©1998 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 12/11/02
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piece of paper or a small calculator is
handy to aid in determining which
sections of the switch to turn on.
When done, you might want to record
the switch settings in table 3 for fu-
ture reference.
Begin by subtracting the base fre-
quency, e.g., 144.000, from the de-
sired frequency to determine the total
value of all the switch sections re-
quired to be turned on.
For starters, if the difference is less
than 5.120 MHz, you don’t need to
jumper E6 to E7.
If the difference is
greater than 2.560 MHz, turn on
switch #1, and subtract 2.560 from
the difference frequency to determine
the remainder. Otherwise, skip
switch #1.
Do the same for each of the other
sections, from highest to lowest
weighting, in sequence. Each time
you consider the remainder, turn on
the switch section with the highest
weighting which will fit within the re-
mainder without exceeding it. Each
time it is found necessary to turn on a
switch section, subtract the value of
that section from the remainder to get
the new remainder.
As an example
, let us consider
how to set the Receiver for 146.94
MHz. The following discussion is bro-
ken down into steps so you can visu-
alize the process easier.
a. 146.940 - 144.000 base freq. =
2.940 MHz remainder. Turn on
switch #1, which represents the larg-
est increment to fit remainder.
b. 2.940 - 2.560 value of switch
#1 = 0.380 MHz. Turn on #4, which
is 0.320 MHz, the largest increment to
fit the remainder.
c. 0.380 - 0.320 = .060 MHz re-
mainder. Turn on switch #7 and
switch #8, which have values of .040
and .020, respectively, which adds up
to the remainder of .060 MHz.
Note
that when the remainder gets down
into the double digit range, it is very
easy to visualize turning on multiple
switch sections to satisfy the entire re-
mainder, such as we just did.
d. When we finished, we had
turned on switch sections 1, 4, 7, and
8.
Note:
Dip switch information is
read by the synthesizer only when
power is first applied. If switch set-
tings are changed, turn the power off
and on again.
Shortcut ---
If you have access to the internet,
our website has a long table of num-
bers which gives the equivalent set-
tings for every possible frequency. We
couldn’t print it here because it takes
13 printed pages of space. Go to
http://www.hamtronics.com/dipswitch.htm
.
Look up the frequency, and it will give
you all the switch settings and tell you
if you need to connect the jumper.
The address is case sensitive.
Tricks ---
Although most users will set up
the Receiver on a single frequency and
perhaps never change it, there may be
applications where you want to
change between two or more nearby
frequencies. In such cases, it is help-
ful to note the switch settings for the
lowest of the frequencies and simply
which of the lower value switch sec-
tions to turn on to raise the frequency
to the higher channels. E.g., to
change from 146.790 to 146.820, note
that you need to turn on switch sec-
tions to add 30 kHz to the setting for
146.790. It is not necessary to recal-
culate the whole range of settings.
Another trick if you want to switch
between two or three frequencies used
regularly is to use a toggle switch or
rotary switch and a series of 1N4148
diodes to p5 to the micro-
controller inputs in place of the dip
switch. The diodes isolate the lines
from each other. This unit is not in-
tended to be used in place of a trans-
ceiver with its fancy frequency
programming, but for simple applica-
tions, several frequencies can be
switched this way. The microcontrol-
ler automatically sends data to the
synthesizer whenever the frequency
information at its input is changed; so
changing the rotary switch will clue
the micro to do the change. (Let us
know if you need help deciding how to
connect diodes; we are interested to
find out how many users want to do
this.)
ALIGNMENT.
General Procedure.
A complete alignment is needed
whenever the frequency is changed by
more than about 1 MHz. Alignment
ensures that the frequency synthe-
sizer is optimized at the center of the
vco range and that all stages are
tuned to resonance.
Equipment needed for alignment is
a sensitive dc voltmeter, a stable and
accurate signal generator for the
channel frequency, and a regulated
13.6Vdc power supply with a 0-200
mA meter internally or externally con-
nected in the supply line.
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 having a
small metal bit. (See A28 and A2
tools in catalog.) All variable capaci-
tors should be set to the center of
their range. Turn them 90° if they
have not previously been aligned (ex-
cept on the optional TCXO).
☞
☞
☞
☞
Note:
Meter indications used as
references are typical but may vary
widely due to many factors not related
to performance, such as type of meter
and circuit tolerances. Typical test
point indications are for the 144 MHz
band unit and may differ for other
bands.
a. Set the SQUELCH pot fully
counterclockwise and the VOLUME
pot just a little clockwise.
b. Connect speaker and +13.6
Vdc. You should hear white noise.
c. Set dip switches for desired
frequency.
d. Connect voltmeter to TP2 (top
lead of R6). Adjust vco coil L1 for
+4.0Vdc. (Although the vco will oper-
ate over a wide range of tuning volt-
ages from about 1V to 5V, operation is
optimum if the vco is adjusted to
4.0V.)
e. Connect voltmeter to TP3 (top
lead of R16). Adjust buffer coil L3 for
a peak, typically about +0.5V (about
+0.6Vdc on 220MHz band).
f. Connect stable signal gener-
ator to TP-4 (the top lead of R19), us-
ing coax clip lead. Connect coax
shield to pcb ground. Set generator to
exactly 10.7000 MHz. Use a fre-
Table 2. Frequency Settings
Device Frequency
Weight
Jumper
E6-E7
5.120
MHz
Switch #1
2.560 MHz
Switch #2
1.280 MHz
Switch
#3
640
kHz
Switch
#4
320
kHz
Switch
#5
160
kHz
Switch #6
80 kHz
Switch #7
40 kHz
Switch #8
20 kHz
Switch #9
10 kHz
Switch #10
5 kHz
Table 3. My Switch Settings
Frequency: MHz
Switch Sections Turned On: (circle)
1 2 3 4 5 6 7 8 9 10