Monday, June 18, 2007

SDR-IQ Image Reception

I received the SDR-IQ over three weeks ago and have been having a lot of fun with it. The ability to visualize the spectrum really changes the way I listen to the radio.

One thing I noticed, though, is that my two local AM stations (1 kW @
1 mile, 5 kW at 3 miles) both show up as "images" at +/- 196 kHz from the fundamental frequencies. These images are down about 60 db, but that puts them at about the same signal level (-90 to -100 db) as most of the other stations I can pick up.

I posted a message to the SDR-IQ group on Yahoo but haven't heard from anyone else whether my experience is unique. More on this if I uncover anything new.

Sunday, June 17, 2007

The Look of IBOC

Several stations seem to be broadcasting IBOC at 8:30-9:00 pm local (EDT) on June 14, as seen in the above graphic of the band from Spectravue as captured on my SDR-IQ.

The image shows 2 IBOC noise bands, one on either side of 760 WJR's carrier. As you can see, 760 itself is clean, but on the "far sides" of 750 and 770 carriers (e.g. lower sideband on 750 and upper on 770) the audio is "white" with a noise band 5 kHz wide. You can also see the same effect, albeit not as strong, around 840 (WHAS?).

What is slightly encouraging is that the sideband opposite the noise (e.g. lower SB on 770, upper SB on 750) are not as polluted by the IBOC noise; they are actually listenable despite the their other sideband being wiped out. The other thing I see is that the noise bands fade in and out at different levels from each other (sometimes only one is visible). Not sure why that is.

Anyway, this is what we will be looking at in the very near future on the US medium wave band.