SV-XPNDR-261 Transponder Installation and Configuration
SkyView HDX System Installation Manual - Revision E 12-11
12.2.8 External Standby Input (Pin 17) (optional)
This input, when connected to Ground, places the SV-XPNDR-261 in Standby mode. It
should be used to switch between transponders in an installation with two (2)
transponders. The input is active low, and will be asserted when the voltage to ground is
pulled below approximately four (4) Volts.
12.2.9 Direct Serial GPS Position Input (Pin 3)
This input is typically used if the aircraft is already equipped with a certified GPS unit
(typically for qualification for IFR flight). This input is connected to a serial port output of
the certified GPS. See SV-XPNDR-261 Settings, GPS Data later in this section for
information on how to configure SkyView to use this capability.
If you connect a certified GPS to this input, you must install a 1.21k resistor (included with
the SV-XPNDR-261) between the certified GPS and the SV-XPNDR-261 as shown in
Figure 75: SV-XPNDR-261 Wiring Diagram.
12.2.10 Antenna Cable
The SV-XPNDR-261 is designed to meet Class 1 requirements with the same 2 dB
allowance. Excessive loss will degrade both transmitter output power and receiver
sensitivity.
Allowing 0.25 dB loss for the connector at each end of the antenna cable assembly leaves
an allowance of 1.5 dB maximum loss for the cable itself.
An acceptable cable:
• Has less than 1.5 dB loss for the run length needed.
• Has a characteristic impedance of 50Ω (50 Ohms).
• Has double braid screens or has a foil and braid screen.
Once the cable run length is known, a cable type with low enough loss per metre that
meets the above requirements can be chosen. Longer runs require lower loss cable.
Consider moving the SV-XPNDR-261 closer to the antenna to minimize the losses in the
antenna cable – subject to the limits identified above, the SV-XPNDR-261 can be at any
distance from the SkyView display(s) without affecting performance in any way.
Note: Low loss cable typically uses foamed or cellular dielectrics and foil screens.
These make such cables especially prone to damage from too-tight bends or from
momentary kinking during installation. Once kinked, these cables do not return to full
performance when straightened.
Table 31 below is a guide to the maximum usable lengths of some common coaxial cable
types. Actual cable loss varies between manufacturers, there are many variants, and the
table is therefore based on typical data. Use it as a guide only and refer to the
manufacturer’s data sheet for your specific chosen cable for accurate values.
To Next Page
Loading...
