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E-Skip and Tropospheric Ducting

Credit Jim - K5ND -
Model of Tropospheric Propagation/Ducting

From time to time, especially as the weather warms up in Northern Arizona, we receive calls from listeners alerting us that “another station has taken over our frequency,” or words to that effect.

What’s happening? A vast anti-public radio conspiracy? Hardly.

We always appreciate your calls about signal issues. Sometimes it alerts us to a system malfunction. Other times it reminds us of a phenomenon called “tropospheric ducting.”

I’m not an engineer but the simple explanation is that under certain atmospheric conditions, radio waves can travel in abnormal ways. For instance, a distant station’s signal can travel hundreds of miles and seem to crowd a local station on the same frequency.

Here’s what Wikipedia has to say:

Some of our repeater stations are licensed to fairly low power and are easily overwhelmed by more powerful signals even if they’re coming from far away. Amateur radio operators actually like the condition, because it allows them to talk over greater distances than normal. I found this video from the Ham point of view (and check out his pretty cool gear):

The only good news really is that ducting works both ways. KNAU’s signal can also travel tremendous distances too.  Here’s a link to an engineering site that actually quotes me about unusual signal reports:

Click here for a more complex discussion and some interesting reader responses:

And finally, a very high geek-factor map:

Our combination of changing seasons, current weather and relatively low-power stations is what’s behind this interference. Assuredly, it will pass. With apologies to Mark Twain, everybody talks about tropospheric ducting but nobody does anything about it.

Our online streams of both news talk and classical remain unaffected.  Listen here: