Active antenna bias network

[dwarffrog]

I have a GPS module that calls for a bias network if an active antenna is going to be used. My question is this: If the cable length from the module to the antenna is about ten inches, is this bias network necessary? If so can anyone point me in the right direction? I have no experience in this area so any help would be appreciated.
Thank you!

 

[Comcokid]

For active GPS antennas, the coax serves to both as wiring for power to a LNA built into the antenna, and a bias network is used to put that DC power on the coax without disrupting the RF signal. Other types of non-GPS antennas may have mixer/downconverts built in as well.

Amplification is necessary when the coax to the antenna is long as coax has loss based on it's length, and the loss is greater for higher frequency signals. However, in your case you should not require an active antenna and bias network, provide the directions for your module indicate that this is optional. I say this because there could be some cheap modules that depend upon a LNA in the antenna because they eliminated it from the module alltogether to save cost.

 

[dwarffrog]

Comoco,

Thanks!

 

[Higgler]

You won't need a bias network if you only 10 inches away. The "active antenna" is just a regular antenna with an amplifier. If you go to Radio Shack you can see examples of how this is done in hardware for remotely located TV amplifiers that you place at your antenna. You add an amplifier at the antenna, use standard coax. and a three connector device indoors at your TV inserts bias (which is just dc power) up the coax. which is used by the amplifier. When the RF energy comes down the cable, the rf can go thru to the TV, but the dc power you sent up the cable is blocked from blowing up the TV by a capacitor in the 3 connector bias injector device.
The only need to add something like this (active antenna) is when you use a long lossy rf cable from your antenna to your GPS receiver. Some companies who put them on their trucks may use 20 feet of cable and maybe they'd use it. Our company used one to bring GPS indoors for antenna testing conditions and we had 100 feet of cable.

Kevin

Kevin