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Overview
I stock a variety of transponders and transponder accessories as you can
see in the table below. Further down this page is a transponder
comparison table.
Transponder Overview Article
Eric Greenwell has written a very nice article which gives an overview
of transponder terminology and available products. This article was
originally published as two articles in Soaring magazine in February and
March 2002,
and updated January, 2008 for publication on the
Soaring Safety Foundation web
site. Eric flies with a Becker transponder in his motorglider.
The article is available here:
http://www.soaringsafety.org/prevention/articles.html.
Transponder Antenna Tips
DG has an excellent document on their web site with details on how to
mount transponder antennas to gliders.
http://www.dg-flugzeugbau.de/Data/TN-DG/service-infos/2004-53-e.pdf
Antenna Cables
I offer transponder antenna cables made by Larry Goddard in several lengths.
They include a TNC connector for connection to the transponder and a BNC
connector for connection to a transponder antenna. They are available
in 3 m (9.84 feet) and 5 m (16.4 feet) lengths.
Transponder Antennas
Several transponder antenna options are listed on the
Antennas page. The RAMI rod style and
"shark fin" styles are the most popular. I recommend the shark fin
style because I recall from my fluid dynamics courses that the two worst
types of bodies in regard to drag are spheres and cylinders. For
installations inside fiberglass, wood and fabric gliders, or in the vertical
fin in carbon fiber gliders (with the fin made of fiberglass) you may want
to consider the L2 antenna from AAE and the SA-005
antenna from Sportcraft.
Aviation Transponder
Interrogation Modes
Below is a link to a Wikipedia page which explains the difference between
Mode A, C and S transponder interrogation modes and other interesting
tidbits.
http://en.wikipedia.org/wiki/Aviation_transponder_interrogation_modes
Size Comparison
Below is a photo showing just how much smaller the TT21 is than a Becker
ATC4401 transponder. The Becker transponder and ACK A-30.4 altitude
encoder are on the left. The TT21 transponder and TC20 control unit
are on the right. Click on the image to view a larger version.
Transponder
Comparison Table
Thank you very much
Darryl Ramm and Eric Greenwell for your help creating this table and
the notes below.
Please see the notes below the table. |
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Becker
ATC 4401-1-175 |
Becker
ATC 4401-1-250 |
Becker
ATC 6401-2-(01) |
Becker
ATC 6401-1-(01) |
Trig
TT21 |
Trig
TT22 |
| Nominal Output
Power (measured at rear connector) |
175 Watts |
250 Watts |
150 Watts |
250 Watts |
130 Watts |
250 Watts |
| Price
for transponder only |
$2070 |
$2270 |
$2903 |
$4990 |
$2095 |
$2395 |
| Altitude
Encoder |
Requires
External |
Requires
External |
Requires
External |
Requires
External |
Built-in |
Built-in |
| Price for
transponder, altitude encoder, and wiring harness |
$2486 |
$2686 |
$3319 |
$5406 |
$2240 |
$2540 |
| Mode* |
Mode C |
Mode C |
Mode S |
Mode S |
Mode S |
Mode S |
| Class** |
Class 2 |
Class 1 |
Class 2 |
Class 1 |
Class 2 |
Class 1 |
| Level*** |
N/A |
N/A |
Level 2
es |
Level 2
es |
Level 2
els |
Level 2
els |
| Maximum
Altitude**** |
15,000
ft |
50,000
ft |
15,000
ft |
50,000 ft |
15,000
ft |
35,000
ft |
| Input
Voltage |
9.5 to
32.2 VDC |
9.5 to
32.2 VDC |
10 to 33
VDC |
10 to 33
VDC |
9 to 33 VDC |
9 to 33 VDC |
| Input
Current (standby) |
0.27 A
at 13.75 V |
0.27 A
at 13.75 V |
0.22 A
at 14 V |
0.22 A
at 14 V |
0.15 A at 14 V |
0.15 A at 14 V |
| Input
Current (typical) |
0.40 A
at 13.75 V (175 W) |
0.50 A
at 13.75 V (250 W) |
0.43 A
at 14 V |
0.43 A
at 14 V |
0.28 A at 14 V |
0.34 A at 14 V |
| Input
Current (standby) - including ACK A-30.4 altitude encoder |
0.37 A at 13.75 V |
0.37 A at 13.75 V |
0.32 A
at 14 V |
0.32 A
at 14 V |
Built-in
Alt. Encoder |
Built-in
Alt. Encoder |
| Input
Current (typical) - including ACK A-30.4 altitude encoder |
0.60 A at 13.75 V (175 W) |
0.70 A at 13.75 V (250 W) |
0.63 A
at 14 V |
0.63 A
at 14 V |
Built-in
Alt. Encoder |
Built-in
Alt. Encoder |
| How is it
programmed with
the
aircraft's unique ICAO address, etc? |
Programming not Required |
Programming not Required |
Address
Module Required
Programmed by Dealer |
Address
Module Required
Programmed by Dealer |
Data
entered using buttons
and knobs on control unit. |
Data
entered using buttons
and knobs on control unit. |
|
1090ES/ADS-B data-out |
N/A |
N/A |
1090ES/ADS-B out |
1090ES/ADS-B out |
1090ES/ADS-B out |
1090ES/ADS-B out |
|
1090ES/ADS-B data-in for traffic data |
N/A |
N/A |
1090ES/ADS-B in |
1090ES/ADS-B in |
no |
no |
|
Dimensions |
61.3 x
61.3 x 204 mm
(2.413 x 2.413 x 8.03 inch) |
61.3 x
61.3 x 204 mm
(2.413 x 2.413 x 8.03 inch) |
61.3 x
61.3 x 205 mm |
61.3 x
61.3 x 205 mm |
Controller: 45 x 45 x 64 mm
Transponder: 62 x 45 x 141 mm |
Controller: 45 x 45 x 64 mm
Transponder: 62 x 45 x 141 mm |
| Weight |
725 g
(1.598 lb) |
725 g
(1.598 lb) |
800 g |
800 g |
1.0 lb (450
g)
(less than 100 g for controller) |
1.0 lb (450
g)
(less than 100 g for controller) |
* Mode
Mode S transponders also support Modes C
and A capabilities. Mode C transponders also support mode A
capabilities.
** Class:
- Class 1 Transponders are higher output
power than class 2 devices and must deliver between 18.5 dBW (125 W) and
27.0 dBW (500 W) at the transponder antena.
- Class 2 transponders are lower power
than class 1 devices and must deliver between 18.5 dBW (70 W) and 27.0
dBW (500 W) at the transponder antenna. Class 2 transponders are limited
by regulations to VFR use, below 15,000 ft MSL and below 175 knots
airspeed.
- For the definition of a decibel (dB) see
http://en.wikipedia.org/wiki/Decibel
For the definition of decibel watt (dBW) see
http://en.wikipedia.org/wiki/Decibel_watt
*** Level:
Transponder Level and extended
capability letter codes are standard ways of describing the the
capabilities of Mode S transponders. This is not relevant to Mode A
or Mode C transponders. In practice all current Mode S transponders
of interest to glider pilots are Level 2 devices. For future
compatibility with ADS-B pilots should look for extended squitter
support which provides 1090ES/ADS-B data out and possibly Data-in
capabilities. The option code "e" below for extended squitter and
whether data out only or data-out and data-in is provided is
important for future ADS-B compatibility. All much of the rest can
effectively be ignored. The level specification is sometimes
accidently confused with the transponder class, so be careful
reading specifications. For the technically interested the
definitions of the different levels are below.
Level 1 (Comm A) No datalink capability - the transponder can
receive 56 bit messages, and reports pressure altitude and and
supports Mode A, and Mode S selective addressing.
Level 2 (Comm B) Level 1 + receive and transmit 112 Bit
Messages Level 2A Same as Level 2 without the support air-initiated
Comm B messages
Level 3 (Comm C) Level 2 + receive 16 linked 112 bit
Extended Length Messages (ELM) segments
Level 4 (Comm D) Level 3 + transmit 16 linked 112 bit
Extended Length Messages (ELM) segments
Note that ELM messages are completely different than the "extended
squitter" that provides ADS-B/1090ES data-out and possibly data-in
capabilities. ELM message types and Level 3 and Level 4 will likely
never be useful for gliders, Level 4 transponders require
prohibitively high power to ensure high enough data rates.
In addition to a transponder level there are capability letter codes
that describe additional transponder capabilities. The ones on
interest to glider pilots are:
- e - Extended squitter,
the ability to send ADS-B/1090ES data. This requires an external
GPS (certified GPS units only). Mode S transponders with 1090ES
capability can always send ADS-B data out but may not be able to
receive ADS-B data in to receive traffic information. The actual
data out and data-in capabilities for each model are shown out
in the table above.
- l - Elementary
surveillance, i.e. basic position reporting derived from SSR
radar, enhanced in the case of a Mode S environment with higher
resolution (25') pressure altitude, unique ICAO aircraft ID and
other Mode S capabilities. Note that this is different than
1090ES/ADS-B data-out capabilities.
- n - Enhanced
surveillance, transmission of a state vector including ground
speed by the transponder. No transponders of interest for
gliders currently include this capability. Note that this is
different than 1090ES/ADS-B data-out capabilities.
- s - Surveillance
Identifier (SI) code. Used by Mode S transponders and Mode S
equipped SSR to limit interrogations to specific transponders.
Typical Mode S transponders of interest to glider pilots will be
Level 2es or Level 2els devices.
**** Altitude Limits
The 15,000 foot altitude limit is a regulatory limit
(see Class 2 in the ** note above). The Trig TT21 will
work to 35,000 feet and the ACK A-30.4 Altitude Encoder used with the Becker
transponders will work up to 30,000 feet.
Other Notes:
Most transponders installed
in gliders are Class 2 devices because of their lower cost
and reduced power consumption. Nominal power outputs for
different transponder appear higher than those required by
the Class requirements to allow for typical antenna cable
losses.
It is the aircraft owner's responsibility to ensure that any
transponder is correctly installed. If in doubt check with
you local A&P. As a part of any transponder installation,
including in experimental aircraft, altimeter/encoder tests
per FAR 43 Appendix E and radio frequency signal tests per
FAR 43 Appendix F are required. For non-IFR aircraft, there
is no ongoing requirement for the FAR 43 Appendix E test,
except they need to be repeated any time the static pressure
system is worked on. Every two years the FAR 43 Appendix E
radio frequency signal check must be repeated.
Altimeter/encoder calibration is *not* checked in these
ongoing "Appendix E" tests. You can confirm the encoder
altitude on the altitude display of most modern
transponders, and always confirm current altitude on initial
contact with ATC.
This information is for the United States, regulations and
certification may be different in other locations.
Some transponders have
connections for GPS input. It is not OK to connect
just any GPS to the device. Only certified GPS units
may be used.
Although some new
transponders incorporate ADS-B functionality, it is not
possible to simply connect your PDA to the unit and display
traffic information on the soaring software in the PDA.
That functionality is not currently available.
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