band pass filters and double half wave transmitter output low pass filter. Transmitter output is 1.5W using a 13.8 volt supply. It can be easily mounted in your own case if you prefer. There are many options for experiment and it can also drive the 10W Linear RF amp. The main PCB is doubled sided about 100 x 100 mm. It includes protection for reversed supplies which should be between 9 and 16 volts. Price is £44.
For bands other than 80m, up to 20m, you can fit a suitable QRP calling frequency crystal instead of the ceramic resonator but the tuning range will only be a few KHz. 14.06 and 7.03 MHz crystals are £2 each. For experienced constructors, the VFO can be derived from the Mini Mixer kit but this is a complication that is really beyond this simple rig so it is better to consider the Berrow instead.
This is a phone transceiver project aimed at builders with limited experience where ease of assembly is important; the PCB has been laid out with plenty of space and it includes a small front panel. It is normally supplied for 80m using a ceramic resonator VFO giving coverage of the lower half of the phone section of the band. (Please consult me if considering bands other than 80m - it has the same restrictions as the Brue above!) Tuning is by a PolyVaricon variable capacitor. The double tuned receiver band pass filters feed the single mixer chip, which acts as a product detector for the direct conversion receiver. The audio amplifier has a bandwidth of 3 KHz suitable for voice signals, with an AFG pot and is able to drive a loud speaker. The transmitter uses double sideband modulation, with a suppressed carrier - this is fully compatible with other stations using single sideband! During transmission, the mixer chip is used as a balanced modulator. The speech amplifier, with a mike gain preset, is designed for low impedance dynamic microphones. The robust IRF510 RF output transistor is mounted on a heatsink to make it more tolerant of abuse, and produces 1.5W of RF on a nominal 12 volt supply. The transmitter RF amplifier has its own RF drive control preset to ensure that the output stage does not limit on speech peaks. A double half wave filter removes the unwanted transmitter harmonics. The rig’s TR relay is controlled from the mike’s PTT switch and mutes the RX during transmission. There are many options for experiment and it can also drive the 10W Linear RF amp described in the Accessories section. The main PCB is double sided 100 x 100 mm. It needs an 9 to 16 volt supply. Price is £49.
This is an entry level superhet receiver project. The superhet principle, when combined with a narrow IF filter, eliminates many of the signals that a plain direct conversion receiver hear because it only receives one of the sidebands. The Tone is for 80m phone operation. It has a 5 crystal ladder 6 MHz IF filter and double tuned RF filters to reject unwanted signals. The audio output stage can drive a small loud speaker or modern Walkman type 32R phones. It uses the common SA602 doubly balanced mixer for the RF mixer and the product detector stages. A 2N3819 JFET VFO running at 2.45 MHz provides the necessary local oscillator signal - it has three tuning sections to achieve a reasonable tuning rate and coverage of much of 80m. The receiver has reversed supply protection and can run off 9 to 15 volt DC supplies. While designed for phone use, it can also be used for CW, where the advantage of single sideband reception will be especially apparent - the band will appear far less crowded through elimination of the unwanted CW sidebands. For CW use, add the Mini CW kit; for AGC add the Mini AGC kit. The Tone kit includes all parts to build it in the small upright format shown below. The matching SSB phone TX is the Parrett (below). The new 3D counter is recommended for those wanting a frequency readout. The Tone price is £44.
This is the matching transmitter to go with the Tone RX. It is also a superhet and provides single sideband phone operation on 80m. The RF output power is nominally 1.5 Watt when used on a 13.8 volt supply. The TX uses the VFO and CIO oscillator signals from the Tone to make operate on the desired frequency so that together they become a transceiver. (Hence the Parrett cannot be used on its own.) The TX has the same supply range as the RX and can share the supply protection. The TX includes a double half wave filter to eliminate unwanted transmitter harmonics and includes the necessary antenna changeover relay. The design also allows for use with the Linear RF amplifier (see the Accessories section) for a higher RF output. The Mini CW kit can be added to provide all the facilities for CW operation. The Parrett is normally mounted immediately behind the receiver as shown below. The Parret price is £35 but when ordered with the Tone, the combined price is discounted to £75.
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