VHF Propagation Surprise

Driving across town this morning I noticed something interesting; a “local” FM radio station was being overpowered by a country station (never managed to catch enough to get a call, but possibly from central IL) .

Because of the way the radio spectrum works, ducting (carrying VHF radio signals long distances in the atmosphere before returning them to earth) starts at lower frequencies and works it way up.Often times I use the reception of distant stations on the FM broadcast band as a gauge of when to check the higher HAM bands.  Well I tuned over to 107.5 and caught the ID for KKDM (Des Moines) coming in perfectly, which is a sure-fire sign that something is happening…

I rerouted myself to a large hill (behind Monroe school in SE Cedar Rapids) and safely pulled off into the parking lot.  Flipped the mobile radio over to 146.520 and hit the push-to-talk and sent out a CQ — basically a broadcast asking any station if they’d like to chat.  I wasn’t expecting to hear anything.  But I was 20 minutes early to my appointment across town, so what the heck…

I heard nothing.  Called CQ again.  Unexpectedly, a station came back.  KC9RJI actually; who immediately stated that he was from Rock Island, IL.  Well, that’s a surprise.

VHF signals usually don’t travel this far.  In fact reaching a station directly between Cedar Rapids and Iowa City (20 miles) can be problematic.   So Rock Island was quite a haul.  I chatted with Bruce for about 10 minutes before deciding that it was time to head to the appointment, so I signed-off with him.  To my surprise, I heard a station calling me directly — from Platteville, WI — Hap Daus or KC9BGA.  That’s two states, a whole lot of miles (64 and  80) , and quite a surprise for me.

Just to show how quick things change on the VHF bands, as soon as I copied KC9BGA and confirmed his call the band closed up the duct, and I couldn’t even finish our conversation.

These certainly aren’t the distances I was accustomed to pulling in on the HF bands, where on a good night there really isn’t any limit to the corner of the globe you can reach.  But for VHF — and from a vehicle — it’s impressive all the same.