11 April, 2009
A QRP transceiver for 7MHz CW only made of single kind of general purpose PNP transistor is presented. No other semiconductor devices (even diodes!) are used. The circuit is built on a solderless breadboard so that it is easy to build, repair and modify it.
Fig.1 7TR1015BB schematic (Click figure to enlarge, or click here to download PDF version).
Figure 1 shows entire schematic of the transceiver. As you can see, it is a simple direct conversion receiver and 4 stage transmitter configuration.
Receiver section is very similar to 7R1015BB receiver, so refer to that receiver page for detail. Major differences are: (1) LC VFO is replaced by VXO. (2) main audio filter is replaced by LC resonator.
Transmitter section is a simple VXO–Buffer–Drive–Final configuration. Keying is done at the driver unit. For the PA stage, Q11~13 are biased by Q10 to obtain 130[mW] output under 3[V] supply voltage condition.
Two stage π-type LPF with 2nd harmonic trap generates clean RF signal which completely agrees with Japanese regulation.
The circuit is built onto a solderless breadboard (e.g. WBU-204), as shown in Fig.2, where alminum front and rear panels are placed on its base board.
Front panel layout is: headphone jack, audio volume knob, RF ATT knob, RX tuning knob, TX tuning knob, calibration and power switches (left to right). On the rear panel, external DC jack, RF connector and key jack are placed.
|(a) Front panel||(b) BB layout and routing||(c) Rear panel|
|RF output||130[mW] @ 3[V] supply voltage|
|Harmonics||< –50[dBc], fully meets Japanese regulations.|
|Sensitivity||20[dBµ] @10[dB] (S+N+D)/(N+D)|
|0[dBµ] signal can be heared clearly. Minimum audible RF signal level is –10[dBµ].|
|Power supply||2 AA alkaline cells or external DC3[V],|
|RF connector||BNC 50[Ω]|
|Keying interface||3.5[mm] monoral, plus keying|
|Audio output interface||3.5[mm] stereo, 16~32[Ω]|
|External DC connector||2.1[mm] standard DC jack, grounded minus|
|Supply current||77[mA] for transmission|
|4.5[mA] for receiver (no RF input)|
|Dimensions||W215×H60×D132[mm], excludes knobs, connectors and so on.|
|Mass||0.54[kg] including batteries.|
Figure 3 shows output waveform and its FFT results. It is clear that there is no visible distortion in waveform and it completely agrees with Japanese regulations.
|(a) Output waveform||(b) Spectrum|