Receiving radiosondes is very easy, provided that you have line-of-sight to the balloon. Any mountains, buildings, trees, or any other obstruction will block the radiosonde signal. If you're close to a launch site, you don't need an expensive antenna or LNA, so save your money and buy dinner for a fellow sonde chaser after your next successful recovery.
If you live within 200 km of a radiosonde launch site, or have line-of-sight to the balloons up in the air, you don't need a preamp/LNA. Standard RTL-SDR dongles are sensitive enough to receive the 60 mW radiosonde transmitter out at several hundred km away, even with 50 feet of RG-8/LMR-400 coax and a splitter.
But maybe you're on top of a mountain far away from a radiosonde site, or you have a long run of lossy coax, or you also want a bandpass filter because of strong interferers nearby. In this case, a low-noise amplifier might be helpful.
As counterintuitive as it may seem, the overall gain of the amplifier is not the most important number. Since any RF signal amplifier not only amplifies the signal you want, but also amplifies noise, it turns out that adding an amplifier doesn't actually let you hear weaker signals.
The overall gain of the LNA is not the important number, as
I had a several
Uputronics Radiosonde LNA
I purchased an Uputronics Radiosonde LNA for two reasons: the noise figure was approximately 0.75 dB, and it has a SAW filter to because the specs seemed good. Only
The main components of the Uputronics Radiosonde Filtered Preamp are:
- LM2940 5 volt 1 amp LDO regulator (pdf
- MiniCircuits PSA4-5043+ low noise amplifier (pdf
- TAI-SAW TA1135A saw filter (pdf