AMATEUR RADIO
BY GARRY CRATT, VK2YBX
Kenwood's mighty little
TH-28A & TH-78A transceivers
The old saying that "bigger is better" is no
longer necessarily correct, as we can report
after checking out Kenwood's latest VHF/UHF
hand-held transceiver offerings.
Kenwood has released two new
identically-sized hand-held transceivers: (1) the model TH-28A covering
the 2-metre band, with a 70cm receive facility; and (2) the TH-78A dualband 2-metre/70cm unit. Both units
offer an unbelievable range of features in such a small package.
In fact, the first impression one gets
of either unit is that operating it will
require hours of study and a degree in
Electrical Engineering. In practice,
nothing could be further from the truth
- they're easy to use.
Designed to fit into the palm of the
(Japanese) hand, both units are quite
heavy, no doubt the result of the use
of a diecast chassis. The units are
supplied with a 7.2V 700mAh nicad
battery pack which slides inside a
protective cavity at the bottom of the
unit. There are various power output
levels available, all selectable by the
Left: the TH-ZBA 2-metre FM
transceiver features dual-band
receiver capability (VHF/UHF) &
extensive multi-scan functions. The
alphanumeric display allows the user
to dedicate a 6-character identifier to
each of 20 memory positions. Other
features include a DTMF memory
function for storing up to 10 different
telephone numbers plus facilities for
digital message transmission.
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user and dependent upon the capacity of the battery pack fitted. More on
this later.
The array of features is comprehensive and, in addition to the standard
features expected on any basic handheld unit, includes programmable
VFO tuning limits (allows the VFO to
be programmed in 1MHz segments)
and selectable RF output power settings of 5W, 2.5W, 2.0W, 0.5W and
20m W. These levels are dependent on
the voltage and current rating of the
power supply or battery used.
The provision of a transmit lockout
function prevents accidental transmission on a dedicated receive channel,
while an in-built timer (with a maximum period of 10 minutes) prevents
the "stuck microphone" problem, often the cause of blocked FM channels
and particularly annoying if the frequency in question happens to be a
repeater input frequency.
One handy feature is the provision
of a lithium microprocessor back-up
battery which lasts for 20 days, even
when the battery pack is removed.
There are 40 user-selectable memories (50 in the TH-78A), ample for the
number of dedicated FM channels in
any capital city. However, the addition of the "ME-1" memory expansion unit increases this to 239 memories for those operators requiring additional capacity.
Another user friendly feature is the
memory channel character display,
allowing the user to dedicate a 6-character alphanumeric identifier (eg,
VKZRWI) to each of 20 memory positions. This is a particularly useful feature if you are travelling interstate, as
the relevant repeater callsigns can be
entered into memory, along with their
frequencies prior to departure. This
eliminates having to refer to repeater
lists and amateur radio handbooks.
For those wishing to scan parts of
the VHF and UHF bands, both models
provide nine separate scanning options, including "band scan" which
instructs the receiver to scan from the
lowest to the highest frequency limits
and "memory scan" which instructs
the receiver to scan all memory channels containing data. Unused memory
channels and those deliberately
locked out are skipped.
The "VFO/ memory scan" function
instructs the receiver to toggle between
the last used memory channe.l and the
VFO frequency. All scanning functions can be carrier or time interval
controlled.
Phone patch capability
The DTMF memory feature allows
telephone numbers of up to 15 digits
to be stored. This is a handy feature
for those involved in phone patch
operations. The 3-digit dual tone
squelch system (DTSS) allows squelch
activation when a transmission encoded with the same 3-digit code is
received. There are 999 user-selectable
codes, and the duration of the code
burst is extended from 250ms to 450ms
to ensure reliable performance when
you are using repeaters. Apart from
numerals 0-9, the alphabetic characters A, B; C and D can also be used for
repeater control.
This feature, when used with the
paging and DTSS functions, forms the
basis of a digital message system. A
pager facility alerts the operator to an
incoming call and the DTSS feature
displays the ID number of the caller.
In addition, up to 10 alphanumeric
messages can be kept in memory for
transmission as needed, by way of
reply.
If the transceiver is left unattended,
the last 10 digital messages (each up
to six characters long) are stored in
memory and can be recalled and displayed later. The "Time Alert" feature
causes the transceiver to display the
time the last message was received.
Cross-band operation is possible
with both units, although the TH-28A
has no transmit facility on the 70cm
band. The TH-78A allows quite extensive cross-band operations, including full duplex cross-band operation,
and has the ability to receive two
frequencies within the same band at
the same time (either VHF + VHF or
UHF + UHF). By using an external
speaker, both signals can be monitored simultaneously.
The TH-78A also comes equipped
with the "automatic band change"
function, enabling independent control of both UHF and VHF operation.
Both the TH-28A and TH-78A are
equipped with automatic power off
and battery saver functions, to maximise battery endurance. These features, combined with user selectable
RF output power settings, assist in
maximising the operating hours.
In addition, numerous optional accessories are available for both models. Specifically for. the TH-78A,
Kenwood Australia has available the
PB-17 12V 700mAh high-power battery pack, the PB-18 7.2V llO0mAh
long-life battery pack, various soft
cases (dependent upon the battery
pack used), the BT-8 alkaline battery
carrier, the PG-3H filtered cigarette
lighter cord, various speaker microphones, a VOX headset (HMC-2) and
a water resistant bag (WR-2).
Many other options are listed and
appear equally suitable for either TH78A or TH-28A.
Specifications
As for the technical parameters of
these units, we can report that both
receivers met the stated sensitivity
claim of 0.18µV for 12dB SINAD and
exhibited good adjacent channel rejection.
Using an external 13.8V DC power
supply, both transmitters drew 1.4A
when operated in the high-power
mode on 2-metres, while the TH-78A
drew 1.5A on high power on the 70cm
band. At the lowest power setting of
20mW, the TH-78A drew 120mA from
the 13.8V supply.
For those interested, both units use
a first IF of 45.05MHz for the 2-metre
receiver and 58.525MHz for the 70cm
receiver. Selectivity is quoted as 60dB
at 28kHz which, considering the size
of the units , is adequate for UHF/VHF
operations.
The TH-78A has similar features to
the TH-28A but is a full VHF/UHF
dual-band transceiver that can
receive two frequencies at the same
time. A dual encoder provides
independent control of the VHF &
UHF bands.
At the recommended price of $549
for the TH-28A and $879.00 for the
TH-78A; both units offer excellent
value for money. They come complete
with Kenwood's 12-month warranty
and are available from authorised
Kenwood outlets.
Acknowledgement: my thanks to
Mr Yan Sabura of the Kenwood service division for his assistance in providing technical information for this
article.
SC
MAY
1993
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