Modify an LNA?

[mojoe]

I want to provide some additional amplification to a GPS antenna, to make up for the loss through a passive splitter. I'm currently using a 2-way splitter, which has a 3 dB loss at each port (yes, I'm DC blocking on the 2nd port). I want to buy the 3-way version that has 4.8 dB loss. The signal levels I'm getting now through the 2-way splitter are sufficient, but on the low end. Another few dB loss will only worsen the situation. The antenna is indoors, and there is no possibility of mounting it outside. It is mounted on a section of PVC pipe, to get it up to the ceiling in the upstairs room.

I could buy a purpose made GPS amplifier, but they are too pricey for me. I have a Nooelec LNA that is rated 20 MHz to 4 GHz. The LNA is powered by the bias tee voltage from an SDR, however, it doesn't pass DC through to the antenna. For SDR use, this is what you want. I need to pass the DC on, to power the HP 58532A GPS antenna that I am using.

Attached is the datasheet for the LNA. In addition, I have clipped the simplified block diagram, so you don't have to download the PDF. There are quite a few more components on the board, including protection diodes on both input and output. My question is, if I add a wire an inductor to jumper the DC to the antenna side, on the left of the capacitor, so DC doesn't get to the amp from that direction, will this work without frying anything? Is this a good idea?

I know that this LNA is very wideband, but the GPS antenna isn't going to pass any unneeded frequencies, and the feedline is double shielded coax.

Edit: Unless someone can point me to an inexpensive, amplified, 3 or 4 port GPS splitter that has moderate gain.

[tszaboo]

You can place a part called "bias T" between the LNA and the antenna, and power it from there. What you plan  to do is building in this bias T into the LNA's box, before and after the LNA, that would work as well if made correctly.

[David Hess]

I am surprised that the HP 58532A GPS antenna does not have enough gain by itself.

[mojoe]

With the antenna indoors, the highest I'm seeing with the 2-way splitter is 42 dBc. The 3-way will knock another 2 dB off of that. Most sats are in the 30's or lower.

[jbb]

Possible stupid idea: why not stick another GPS antenna up next to your existing one?

[mojoe]

To compare things, I want to use the same antenna and feedline. Besides, the HP antenna is much better than any other GPS antenna that I have.