DVB-T tuning specifics and quality
AIW Radeon X1900, AIW Radeon X1800 XL and the Nebula DigiTV were all asked to find and tune as many DVB-T TV channels as possible, each using the same antenna feed (a fixed rooftop antenna), within 2 hours of each other in the same system, in the same weather conditions (don't laugh, it matters!). Windows XP was used for this test, with MMC and DigiTV used to detect and lock the channels for their respective tuners.Additionally, a Daewoo DS700 set-top receiver (under £40 new now and a popular model in the UK) was asked to do the same.
For reference, the building the tests were performed in is located barely a few hundred metres from the local TV mast. Signal strength at the point of testing is therefore as good as can possibly be expected, since the mast is within visible line of sight at all times and it's a base transmitter, not a repeater.
The DigiTV and the Daewoo both tuned all available (non-pay) channels, and all were watchable at excellent quality. Both the Daewoo's interface and the DigiTV software report nearly perfect signal quality throughout. The AIWs, however, only picked up ~80% of those channels, with a couple of those (the same two each time) unwatchable. MMC reported full signal quality for every channel, however its signal meter is crude.
Current testing indicates that the signal is actually too strong for the AIW, causing it to fail on tuning some of the channels.
Tuner quality
While we didn't have the setup available to have all four tuners tune at the same time, and capture the same frame of TV simultaneously, we can give you a subjective analysis of the image quality.When the AIWs could tune the channel successfully, the image looked great. Same with the DigiTV and the same with the Daewoo set-top receiver. The AIW is therefore just let down by not being able to tune everything available.
For examples of tuner quality from the AIW Radeon X1900, click the following thumbnails.
A short visual inspection test with all tuners, on a range of programme content spat out from one MUX, shows all doing well when deinterlacing broadcast DVB-T in the UK. The 4:2:0 (and possibly 4:2:2) broadcast cadence is apparently detected and handled by all, without any issue, from the 16QAM transmission being tuned.
In short - the tuners can tune. (Ed. !)
Summary
The AIW does subjectively well in the image quality test, when tuning an interlaced, broadcast MPEG-2 DVB-T stream from a strong signal source. However, it seems that overly strong signals are able to faze the AIW boards and their MT2121F and Nxt6000 ASIC combo. The other two tuners on test fare better, comparatively.Remember that tuning tests like these are location specific and shouldn't be taken as an indication of the channel count you might be able to successfully tune in your area. It's our opinion that for the vast majority of AIW customers, the AIW Radeon X1900 (and other DVB-T-able AIWs) will tune the same channel count as a set-top receiver.
