HAMTRONICS R451 Installation Operation & Maintenance

INSTALLATION, OPERATION, & MAINTENANCE
FUNCTIONAL DESCRIPTION.
The R451 is a premium, com-
mercial- grade single-channel uhf fm
receiver. It features a GaAs FET rf
amplifier for very good sensitivity, an
8-pole crystal filter plus a ceramic
filter for supe rior i-f selectivity, and a
hysteresis squelch circuit to lock
onto fading signals.
The R451 kit is available for the
420-470 MHz band, and wired units
are available for this band and also
the commercial and
bands directly above and below this
range.
CRYSTALS.
The channel crystal plugs into
sockets identified in component lo-
cation diagram as Y1. We can order
crystals for any frequency desired. If
you order your own, be sure to supply
these specs.
The receiver uses 32 pF parallel
resonant crystals in HC-25/u hold-
ers. Crystals operate in the funda-
mental mode at a frequency of (F-
10.7)/27. Frequency tolerance is
.001%. We recommend that any new
crystals be ordered directly from us
to be sure that they will perform
properly over the -30 to +60°C range
for which the unit was designed.
This is especially true for commercial
receivers with the
compensated crystal
(TCXO) option, since the crystal must
be matched exactly to the compen-
sation circuit in the receiver. If you
use an OV-1 crystal oven, spe cify a
crystal with a 60°C breakpoint.
POWER CONNECTIONS.
The receiver operates on +13.6
Vdc at about 150 mA peak with full
audio. Current drain with no audio is
only 35-40 mA. A crystal oven adds
about 450 mA peak current drain
when cold and only about 25 mA
when warm. A well regulated power
supply should be used.
Be sure that the power source
does not carry high voltage or reverse
polarity transients on the line, since
semiconductors in the receiver can
be damaged. The positive power sup-
©1994 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark.
HAMTRONICS® R451 UHF FM RECEIVER:
ply lead should be connected to the
receiver at terminal E3, and the
negative power lead should be con-
nected to the ground plane of the
board through the mounting hard-
ware or the shield of the coaxial ca-
ble. Be sure to observe polarity!
SPEAKER.
An 8Ω loudspeaker should be con-
nected to E2 with ground return to
the ground plane through the mount-
ing hardware.
government ance speaker or shorting of speaker
terminal can result in ic damage.
The receiver can also drive higher
impe dances, like 1K to 10K input im-
pedances of COR boards, etc. There
is no need to load down the output to
8Ω.
Note that the audio output ic is
designed to be heat sunk to the pc
board through the many ground pins
on the ic. When running moderately
low audio levels as most applications
require, it is no problem to use an ic
socket; so we have provided one for
your convenience. If you will be run-
ning high audio levels, check to see if
the ic is getting hot. If so, you should
remove the ic socket, and solder the
LM-380 ic directly to the board for
better heatsinking.
ANTENNA CONNECTIONS.
temperature- The antenna connection should be
oscillator made to the receiver with a phono
plug. If you want to extend the an-
tenna connection to a panel connec-
tor, we recommend using a
length of RG-174/u coax and a good
phono plug with cable clamp (see
catalog). We do not recommend try-
ing to use direct coax soldered to
board or another type of connector.
The method designed into the board
results
When soldering the cable, keep the
stripped ends as short as possible.
ALIGNMENT.
Equipment needed for alignment
is an fet voltmeter, an rf signal gen-
erator, a regulated 13.6Vdc power
supply with a 0-200 mA meter inter-
nally or externally connected in the
supply line.
Use of lower impe d-
short
in lowest loss practical.
The slug tuned coils in the re-
ceiver should be adjusted with the
proper .062" square tuning tool to
avoid cracking the powdered iron
slugs. Variable capacitors should be
adjusted with a plastic tool with a
small metal bit on the end. Tools are
available for adjusting the rf coils
(model A28) and for variable capaci-
tors (model A2).
Unless already tuned once, vari-
able capacitors C1, C5-C8, and C14
should be set to midrange, as in-
dicated by the slot on the rotor being
aligned with the ends of the capaci-
tor (as illustrated for C6 in the parts
location diagram). The SQUELCH pot
should be set fully counterclockwise.
a. Install channel crystal in
socket Y1.
b. Connect speaker and +13.6
Vdc. You should hear white noise.
c. Connect dc voltmeter to TP3
(top lead of R18). Adjust first L4,
then L3 and L4 alternately for maxi-
mum response. (Typical indication is
about +1.5 Vdc.)
d. Connect dc voltmeter to TP4
(top lead of R9). Adjust L5 and L6 al-
ternately for maximum
(Typical indication is about +1.5 Vdc.)
e. Connect stable signal gener-
ator to TP5 (left end of coil L11), us-
ing coax clip lead. Set generator to
exactly 10.7000 MHz.
quency counter or synthesized signal
generator. Set level
enough for full quieting. (At 5-10 uV,
you should notice some quieting, but
you need something near full quiet-
ing for the test.
f. Connect dc voltmeter to TP1
(top lead of R16). Adjust discrim-
inator transformer L8 for +3.5Vdc.
Note that the voltage changes very
rapidly with tuning. Full swing of
about 1 to 8V occurs within a few
kHz.
Note: There are two methods of
adjusting the mixer and front end.
One is to use an fet voltmeter with
test point TP2, which is the top lead
of CR3. The voltage at this point is
proportional to the amount of noise
detected in the squelch circuit; so it
gives an indication of the quieting of
Revised: 10/23/02
response.
Use a fre-
just high
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