I heard some radio frequency noise at Lake Georgetown while operating QRP portable but didn't think much of it. I was able to go back to the opposite side of the lake and receive the same noise using my vehicle mounted receiver. The noise was again S8 or S9.

All noise samples were recorded with the following configuration

1. Yaesu FT-857
2. Yaesu antenna tuner connected to my stainless steel whip vertical
3. Noise blanker on
4. Vehicle engine off
5. Noise reductions features of the radio off
6. "Intercept point optimization" in the radio off, which turns off the preamp.

I do not have a good way to record audio from my radio in the truck, so I just put my camera phone near the speaker and recorded video. I extracted out 30 seconds of audio with the least background noise.

40m noise

This audio was recorded on 7.2901 MHz in lower sideband phone mode. I am only showing the audio range of 0 to 3500 Hz as there isn't going to be any audio coming out of the radio beyond those frequencies. I show the spectrogram in "combined" mode since my phone actually creates a stereo audio file.

Spectrogram

If you look at this you can see there is noise in the 400 Hz to 2600 Hz range. The places I have labeled "A" & "B" on the spectrogram give this noise a unique charateristic. Event "A" happens around 6.3 seconds. Event "B" 22.2 seconds. The time period between them is 15.9 seconds. Event "A" sounds like a pause, a pop, & a longer pause. Event "B" sounds like a pause. This pattern of pauses repeats indefinitely.

Any peaks or dips in the noise spectrum I wouldn't place too much emphasis on. It's more than likely just the result of the speaker nor the microphone being very good audio equipment.

30m noise

I also recorded on 10.10245 MHz in upper sideband mode. The noise is the same, but you can never hear the pauses when listening to the receiver. There are two dips in the noise I labeled, but the they are not nearly as long as the dips seen on 40m noise. My conclusion is they aren't meaningful. The pauses simply do not seem to happen on the 30m band.

Spectrogram

Summary

There is extremely strong RFI on 30m & 40m band in the vicinty of Lake Georgetown. I don't have a good enough 80m portable antenna to tell if it is present there as well.