Dynon Avionics SkyView System Installation Guide User Manual
Page 233
SV-XPNDR-261/262 Installation, Configuration, and Testing
SkyView System Installation Guide – Revision S
11-13
Heavyweight cooking foil meets the technical requirements, but obviously needs to be properly
supported.
Antenna Cable
The SV-XPNDR-262 is designed to meet Class 2 requirements with an allowance of 2 dB for loss
in the connectors and cable used to connect it to the antenna. 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 0.25dB loss for the connector at each end of the antenna cable assembly leaves an
allowance of 1.5dB 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 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-261/262 closer to the antenna to minimize the losses in the antenna cable –
subject to the limits identified above, the SV-XPNDR-261/262 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.
The following table is a guide to the maximum usable lengths of some common 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.
Max Length
in Meters
Max
Length
in Feet
Insertion Loss
dB/meter at
1090MHz
MIL-C-17
Cables
Electronic
Cable
Specialists
Type
SSB
Electronic
2.54
8’ 4”
0.59
M17/128
(RG400)
3.16
10’ 4”
0.47
3C142B
3.81
12’ 6”
0.39
M17/112
(RG304)