Reviewed 1/20/2001
In upgrading the radios in my Cessna Airmaster, I needed a new radio but had to deal with an extreme lack of panel space. The Airmaster has no room to hang a standard-sized radio underneath the panel, and it also doesn't have much depth available due to an oil tank located behind the firewall. I did have a 2.25" round cutout available on the panel.
There are two small radios that fit
the micro-sized panel mounted category. The smallest is
actually the Microair 760. The
Microair is a good looking unit, however it is not TSO'ed which
will make installation in a certified aircraft difficult. The Microair
front panel interface is also a bit clunky in my opinion. The other choice
is the Becker AR4201, which is
certified, but longer in depth than the the Microair.
The Becker unit is well-built and solid. It shows its European roots by using metric-sized through-screws to bolt to the panel. The data connector is located on the back of the unit and uses a standard DB-25 size, which is good. The connector also uses slide-bar locking of a unique style, which is bad. If you buy the radio new from Becker, the connector/backshell assembly supplied by Becker fits and locks very nicely. Unfortunately I bought my unit used and it did not include the connector. Buyer beware. It is probably possible to convert the unit to use lock screws to secure the connector, but this would require disassembling the unit. That was more trouble than I wanted to get into so I just called Becker to order an additional connector/backshell assembly.
For depth-restricted installations, the data and power connector is located in a stepped-in section on the lower rear of the unit, so much of the connector backshell does not protrude beyond the rear of the radio case. The antenna BNC connector is not located in the stepped-in area, though, so if you're worried about depth you should add an allowance for a right-angle BNC connector.
Installation was relatively easy. The install instructions and wiring diagrams are clear except for how to deal with dynamic vs. standard microphone wiring. The two types are wired differently to deal with the different levels of mic bias voltages required. Becker could also improve their instructions by providing a diagram that shows connections to a standard US-style intercom. They show connections to a Becker intercom but the diagram uses non-standard nomenclature and it is mostly focused on what pins to connect to on Becker's proprietary connector layout.
The AR4201 supports separate ground lines for radio and mic grounds, but it works fine in a common-ground wiring scheme. I did not use the built-in intercom feature but the Becker does support it.
The installation and operation manual is obviously a translation from the original German, but it is readable. It is annoying that the manual is supplied on A4-sized paper which will not fit into a US-sized notebook or binder.
One intriguing feature is that the Becker supports RS-232 interfaces to control the unit remotely. The data formats are documented in the manual. This feature could be used to set up a headless avionics system controlled by a unified glass cockpit display, although for an experimental aircraft the Microair might be a better choice due to smaller size and lower cost. The Microair also supports the remote control feature via RS-232.
The radio operates like most any COM radio with standby tuning. It uses intuitive concentric knobs to tune the standby channel, which is selected as the active channel by pressing a active/standby swap button. Power and volume are on the other knob. Squelch is automatic and can be overridden with a front panel push button. The squelch threshold is a programmable setting accessed from the configuration mode.
The display screen is a standard calculator-style passive LCD screen with backlighting. To simplify wiring and switches I wired the installation so that the backlighting is always on when the avionics master is on, but it could just as easily be connected to a panel lighting dimmer. Readability of the display is adequate but not great, and off-axis viewing is relatively poor especially in the vertical plane. Make sure you can read the unit if you plan to mount it in an unusual location - angling of the mount may be necessary.
The AR4201 has several display modes and can be configured to show either the standby channel, the input voltage, or the outside temperature if an optional temperature probe is connected.
Memory channels are available and are useful for commonly selected ATIS, tower and ground frequencies. Memory channels are recalled by changing the mode and scrolling through a set of stored choices indicated by number. Programming is relatively easy and is accessible in flight by hitting the store button and selecting a storage "channel", which stores the active frequency.
Other settings of the AR4201 are software programmable, such as sidetone volume and squelch break sensitivity. These settings are accessed from a configuration mode that is not designed to be used in flight. While software programming is a big step up from trimmer pots located on the back case of the unit, the programming interface still leaves something to be desired in usability. You need the manual to be able to understand it. Avionics manufacturers could learn something from cell phone manufacturers like Nokia in terms of setting up a relatively easy user interface.