Fig. 4
-
Rf
envelope vs. keying waveform of
the unit as received. The upper trace
is
the
switching waveform at the FT-7B key jack and
the lower trace is the output envelope. The
horizontal scale
is
10 msec per division.
Fig. 5
-
After radical surgery, the keying
looked like this. In this photo, the horizontal
scale
is
5 msec per division. The modification
information is printed in "Hints and Kinks."
Fig.
6
-
Here's the keying resulting from
Yaesu's suggested modification (see text).
Horizontal scale is 5 ms per division.
The
YC-7B
Frequency Display
Mobile operators must be able to determine
their frequency quickly, with no more than a
glance away from the road. The
YC-7B remote
digital display fills this need. The unit is an op-
tional accessory that plugs into a rear-panel
socket of the FT-7B. Stick-on Velcro strips
allow the display to be mounted anywhere
within reach of the umbilical cable.
The YC-7B counts the final mixer injection
frequency. Preset commands from the FT-7B
ensure proper carrier frequency readout on all
modes. On 80 meters, an 18-MHz crystal
oscillator heterodynes the LO signal to the
proper range for the counter. The time-base
frequency is 655.36 kHz. No special
temperature compensation is used, but the
overall stability should be at least an order of
magnitude better than that of the FT-7B VFO.
The readout resolution is 100 Hz, but the in-
strument counts down to 10 Hz, with a
0.1-second gate time. This unit does not add
any spurious responses to the receiver.
Construction
Most of the FT-7B circuitry is assembled on
a dozen phenolic pc cards which plug into three
mother boards. The card sockets are individual
gold-plated spring pins soldered into the
mother boards. The mobile operator needn't
worry about the reliability of the sockets -the
cards are held firmly in place by the top cover.
Two wired-in pc boards and the VFO and PA
modules complete the electronics. The VFO
and PA are shielded, of course. Most of the
tuned circuits are on the mother boards, so you
can repeatedly remove and reinstall the plug-in
cards without upsetting the alignment. The PA
heat sink protrudes from the rear panel. The
sink is adequate for voice and cw duty cycles.
The a-m rating applies to RTTY and SSTV ser-
vice. Two screws secure a flat plate to the heat
sink fins. A small fan could be mounted to this
plate very conveniently.
Aesthetics and Impressions
The unit certainly is compact. That's not sur-
prising, considering the cars it was designed to
be installed in. At a time when the styling of
Amateur Radio equipment is diverging toward
the "military" and
"hi-fi/furnitureM looks,
the FT-7B represents a refreshing alternative to
these extremes. The cabinet is painted a
businesslike metallic blue that won't look
out-
of-place in your car or on your kitchen table.
The four-color dial and meter are highly visi-
ble, yet not at all garish. For fixed service, the
Table
2
YC-7B
Remote Digital Frequency Display
Specifications
Resolution: 100 Hz
Clock frequency: 655.36 kHz
Gate time: 0.1
sec.
Operating temperature: 0-40" C
Power connections: from FT-7B
Dimensions (HWD):
1-518
x
3-518
x
5-318
inches (40
x
93
x
135 mm)
Weight: 12-112 oz (360 g)
Price class: $1 10
Manufacturer: Yaesu
Musen Co., Ltd., Tokyo,
Japan
analog dial is easy to read, and with its 1-kHz
resolution and good linearity, you really don't
need the optional digital readout. It's handy,
though, for precise clarifier tuning and keeping
track of the VFO. All of the controls are con-
veniently located.
I experienced a small amount of TVI while
operating the rig into a dummy load on the
same table with my plastic-encased television
set. You may have to scrape some paint off the
mating metallic surfaces of the FT-7B
enclosure if you live in a weak TV signal area.
A
QST
advertisement for the FT-7B reads:
"Enough power to drive those linears!" The
manual makes no mention of using the
transceiver with an external amplifier, but if
you dig into the schematic diagram, you'll find
that the
alc line and the 13.8-volt transmit line
(to control a relay) are brought out to the
power connector. There's an unused set of con-
tacts on the T-R relay, but they aren't accessi-
ble from outside the transceiver.
The attention Yaesu paid to the a-m mode is
perplexing. If the intent was to make the
transceiver compatible with converted CB rigs,
a better solution is to install
BFOs in the CB
rigs. If you want to participate in the second
genesis of a-m, you'll never compete with those
plate-modulated Valiants and
DX-IOOs! I
would much prefer to see the a-m mode scrap-
ped in favor of some advanced
ssb/cw
features, such as sharp i-f selectivity, full
break-in, VOX and even (bite my tongue)
speech processing.
Tinkerers will love this rig, for one can
remove most of the cards without unsoldering
any wires. If you like, you can fabricate a com-
pletely new set of cards. Serious experimenters
will undoubtedly conceive numerous worth-
while modifications. With a little ingenuity, a
remote VFO could be plugged into one of the
fixed-channel crystal sockets. Another possible
improvement would be a VFO drift correction
circuit using feedback from the YC-7B. If you
apply the correction voltage to the wiper of the
dial calibration potentiometer, you won't have
to violate the VFO compartment.
The FT-7B offers something for everybody.
You can have plenty of fun with it just like it is.
And if you're ambitious, you can turn it into a
truly deluxe station. The equipment is covered
by a three-month limited warranty.
-
George
Woodward,
WlRN
HEATH
SB-221
LINEAR AMPLIFIER
10
Y
I<=-r
a~~c~'~
How does the SB-221 differ from the earlier
SB-220' amplifier? The major difference, elec-
trically, is an unfortunate by-product of FCC
action to prevent amateur-equipment manufac-
turers from including our 10-meter band in
linear amplifiers: The SB-221 does not operate
on 10 meters! The band-switch panel markings
read only "80, 40, 20 and 15" (meters).
Heath Company and other commercial
manufacturers of hf-band amateur amplifiers
are required to ensure that all amplifiers re-
quire at least 50 watts of driving power and
that they must be incapable of operation at 27
MHz. They can't, therefore, operate at 28
MHz without elaborate and highly expensive
circuitry which is beyond manufacturing
reason. All of this came to pass because of
widespread illegal operation by
CBers who pur-
chased amateur-band linear amplifiers and
employed them at 27 MHz. The FCC's inabili-
ty to enforce the CB regulations imposed a
severe economic and marketing hardship on
the amateur-equipment manufacturers as well
as the amateurs. These regulations, fortunate-
ly, do not apply to vhf and uhf types of
amplifiers.
SB-221
Features
The popular and reasonably priced amplifier
can be made to work satisfactorily on 10 meters
by converting it back to an SB-220. More on
that later. But, let's examine the circuit and
features for the benefit of those who are con-
templating the purchase of a "pair of shoes"
for that presently "barefoot" 'exciter.
In its present form, the SB-221 operates in
the 80, 40, 20 and 15-meter bands. The re-
quired driving power is 100 watts maximum.
Rf power amplification is accomplished by
means of two
3-5002 triode tubes which are
forced-air cooled. These well-proven tubes
"'Recent Equipment,"
QST,
August
1970,
p.
45.
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