MAR6 for GPS LNA

[metrologist]

I was planning to use a MAR6 in a simple GPS LNA, like a LNA4ALL.

I was just going to solder it to the end of the semi-rigid coax on my QFH antenna, with a 100n decoupling capacitor on the antenna side. Should I use a smaller value decoupling capacitor, any shunt capacitance, or series inductance on the output side?

If this won't work, then I just want to fool my GPS because it detects that the antenna as it is (without the MAR6) is OC and it won't function., so how could I do that? Resistor across/instead of the cap? I think it just wants to see some current, but not sure how it's detecting a proper antenna.

[metrologist]

Well, this is what I made, both with a MAR6 and a MAR3 shown here. They don't work for my GPS antenna.

I used this site (http://www.changpuak.ch/electronics/mar_era_bias.php) to get values, but am not using the supply circuit nor the receiver side decoupling capacitor because that feeds DC to the amp. Otherwise, would I need to use the supply circuit and connect the supply and output nodes together?

[KE5FX]

One thing to watch out for is oscillation, especially if you have a lot of wiring away from the ground plane as in metrologist's photo.  MAR-6s have a lot of gain.  If that preamp goes into an enclosed box of some kind, there's a good chance that it will jam somebody, somewhere.

[metrologist]

I think there is too much front end overload. I poked it with a spectrum analyzer and there are a lot of other signals. I was just using my scope probe, so couldn't see anything in the GHz range.

The LNA4ALL sells for 20 euro with the SMA connectors.

Anyway, this was just something to do while I wait for my Chinese GPS antennas. The MAR6 came from a scrap board and I cut out the entire section with the DC input components intact, so I could still use it as a general purpose LNA.

Thanks for all the insights.