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Elevation..
- Thread starter Splash1
- Start date
Buy or loan a GPS, find a map source with elevations, maybe locate a geographic marker near your home or try Google Earth. Any of these should work for you.
mechanic
Before I had the handheld GPS unit I just used a topographic map of the area. Google Earth is good but generally not that good for elevation readings especially if the terrain is hilly.
That's something I've never quite understood, what difference does your home's elevation above sea level make? Above Sea Level, ASL, means very little as far as radios are concerned. An antenna's level Above Ground Level, AGL, certainly does/can make a difference. ASL and AGL are not the same things at all. My home's about 650 feet ASL. It's also about 20-50 feet below the nearest AGL hills. Which do you think makes the most difference?
ASL is a means of finding AGL, it's a reference point. Ask a pilot if ASL means as much to him/her as AGL.
- 'Doc
ASL is a means of finding AGL, it's a reference point. Ask a pilot if ASL means as much to him/her as AGL.
- 'Doc
how would you figure agl in hilly country ? i tried altitude on google maps with no luck ,also i have a garmin gps but they say the elevation feature on handhelds is very iffy..i guess your location compared to the highest points in your area would be a better indicater of a good location as opposed to the agl or asl..
Doc has a point but sometimes you may have an antenna that is only 40 feet high but you live at the top of a 600 foot high hill with nothing around that is higher than you. In that case it makes sense to take both figures into account.The most accurate way is to use HAAT or Height Above Average Terrain Height above average terrain - Wikipedia, the free encyclopedia that is what the broadcast industry uses in order to compute antenna height for coverage areas.It is also called EHAAT or Effective HAAT. The tower itself is still measured from the ground to the top but the EHAAT is measured over many miles from the tower and the average height is taken from measuring at several points along the way. I remember spending many hours staring at topographical maps and taking reading at various compass points extending out several miles in order to compute EHAAT figures for new FM sites.
"how would you figure agl in hilly country ?"
Basically, the same way a surveyor would. Base your calculations on a known point. Then it's strictly a matter of how exact those measurements are.
If you're going to use a GPS, which isn't exactly all that accurate, then the 'best', or most practical method is by finding the average of several readings. Won't be very accurate, but more accurate than guessing probably.
Or, the same way it's commonly done, use a very accurate altimeter and barometer. Again, not the most accurate method in the world, but more accurate than you might think. (Never inches, seldom feet, mostly yards, if that. And strictly a matter of how accurate that reference point is.)
Somebody always has to do it the 'hard way'. Then it's just a matter of finding/using those results to find out what you particularly want.
- 'Doc
Basically, the same way a surveyor would. Base your calculations on a known point. Then it's strictly a matter of how exact those measurements are.
If you're going to use a GPS, which isn't exactly all that accurate, then the 'best', or most practical method is by finding the average of several readings. Won't be very accurate, but more accurate than guessing probably.
Or, the same way it's commonly done, use a very accurate altimeter and barometer. Again, not the most accurate method in the world, but more accurate than you might think. (Never inches, seldom feet, mostly yards, if that. And strictly a matter of how accurate that reference point is.)
Somebody always has to do it the 'hard way'. Then it's just a matter of finding/using those results to find out what you particularly want.
- 'Doc
See if this will help SkyVector.com - Aeronautical Charts - Flight Planning
This is how I did it years ago before you could access these on-line.
This is how I did it years ago before you could access these on-line.
I kan find mine on the sign at the city limits which is 3736 ft or you could just type in your location at google.com and go from there.
I just took a few measurements. Fisrtly, from my super accurate GPS sensor, I determined that I am 142 feet above sea level (ASL), +/- its reported 6 foots accuracy.
Then I measured with a tape measure from the soil to the feed point of my antenna, which was 38 foots above ground level (AGL).
So my antenna is 180 foots ASL and 38 foots AGL.
I do recall a web app that would plot the elevation terrain between two antennas. All you had to enter was the coordinates and the AGL of the antenna, then it would also draw a line so you could see line of sight soil obstructions, or see if your signal would need to go below the radio horizon, it had something in there to figure the, whatever the term is that I'm forgetting that increases the radio horizon, and it's not tropospheric ducting...
Then I measured with a tape measure from the soil to the feed point of my antenna, which was 38 foots above ground level (AGL).
So my antenna is 180 foots ASL and 38 foots AGL.
I do recall a web app that would plot the elevation terrain between two antennas. All you had to enter was the coordinates and the AGL of the antenna, then it would also draw a line so you could see line of sight soil obstructions, or see if your signal would need to go below the radio horizon, it had something in there to figure the, whatever the term is that I'm forgetting that increases the radio horizon, and it's not tropospheric ducting...
I'm right at sea level here on the seacoast of New Hampshire, USA. My beam is <>30' off the ground. I've been getting out approx. 1500mi. to the South and Southwest. I'd like to shoot across the ocean to Europe, but due to poor conditions, and the lack of channels (23 channel cb/ssb)that hasn't happened yet. I haven't gotten out too far to the West or the North, possibly due to the fact that there are mountains within 100 miles of here, but again it could just be poor conditions.
I'm planning on raising the antenna another 10', or so to see if it makes any difference. I guess now is a good time to tweak the antenna for best results, so that when the conditions for propagation improve, I'll be in good shape.
I know, a better radio would be good too.
I'm planning on raising the antenna another 10', or so to see if it makes any difference. I guess now is a good time to tweak the antenna for best results, so that when the conditions for propagation improve, I'll be in good shape.
I know, a better radio would be good too.
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@ ButtFuzz:Please advise me to what is a good replacement mic for my SR-497HPC... Answer: 497 is "wired like Cobra", so many choices available. That radio does not need a power mic, so purchase a stock "coffin style" mic with a decent cord, like the ones that Astatic uses. The Superstar DM-507 is my go-to. https://www.ebay.com/itm/3050474478...adANq91JSiEEnz8EGqPJRBloTgEyaVsBoCtoMQAvD_BwE $12.99 + .99 cent shipping.
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