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Two Band low power Transceiver
Winner of the project is Hannes Coetzee ZS6BZP. The
transceiver is also available in kit form at around R1100 including all
hardware and cabinet. For details contact Hannes at 012 653 3792 or 082
224 5790
A Homebrew 20/40m Binaural CW Transceiver
 
Pictures by ZR6VT
Hannes Coetzee, B. Eng (Electron), ZS6BZP and Christo Pelster, M.Eng
(Electron), ZS6AHQ
A binaural
CW transceiver covering the 20 and 40m amateur bands is presented. (40m
is ideal for country wide contacts and 20m offers the opportunity for DX
contacts.) Power levels of 10W on 40m and 5W on 20m ensure reliable
contacts with reasonable power drain if battery operation is required.
The design has been optimised for reproducibility by relatively
inexperienced persons having only access to the minimum amount of test
instruments (if they are comfortable working with SMD components). The
result is ideally suited as a club project or for hams wishing to
construct their own gear for “Summits-on-the-Air” (SOTA) activities.
Introduction
When the achievable performance of the various receiver architectures is
compared to the complexity, cost and availability of components and
reproducibility, few can beat the Direct Receiver (DC) configuration.
But unfortunately the basic DC receiver is not without its drawbacks and
shortcomings.
The
major drawback of a DC receiver is the lack of image suppression. It is
very apparent in a busy band with closely spaced CW signals. Despite
this the DC receiver is very popular for homebrewing and low power,
portable equipment. This may be an indication that the image problem is
not as serious as what may be thought at first and that it may be
possible to enjoy amateur radio to the fullest despite this inherent
drawback.
It
was decided to make use of a Binaural DC [1] receiver design to help
overcome some of the drawbacks. The design can also form the basis for
a full featured, phasing method Single-Side band transceiver.
Basic
DC Receiver
A
local oscillator (LO) signal, operating very close to the received
frequency, is mixed with the received signal. The result of this mixing
process is two frequencies, the sum component at double the operating
frequency, and the difference component at audio or base-band. The
difference (audio) component is filtered out (selected) and amplified to
a suitable level.
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