Whilst I was planning my demo I realised that as the club meetings are in the evenings and HF conditions have been very poor lately it was quite possible that we would have very little to listen to. Then it occurred to me- Most SDR software has a facility to record. Not simply to make an audio recording, although it can do that as well as required. The clever bit about recording from an SDR receiver is that you can also "record" a whole bandwidth of signals. In the case of my Elad SDR radio it can receive and record up to 6mhz of bandwidth. The picture below shows it receiving the full 6mhz using the SDR console v3 software.
Using this facility I was able to record part of the spectrum in the daytime, when the bands were busy and use this to demonstrate the SDR software and receivers.
The received part of the spectrum can be recorded onto a hard drive (or any other media). When played back you can tune through the spectrum (in the example above from around 11 to 17 mhz) using whatever mode you want.
In effect you have a snapshot of that bit of the HF spectrum which you can listen to as if you were sat at your receiver when the recording was taken.
This set me thinking, if only we had this technology years ago. Today we would be able to tune through the HF bands of the 40s,50's 60's as if we were there!
I wonder if anyone is recording the bands on a large scale now. The downside of this is at the moment these recordings use a lot of space. The recording in my picture above was for a 10 minute recording of 6mhz of spectrum which used 7gb of storage. I reckon to record the whole 30mhz of LF/HF (if you had a receiver with such a wide bandwidth) for 24 hours would use in the region of 8.4 tb. If you were attempting to record for any length of time you would need a massive amount of storage. But just imagine if we were able to tune through the bands of yesteryear!........................................