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Author Topic: Mountain Valley antenna configuration  (Read 1804 times)
KK4IKO
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Posts: 67




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« on: May 06, 2012, 06:08:29 AM »

Hi, do any of you folks have your stations in narrow, north-south oriented mountain valleys?  If so, what types of antenna setups do you use for DX on HF?  No fair putting the antenna on top of the mountain, LOL!

73
Bruce, KK4IKO
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AA5TB
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Posts: 81


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« Reply #1 on: May 07, 2012, 08:55:06 AM »

I don't have your situations but it sounds like you're a candidate for a NVIS antenna.  Try a dipole no more than about 1/4 wave length high on bands 30 m and below.  For DX operate at your local sunrise and sunset time periods.  At these times high angle antennas can perform pretty well for DX on bands like 40 m (may be due to a tilt of the ionosphere at these times).  I wouldn't expect much from your situation but I've had surprising success while operating portable in mountains under similar constraints.

73,
Steve - AA5TB
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K4SAV
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Posts: 1834




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« Reply #2 on: May 07, 2012, 11:38:33 AM »

Depending on the exact terrain, shooting a signal down the valley may not be significantly different from being on flat land.  However your signal isn't going to go thru the mountains.  You will be blocked at low angles by the mountains.  Due to signals refracted off the mountain tops, the minimum elevation angle that will work is probably a little less than that obstructed by the mountains.  DX can be worked at high angles but it takes more hops and the signals will be much weaker.  DX, the easiest way, is a low angle game.  The exception to that is for ducting but I don't know how common that is on the high bands.  It does occur on the low bands but is rare.  So if you want to improve your chances, you will have to add more antenna gain and put the antenna at a higher height.  That still won't bring back the low angles blocked by the mountains, but it will increase the amount of signal that gets over the mountains.

Local signals should be easy for you, maybe even better than flat land.  In some cases the mountains take those low angle signals and reflect them up at a high angle.  That improves the NVIS gain.

If you want to know the best angles for working particular DX stations, HAMCAP can give you an estimate.  It's free.
http://dxatlas.com/HamCap/
If you want an estimate of what your local terrain does to your signal, HFTA (free with the ARRL Antenna Book) can give you that.

Jerry, K4SAV
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KK4IKO
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Posts: 67




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« Reply #3 on: May 08, 2012, 04:15:38 PM »

Thanks for the info folks, I've already been advised that an NVIS oriented with the valley can work out to 200+ miles, and that an inverted V placed crosswise might be able to direct signals over the peaks, but I'm still open to other suggestions.  It will be several months before I test for General so I can put my HF rig on the air, so I have plenty of time to ruminate over the possibilities for antennas.

Bruce, KK4IKO
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WB6BYU
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Posts: 13113




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« Reply #4 on: May 08, 2012, 05:12:34 PM »

How wide is the valley, and how high are the hills?  Things often aren't actually
as bad as they seem.
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KK4IKO
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Posts: 67




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« Reply #5 on: May 08, 2012, 05:45:46 PM »

WB6BYU

The ridge lines on each side are 450' higher than my house and about a half mile apart, maybe less  I'm pretty much centered between them.  I live a mile and a half up from the slightly wider E/W valley at the lower end, and the upper end is about 2 miles away and closed except for a high road gap.  My house is at 2400 feet elevation, so the ridges are about 2800+.

From my yard, I can access a 2meter repeater located at nearly 7000' and about 16 miles away on my mobile, but not any others unless I go to the top of the road gap at the upper end.

Bruce, KK4IKO
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WB6BYU
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« Reply #6 on: May 08, 2012, 08:47:36 PM »

Quote from: KK4IKO

The ridge lines on each side are 450' higher than my house and about a half mile apart, maybe less



So let's assume that the peaks are 450' above your house and 1200' away.  (That assumes that
the 1/2 mile figure is to the peaks of the ridge rather than the base.)  Applying a bit of math, that
makes the angle from your house to the top of the peaks about 20 degrees.  That's really not so
bad, though not optimum for DX signals.  Twenty degrees should get you out to 1000 miles or so
pretty reliably, and sometimes beyond that due to multi-hop or other interesting modes.

I'm going to guess that you'll find better results on 20m and 40m during the day, and likely 80m at
night (or perhaps 160m if you have room for an antenna.)  40m is one of my favorite bands, and a
simple dipole should give you plenty of contacts.

And that is going East / West, where the hills are closest.  In other directions you'll have a
lower angle of radiation and be able to work longer distances.
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