2 replies to this topic

[CaptainKoloth1]

Hello everyone:

 

I've been getting into SDR radio astronomy the last few months and with the Quadrantids coming up I wanted to try my hand at radio meteor detection. However, I'm quite confused with regard to what frequencies I should be monitoring. I'm in southern California. Almost all the tutorials I've seen are either geared toward the UK, or suggest looking for specific empty FM bands or TV channels. However, being near Los Angeles I have strong local transmissions at nearly every "standard" frequency I've seen recommended for this purpose. Has anyone successfully done radio meteor detection from this area in the last ~10 years?

[triplemon]

Yeah, sitting in a highly RF polluted area is tough for passive radar applications like this.

 

In general, any frequency beween some 50MHz and some 150MHz will work, returns diminish with higher frequencies. You want a frequency with a strong distant transmitter thats just a bit too far away to be heard directly, or even better, not so distant, but blocked by mountains. And no local one on the same channel. You can look up TV stations https://www.antennas...er-locator.html and for FM stations its a bit more complicated via https://www.fcc.gov/media/radio/fm-query

 

I have never tried an digital TV station, which will give you a bit worse sensitivity due to the bandwidth of the signal. But I every now and then I run my receiver here in Portland on a FM station at the coast, some 100 miles away and I get regular pings. Having a modestly directional antenna pointing in the general direction and a rather high dynamic range amateur radio receiver also helps me with suppressing local RFI a little bit.

 

Its a lot easier though if you sit away from civilization and listen towards all the commotion - we just last summer had a little RTL-SDR dongle running with just a wire dipole at our astronomy clubs dark site on the east side of the cascades and listened to FM stations in Portland, a 180 mile path over the mountains.
 

Cheers, AD7IC

Edited by triplemon, 02 January 2025 - 03:53 AM.

[555aaa]

We did a project here (Washington State) using a DTV carrier from a station in Oregon. The nice thing about DTV is that the "carrier" is very narrow band, however it seems that there's fewer and fewer of these stations. I worked with some CWU students to build a custom Yagi antenna and some live processing software to do automated collection of reflections. It was a fun project, but my site is fairly radio quiet which is a big help. When they tried to put the antenna on campus they had problems.

 

One thing I did at the start was do a survey using a simple monopole (a stub antenna over a ground plane)  to find the bands where I had minimal local noise but also overlapped the ATSC digital carrier from remote stations. In ATSC digital most of the energy is spread over about 6MHz but there is a nice sharp reference signal offset 310 KHz from the start of the band IIRC. We did get some meteors off of the monopole. I think we got the best results at 76.31MHz for the KOBI transmitter in Medford. So we use the SDR radio in lower sideband mode and that gives us an audio tone, which we captured live onto a little custom DSP board that then analyzes it and stores off the intensity, duration, and time.

Edited by 555aaa, 13 January 2025 - 04:53 PM.