Although I have used an external antenna for my meteobridge PRO Red unit, I felt that the signal was marginal still.
I decided to add the leftover mini-circuits preamp that I used previously on a repeater project. This is the ZFL-1000GH.
This preamp's gain is dependent on the power supply, so I am using a regulated power supply of 15V. Lower voltages reduce the gain.
You can see the difference in the signal strength in the attached image. I was running without the preamp prior to 9 AM (09 on the chart). After 9AM, the preamp is in the circuit. As you can see I picked up about 20dB. I needed to reduce the "RF Sens" to -75dB, since nothing worked at the higher gain settings. I suspect over driving the RF input on the PRO Red was causing spurious responses. I see this on the various digital modes for Ham radio on the waterfall display if the gains are set too high. Can't tell what is going on here however, so some guesswork is needed.
The minimum signal readings are now about what the best case was previously. Without the preamp, signals could dip to -90dB. Now they are averaging around -50dB, with the minimum at about -70dB.
The mini-circuit preamps are really expensive if you go to buy a new one, but I have had good luck with them from eBay at a much lower price. They have been removed from equipment and are available for resale. As long as the preamp chosen has the bandwidth including the 900MHz band, it doesn't need to be the ZFL-1000GH model. I replaced the ZFL-1000GH with a ZRL-1150LN+. This preamp has much higher gain though and would require a different "RF Sens" setting accordingly to prevent overload. The ZRL or other preamplifiers would work. They don't need to be mini-circuits either, I just use them because I was somewhat familiar with them.
Here is the installed preamp, just above the MB. Antenna is not visible, but the coax is running up the wall.