gps antenna

[Wayne Berg]

Can someone describe the difference between an active and passive GPS antenna?

 

[Gregory S]

I don't know, but I just bought an active for $175.00!!!!!

 

[Billylll]

A passive GPS antenna requires no power and the reciever is generally in the device you are hooking it up to. An active GPS can be anything from the full GPS/WAAS reciever mounted under the antenna inside the puck if NMEA0183 or NMEA2000 or in commercial applications an LNA (low noise amplifier) and the antenna itself inside the puck.
Most marine applications require amplified antennas or NMEA0183/2000 units unless they are used with a GPS stand alone reciever and within a few feet of said GPS reciever. Most modern MFD's require NMEA2000 active GPS recievers.
Early chartplotters require active (LNA) style or NMEA0183 active GPS antennas.
Bill

 

[Wayne Berg]

Thanks, I suspected that it had to do with a power supply. I will try to digest your info and apply it to my situation.

 

[stmbtwle]

The active GPS antenna is actually a RECEIVER, and sends the appropriate code down a multistrand cable to the display. There is no receiver in the display unit. With the appropriate connections you can connect an active "antenna" directly to your computer if you have the appropriate software.

The passive antenna is little more than a piece of wire or foil... and the actual receiver is in the display unit.

The two are not interchangeable.

As far as which one is better I don't know, but I DO know that an active antenna/receiver can be fried by a radar (been there). Never had that problem with a passive antenna.

 

[mdoherty]

quote:

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Originally posted by stmbtwle

The active GPS antenna is actually a RECEIVER, and sends the appropriate code down a multistrand cable to the display.

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Incorrect. An active antenna has an amplifier inside the antenna unit. It will have a standard RF output coax cable. Anything that outputs a digital signal is a full GPS reciever.

 

[Billylll]

quote:

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Originally posted by mdoherty

Originally posted by stmbtwle

The active GPS antenna is actually a RECEIVER, and sends the appropriate code down a multistrand cable to the display.

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Incorrect. An active antenna has an amplifier inside the antenna unit. It will have a standard RF output coax cable. Anything that outputs a digital signal is a full GPS reciever.
[/quote)

Actually as I mentioned above it depends on the application and manufactures naming of the device. A Garmin 740s for instance can use either an active GPS external antenna or a NMEA0183 or NMEA2000 in other words all 3 would be considered by their terms an active GPS antenna. There are active GPS antennas where the LNA and antenna are packaged without a reciever these usually have BNC coaxial cables, but there are active GPS antennas where the manufacture call them active that have the reciever and proper protocol as in NMEA0183 or NMEA2000 chipset (reciever). The manufactures have caused the confusion.
I do agree a NMEA0183 or NMEA2000 sould be called a GPS reciever not an active GPS but they are.
On my Son's boat I use a NMEA2000 backbone with the NMEA2000 GPS antenna/ reciever that outputs NMEA2000 yet you can install an LNA based GPS antenna on it.
On my 40SB I have the back up GPS using the LNA/GPS as well as my NMEA2000 GPS reciever that feeds the NMEA2000 network I can list the GPS priorities from my Garmin 6212 and or Garmin 4210 NMEA2000 device manager in the network configuration screen. If I loose my NMEA2000 GPS sources it gets data through my 740s external LNA style GPS antenna and even if that fails my Navonics NAIS300L AIS class B transponder's GPS antenna can and will automatically give me my GPS position it does tell me low accuracy when I intentionally upset the normal NMEA2000 GPS position data stream. If the LNA/GPS fails on the Garmin 740s the internal antenna will still give position updates to the entire Garmin network, also my SmartCraft network which requires NMEA0183 GPS data.

Bill