The Model AS0087800 GPS Active Antenna is intended for precision timing and navigation applications. It is designed for nominal 5-volt systems, and contains internal voltage regulation, providing consistent performance over an input voltage range from 3.4 Vdc to 5.5 Vdc. This exclusive feature ensures that performance does not degrade with long antenna cables, as can happen with other antennas due to loss in the dc power supply voltage caused by the dc resistance of the antenna cable. While not optimized for 3-volt operation, the Model AS0087800 antenna will operate with dc power down to 2.75 volts, with short antenna cables (typically up to 45 m or 150 ft), delivering acceptable performance with the M12M and many other GPS Engines.
The Active Antenna is designed for long life in challenging environments. The radome is molded of ASA resin, for excellent weatherability. Weather-resistant EPDM O-ring seals are standard. A plated and threaded metal coupling nut provides outstanding corrosion resistance and accepts both 1 in – 14 marine mount and 0.75 in NPT pipe thread. Exposed assembly screws are stainless steel. A separate mounting bracket kit is also offered (p/n AS0044600).
A built-in LED with weatherproof light pipe indicates that the antenna is receiving power, and therefore that the cable is correctly connected to the GPS Receiver. This is another exclusive feature simplifying installation and commissioning.
This antenna has exceptional rejection of interfering signals, low noise figure, and high gain. When used with the iLotus M12M receiver, the nominal attenuation budget is 2 dB to 20 dB, with acceptable performance for cable loss up to 28 dB. With a specified temperature range down to – 55 °C, the Active Antenna is usable in almost any location worldwide.
A separate in-line pre-amplifier (p/n AS0044700) provides 21 dB of gain for applications that require longer antenna cable runs, up to 240 m (800 ft).
|Center Frequency||1575.42 MHz nominal (GNSS L1 band)|
|Gain||LNA: + 38 dB at 1575 MHz, nominal|
Antenna element: + 5 dBi (at zenith); -1 dBi (10 ° elevation)
Total, including antenna element: + 43 dBi (at zenith)
|Input Impedance||50 Ω. Compatible with 75 Ω cable.|
|Polarization||Right-hand circular (RHCP)|
|Out of Band Rejection||> 60 dB, for f < 1525 MHz and f > 1625 MHz|
> 90 dB, for f < 1500 MHz and f > 1650 MHz
|Noise Figure||LNA: 2.7 dB typical at 1575 MHz|
Overall including antenna element: 1.0 dB typical (at zenith)
|Bandwidth||Compatible with GPS L1 C/A signal|
|Group Delay||43 ns, typical|
|Output 3rd Order Intercept||+ 7 dBm, typical, 1575+1576 MHz two-tone test|
|Output 1 dB Compression||+ 1 dBm, typical|
|Power Requirement||3.4 Vdc to 5.5 Vdc, 29 mA nominal; internally regulated|
Operational to 2.75 Vdc
|Status Indicator||Bi-Color LED: Green (normal); Orange (power < 3.3 Vdc)|
|Temperature||– 55 °C to + 65 °C, operating|
|Connector||Type F coaxial receptacle, environmentally sealed|
|Enclosure||ASA Thermoplastic with EPDM O-ring seals; meets IP68 of ANSI/EN IEC 60529 and NEMA Types 4X and 6P (when mated to sealed type F connector)|
|EMS (pending||IEC 61000-4-2 ESD; 8 kV contact, 15 kV air discharge|
IEC 61000-4-5 1.2/50 µs Lightning Surge; 4 kV/1 kA
|Mounting||Metal coupling nut for 1 in – 14 marine mount and 0.75 in NPT thread|
Nut: 1.25 in hex, corrosion-resistant plating
Separate mounting bracket also available (AS0044600)
Mounting hardware is grounded to connector and LNA
|Dimensions||80 mm hex (across flats) x 84 mm tall (3.2 in x 3.3 in), including connector|
Typical Cable Length Configurations
|For dc power input of 4.5 Vdc minimum, at receiver end of cable (5 Vdc with inline preamplifier)|
|15 m to 75 m (50 ft to 250 ft)1||No inline preamplifier; Size 6 cable2|
|90 m to 120 m (300 ft to 400 ft)1||No inline preamplifier; Size 11 cable3|
|90 m to 150 m (300 ft to 500 ft)1||One inline preamplifier; Size 6 cable2,4|
|135 m to 240 m (450 ft to 800 ft)1||One inline preamplifier; Size 11 cable3,5|
|Conversions are approximate, based on 30 m = 100 ft.|
|1Maximum cable length limited by attenuation.|
|2Times Fiber T6T77 or equivalent – total dc resistance 118 ohm/km, attenuation 270 dB/km maximum.|
|3Times Fiber T11T60 or equivalent – total dc resistance 55 ohm/km, attenuation 179 dB/km maximum.|
|4Inline preamplifier is ideally located at 75 m (250 ft) from GPS clock.|
|5Inline preamplifier is ideally located at 120 m (400 ft) from GPS Clock.|
For precise timing applications, the delay of the antenna system must be taken into account when configuring the receiver.This delay consists of two components: (a) the delay of the antenna cable(s); and (b) the delay of the LNA in the active antenna.The cable delay TC can be found from:
Tc = L / cv
Where L is the cable length in meters; c is the speed of light (3.0 x 108 m/s); and v is the velocity factor of the cable expressed as a number less than 1. For example, v is 85 % or 0.85 for the cables listed above.You must determine the correct value for v for the cable you are using from the cable documentation. For the cables shown above, cable delay is 3.92 ns/m. For example, for L = 30 m, TC = 118 ns.
This value is added to the measured group delay of the active antenna LNA, which is largely a function of the bandpass filters in the LNA. Generally, the greater the rejection of the bandpass filters, the greater the delay. (Most active antennas do not provide this delay, which leads to an uncompensated error in timing performance.) The resulting total delay value must be entered into the receiver for the most accurate timing performance. For this example: 118 ns cable delay + 43 ns antenna delay = 161 ns. Enter this number as ”Antenna Delay” in the GPS clock.
For navigation or frequency control applications, time offsets due to the fixed delay of the antenna system are of no consequence, so this delay may safely be ignored. (For timing applications having lower performance requirements, you may also be able to ignore this delay.)