View Full Version : Waterfall Diagram and DRM
I think that a DRM-modulated signal leaving the transmitter is a quite good source to analyse the influence of the propagation path or transmitter quality.
The original signal is rectangular with a lot of carriers with equal amplitudes and I would like to say it is compareable with a white noise source that can be used for measurements.
In the threat
Roland descibes the patterns outside the DRM-signal as sideband power of the transmitter.
In the picture I attached it can be seen that the signal from B5akt has mostly fast fading over 10 kHz and the fading of RTL is selective on some frequencies inside the DRM-signal. To record this picture I tuned the receiver to 6090 and used a 20 kHz wide filter of my TS850.
If we collect observations like these in this threat perhaps we can
learn more about propagation at all or for DRM especially.
in the picture you can see in the lower part a waterfall which
has a signature like a chessboard recorded from "The Mighty". The signature can also be seen in the sideband power.
as already shown by Bernd, the Mighty, in cooperation with ionospheric propagation, often produces fascinating waterfall plots.
Attached is a plot recorded at the end of yesterday's transmission on 7430 kHz. The sidebands are clearly visible. However, although the sidebands look nice, one should try to improve their suppression because they could cause quite some interference considering the strong signal the Mighty produces in Southern Germany.
I "measured" the sideband power from 6 DRM-stations using the software Spectrum Laboratory. This software shows the level of the cursor pointed to the interesting point in the waterfall diagram. Moving the cursor horizontally between the DRM signal and the sideband you can determine the difference.
All stations had an attenuated sideband power of 25 to 35 dB relatively to the main signal. The Mighty, with more than 30 dB attenuation, is one of the better ones.
The attached file shows RTL on 6095. Here the sidebands have different power. The lower sideband is displayed about 10 dBs stronger than the upper one. I don t know if the transmitter is really unsymmetrical or some power from B5akt on 6085 is added to the displayed sideband pattern.
I donīt think you can really measure the out of band power this way. In my location the signal strength from 6085 kHz and 6095 kHz are often the same, so this method wonīt work. This has to be measured at the Tx control output and there are recommendations from ITU, like 30 dB attenuation at ą0.53 channel bandwidth, and beyond a slope of -12 dB/octave to -60 dB, you will never be able to measure this. Here is an example of the spectrum mask limits for a 10kHz channel (from an ITU draft, not sure if it was already finally agreed like this).
In the past Carlos posted some spectrum plots from the Sines transmitters which looked very good, but it would be interesting to see some spectrum masks of other stations too :)
you are right, to "measure" the sideband power in the configuration RTL - B5akt at the receiver side is not meaningful because here a DRM signal is side by side with an other one. But during daytime many strong DRM stations with no adjacent stations are available to "measure" in this way and the results with 25 to 35 dB match quite well the spectrum limit mask you mentioned. According to this mask 30 dB are demanded 5.3 kHz from the center of the DRM signal.
I used measure in " ", because it is really not more than an estimation with the equipment available here. (I don t know if it correct to use " " in English if you want to express that this word is not used in the correct meaning. In German we use " ". Does anybody know what is correct in English?)
More funny waterfall pictures.
DRT1 tuned to RTL 6095kHz, BR-B5akt 6085kHz to the left.
I was just wondering the waterfall pictures. I can't see any sideband power in my on air tests. I can get sidebands power when overdriving the dream -t transmitter output to the receiver.
What about, if the sideband power is coming from the 3rd order distortion in your receiver.
I add three pictures, one is a waterfall from VoR,BBC and DW.
They were strong signals here in Helsinki today. 25 - 34 dB SNR
The second picture is overdriving my receiver and the third picture is SNR spectrum with dream -t at level RX input -91 dBm 50 ohm. When overdriving the level was about -30 to -20 dBm.
DW frequency is 15545 kHz NOT 15445 kHz! Sorry.
The second picture is overdriving the RX.
And the last one SNR spectrum during tests.
I'll add one waterfall more. It is 15440 kHz at 14:26 UTC today.
I had a different intention when posting the screenshot.
On 49 meters I have two stations on adjacent frequencies.
Bavaria from sse direction on 6085kHz and Luxembourg from ssw on 6095kHz. I live in northwestern Germany.
I wanted to show the sometimes totally different fading schemes on the two signals which are very similar in frequency and distance to me.
If I have a single clean drm signal I also see no sidebands.
I added some more screenshots. In the picture you first see three different shots in a row with the DRT1 tuned to 6093kHz and DREAM tuned to 14kHz.
BR-B5akt to the left, RTL to the right.
The separate waterfall at the bottom is DW on 13790kHz as you would like to see it.
( We know you are a linearity purist/extremist.... ) :D
Yes, now I understand your intentions.
I was not reading your posts carefully.
We know you are a linearity purist/extremist....
Yes, if you don't have dreams, they can never come true. :)
I just add 6085,6095kHz waterfall, too. Rx was tuned 6090kHz
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