I spent the better part of Memorial Day doing a survey of Quadrant 3 of the 
Milky Way. The attached image shows the area of the six scans I made. These 
were 30-second integrations. I have also attached an image showing the 
combined spectra of the scans. All have the same general profile with a 
bump around 1420.3 MHz (presumably the hydrogen line) and another around 
1419.5 MHz (source unknown), plus some noise at the left end of the scans. 
A scan of an area away from the galactic plane removes both bumps but 
leaves the noise at the left side.

I have two questions:

First, does anyone have any idea what the bump at 1419.5 could be? I 
thought it was just interference, but because it disappeared when pointed 
away from the galactic plane that explanation doesn't seem to fit.

Second, should the scans of hydrogen across that area show bumps with 
identical red shifts? I would have expected the speed of the hydrogen to be 
different at various points, so I'm surprised  they all spanned 
1420.23–1420.37 MHz. The only difference is in the signal strength. Is that 
normal? I want to make sure that what I am detecting is actually the 
hydrogen line and not something else.

I made scans that included integrations of up to 10 minutes, but those 
didn't seem to change the basic profile of the spectrum. All the scans 
combine in the attached spectrum were 30-second integrations.

Any help on this would be appreciated. I'm new to radio astronomy, but I've 
been doing visual astronomy as a hobby for 40 years. This horn antenna for 
hydrogen is my second radio astronomy build.

System:

   - horn antenna
   - Nooelec LDA with hydrogen line filter
   - Nooelec SDR dongle
   - Raspberry Pi 4 using GNU Radio with a spectrometer created by the 
   Digital Signal Processing in Radio Astronomy (DSPIRA) group at the 
   University of West Virginia
   - SMU9250 to read altitude and azimuth

Kevin A. Wilson