5 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 2/1/00
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GENERAL DESCRIPTION.
The CA( ) series of VHF Receiv-
ing Converter modules are designed
to amplify and convert the frequency
of vhf signals in specific bands to 28-
30 MHz.
The input and output connectors
are BNC type when the unit is sup-
plied in a case and RCA type when
the unit is supplied without a case.
The Converter is used to convert
vhf frequencies in a block down to
28-30 MHz so they can be heard on
a 10 meter receiver.
CONSTRUCTION.
Refer to schematic and compo-
nent location diagrams during as-
sembly and the list of frequency-
sensitive parts for your particular
model. Note that there are varia-
tions depending on the use and
packaging of the module. The cor-
rect parts have been supplied for
your particular model to avoid confu-
sion.
General Construction Notes.
Proper polarity must be observed
on diodes and electrolytic capac-
itors. The banded end of a diode is
the cathode. This corresponds to
the bar on the diode schematic sym-
bol used on component location dia-
gram.
Resistors and diodes installed
vertically on a pc board are shown
on component location diagrams as
a circle, denoting the position of the
body of the component, with a line
representing the top lead going over
to the other pc board hole.
Capacitors may be marked in pf
with two significant figures and a
multiplier, much as resistors are
marked. For instance, a 220 pf ca-
pacitor may be marked "221", a .001
uf capacitor may be marked "102"
(1000 pf) or it may be marked 1nK
(for 1 nano-farad with 10% "K" tol-
erance), and a .01 uf capacitor may
be marked "103" (10,000 pf).
A tuning tool of the proper type
must be used to avoid cracking the
slugs in the coils. This is a .060"
square slot type tool. (See "A28
Tuning Tool" in catalog.) The slugs
are teflon coated; so they turn eas-
ily. However, if a loosely fitting tool
or a tool only partially inserted in
the slot is allowed to slip in the slot,
the sideways force cracks the pow-
dered iron slug. Should this hap-
pen, the slug must be drilled out
and replaced.
Assembly Procedure.
a. Install RCA jacks J1 and J2
on pc board except when optional
cabinet is used. Be sure to solder
all tabs. If the connector has only
one tab on the center conductor, po-
sition the connector with that tab
closest to the circuit side of the hole
in the board. Note that the CA120-
10.7 does not use J2 because the
output is tied directly to an adjacent
IF board.
b. Install all resistors on top of
the board. R5 and R6 usually are
not used. Leave small loop at top of
R14 to used as test point. If you are
building the 50 MHz version of the
converter, please read notes on
parts list pages for discussion of
parts not used on that model.
c. Install transistors and zener
diode, being careful to observe
proper orientation. Be sure to keep
lettering (not color bars) up on Q1,
and bend the leads at a 90° angle to
fit the board. Components are not
especially heat sensitive, but Q1
and Q2 are static sensitive; so pre-
cautions should be taken, including
using a soldering iron with a
grounded tip.
d. Refer to parts list for ca-
pacitor values for your particular
model, and install them. The size
and shape of capacitors may vary
with frequency. For example, C6,
C8, and C24 may be disc type capac-
itors instead of tubular type il-
lustrated. It may be necessary to
form the leads of capacitors to fit
the hole spacing of the board.
C26 must be tack soldered under
the board with very short leads as
direct as possible from the gate-2
lead of Q1 to ground along the front
edge of the board. Its purpose is to
provide a good bypass at 900 MHz to
keep the transistor stable; so short
leads are a must. The body of the
capacitor should hang straight down
below the board, not laid over flat
against the pc board traces to avoid
coupling to other circuits.
When the module is to be used
in optional cabinet, C1, C27, C13,
and C14 are connected be tween the
pc board and the BNC jacks. Con-
nect one lead of each to the pc
board as shown. The other end will
be connected later, using shortest
and most direct routing.
e. Install variable capacitor C15
on the top of the board as shown.
After soldering, tack solder C28
across the leads of C15 under the
board, using shortest possible leads.
f. Install crystal Y1. Insert
leads through board and solder,
using care not to apply excessive
heat. Normal soldering heat is OK,
but avoid "cooking" the crystal by
heating pads for excessive periods of
time.
g. Install ferrite bead Z1 as you
would a resistor. It is supplied
prestrung on a piece of bus wire.
h. Coil L5 is no longer used. In-
stall a jumper wire on the top of the
board in place of L5, using #22 bus
wire from a discarded component
lead clipping. Keep the jumper as
short as possible. No shield is used.
i. Install slug tuned coils as
shown, and install coil shields. The
2-1/2 turn (red) coils come with
shields already on the coils; how-
ever, in some cases, the shield
must be removed and rotated 90° in
order to fit holes in pc board. Other
coils have shields supplied sepa-
rately.
Be sure L4 is oriented as shown;
the board is designed to accommodate
several types of coils.
Make sure the coils and shields
are fully seated, and solder both
shield lugs. (Do not bend lugs over,
but you can bend the coil leads over
a little to hold them in place while
soldering.) Note that some coils are
slightly taller than others; so some
coil shield lugs may just barely go
HAMTRONICS® VHF RECEIVING CONVERTERS
HAMTRONICS® VHF RECEIVING CONVERTERS
CONSTRUCTION, ALIGNMENT, & INSTALLATION INSTRUCTIONS
CONSTRUCTION, ALIGNMENT, & INSTALLATION INSTRUCTIONS ©1995 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 2/1/00
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through the board. Hold those in
place carefully while soldering to
make sure solder bonds to the
ground lugs and that the shield re-
mains tight against the board.
Install tuning slugs in any coils
which do not already have them.
j.
Install R15 under the board
as shown. Tack solder it with very
short leads directly across leads of
coil L2.
k. Install any remaining parts,
and check over all parts carefully. If
any parts are left over, be sure they
don't belong somewhere. Check
solder connections.
CASE ASSEMBLY.
If the converter was purchased
with optional case, perform these
additional steps.
a. Set lower half of case on
bench oriented as shown.
b. Fasten one angle nut to hole
half way back on each side, between
the two pc board mtg holes shown in
diagram. (See detail.) Insert 4-40 x
1/4" screw from bottom of case;
then install angle nut from top of
case. The leg with the longer di-
mension from the bend to the hole
goes over the screw, leaving the
side with the shorter dimension for
the cover screws to engage. Before
tightening the screws, carefully
align the angle nuts flush with the
edge of the chassis.
c. Install pc board in case as
shown, using four threaded stand-
offs with 4-40 x 1/4 inch screws to
secure the standoffs to the case and
four more screws to fasten the
board to the standoffs.
d. Install the two BNC jacks as
shown. Put connector through hole,
and align "D" shaped shoulder with
hole. Then, secure with mating
nut. (Note: solder lugs may be sup-
plied with case kit, but they are not
used on vhf converters.)
e. Install feedthrough cap from
front of case, and secure with mat-
ing nut and lockwasher.
f. Tack solder leads of C1, C27,
C13, and C14 to respective BNC
connector center conductors, using
shortest and most direct routing.
g. Solder length of #22 hookup
wire from pad E1 on the board to the
B+ feedthrough terminal on the
front panel, routing neatly as
shown. Keep wire away from C13
and C14, and route it such that it
won't get damaged by the screw in-
stalled later to fasten the cover to
the angle nut.
h. Remove backing paper from
the rubber feet, and stick one in
each corner on the bottom of the
case about 1/2 inch in each way.
i. This completes assembly. Af-
ter alignment, slide top cover over
case, and secure with one 4-40 x
1/4 inch screw in each side.
CRYSTALS.
The converter has recently been
redesigned so it can use either the
traditional third overtone crystals or
fundamental crystals. Your unit
may be supplied with either type,
depending on which type was avail-
able when shipped.
Both are supplied in either HC-
49/u holder (solid pins) or HC-50/u
(wire leads). Either type is soldered
to the board, using care not to apply
excessive heat. Normal soldering
heat is OK, but avoid "cooking" the
crystal by heating pads for excessive
periods of time.
We can provide either standard
or special frequency crytals for the
converter. If you order a special
crystal, you may wish to use a fun-
damental crystal rather than ove r-
tone because they generally cost a
little less at most crystal labs. They
also provide a little more trimming
range. You may also want to specify
HC-50/u holder, which has the wire
leads that are a little easier to sol-
der.
If you use third overtone crys-
tals, specify series resonance for
the crystal. The standard crystal
frequency, and the formula should
you want to order a crystal for a
special application, is as follows.
Model
Crystal
Formula
CA137-28
36.000