September 27, 2011

SPLATTER = "Nasty Stuff"

We made a nice contact today on 20m PSK31 with a YL (Mary).  Mary commented that our signal was very clean with "none of those lines and nasty stuff" on the waterfall.  We traded anecdotes of our recent experiences observing poor quality PSK signals that were overdmodulated and as a result created interference for neighboring PSK stations.

Splatter is a type of interference to stations on nearby frequencies.  Splatter occurs when a transmitter is overmodulated.  The goal is to make sure your signal is never overmodulated.

Splatter is easy to identify and in many cases just as easy to clean up.  The waterfall screen used for digital communication with tools like DM780 provides an excellent way to visualize the effects of splatter.  You are seeing splatter on the waterfall whenever you see a signal with ghost lines on either side of the original signal.  In general, the wider the ghost lines appear the worse the offending signal is splattering. 

Example of splatter.  Here are two strong PSK31 signals.  Notice the ghost images on the left signal - indicating splatter?  Notice how nice and clean the right signal is?

If you have a particularly horrible example of splatter on a waterfall in the form of a screenshot, please do send me an email with it and a short description of what you observed.  I will compile the worst of the worst for a future post here.

You can check if your signal is splattering by asking a contact you are working to check your signal for splatter and overall quality.  If the report comes back indicating your PSK signal is splattering, try turning down the signal input into your transmitter until the splatter is eliminated.

Power doesn't cause splatter; however, remember also to use the least amount of power necessary to work your contact.  PSK31 and JT-65 are remarkably effective at minimal power.  QRP operators do quite well making DX contacts on PSK31 and JT-65.