![]() The purpose of the LNA is to raise the signal by 10dB which compensates for the cable losses and maybe the receiver noise floor. ![]() It is a bit of testing but the LNA noise figure (NF) appears to be about 2 dB. This looks less attractive (perhaps) but you don’t want any other signal on the LNA input than the antenna input signal, or stay signals in the neighborhood of the amplifier.Īlso, I tweaked around with several metal matches on the PCB of the LNA until all parasitic signals disappear. ![]() Also the LNA can use some improvement compared to the previous post, the best advise I can give is to put it in a shielded metal box. The intention of the LNA is to boost the signal by 10 dB at cost of some noise which comes from the LNA itself. This QFH antenna has the right sense of rotation, which is a difference of nearly 20 dB, in other words the previous QFH was looking at the reflected signal (RHCP becomes LHCP after a reflection) rather than the direct (through the roof) signal of the satellites, a stupid mistake.Īlso, there is 30 meter of cable between the QFH and the SDR, together with the connectors and so on it results in loss of a couple of dBs. But of a blunder but after some soldering, bending and twisting you finally end up with this: The first results where rather disappointing because the NOAA satellites transmit as right hand circularized (RHCP), and, if you look at the antenna in the previous post then it is really LHCP. And for the rest you wait as the images come by, it is a system that you can leave on all the time. ![]() I decided to evaluate the QFH antenna performance described in the previous blog post, the frequencies of the satellites are 137.1 MHz (NOAA 19), 137.620 MHz (NOAA 15) and 137.9125 (NOAA 18) which is below the designed resonance frequency, but the bandwidth is sufficient to cope with this.Īt the before mentioned frequencies you set the demodulation to 60k WFM on a rspduo receiver, redirect the audio output to a virtual audio cable and select the VAC as input into the WXtoimg software. There are three satellites called NOAA 15, 18 and 19 that routinely transmit scanned images of the cloud deck in infrared and visual. This blog article is about receiving and decoding the NOAA weather data, it is an old system that still produces data that you can receive with a SDR and a right handed circular polarized (RHCP) antenna called the QFH that I mentioned in the previous blog post. ![]()
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