The Bridge - Issue 2, 2019 - 16

Feature

Fig. 8: TUARC K3TU HF, LEO satellite, VHF and UHF stations.

message but results in a narrow bandwidth quite
immune to noise and interference. However, that
was not the only technical innovation. Text characters
are produced as a variable length code (varicode)
where the boundaries between character codes are
marked by two or more consecutive zeros.
Like all such Fibonacci codes, the varicode has
no character codes that contain more than one
consecutive zero. The spaces between characters
can be readily found regardless of the length of the
character. The more frequently occurring characters
have the shortest encodings. Varicode is also selfsynchronizing if reception is impaired by sporadic
HF channel fading.
Freeware PC processing software, such as DigiPan
(Digital Panoramic Tuning), encodes and decodes
the varicode text characters and uses the FFT DSP
technique to select the narrow bandwidth signal
to decode. A typical received SSB AM bandwidth is
3 kHz which contains many PSK31 signals shown as
waterfall display and with the cursor selected signal
as an in-phase and quadrature (I-Q) phase plot and
decoded text. In addition to PSK31 there are many
other amateur radio weak signal digital modes such
as QPSK31, MT63, Throb, Olivia and Hellschreiber
(http://wb8nut.com/digital/).

THE BRIDGE

A recent weak signal data communication mode
is JT65 which was developed by Dr. Joseph Taylor
(K1JT) who is a Nobel Laureate in Physics and an
amateur radio operator. The freeware JT65 mode
is intended for extremely weak but slowly varying
signals, such as those found on tropospheric scatter
(troposcatter) or EME (moon bounce) paths. JT65
can decode signals that are many decibels below
the noise in a 2.5 kHz band. This performance
often allows the successful exchange of contact
information without the signals even being audible.
JT65 uses Multiple Frequency Shift Keying (MFSK)
and messages are transmitted as data packets
after being compressed and then encoded with
Reed-Solomon Forward Error Correction (FEC).
FEC adds redundancy to the data and messages
can be recovered by the receiver even if some of
the data is corrupted.

From Faculty Advisor to Station Trustee
The involvement of an ECE faculty member is
crucial to the eventual establishment of an amateur
radio resource for ECE courses and capstone
design projects. The ECE faculty responsible
for the curriculum in digital data and wireless
communication, DSP and EM wave propagation
are the obvious sponsors of that effort. A faculty
advisor can promote an amateur radio station as a
laboratory facility of the ECE department, obtain an

http://www.temple.edu/k3tu http://www.temple.edu/k3tu http://www.wb8nut.com/digital/ https://hkn.ieee.org/ https://hkn.ieee.org/

The Bridge - Issue 2, 2019

Table of Contents for the Digital Edition of The Bridge - Issue 2, 2019