GW4GTE RAT5 Quick setup guide

RAT5 Information Manual 1.2.0
August 2010
This manual is the complete reference document for RAT5, containing all aspects of
construction and operation.
This manual refers to RAT5 hardware version 1.2
Please check you are reading the latest version of this document by checking
www.s9plus.com for any updates.
Please read this document fully before commencing construction
There are bound to be errors please report any you find !
© GW4GTE 2010
www.s9plus.com

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RAT 5
A Single-Conversion AM Re eiver Kit for 160m or 80m
RAT5 kit of parts
Easy to Build
This kit is suitable for constructors with little or no previous experience of kit-
building. A basic level of soldering ability is however required. All components
are through-hole mounted i.e. no surface mount parts.

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Contents
1 Introdu tion………………………………..……….….…….. 4
1.1 Modification Record - updates and corrections
2 Cir uit Des ription……………………….…………...……. 7
2.1 Key Features
2.2 RF / IF Circuits
2.2.1 RF Filter
2.2.2 Local Oscillator
2.2.3 IF Filter
2.3 AF and Squelch circuits
2.3.1 Squelch
2.3.2 Audio Filtering
2.3.3. Audio Amplifier
3 Constru tion….……………………………………..……… 10
4 Testing and Alignment …………………………………… 13
4.1 Power-off Tests
4.2 Power-on Tests
4.3 Local Oscillator alignment
4.4 IF and RF Alignment
4.4.1 IF Alignment
5 Interfa ing …………………………………………….…….. 18
5.1 Connection Method
5.2 Connections
5.3 Connecting an S-Meter
5.3.1 Calibration
5.4 Operation with a transmitter
5.5 Squelch Out
5.6 Power Sources
5.7 Choice of enclosure and Dimensions
6 Troubleshooting………………………..…………….…….. 22
6.1 Continuity checks
6.2 Voltage checks
7 Appendi es…………………………………………….…….. 23
7.1 Parts List
7.2 Circuit diagrams - larger version
7.3 PCB Layout
7.4 “Anti-SSB” AGC modification for nuisance-free monitoring
7.5 Builder’s Gallery

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1. Introdu tion
What is it?
The RAT5 is a single conversion AM receiver for 80m and 160m (operation on other
frequencies is also possible).
The receiver is based on the TDA1072A AM receiver IC which although obsolete is still
available in quantity from at least one source and a reasonable number has already been
obtained for kit builders.
The low cost and ease of construction make this an ideal club project, and to this end
component values are also provided to cover the Medium Wave where signals to tune into
are plentiful. No previous experience of kit-building is required, just basic soldering skills.
What does RAT5/FAT5 mean?
For some years now the author has been playing about with home brew solid state AM
transmitters, largely based on solid-state Class-E designs using low cost FETs. This is the so-
called FAT5 series.
The FAT5 name came from the original idea of making a solid state version of the AT5, using
FETs. So, FET-AT5 became truncated to FAT5. RAT5 is an AM receiver to go with the FAT5
transmitter project. Maybe the complete RX/TX could be the FAT-RAT project?
Is there a kit?
Yes. Based around a 3”x2” drilled and tinned single-sided fibre-glass PCB the kit contains all
the components for the project. All that is required in addition is an antenna, power source,
loudspeaker, control knobs and case. For ordering details check www.s9plus.com or email
the culprits below.
It’s a big manual for a little kit?
This is the complete reference document containing everything about RAT5. To just build the
kit most of the sections can be ignored. Please read the entire document before starting
construction.
Proje t Support
This is a supported project, with free advice offered before, during and after construction.
Who to Blame
Circuit design and PCB layout by Dave GW4GTE.
PCB production and kit distribution by Eric GW8LJJ.
Conta t Points
Dave GW4GTE: gw4gte @s9plus.com; address is QTHR or see QRZ.com
Eric GW8LJJ: [e-mail] ; address is QTHR or see QRZ.com
A knowledgements
The author extends grateful thanks to ‘Ferric’ Eric GW8LJJ for the production of such
excellent PCBs at ham-friendly prices. It is no exaggeration to say this and several other
designs would never have seen the light of day as completed projects without Eric’s
enthusiasm and support.

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1.1 Modifi ation Re ord
Changes to the information manual
This manual is Version 1.2.0. The previous manual was version 1.1.4
• A drawing error was reported in the previous circuit diagrams figure 2.1 and
Appendix 2 : VR1 was drawn as fed from the C13 side of R2. It should be
connected to the C28 side. This is now corrected.
• FL1 in the circuit diagrams of figure 2.1 and appendix 2 is now annotated as
ALFY455GT to reflect the part change (see below)
• Appendix 3 (PCB layout) incorporates the track changes detailed below.
Changes to the PCB
The PCB to which this manual refers is version 1.2. The previous PCB was version 1.1.
New IF filter
PCB Version 1.2 incorporates a different 455kHz filter. We have now managed to
source a slightly narrower filter while keeping the kit price the same. The new filter is
+/- 4.5 Khz wide at -6dB, previously it was +/- 6kHz wide at -6dB. The filter pinout is
slightly different, requiring a modification to the PCB layout. If existing kit owners wish
to try the new filter and are happy to adapt the previous PCB the new filter can be
supplied as an upgrade. No other circuit changes are required.
Tra k modifi ation
The PCB track around the pins of RV1, RV2 and RV3 have been thickened to provide
more strength when using the potentiometer fixing threads to support the PCB.

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2. Cir uit Des ription
Abbreviations: LO – Local Oscillator, CW – clockwise, CCW – Counter-clockwise
PD – Potential difference, MW – Medium Wave, F – adio Frequency
IF – Intermediate Frequency, IC – Integrated circuit, AM – Amplitude Modulation
AF – Audio Frequency, AGC – Automatic Gain control, X – eceive(r)
RAT5 is a varicap tuned single conversion superhet of conventional design based around the
TDA1072A AM receiver IC. Figures 2.2 (RF/IF) and 2.5 (AF/Squelch) show the circuit in its
entirety.
2.1 Key features
High sensitivity
Signals around 1uV PD are detectable.
Good AM sele tivity
A 6-pole 455kHz AM filter has been selected for good adjacent channel selectivity. Bandwidth
is +/-4.5 kHz at -6dB and +/-10kHz at -50dB. (previous version used a 6kHz filter).
Input bandpass filter
A two stage bandpass filter provides adequate protection against image breakthrough.
Carrier Squel h
The TDA1072A does not provide a squelch facility as it is intended for broadcast AM
reception in consumer equipment. In amateur use a squelch feature is useful and this has
been designed into the circuit.
Low power onsumption
RAT5 consumes typically less than 50mA from a 9V to 15V supply making it suitable for
battery operation.
2.2 RF/IF ir uits
Refer to Figure 2.1
The only active component in the RF/IF section apart from regulator VR1 is U1, a TDA1072A
AM receiver IC around which everything else based. U1 performs all the main functions of a
single conversion AM superhet including RF amplifier, LO, mixer, detector, AF pre-amp and
AGC system, considerably simplifying the supporting circuitry.
2.2.1 RF Filter
With a 455kHz IF the image frequency is 910kHz away from the wanted signal. T1
and T2 together with C1 C2 and C3 form a two section bandpass filter with sufficient
selectivity to prevent image breakthrough.
Toko KANK3333 RF transformers are used for T1 and T2 as well as for L1 and L2.
These are no longer manufactured by Toko, but equivalent transformers have
recently become available in quantity. For simplicity the bandpass filter is fixed tuned.
The added complication and expense of tracking varicap tuning is unnecessary for
the narrow range of frequencies the intended application covers i.e. AM frequencies
on 80m/160m

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Figure 2.1 RF and IF ir uit
A low-side LO on 80m and a high-side LO on 160m places the image in relatively
quiet parts of the spectrum. The image frequency for 3615kHz is 2705kHz and the
image frequency for 1963kHz is 2873kHz. Compare with say a low-side LO on 160m
which would produce an image frequency in the MW broadcast band!
Figure 2.2 below is an actual plot of the bandpass filter on 80m showing the image
attenuation for a receive frequency of 3615kHz
Figure 2.2 A tual plot of RF bandpass filter on 80m

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2.2.2 Lo al Os illator (LO)
The LO frequency is determined by L1 C14 and the series combination of VC1 and
varicap diode D1. VR1 provides a stabilised 5 V for tuning control RV1. VC1 can be
varied to control the tuning range provided by RV1. R17 limits the minimum tuning
voltage to around 0.9 V reducing the non-linearity at that end of the varicap’s tuning
characteristic.
The circuit values given are for a low-side LO on 80m and a high-side LO on 160m.
e.g. 3615kHZ RX, LO = 3160kHz ; 1963kHz RX, LO = 2418kHz
For Medium Wave operation it is suggested the LO runs on the high side.
The IC provides a buffered local oscillator output, and this is brought out to PL2 for
use with a frequency display (future add-on project) and to assist with setting up.
2.2.3 IF Filter
The IF tuned circuit L2/C4 is tuned to 455kHz giving a good match into the IF filter
FL1, a 6-pole ladder filter from Toko. This is a simpler solution than the circuit
suggestions in the IC manufacturer’s data sheet. Figure 2.3 below shows an actual
plot of the IF passband. (Note the graph shows passband response only, not ultimate
out-of-band rejection for which a larger test signal would be required).
Figure 2.3 A tual plot of IF passband response of 6kHz filter
(4.5kHz filter now supplied – response similar but narrower).
C9 and C10 give time constants for the internal AGC circuitry in line with data sheet
recommendations. The AGC has a fast response which copes well with rapid signal
fading.
The S-meter output is brought out to PL4 for use with a meter or other display (see
Section 5.3). The same line feeds the squelch circuitry shown in Figure 2.4.

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2.3 AF and Squel h ir uits
Refer to Figure 2.4
2.3.1 Squel h
U2/a is one half of an LM358 op-amp IC, wired as a comparator. The LM358 was
chosen for its ability to function at near-ground input levels while working off a single
rail supply.
RV2 sets the voltage on the non-inverting pin. AGC volts are fed into the inverting pin.
With no input signal RV2 is adjusted such that pin 3 is more positive than pin 2. The
output on pin 1 is high, saturating Q1 via D2 and R10. Q1, working as a potential
divider with the U1 demodulated audio output impedance of 3k5 (as stated in
datasheet) attenuates the ongoing signal to inaudible levels.
When a carrier is received such that the AGC line at U2 pin 2 goes more positive than
the level on pin 3 the comparator output will drop to zero, cutting off Q1 and enabling
the audio path.
The time constant provided by C30 / R10 reduces squelch clicks, as does the use of
C20 to isolate Q1 from the bias chain R11/R12.
External override muting is provided via limiting resistor R8. U2 is isolated by D2.
Apply a positive voltage of 5V to 12V to PL3/6 to mute the receiver. This is intended
for transceiver use as a means of muting the receiver while keeping the local
oscillator running. C20 prevents squelch operation affecting the bias on U2/b, giving
a clean squelch function with no clicks or thumps.
Figure 2.4 Audio and Squel h ir uit
PL3/6 can also be used as an output to drive a squelch LED (see Section 5.5). PL3/6
is high on mute and low when the squelch is open.

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2.3.2 Audio Filtering
The basic filtering suggested in the manufacturer’s data sheet has been discarded in
favour of the circuitry shown. U2/b is an active low-pass filter with values chosen for
the required response. R16 / C26 also add another pole of filtering. The aim was to
produce a broadly level response from 300Hz to 3000Hz with a gentle roll-off at LF,
steeper roll-off at HF, and a slightly rising response through the passband to improve
clarity. Figure 2.5 below shows an actual frequency response plot of a prototype unit.
The steepening LF roll-off is caused by the increasing reactance of C27 which
becomes significant at lower frequencies.
2.3.3 Audio Amplifier
The loudspeaker amplifier U3 is an LM386. This inexpensive 8 pin DIP package
provides adequate volume with any loudspeaker of average efficiency. It was found
that the IC’s minimum gain of 20 was more than required so one of the gain control
pins (pin 8) was used to apply negative feedback via the negative input (pin 2) to
reduce gain further.
C25 / R15 create a pole to eliminate high frequency instability (values as per
datasheet), and no such problems have been encountered during testing.
Figure 2.5 A tual plot of audio response at LS output
.

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3. Constru tion
Before you start
(Tick when done)
(__) Make life easy for yourself by clearing a good sized work-space on the
bench. You’re going to need a pair of thin-nosed pliers, some side-cutters
and a good soldering iron with a small tip fitted e.g. Weller. A tip temperature
of 700C (Weller tip number 7) is recommended, as is the use of ‘proper’
60/40 flux cored colder. Use 22swg solder if possible. Anything thicker is
almost certain to bridge tracks.
A bench vice or ‘helping hands’ may be useful for holding the PCB during
assembly and a stamp loupe is handy for checking your work and inspecting
tracks. Maplin sell a range of these.
(__) Print out the parts list, circuit diagrams and PCB layout from the appendix at
the end of this document and keep them to hand.
(__) Check the components supplied against the parts list. You may wish to
arrange them in some sort of order as you proceed to ease identification
later.
(__) Inspect the PCB. In the interest of cost the boards have been produced
without a solder resist layer or a silk screen layer. Careful soldering and a
logical assembly order make these features non-essential. Hold the PCB up
to a suitable light source or simply hold up to the sky, looking from the copper
side, then check all holes are drilled. The boards will have been carefully
checked but as they are hand-drilled there is always the chance a hole could
be missed. It’s easier to correct any problems now rather than when the PCB
is half populated.
(__) Before soldering anything, offer the following parts to the PCB to check for fit:
T1 and T2, L1 and L2, RV1, 2 and 3 and FL1. Also the board connectors
marked as PL1, PL2 and PL3. Note you may need to snip the header strip
supplied to the correct length. T1, T2, L1 and L2 have two screen tabs. Only
one is used. Identify which is unused and snip off. The same tab is unused on
all four components.
Start Soldering
The project is PCB based and no surface mounted components are used, making
construction quite straightforward.
First though a few words about soldering. Don’t use the soldering iron as a solder transport
system (You don’t want to start off with a big blob of solder, or burn off all the flux before you
get to the joint and the connections to be soldered should be up to temperature before they
see the solder). The two parts of the joint should be mechanically touching (as far as is
possible with PCB track and components) then heat applied from a clean, tinned-tip iron for a
couple of seconds. Then apply solder to the site, letting the iron heat the job properly to give a
smooth solder flow. Then remove the iron, taking care to lift the iron vertically away to reduce
the risk of bridging to an adjacent track. Don’t rush it – the components are designed to take
the heat.

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The following is merely a recommendation for assembly order:
(__) Solder the IC so kets for U1, U2 and U3. These will serve as landmarks to
assist component placement. Make sure the sockets are fitted the correct
way round. Support the sockets to keep them flush with the board when
soldering. At first only solder two diagonal pins then check for correct
alignment before continuing.
(__) Solder all the resistors, ticking them off from the parts list as you proceed. If
any values are difficult to identify use a multi-meter to check. All resistors
have the same lead spacing on the PCB and all are mounted horizontally.
Bend the leads close to the resistor body by simply bending using a finger.
Gentle pressure should produce the correct lead spacing. Take care to align
the colour codes so that all resistors can be read in the same direction. Push
the leads through the PCB holes then bend the leads outwards slightly to
hold the part in place. Several resistors can be placed at a time in this way
then soldering done in batches. Snip the leads after soldering not before (this
reduces the thermal shock slightly and removes the risk of cutting the lead
too short before soldering)
(__) Solder all the erami apa itors, ticking them off from the parts list as you
proceed. Little if any lead bending will be needed. Solder in batches if
preferred. Orient the capacitors such that the values are visible from the
same side.
(__) Solder Q1 VR1 and D1 taking care not to mix them up they look similar.
Follow the case orientation shown on the PCB layout. The middle pin of Q1
may require bending depending on the type supplied.
(__) Solder D2, 1N4148 making sure the band orientation matches the PCB
layout image.
(__) Solder FL1. Take extra care not to overheat this component.
(__) Solder VC1, ceramic trimmer applying extra solder onto the larger pads for
greater mechanical rigidity.
(__) Solder the ele trolyti apa itors, carefully observing the correct polarity.
The negative pin is adjacent to the side marked with a stripe down the side of
the plastic case insulation. Polarity is marked on the PCB layout.
(__) Solder the transformers T1, T2 and indu tors L1 and L2. Note they are all
the same component type. If the unused screen tabs haven’t been snipped
off already, snip off now, double checking you are snipping the correct one!
All four parts use the tab on the same side. Tin the earth tab before inserting
the coil into the PCB this avoids overheating the PCB track should tinning
take a while to complete.
(__) Solder PL1, PL2, PL3 and PL4. Snip the pin strip supplied if required. Note
PL3 can be left as a 10-pin strip. Snip pins flush to the PCB in unused
positions. SK3 can be left as a 10-pin connector. See Section 4.1 for
suggestions re connecting external leads.
(__) Solder RV1, RV2 and RV3 Note RV1 and RV2 are linear (marked B10k),
RV3 (volume) is logarithmic (marked A10k).
This ompletes the PCB soldering pro edure. Next arry out the
ontinuity he ks in se tion 3.1 below.

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3.1 Continuity he ks.
IMPORTANT
Please do not omit these he ks. The only returns to date have been due
to solder bridges whi h the he ks below would have found.
(__) Carry out a careful visual inspection of the track using a magnifying aid.
(__) With no ICs inserted, carry out a resistance test from each IC pin to the
adjacent ones. There should be no short circuits detected except U2 pins 6
and 7. The only low resistance should be between U1 pins 11 to 12, reading
through L1 and R3 (typical reading: 23 ohms)
(__) Carry out a resistance test from each IC pin to earth. The only pins that
should be directly connected to 0 V are: U1/2, U1/16, U2/4, and U3/4.
U2/3 and U3/3 will read to earth via RV2 and RV3 sliders respectively when
the controls are fully CCW vary the controls to confirm.
Before inserting the ICs carefully check all soldered joints using a magnifier, looking for solder
bridges. Hold the PCB up to a light source and check for any remaining holes that indicate
missed off components.
(__) Fit the ICs. They are not over-sensitive to static but take basic precautions
anyway for safety. Before handling the ICs hold the PCB earth plane and at
the same time touch something at earth potential. Double check the ICs are
inserted the correct way round. Some ICs may supplied with pins splayed out
slightly and may need bending parallel to ease insertion. Take care not to
confuse U2 (LM358) and U3 (LM386).
This ompletes the PCB assembly
Your completed PCB should look like this:
Figure 3.1 Completed PCB
Now pro eed to Se tion 4. Testing and Alignment.

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4. Testing and Alignment
Having completed Section 3, the receiver can now be tested and aligned. No special test
equipment is needed although a frequency counter and signal generator would prove useful.
Instead of a counter an HF receiver can be used to measure the LO frequency. Instead of a
signal generator a transceiver set to CW or FM with the power turned to minimum can be
used together with a suitable attenuator. Do not connect a transmitter directly into the RAT5
antenna input use a tapped attenuator or sniffer wire. Please contact the authors if unsure
how to proceed.
This looks diffi ult?
The procedure may at first glance seem involved. In actual fact it amounts to little more than
tuning the LO coil to the correct frequency and peaking three other coils for a maximum meter
reading.
If any tests fail, carefully repeat the procedure to confirm the problem then
refer to Section 6 : Troubleshooting.
4.1 Power-off Tests.
(__) Firstly and most importantly carry out a careful visual inspection of the track
using a magnifying aid.
(__) With no leads connected, using a multi-meter, measure the resistance across
the power input pins, PL3/1, 2. Connect the positive (red) meter lead to
PL3/2. A typical reading is 24k ohms after allowing the reading to settle. A
lower reading or a short circuit indicates a fault.
4.2 Power-on Tests.
Refer to Section 5, Interfacing for connection details. The Squelch / Mute connector PL3/5, 6
is unused in these tests.
Preparation.
(__) Do not switch on just yet. Connect an unpowered DC power supply of
between 9V and 15V to PL3/1, 2. (Pin 1 is 0V). Connect a milli-ammeter or
multi-meter set to DC mA in series with the supply.
(__) Conne t LO-Out PL2/1, 2 to a frequen y ounter. A resolution of 1 kHz is
sufficient. In the absence of a suitable counter, attach a length of wire such
that a suitable receiver can pick up the signal. Do not directly connect the
receiver the LO output is too high a level.
(__) Loudspeaker (LS) PL3/9, 10
Connect an 8 ohm or higher impedance loudspeaker to PL3/9, 10.
(__) Set the potentiometers as follows:
RV1 (tuning) to centre travel. RV2 (squelch) fully CCW. RV3 (volume) fully
CCW.
(__) Pre-set T1, T2, L1 and L2 by adjusting the ferrite ores.
Carefully unscrew each core CCW until the top of the core is flush with the
nylon thread. Now screw the core 3 turns (6 half-turns may be easier to
count) CW back down into the inductor.

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(__) Pre-set VC1 by adjusting to a entre position. Set the VC1 screwdriver
slot perpendicular to the line of pins of U1.
Test Pro edure
(__) Apply power.
Check the current drawn is in the region of 45mA. The milli-ammeter may
now be removed if preferred.
(__) Slowly advan e the volume ontrol until a slight hiss is heard, then
advance the squelch control until the hiss stops. This tests the basic squelch
and audio circuitry functionality.
(__) Return the squelch control to the fully CCW position and set the volume
control to about 30%
4.3 LO Alignment
LO Alignment Overview
Using L1 and VC1 adjust the LO frequency so that tuning control RV1 gives the desired
coverage.
Alignment of the RAT5 is a straightforward procedure. Units tested so far have needed very
little coil adjustment from the preset settings detailed earlier. The procedure below basically
consists of setting the LO frequency, applying a strong signal, then tuning the RF and IF coils
for a maximum S-meter reading.
Detailed des ription:
(__) Set the LO frequen y.
Firstly establish the LO is running by connecting a frequency counter to the
LO output. If no counter is available use an oscilloscope. Failing that, assume
the LO is running and search for the signal on a receiver.
Decide on a receive centre frequency to use. 3615 kHz for 80m or 1950 kHz
for 160m is suggested. From this, the LO frequency required can be
calculated. Subtract 455 kHz to the RX frequency to determine the LO
frequency on 80m. Add 455 kHz from the RX frequency to determine the LO
frequency on 160m.
80m RX: 3615kHz LO: 3160kHz 160m RX:1950kHz LO: 2405kHz
For Medium Wave reception use an LO on the high side and use the same
calculation for LO frequency after deciding on a band centre. Capacitor
values are given in the RF/IF circuit diagrams and parts list.
Using a ounter
If a frequency counter is used the LO frequency will be immediately
apparent. Adjust L1 to achieve the correct frequency.
Now rotate the tuning control to a fully CCW and fully CW position,
noting the band of frequencies covered. If the range is considered too
great or too small, adjust VC1. At any starting frequency, if a rotation
of VC1 causes the frequency to increase then VC1 is being reduced
in value, and the control range is being reduced. Adjust L1 to return
the centre frequency to the correct point. The adjustments may need
to be repeated until the correct range is achieved. Note there will be
a slight bandspread effect towards the lower end of the tuning range
due to characteristics of the varicap diode.

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Or:
Using a re eiver
Tuning by means of a separate HF receiver is a little more involved
but the principle is the same. Set the HF receiver to 3160kHz or
2405kHz and attempt to tune through the channel by rotating the
RAT5 tuning control. If a signal is not heard, return the tuning control
to a central position then adjust L1 by several turns CW and antiCW
from the preset position. It should be possible to eventually find the
signal. Then determine the tuning range by following the signal on
the separate receiver as the tuning pot is rotated. Adjust VC1 and L1
as required in a similar way to alignment using a counter.
While the receiver is stable enough for normal use, stability can
nonetheless be improved by minimising the tuning range, as the
greatest source of drift is the temperature coefficient of the varicap
diode D1 and the trimmer capacitor VC1. The less contribution they
make (by minimising the tuning range) the better the stability.
Based on a centre frequency of 3615kHz, with VC1 set to minimum,
the tuning range is typically +/-20kHz. With VC1 set to maximum and
L1 re-adjusted for 3615kHz the tuning range is typically +/- 150kHz.
4.4 IF and RF Alignment
IF/RF Alignment Overview
Apply a signal on the correct receive frequency then tune T1, T2 and L2 for maximum reading
on PL4/2 (S-meter o/p)
If the ferrite cores of T1, T2 and L2 have been pre-set as described earlier, the chances are
that a medium/strong on-channel RF signal can now be received. Constructors lucky enough
to have a signal generator will need no instruction how to produce a suitable signal.
Detailed des ription:
4.4.1 IF Alignment.
(__) Power off the RAT5
(__) Make sure the squelch control is fully CCW. Advance the volume control
about 25% from its minimum position.
(__) Attach a multi-meter to the S-meter output PL4. Set it to display voltages of
up to 5V.
(__) Connect a signal source directly to the antenna input at a starting level of
around 100uV. If using a transmitter do not use a direct connection. A fly
lead from the RAT5 antenna input wrapped round the coax from the test
transmitter to a dummy load should suffice. Set the signal source to the
receive frequency based on the LO frequency established in the previous
procedure.
(__) Re-apply power.

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(__) With an input signal present, If a signal cannot be heard in the loudspeaker,
double-check the LO frequency. Rotate the tuning control and also try
increasing the signal level applied to the antenna input.
(__) Assuming an RF signal is being received, check the S-meter reading (multi-
meter). Keep the voltage in the centre portion of the range as you proceed
i.e. about 1V to 2V. Adjust the RF input level as required.
Tune L2 by rotating the ferrite core from its preset position, tuning for a
maximum S-meter reading. The tuning will be quite broad, but it should be
possible to establish a centre position for the core. It’s a good idea to monitor
the LO at the same time, making sure the test carrier is tuned correctly so as
to place the IF signal in the centre of the filter.
4.4.2 RF Alignment.
(__) Check the S-meter reading (multi-meter). Keep the voltage in the one volt
area of the range for best sensitivity. Adjust the RF input level as required.
Tune the ferrite cores of T1 then T2 for a maximum S-meter reading. Repeat
the procedure until no further improvement can be made. The input signal
level may need to be reduced as the filter is adjusted.
RAT5 alignment is now omplete

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4.5 Further Tests.
These tests are optional.
(__) Sensitivity he k
Carrier: 5uV PD Modulation: AM, 1kHz, 50%
Apply an on-channel carrier from the signal generator. This should be clearly
heard out of the loudspeaker.
The S-meter output (un-terminated) should read typically 350 mV
Alternatively, connect RAT5 to a known good antenna. Band noise should be
readily heard.
(__) Squel h he k
With a test signal or band noise present, rotate the squelch control CW until
the audio disappears. Return the control to a squelch open position. There
should be no clicks or thumps associated with opening or closing the squelch.
Further signal generator based squel h tests:
• Set the squelch so that it just mutes the receiver. Apply a carrier of
3uV PD. Check the squelch opens at this level.
• Apply a 1V PD carrier. Confirm the squelch control can still mute the
receiver when turned fully CW.
(__) Audio output he k
Expedite this test, returning the volume to a safe level to avoid damaging
the LM386 which will heat up quickly when outputting a constant tone at
full power.
• Connect an oscilloscope across the loudspeaker.
• Apply a strong 50% modulated carrier with a 1kHz tone.
• Advance the RAT5 volume control until distortion appears on the
trough of the ‘scope trace.
• Note the voltage level on the ‘scope. With a 12V supply voltage and 8
ohm speaker or load the reading should be around 2.5V P/P
representing an RMS output of 100mW.
• Note the RAT5 current consumption at full output typically 150mA.

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5. Interfa ing
5.1 Conne tion Method
There are several options. Soldering wires directly to the PCB is perfectly acceptable if the
supplied connectors are not preferred.
PL3 is a 10-way strip with pins 3, 4, 7 and 8 unused.
Wires can also be soldered directly to the pins of PL3, but
the recommended method is to use the companion
socket strips. Again, wires can be soldered directly to the
strips but the method preferred by the author is to saw off
a small piece of stripboard via which wires can be
soldered. Socket strips can be cut into shorter lengths by
sacrificing one pin at the cutting point.
Figure 5.1 opposite shows a connector with wires
attached.
Figure 5.1 Conne tion method
5.2 Conne tions
Figure 5.2 Conne tion Diagram

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• Antenna PL1/1,2
A case mounted antenna connector may be planned but for testing a couple of short
pieces of unscreened wire twisted together will suffice to attach an antenna connector
of your choice to the antenna input PL1.
• LO output PL2/1,2
A buffered LO out has been provided for LO alignment and for future use. The level is
200mV P/P.
• Power Sour e PL3/1,2
Any Voltage from 9V to 15V is suitable. Absolute maximum is 18V.
• SQL / Mute PL3/5, 6
This is a dual function connection. As an output, a voltage of (supply volts -1) is
present on squelch mute. An input of around 5V to 12V can be used to override the
normal squelch function and force a mute.
• Loudspeaker (LS) PL3/9, 10
Use an 8 ohm or higher impedance loudspeaker or headphones.
5.3 Conne ting an S-Meter.
PL4 (located near the tuning trimmer VC1) provides an output suitable for driving an external
S-meter. A meter with a movement of 500uA FSD would be ideal. As the same line is used to
drive the squelch circuit, the extra loading may have a slight effect on the squelch trigger
position of RV2 but the effect is small and of no consequence.
A 10k series variable resistor can be used to set the meter level as required.
5.3.1 Calibration
Calibration of the S-meter can be attempted. If a calibrated signal generator is not
available, one suggestion is to set the meter FSD by comparing with the S-meter of
say a transceiver. Based on a level of S9 +30dB for FSD the following levels were
noted on a test receiver using a 500uA FSD meter:
Signal level Reading
Signal level Reading
S9 + 30dB (-43dBm, 1580uV) 500 S7 (-85dBm, 12.5uV) 240
S9 + 20dB (-53dBm, 500uV) 460 S6 (-91dBm, 6.3uV) 90
S9 + 10dB (-63dBm, 158uV) 430 S5 (-97dBm, 3.2uV) 10
S9 (-73dBm, 50uV) 400 S4 (-103dBm, 1.6uV) Zero
S8 (-79dBm, 25uV) 360 S3 (-109dBm, 0.8uV) zero
The rapid fall-off in level below S7 is understandable as the TDA1072 is intended as
a car radio receiver handling millivolt level signals. A circuit could be devised to
compensate for the non-linearity at lower signal levels.
5.4 Operation with a Transmitter
The receiver settle-time after switch on is virtually zero, so integrating RAT5 into a transceive
setup is no more difficult than arranging a relay to switch the supply along with an antenna
changeover relay.
Alternatively, the Squelch/Mute line at PL3/6 can be used. This line has a dual function. Used
as an input, a voltage between 5V and 12V will mute the audio regardless of the setting of the
squelch control. This allows the receiver LO to stay running.