I had an opportunity to plug into the Reading PA system and use an application called Touchstone on my computer to map out the RF spectrum using an RTL-SDR usb software defined radio dongle. I grew up in this system but moved away in 2010 and boy have things changed in that time.
My SDR reliably goes down to 24 MHz so I started the scan there, and Touchstone only scans in 300 MHz blocks at a time (at least the free version), so I broke it up, which is fine because its easier to see.
The system runs on a lot of Scientific Atlanta System II gear that was installed in the late 1990's. There have been a lot of gear swapped out for the newer Cisco Gainmaker units since I've lived in the area, and many new aurora nodes have been put in to supplement SA 6940 nodes. Though there's a good number of newer gainmaker and aurora nodes, there's still plenty of the old stuff out there so they can't really make use of much past 750 Mhz until the entire system is re-engineered. I can see blips of Pathtrack around 50 Mhz, and set top box OOB channels exist at 74 and 110 MHz. Besides that, every channel is used up with QAM (or OFDM) except for an analog channel on Ch 61 which is used for amplifier AGC.
I see they did push a little past 750 MHz, but after ch 123 (792 MHz) there is absolutely nothing on the plant. It goes to show you that even after over-compressing mpeg4, there is absolutely no room to add anything else, or even expand OFDM. Any new channels would have to be delivered via IP from the CMTS down a docisis qam or ofdm channel. I have to wonder since this system is 20 years old now, if an upgrade is in order to stay competitive.
I also have to wonder, much like the TWC/Spectrum system I have plotted, there are some groups of 5QAMs that appear to be similar in signal level. You can look closely and see the slight difference in these small groups. I have to wonder if they are just coming out of a different device.
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