The Euro "splatter" problem
Introduction
The following sequence of images are screenshots of the On-line Receiver taken on the morning of 19th November around 08.00 UTC. The images have been cropped from the full frame capture and
converted to GIF format. No other image manipulation has been done.
The receiver settings have been set to a bandwidth of 9 kHz and these are marked by the two outer vertical red lines in the spectrum display
( the centre one is the marked frequency). The two vertical green lines are markers at + and - 5 kHz from the centre frequency, each vertical line on the grid represents 1.0 kHz. The WiNRADiO
G313 uses a 15 kHz crystal filter which accounts for the falling away of the trace at the outer edges.
Image 1
The first image is with the receiver tuned to BBC Radio 5 Live on 909 kHz. being transmitted from the 1kW local TX at Fareham, Hampshire. Notice how the trace in each case extrends almost to the 4.5 kHz
marker and then decays rapidly to the 5 khz marker, giving a bandwith for both sidebands of nominally 9kHz, and certainly no more than 10 kHz, which is to be expected for the channel spacing of 9 kHz.
Now lets look at the trace for Virgin 1215 from the same transmitter site.
Image 2
In the above trace the energy levels in each sideband extend beyond the 4.5 kHz marker and even pass the 5kHz mark and extend to 6kHz from the centre frequency mark, giving a channel bandwith of
12 khz. Notice also, when compared to the first image the tailing off of the energy levels takes another 1kHz to fall to the receiver noise floor. It is reasonable to assume that Virgin Radio is using an
Optimod to improve on the received sound.
Image 3
The third image is of Big L on 1395 kHz from Trintelhaven in the Netherlands. Again the bandwidth is approximately 12 kHz.
Conclusion
I observed the traces for a number of national and local BBC transmissions, in all cases the bandwidth was around 9 kHz. Monitoring Independant National and local radio, in all cases, the bandwidth was between 11 and 12 kHz. Several members have commented recently on the amount of "splatter" in the band. It would be interesting to see if the amount of "splatter" was greater for ILR stations.
And finally...
By way of contrast an image of the RTL 1440 kHz DRM transmission.
