©2005 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 5/17/05
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c. 0.380 - 0.320 = .060 MHz re-
mainder. Turn on switch #8 and
switch #9, 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
remainder, such as we just did.
d. When we finished, we had
turned on switch sections 2, 5, 8, and
9.
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 binary
number settings for every possible
frequency. We couldn’t print it here
because it takes many printed pages
of space. Surf to our website at
www.hamtronics.com
and look for Dip
Switch Freq Programming for R302
under Reference Info near the bottom
of the Table of Contents. Look up the
frequency, and it will give you all the
binary switch settings.
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.
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 TP1. Ad-
just vco coil L1 for +2.0Vdc. (Al-
though the vco will operate over a
wide range of tuning voltages from
about 0.5V to 4.5V, operation is opti-
mum if the vco is adjusted to 2.0V.)
e. Connect voltmeter to TP2. Ad-
just buffer coil L3 for a peak, typically
about +0.35V.
f. Connect stable signal gener-
ator to TP-3. Set generator to exactly
10.7000 MHz. Use a frequency
counter or synthesized signal genera-
tor. Set level just high enough for full
quieting. At 1 uV, you should notice
some quieting, but you need some-
thing near full quieting for the test
(about 20µV).
g. Connect dc voltmeter to Dis-
criminator terminal E4. Adjust dis-
criminator transformer T2 for
+3.3Vdc.
0
Be careful not to turn the slug
tight against either the top or bottom
because the winding of the transformer
can be broken. The tuning response is
an S-curve; so if you turn the slug sev-
eral turns, you may think you are go-
ing in the proper direction even though
you are tuning further away from cen-
ter frequency.
h. Connect signal generator to J1
using a coax cable with RCA plug.
Adjust signal generator to exact chan-
nel frequency, and turn output level
up fairly high (about 1000µV). Adjust
frequency trimmer in TCXO to net the
crystal to channel frequency, indi-
cated by +3.3Vdc at E4.
Note:
There are two methods of
adjusting the mixer and front end.
One is to use a voltmeter with test
point TP-4. 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
the receiver. With SQUELCH control
fully ccw, the dc voltage at TP-4 varies
from -0.5 Vdc with no signal (full
noise) to +1 Vdc with full quieting sig-
nal.
The other method is to use a regu-
lar professional SINAD meter and a
tone modulated signal.
In either case, a weak to moderate
signal is required to observe any
change in noise. If the signal is too
strong, there will be no change in the
reading as tuning progresses; so keep
the signal generator turned down as
receiver sensitivity increases during
tuning.
If you use TP-4 with a voltmeter,
the signal can be modulated or un-
modulated. If you use a SINAD meter,
the standard method is a 1000 Hz
tone with 3 kHz deviation.
i. Connect fet dc voltmeter to
TP4. Set signal generator for relatively
weak signal, one which shows some
change in the dc voltage indication at
TP4. Alternately peak RF amplifier
and mixer coils L4-L8 until no further
improvement can be made.
When properly tuned, sensitivity
should be about 0.15 to 0.2µV for 12
dB SINAD.
Table 2. Frequency Settings
Device Frequency
Weight
Switch
#1
5.120
MHz
Switch
#2
2.560
MHz
Switch
#3
1.280
MHz
Switch
#4
640
kHz
Switch
#5
320
kHz
Switch
#6
160
kHz
Switch #7
80 kHz
Switch #8
40 kHz
Switch #9
20 kHz
Switch #10
10 kHz
Switch
#11
5
kHz
Table 3. My Switch Settings
Frequency: MHz
Switch Sections Turned On: (circle)
1 2 3 4 5 6 7 8 9 10 11
+3.3Vdc
Figure 1. Discriminator tuning curve.
