The Bridge - Issue 2, 2019 - 15

Feature

Electrical and Computer Engineering and Amateur Radio

Digital Voice

Microwave Technology

Amateur radio communication began simply with
Continuous Wave (CW) Morse code transmissions
but was using Double Sideband Amplitude
Modulation (DSBAM) even before that of broadcast
radio. Because of a limited available spectrum for
its exclusive use amateur radio then employed early
practical forms of SSB AM modulation, removing the
redundant sideband of DSB AM, and demonstrated
its performance in HF communication.

Amateur radio experimentation in SHF has had a
long tradition and is the last frontier before optical
data transmission. Early generations of microwave
engineers acquired much of their technical training
by such activities. Amateur radio transmitter and
receiver design and propagation studies have
occurred even up to 250 GHz. There are microwave
amateur radio contest events when hill topping
(operating from a high elevation and in the clear)
is needed. Transmitting and receiving in the SHF
amateur radio band requires distributed or stripline
design and the use of MMIC devices, like the
example in Figure 7.

Amateur radio now also employs very low bit rate,
compressed digital voice using AMBE on a DSP
device. An ECE capstone design project used the
AMBE-2020 (www.dvsinc.com) to produce a digital
vocoder (voice encoder). Although a proprietary
vocoder was used, there were frame data and
processor control protocols developed for the
project. A DSP audio frequency modem was also
developed and the digital voice project report is
posted on the TUARC website. The system is shown
in Figure 6.

Fig. 7: Amateur radio microwave stripline design using MMICs.

Fig. 6: Digital vocoder and DSP audio frequency modem.

This ECE capstone design project was published
and presented at an ARRL Digital Communication
Conference, which demonstrates that even
undergraduate projects can add significantly to the
base of knowledge in amateur radio [2]. Work is
currently being done on a freeware software solution
for compressed digital voice in amateur radio
(https://freedv.org/).

An early ECE capstone design project in microwave
technology was a 2 Mbps, high-speed (for 1994)
digital data communication system using the
10 GHz amateur radio frequency and FSK. Gunn
diode transceivers (known as Gunnplexers) were
used with automatic frequency control (AFC) using
a stripline design with MMICs. The ECE capstone
design project system was demonstrated by a data
transmission across the Temple University campus,
between the Engineering and Computer Science
buildings. At the time 10BASE-T wired, twisted pair
Ethernet data communication was only 10 Mbps.

Weak-Signal Data Communication
Amateur radio has leveraged the advanced
processor and sound card interface of the modern
PC to produce several modes of weak-signal data
communication. An amateur radio development in
1998 was PSK31 at 31 b/sec (www.bpsk31.com).
This slow data rate is essentially that of a keyboard

HKN.ORG

15
http://ieee-hkn.careerwebsite.com/ http://www.dvsinc.com https://www.freedv.org/ http://www.bpsk31.com https://hkn.ieee.org/ https://hkn.ieee.org/
The Bridge - Issue 2, 2019

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