There is an interesting network of wideband receivers with close to 100 different sites that can be used for tuning the bands around the world. HA7ILM, András Retzler, operates a web site that provides a list of all receivers currently on line at this link: sdr.hu.
The home page provides a list and at the upper right there is a link to a global map page with links to each receiver. When you zoom in and click on a single "balloon" on the map, it then gives information about the location and a link for connecting.
The sdr.hu page lists all receivers that run the OpenWebRX application provided by András. There are currently about 90 receivers online and my guess is that most of them are the KiwiSDR that covers 10 KHz to 30 MHz. I have no idea how many of the Kiwi have decent VLF antennas and low noise environments. Many are useful for the CW bands.
It takes a bit of playing around to learn the user interface for tuning around, zooming in and out on the waterfall, changing filter characteristics etc. but it is in interesting system for tuning the bands.
There is a box at the top where you can optionally enter your callsign (or name). Many users do not enter anything, but it is interesting for me to see callsigns on the logins.
This video: G8JNJ Kiwi, 80M during CW contest is an example of an active band!
This video: Decoding Kiwi signals was also done on the G8JNJ receiver. I was comparing the FLDIGI decoder to my PIC32. Something strange was happening with FLDIGI, it was displaying a space between every character for some reason. I have no idea why but know this is not normal for FLDIGI.
My Kiwi is connected to a poor wire antenna but does a decent job. You can find it by zooming in on the map to New Mexico. You can connect to any of the receivers using parameters like this:
This specifies the frequency, the mode, and the waterfall zoom level. A control panel on the waterfall allows you to change the WF max and WF min display settings. If the band noise is "too bright" you can adjust the settings so that the background is dim and the signals stand out more.
This link: Passband adjustments gives instructions for playing with the bandwidth, offset, etc.
There is a limit of four simultaneous users on the Kiwis. If you try to connect and there is not a free slot open, the web page notifies you to try later.
If you were using my Kiwi when I am on the air, you would see that the input A/D is overloaded when I am keying, but I am only active on the air once a day normally so most of the time this would not be a problem.
I just looked at my Kiwi and immediately knew that one of the frequent CWOPS CWT events was running. They are obvious because of all the strong signals in the 7025 to 7035 portion of 40M (screen shot attached). I do not see the image in the "preview" mode but assume it will show up in the actual post.