What is the longest 950mhz composite STL single hop you have ever pulled off or at least worked with? I'm on cloud 9 having just pulled off a 42 air mile shot. 49dbuv at the receive end with no preamp. 8' dishes at each end with 7/8" line. 490' AGL transmit and 125' AGL receive. And this is in the Ohio Valley...no mountains involved.
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950 mhz STL hop
- Thread starter BobOnTheJob
- Start date
Great job, Bob!
That's excellent for no mountains. I assume both ends were pretty high off the ground?
We did a 47 mile hop from downtown Portland, OR to a mountain site in the Cascades. We did the rough alignment of the XMIT dish by having our guys at the site point the truck headlights towards town and, looking through a scope mounted along the center of the dish, visually aimed at the headlights. Worked like a charm. Because we were in a tall office building, the 7/8" feedline from transmitter to the dish had to be about 750' long. We could turn the composite STL down to less than 100mW TPO before noise could be faintly heard on the signal.
The longest run I've personally been involved with was 66 miles from Mesa, AZ to a mountain top site near Globe, AZ.
We did a 47 mile hop from downtown Portland, OR to a mountain site in the Cascades. We did the rough alignment of the XMIT dish by having our guys at the site point the truck headlights towards town and, looking through a scope mounted along the center of the dish, visually aimed at the headlights. Worked like a charm. Because we were in a tall office building, the 7/8" feedline from transmitter to the dish had to be about 750' long. We could turn the composite STL down to less than 100mW TPO before noise could be faintly heard on the signal.
The longest run I've personally been involved with was 66 miles from Mesa, AZ to a mountain top site near Globe, AZ.
How about nearly 80 miles with a 606. Eastern Idaho.
The transmit end is at 4700 feet and the receive end is over 9700 feet.
I know of a short hop that doesn't clear the Fresnel zone. But it’s been up for ten years with no fades. Sometimes ya got to just grit your teeth and try it.
The transmit end is at 4700 feet and the receive end is over 9700 feet.
I know of a short hop that doesn't clear the Fresnel zone. But it’s been up for ten years with no fades. Sometimes ya got to just grit your teeth and try it.
The distance to the radio horizon is greater than to the line-of-sight horizon, due to atmospheric refraction of the EM wave along the propagation path -- which tends to bend the wave toward the earth. For normal atmospheric conditions this equation commonly is used:
Radio Horizon = SQRT(2*H), where H is the height of
the transmit antenna in feet above a smooth earth,
and H is the distance to the radio horizon in miles.
For typical conditions for a 490' antenna height, the distance to the radio horizon is about 31.3 miles, and for a 125' height it is about 13.8 miles.
So a total path length of 31.3 + 15.8 miles = 47.1 miles, and that path would just barely clear earth "bulge" between the tx/rx antennas. IOW, it would be a grazing path that has insufficient terrain clearance for free space performance (which needs clearance at least up to the 0.6 first Fresnel zone).
A grazing path over a rounded obstacle such as smooth earth or a rounded hilltop can add 15 dB or more additional loss to the value for a free-space path of that length having adequate Fresnel zone clearance.
Atmospheric conditions can greatly affect the performance of microwave systems, depending on frequency, overall path length, and other system parameters.
So there are lots of considerations when designing/defining a microwave system.
F
fugazi
Guest
Bob,
With a nice temperature inversion atmosferic condition i did shoot about 240 kilometers on UHF/SHF with just 10 watts and the antenna on 8 meters above sea level.
The nice thing about temperature inversion are that the radio horizon vanishes and propagation becomes ducting. It happens about 4 times a year and will mostly happen after a hot day followed by a rapid cool down in the evening. ( no rain ).
With normal conditions however your distance is quitte a shootout!
Evert
With a nice temperature inversion atmosferic condition i did shoot about 240 kilometers on UHF/SHF with just 10 watts and the antenna on 8 meters above sea level.
The nice thing about temperature inversion are that the radio horizon vanishes and propagation becomes ducting. It happens about 4 times a year and will mostly happen after a hot day followed by a rapid cool down in the evening. ( no rain ).
With normal conditions however your distance is quitte a shootout!
Evert
Thanks to all who chimed in.
R. Fry...I've always lived on belief that visual line of sight was the square root of 1.5 x height of eyes. For example, looking out into the ocean, eyes at 6' see water for 3 miles. Substituting 2 for the 1.5 factor shows the radio horizon. It's good to see someone whom I consider to be an expert using this formula. I also had suspected that when the two tower heights were figured separately, the paths could be added together. It was also good to see you adding those numbers. Do you also have a similar formula to calculate earth bulge? I found a formula years ago and calculated the bulge every 2 miles and recorded the numbers but did not keep the formula. My calculation at the time for a 42 mile path showed 230.5' feet at the center point.
Regarding the smoothness of the ground between the towers, Topo USA shows that the path is essentially flat (+/-50') except where it crosses a river a few miles from the receive site. So the 'standard' earth bulge at the center point should be valid.
R. Fry...I've always lived on belief that visual line of sight was the square root of 1.5 x height of eyes. For example, looking out into the ocean, eyes at 6' see water for 3 miles. Substituting 2 for the 1.5 factor shows the radio horizon. It's good to see someone whom I consider to be an expert using this formula. I also had suspected that when the two tower heights were figured separately, the paths could be added together. It was also good to see you adding those numbers. Do you also have a similar formula to calculate earth bulge? I found a formula years ago and calculated the bulge every 2 miles and recorded the numbers but did not keep the formula. My calculation at the time for a 42 mile path showed 230.5' feet at the center point.
Regarding the smoothness of the ground between the towers, Topo USA shows that the path is essentially flat (+/-50') except where it crosses a river a few miles from the receive site. So the 'standard' earth bulge at the center point should be valid.
I had a 55 mile shot that worked about 70% of the time, its was in costal texas so the tropo would mess with it something awful. There were amps on the transmit and receive ends with CD Link radios.
Thankfully the T-1 worked well as did the link from the "main" community of license studio.
Thankfully the T-1 worked well as did the link from the "main" community of license studio.
BobOnTheJob said:
BOTJ: The equation is
h = d2/1.5K
where h is earth bulge in feet, d is the distance in miles to the
grazing point of a radio path over smooth earth, and K is the
equivalent earth radius factor.
A K factor of 4/3 gives the earth bulge for normal atmospheric conditions. K factors less than 4/3 mean the effective earth curvature is greater than that of the physical earth, which can occur for some (common) atmospheric conditions.
For K = 4/3, earth bulge at the center of a 40 mile point-point path over smooth earth is 200 feet. The center of the beam of a microwave antenna installed at 200' AGL would just graze the earth 20 miles away.
For K factors less than 4/3 in this example, the direct path would be blocked by the earth, and the beam would need to diffract along a section of the earth in order to reach the other end of the link. Of course that produces much greater loss than if the path had clearance on all sides to at least the 0.6 first Fresnel zone.
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