The pitfalls of DXing at the bottom of a hill

credit: stock.xchng

credit: stock.xchng

It seems that location and quality of equipment isn’t everything when it comes to getting the most and best-quality DX.  The elevation of your home, from my experience, seems to be the be-all-end-all determinant of how well your radio can receive distant FM signals.  Your height above sea level could mean the difference between getting a strong tropo duct FM or static.

For a small-scale experiment of how height can affect DX, perform a dial scan of the local FM band with an indoor radio in your basement, then do another dial scan on the top floor or attic, if accessible.  I’d predict that you would receive many more signals (or a better-quality signal from the same stations) at the higher altitude.

I live in a fairly hilly portion of Northern Virginia, about 60 miles east of the Appalachian Mountains.  It is not uncommon to find hills that are over 150 feet tall next to rivers at zero feet nearby.  During my first three years of DXing, 1999 to 2002, I lived in a home about a mile west of my current location.  The home was 243 feet above sea level, high atop a steep hill.  In comparison, it was 67 feet above sea level at the bottom of the hill about 80 feet away.  While in this older home, I experienced great tropo with paths into areas such as Harrisonburg, VA, Roanoke, VA and South Carolina, all received with indoor whip antennas and without a preamp.

I saw a major difference in FM reception when I moved to my current home in 2002.  My street has a hill that is 62 feet above sea level at the top and 49 feet at the bottom where my house is located.  The hill, which thankfully is to the west where I wouldn’t get many FM signals from anyway, due to the nearby mountains, is high enough to have a ‘horizon effect’, in other words, the peak of the hill acts as a ‘horizon’ for sunsets and general views, as I cannot see past the peak.

In about all other directions there’s a hill that goes into the 60-foot height range within a mile.  So, I’m kind of situated in a valley surrounded by higher land in all directions.  Due to this, even strong 50kw FM signals within 20 miles are almost complete static indoors.  A roof antenna is a must for DXing in this environment, and a preamp is needed to get anything further than local FM signals.

Due to my limits, my typical tropo range maxes out at 150-250 miles.  My FM record is at 420 miles, but signals further than 250 miles are few and far between.

height

The graph above shows the difference in height between several things, including sea level, my current location, the aforementioned top of the hill on my street, and the hill where my previous home was located on.

Although I’m not a scientist and I have not performed reception tests at the same time from my current home and locations over 200 feet above sea level, I believe a DXer needs to be at least 100-150 feet above sea level to get maximum-quality DX.

Click to enlarge.

Click to enlarge.

In the picture to the left, it shows a vertical cross-section of land with two homes, one at 50 feet, the other at 250 feet.  The blue wavy line represents an active tropo duct in the same area.  The green portion represents land.  Since the antenna of the home at 250 feet above sea level is closer to the duct, a DXer at that location would be more likely to receive top-quality distant FM signals from the duct, while the DXer in the home at the lower elevation may miss out on the opening altogether, or receive weak signals from less-desirable closer stations (likely relogs).  As this is an illustration, it is not to scale and the tropo duct is likely much higher in the sky, but I feel, based on experience, the overall illustration is correct in terms of showing how DXers at higher elevations get better DX.

Click to enlarge.

Click to enlarge.

But all is not bad with living in a low altitude.  I believe being at 49 feet above sea level puts me in a better spot to receive meteor scatter or Sporadic E signals.  As meteor scatter happens the most in the overnight hours when tropo ducts are likely to occur, a DXer at a higher altitude who is enjoying the ducted signals would likely miss out on same-frequency meteor scatter because their radio would be receiving stronger signals via tropo (the ping would make it to the radio but not be heard because a stronger signal is being received via tropo duct).  At the same time, the home at a lower altitude who is receiving deadband conditions due to not being in the best spot for the tropo duct would likely receive the meteor scatter ping instead.

Although it appears as though the meteor scatter ping is crossing the tropo duct in one place but is being blocked in another, it isn’t necessarily true.  The red ‘reflections’ that seems to be eaten up by the duct represent what the radio would get:  If a strong tropo signal is being brought in by the duct, a meteor ping would likely NOT be received.  While I’m not an expert on this by any means, I’d suspect the tropo-ducted signals would be received by an antenna at a more horizontal angle (not exact as the earth is round and ducts curve signals past their intended signal area).  Likewise, a meteor scatter signal would likely be reflected at a more vertical angle, given the meteor is high in the sky.  And tropo ducts aren’t as uniform as in my diagrams.  They may be thinner in some places and have holes in it (causing DXers under the ‘hole’ to not benefit from the opening).

Overall, height is a major factor to consider when DXing.  I’d choose to be as high as possible elevation-wise for DXing.  But at the same time, it may be beneficial to have a secondary antenna at a lower height for some signal propagation methods to get the best of both worlds.

Note: Terrain elevations in this article are based on Google’s altitude algorithm.  I cannot attest to the accuracy of Google’s readings so they may be off a little bit vs. a true in-the-field reading with actual equipment.  This website post is for fun so even if the numbers are off, the general relationship between the heights of different DXing areas noted above are likely the same.

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