Ramsey Electronics AR2WT User manual

AIRCRAFT
RECEIVER KIT
Ramsey Electronics Model No. AR2WT
• Tunes the entire 118 - 136 MHz Air band
• Operates on 12 to 15 VDC
• Scan function “finds” the signals for you; no more laborious
tuning to find a transmission
• Memory locations make it easy to refind your local favorites
• Listen to control towers, centers, and planes en-route
• Very sensitive; picks up planes 100 miles away!
• Great project for all pilots and flight students
• Clear, concise step-by-step instructions carefully guide you to a
finished kit that not only works - but you’ll learn too!
A new and improved version of our popular Aircraft Receiver kit,
this new model features an LCD display, scan function, and
increased sensitivity, all in a rugged metal enclosure. Rivals
professional units costing much more!

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PARTIAL LIST OF AVAILABLE KITS:
RAMSEY TRANSMITTER KITS
• FM10A, FM25B, FM30, FM Stereo Transmitters
• FM100B, FM35 Professional FM Stereo Transmitters
• AM1, AM25 AM Broadcast Band Transmitters
RAMSEY RECEIVER KITS
• FR1 FM Broadcast Receiver
• AR1 Aircraft Band Receiver
• SR2 Shortwave Receiver
• AA7 Active Antenna
• SC1 Shortwave Converter
RAMSEY HOBBY KITS
• SG7 Personal Speed Radar
• SS70C Speech Scrambler/Descrambler
• TT1 Telephone Recorder
• SP1 Speakerphone
• MD3 Microwave Motion Detector
• PH14 Peak hold Meter
• LC1 Inductance-Capacitance Meter
RAMSEY AMATEUR RADIO KITS
• HR Series HF All Mode Receivers
• DDF1 Doppler Direction Finder Kit
• QRP Series HF CW Transmitters
• CW7 CW Keyer
• QRP Power Amplifiers
RAMSEY MINI-KITS
Many other kits are available for hobby, school, scouts and just plain FUN. New
kits are always under development. Write or call for our free Ramsey catalog.
AR2
Ramsey Electronics publication No. AR2 Rev. 1.3a
July 2005
COPYRIGHT ©2004 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Victor, New York
14564. All rights reserved. No portion of this publication may be copied or duplicated without the
written permission of Ramsey Electronics, Inc. Printed in the United States of America.

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AIRCRAFT RECEIVER
Ramsey Publication No. AR2
Manual Price Only $5.00
TABLE OF CONTENTS
Introduction ..........................................4
What You Can Expect to Hear ............4
Circuit Description................................8
Block Diagram ...................................10
AR2 Schematic Centerfold ................12
Antenna Considerations .................... 16
Modes of Operation ...........................17
Warranty ............................................35
INSTRUCTION MANUAL FOR

AR2 •4
INTRODUCTION TO THE AR2 AVIATION RECEIVER KIT
The Ramsey AR2 Aviation Receiver is a new design of our original Ramsey
AR1 Aircraft Receiver. The AR1 has been built and loved for years by
hobbyists with an interest in both aviation and electronics. The AR2 design
takes the best of the AR1 and adds scanning functions, and a slick metal case
for superior noise reduction. It is characterized by exceptional sensitivity,
image rejection, signal-to-noise ratio and stability. It is designed for casual
"listening in"- on both ground and air communication, for both commercial
airlines and general aviation. The AR2 has been built by folks of all ages and
skill levels, and in less time than it takes to fly solo!
118-136 MHz, WHAT YOU CAN EXPECT TO HEAR
A basic fact about the VHF Aviation Band which even licensed pilots can
overlook or forget is that communications are in the AM mode, not FM, as in
the case of the FM broadcast band immediately below it, and the VHF public
service and ham bands immediately above it.
No matter where you live you will be able to receive at least the airborne side
of many air traffic communications. You'll hear any aircraft you can see, PLUS
planes up to 100 miles away and more, since VHF signals travel "line of
sight." An airliner at 35,000 feet altitude is still line of sight to your antenna.
Similarly, whatever ground stations you may hear are also determined by this
"line of sight" characteristic of VHF communication. If there are no major
obstacles between your antenna and an airport (tall buildings, hills, etc.) you'll
be able to hear both sides of many kinds of aviation communication. Be
prepared for them to be fast and to the point, and for the same airplane to
move to several different frequencies in the span of a few minutes! Here's a
brief listing of the most common types of services in the NAS (National
Airspace System) with which pilots communicate:
Clearance Delivery
At most metropolitan airports a pilot communicates with the FAA on a
frequency called "Clearance Delivery" to obtain approval or clearance of the
intended flight plan. This communication is done before contacting ground
control for taxi instructions.
Ground Control
From the control tower, ground movements on ramps and taxiways are
handled on the “Ground Control” frequency.
Control Tower
Runway and in-flight maneuvers near the airport, usually within three miles
(takeoffs, local traffic patterns, final approaches and landings) are on the
“Control Tower” frequency.

AR2 • 5
ATIS – Automated Terminal Information System
ATIS, is a repeated broadcast about basic weather information, runways in
use, and any special information such as closed taxiways or runways.
ASOS/AWOS – Automated Surface Observing System/Automated Weather
Observing System
This system is similar to ATIS but usually located at un-towered airports.
Approach Control & Departure Control
These air traffic radar controllers coordinate all flight operations in the vicinity
of busy metropolitan airport areas.
ARTCC – Air Route Traffic Control Center
When you hear a pilot talking with "Jacksonville Center" or "Indianapolis
Center", you know the aircraft is really enroute on a flight rather than just
leaving or just approaching a destination. A pilot will be in touch with several
different "Regional Centers" during a cross-country flight.
CTAF – Common Traffic Advisory Frequency
Airports without control towers are controlled by the pilots themselves and
they rely on the local CTAF frequency dedicated only to advisory
communications between pilots and ground personnel such as fuel service
operators. The people on the ground can advise the pilot on the status of
incoming or outgoing aircraft, but the pilot remains responsible for landing and
takeoff decisions. Typical CTAF frequencies are 122.7, 122.8 and 123.0 MHz.
Unicom frequencies are used at manned towered airports for day to day
businesses at 122.75, 122.85, and 122.95 MHz.
FSS - FAA Flight Service Stations
The FAA's network of Flight Service Stations keeps track of flight plans and
provides weather briefings and other services to pilots. Some advisory radio
communication takes place between pilots and a regional "FSS". If there is an
FSS in your local area, but no airport control towers, the FSS radio frequency
will stay interesting. Typical frequencies are 122.1, 122.6, and 123.6 MHz.
Pilots always address the FSS by calling the FSS name followed by “Radio”.
ELT – Emergency Locator Transmitters
Emergency and guard channels are used by airplanes in flight operations
during an emergency or talking on official business and can be heard on
121.5MHz.
ACARS - Aircraft Communication Addressing and Reporting System
ACARS is a digital VHF radio data link which allows airline flight operations
departments to communicate with the various aircraft in their fleet. ACARS is
used by many civilian and business aircraft and is similar to “email for
airplanes". Each aircraft has its own unique address in the system. Traffic is

AR2 •6
routed via computers to the proper company, relieving some of the necessity
for routine voice communication. With ACARS, routine items such as
departure reports, arrival reports, passenger loads, fuel data, engine
performance data, and more can be retrieved from the aircraft at automatic
intervals. The transmission will sound like a short data burst to the ABM1 user.
THOSE FAST-TALKING PILOTS AND CONTROLLERS!
Aviation communication is brief but it is clear and full of meaning. Usually,
pilots repeat back exactly what they hear from a controller so that both know
that the message or instructions were correctly interpreted. If you are listening
in it is hard to track everything said from a cockpit, particularly in big city
areas. Just to taxi, take off, and fly a few miles, a pilot may talk with 6 or 8
different air traffic control operations, all on different frequencies, all within a
few minutes! Here are the meanings of a few typical communications:
"Miami Center, Delta 545 Heavy out of three-zero for two-five."
Delta Flight 545 acknowledges Miami Center's clearance to descend from
30,000 feet to 25,000 feet altitude. The word "heavy" means that the plane is
a jumbo jet such as 747, DC-10, etc.
"Seneca 432 Lima cleared to outer marker. Contact Tower 118.7."
The local Approach Control is saying that the Piper Seneca with the N-number
(tail number) ending in "432L" is cleared to continue flying an instrument
approach to the outer marker (a precision radio beacon located near the
airport) and should immediately call the airport radio control tower at 118.7
Mhz. This message also implies that the approach controller does not expect
to talk again with that aircraft.
"Cessna 723, squawk 6750, climb and maintain five thousand."
A controller is telling the Cessna pilot to set the airplane's radar transponder to
code 6750, climb to and fly level at an altitude of 5000 feet.
"United 330, traffic at 9 o'clock, 4 miles, altitude unknown."
The controller alerts United Airlines flight #330 of radar contact with some
other aircraft off to the pilot's left at a 9 o'clock position. Since the unknown
plane's altitude is also unknown, both controller and pilot realize that it is a
smaller private plane not equipped with altitude-reporting equipment.
ELECTRONICS & FLYING: DOING IT "BY THE NUMBERS"
A peek at the sample FAA "instrument approach" chart for medium-large
airports shows that pilots deal with many vitally important numbers and must
do so quickly. Among the numbers on that chart, can you find the air-ground
communications frequencies which can be heard on the ABM1 receiver? Can
you find frequencies for uses other than communications?

AR2 • 7

AR2 •8
CIRCUIT DESCRIPTION
Radio Basics:
We’ll take the circuit section by section; the letters show which part of the
block diagram we’re explaining in each section.
The AR2 is a simple super-heterodyne receiver. A heterodyne receiver is a
receiver that first converts the desired received frequency into an IF
frequency, or Intermediate Frequency. Many radios are designed this way due
to a variety of reasons, but primarily because it is easy to perform filtering and
amplification on the IF signal rather than the RF signal because the IF is a
single frequency or small band of frequencies, whereas RF is quite a bit wider
and usually much higher in frequency than IF.
To create an IF frequency we use a mixer (D) to down-convert the band of
interest to the single IF frequency. A mixer is a non-linear device, meaning it
will distort the incoming signal with an applied signal. In the case of a mixer
used on a radio this means you will have two different frequencies on the
inputs, which results in four signals on the output. The received frequency is
connected to one input and the local oscillator or LO is supplied to the other.
On the output you will have these two important frequencies as well as the
sum and difference between the two frequencies.
For example the aircraft band goes from
118MHz to 139MHz, and we plan to use
an IF frequency of 10.7MHz, we need to
have an LO of either 10.7MHz above the
frequency we wish to receive, or
10.7MHz below. It is a matter of
preference in which mixing byproduct you
wish to work with, but in the case of the
AR2 we use an LO of 10.7MHz above the
frequency we wish to receive. This
means that the LO needs to tune from
128.7MHz to 149.7MHz. This is called
high-side mixing since the LO is above
the frequency of interest. The LO is
generated using a phase locked loop
and voltage controlled oscillator on the
AR2 (J, D).
Let’s say for example that we wish to
listen to the control tower at ROC
(Rochester International Airport) at
118.300MHz. The LO frequency would
IF LOFr Fi Sum
F
IF LOFr Fi Sum
F
Figure 1
Figure 2

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have to be set at 118.300 MHz + 10.700 MHz or 129.000MHz. It would then
be sent to the mixer and on the output there would be 129.000MHz (LO),
118.3MHz(Fr), 247.3MHz(Sum) and 10.700MHz (IF). (See Figure 1)
After the mixer we use a narrow-band filter (E) to reject everything but the
10.7MHz IF signal output from the mixer. This works well because 10.7MHz is
far from the next highest frequency, 118.3MHz, so it’s easy to reject
everything but the signal of interest. However, there is another signal you can
receive that is 10.7MHz above the LO frequency. This is called the image
frequency, and can be a real hassle in radio designs. In this case we could
receive not only 118.3MHz but also 139.7MHz (2x IF + Fr). In this case this
“image” is only 700kHz outside the band of interest and is almost impossible
to filter out.
The AR2 reduces the reception of image
frequencies by using good band-pass filters
on the input to reject the image frequencies
before they make it to the mixer (A, C).
Figure 3 to the left shows what the RF input
to the mixer looks like. Notice the Fi is
greatly reduced by the input band pass
filter, but not completely eliminated. The
band pass filter certainly helps and gets rid
of all but the strongest image signals
outside the band.
Now that we have our filtered 10.7MHz IF at the output of the IF filter we can
do some simple amplification on it (F), then send it to be demodulated into
audio.
The IF signal is then sent to the AM detector part (G), where it is mixed down
to yet another IF frequency of 450kHz by combining 10.7MHz with 10.25MHz.
450kHz is used due to the large array of components available at 450kHz, and
it is also the frequency at which our particular AM demodulator works best.
The signal is then amplified greatly to a consistent level using “slow” AGC
within the detector part. The detector is able to receive quality AM signals in a
90dB range, since the AGC can amplify the signal up 90dB. The AGC is
important in that all received signals within its range will be of the same audio
amplitude. Otherwise weak signals would be very quiet, and nearby ones
would be very loud. The reason it is “slow” is to allow changes in level due to
audio to be left alone, but longer-term signal level changes due to distant
signals and close signals to be compensated for.
The 450kHz IF, now that it is a consistent level, is demodulated using a full-
wave rectifier and filter to remove the 450kHz, and leave the AM level behind
as shown.
IF LOFr Fi Sum
F
Figure 3

AR2 •10
PLL
Micro- controller
10.25MHz Reference
10.25MHz Vtune
VCO
118-139MHz 118-139MHz 10.7MHz
450kHz Audio
Detector IC (Simplified)
Display /Control
RSSI
IF1 Mixer IF2 Mixer
IF AMPRF Amp Detector
Antenna
Speaker
A
B
C
D
E
F
G
H
Audio Amp
I
J
K
L
12V Regulator
5V Regulator
12V 5V
M

AR2 • 11
Since the AR2 is a relatively complex (and educational!) product, it’s easiest to
show you how things work by using a block diagram and explaining the
different sections. This is a simplified block diagram, but is suitable for our
needs.
Block A. RF band pass pre-filter. This is one of the two filters that helps
reject image frequencies. Note the PCB layout has coils built right in! This
makes for very precise, repeatable coils, and since the inductance for this
design needed to be very small, this was a lot easier than installing a 1 ½ turn
coil.
Block B. RF amplifier. This amplifier makes up for the “insertion loss” of the
two filters, and increases the radio’s sensitivity to weak signals. Insertion loss
is defined as how much desired signal is lost by a filter or device.
Block C. RF band pass secondary filter. This section further reduces the
possibility of image frequencies being received.
Block D. IF Mixer/VCO. This section consists of an NE602 mixer/oscillator
that can be tuned using what is called a varactor diode in the oscillator
section. A varactor diode is a reverse-biased diode that changes capacitance
according to the reverse voltage. The higher the voltage, the wider the
insulation (depletion layer) and the smaller the capacitance. Thus as the
voltage goes up across the diode, so does the frequency! The tuned inductor
sets the center frequency of our tunable band. We are limited to a little more
than 21MHz, but we are never sure where this range is due to part variances.
The coil allows us to get the 21MHz range centered in our band of interest so
that the frequency will always remain locked throughout the band.
Block E. 10.7MHz IF filter. This is a special ceramic 10.7MHz filter for
narrow-band AM. This helps in rejecting adjacent channels which are only
25kHz away. The filter is 13kHz wide, meaning 6.5kHz to either side.
Block F. This is a simple, single transistor IF amplifier. It has quite a lot of
gain to make up for the insertion loss of the mixer/VCO as well as the
10.7MHz IF filter. This is the advantage of using a low frequency IF since a
simple transistor amplifier works well here.
AM + 450kHz Detector + Audio Out

AR2 •12

AR2 • 13

AR2 •14
Block G. This is the main detector, AGC, 2nd LO, reference oscillator, and
filtering all wrapped into one part.
Block H. 2nd IF filtering. This section is for further attenuating adjacent
signals. The goal is to reduce signals 25kHz away more than 90dB, or the
range of the AGC of the detector component. Two cascaded 450kHz filters are
used here on top of the 10.7MHz ceramic filter.
Block I. After the AM has been detected the small level of audio signal is
amplified enough to drive a speaker to respectable volumes
Block J. The Phase Locked Loop works in conjunction with the VCO (NE602
and varactor diode) and the reference 10.25MHz oscillator. The PLL part (U2,
MC145170P2) has two dividers and some option registers for different designs
that are usually set only once. One of the two dividers divides down the LO
frequency from the VCO to make the channel step size 25kHz (N divider), and
the other divides down the reference oscillator to the specific channel step size
of 25kHz (C divider). The 25kHz is the reference comparator frequency, and
the output of the PLL tries to make the VCO tune so that the output of it
s divider is also “Locked” to 25kHz. A correction pulse is generated for each
phase of the reference, and that is where phase locked loop comes from!
For example the PLL is programmed by the microcontroller to have a C value
of 410. This means the reference clock of 10.25MHz is divided by 410 to give a
divider output of 25kHz. This value remains constant throughout the AR2
circuit. To receive 118.3MHz we have to set the N value of the divider to give
us 25kHz from the divided down RF of the LO frequency. Take (118.3MHz +
10.7MHz)/25kHz = N or 5160. Now the dividers are set up to request this LO
frequency, however the VCO has not been tuned there yet. If there is any error
between the “C” output and the “N” divider output, which there should be after
switching the N divider, an internal comparator looks at the two 25kHz signals
together then provides error correction pulses to tune the VCO to correct the
difference.
For example the VCO frequency is too low, which results in 24.999kHz output
at the N divider rather than 25kHz at the C divider. The PLL comparator output
will then provide some high-going pulses to the PLL filter (U5:A and
surrounding parts) to bring the tuning voltage up so the 25kHz divider outputs
begin to come closer. Once the two frequencies match, small error pulses “tap”
the VCO to keep it “phase locked” to the divided reference clock and make up
for any environmental changes such as temperature and vibration.
The PLL filter removes the comparator error correcting pulses of 25kHz by low-
pass filtering them. These tuning filters are also called integrators since they
have no DC feedback. What results is a steady tuning voltage that allows the
VCO to change smoothly from one channel to the next without 25kHz signals

AR2 • 15
being “imposed” on the VCO. It also provides some amplification to give the
VCO 0-12V of tuning from a 5V PLL part.
Block K. The microcontroller is the “brains” of the entire project. This device
programs the PLL to get the frequencies desired, handles the jog dial by
interpreting it’s pulses, and then writes the data to the displays. Quite a bit of
coding is required to handle the scanning functions and the user interface, so
don’t underestimate what goes on inside this little device!
Block L. This is the display and the user control devices.
Block M. Power supply section.

AR2 •16
ANTENNA CONSIDERATIONS
An antenna for your AR1C can be as simple as a 21" piece of wire or a fancy
roof-mounted aviation antenna. Most folks near an airport will get plenty of in-
the-air action from the wire, but if you're more than a few miles away, a decent
roof-mount job is the way to go. A low cost TV antenna works well, even better
if rotated 90 degrees (remember aircraft antennas are vertically polarized). If
you really want to learn and experiment, check out any book on antennas from
your local library or do a search on the internet; there’s a wealth of information
out there.

AR2 • 17
MODES OF OPERATION:
The AR2 uses an advanced way to access the many useful features built in to
the unit. What looks like a volume control at first glance is actually a jog dial.
No, it doesn’t go for a jog at the end of a long work day, instead it allows you
to enter values digitally in a convenient way.
There are a few modes of entry of using the jog dial:
a. Turn clockwise and counter clockwise
b. Press the knob and turn
c. Press the knob briefly
d. Press and hold.
By pressing and turning the knob you can select the various modes of
operation of the AR2. As you turn the knob while holding it in, the display will
show the current selected mode. Release the knob to choose that selection.
The modes are as follows:
1. Normal receive mode. This mode operates much like the old AR1,
allowing the jog dial to select frequencies within the aircraft band to listen
to. The display shows both frequency and the field strength of the signal
(RSSI).
2. Lighting Control Mode. This mode allows a user to access an external
circuit to remotely control runway lights in small airports by keying the
radio at the frequency to which the AR2 is set.
3. Full Scanner Mode. This mode operates like normal receive mode but
will scan for the next frequency that opens the squelch when you press
the knob briefly.
4. Scanner 1 Mode. This mode allows you to scan up to 20 frequencies
saved in the Scanner 1 Setup mode.
5. Scanner 2 Mode. This mode allows you to scan up to 20 frequencies
saved in the Scanner 2 Setup mode.
6. Scanner 3 Mode. This mode allows you to scan up to 20 frequencies
saved in the Scanner 3 Setup mode.
7. Scanner 4 Mode. This mode allows you to scan up to 20 frequencies
saved in the Scanner 4 Setup mode.
8. Scanner Skip Mode. This mode operates like Mode 2, except that it skips
automatically to the next active frequency after a specified period of time
that you’ve preset in the skip timer setup screen.
9. Skip Scanner 1 Mode. This mode allows you to scan up to 20
frequencies saved in the Scanner 1 Setup mode, only this will

AR2 •18
automatically skip to the next frequency after a specified time.
10. Skip Scanner 2 Mode. This mode allows you to scan up to 20
frequencies saved in the Scanner 2 Setup mode, only this will
automatically skip to the next frequency after a specified time.
11. Skip Scanner 3 Mode. This mode allows you to scan up to 20
frequencies saved in the Scanner 3 Setup mode, only this will
automatically skip to the next frequency after a specified time.
12. Skip Scanner 4 Mode. This mode allows you to scan up to 20
frequencies saved in the Scanner 4 Setup mode, only this will
automatically skip to the next frequency after a specified time.
13. Setup Scanner 1 Mode. Allows you to save and delete frequency
memories from scanner 1.
14. Setup Scanner 2 Mode. Allows you to save and delete frequency
memories from scanner 2.
15. Setup Scanner 3 Mode. Allows you to save and delete frequency
memories from scanner 3.
16. Setup Scanner 4 Mode. Allows you to save and delete frequency
memories from scanner 4.
17. Setup skip timer. Allows you to select the amount of time to keep a
particular frequency active before skipping to the next active frequency.
18. Lighting timeout. This allows setting of the time the lights in the Lighting
Control mode are kept on before turning them back off again.
Receive Mode Controls:
Use the jog dial to select the current frequency. The faster you turn the knob,
the faster the frequency will change due to a built in accelerator function.
Press and hold the jog dial for two seconds to save this as the default power
on mode.
Lighting Mode Controls:
Use the jog dial to select the frequency you wish to use for remote keying
control of the lighting system before entering Lighting Control Mode.
Press and hold the jog dial for two seconds to save this as the default power
on mode.
Full Scanner Mode and skip mode.
Use the jog dial to select a frequency.
Press and release the knob to skip to the next active frequency.

AR2 • 19
Skipping to the next channel will occur after timeout in skip mode only.
Standard Scanner Modes 1-4 and skip modes:
Use the jog dial to select a frequency other than what is currently running.
Press and release the jog dial to skip to the next active memory
Press and hold the jog dial to prevent stopping at this frequency for the
duration of the selection of this mode.
Skipping to next channel will occur after timeout in skip mode only.
Setup Scanner Modes 1-4
Use the jog dial to select frequencies
If the frequency is already in the list, a + sign will appear in the lower right to
indicate it is already in the list. – if it is not.
Press and release the jog dial to add a frequency not in the list
Press and release the jog dial to remove a frequency from the list.
Press and hold the jog dial for two seconds to save your selections to FLASH.
Setup Skip Timer
Use the jog dial to select an appropriate time to stay on any particular
frequency before skipping to the next.
Press and hold the jog dial to save the changes to FLASH.
Setup Lighting Timer
Use the jog dial to select an appropriate time out value which determines how
long the lights are left on before shutting off.
Press and hold the jog dial to save the changes to FLASH.

AR2 •20
CONCLUSION
We sincerely hope that you will enjoy the use of this Ramsey product. As
always, we have tried to compose our manual in the easiest, most “user
friendly” format possible. We value your opinions, comments, and additions
you’d like to see in future publications. Please submit comments or ideas to:
Ramsey Electronics Inc. or email us at techsu[email protected]
Attn. Hobby Kit Department
590 Fishers Station Drive
Victor, NY 14564
And once again, thanks from the folks at Ramsey!
If you enjoyed this Ramsey product, there are plenty more to choose from in
our catalog - write or call today!