I'm tasked with finding the true azimuth of various antennas affixed to radio towers, accurate within plus or minus three degrees. There are 100's of antennas to measure on dozens of radio towers. The antennas come in a variety of shapes and sizes, but they always have a straight metal backplate that is perpendicular to the center radiation beam. All of these antennas will be live, emitting RF, are constructed using various metals, and in close proximity to a steel radio tower. The work will be performed at height, so a small form factor and expediency in measuring are valuable attributes.
I am inexperienced with surveyor's tools, so I thought this would be a good place start. My ideal (perhaps imaginary) solution would be a compact device that could measure against the antenna's backplate, not distorted by close proximity to metals, and simply display a true azimuth reading.?ÿ This is my first post on this forum. Thank you in advance for your time and recommendations.
Scott
No such device exists, only in your dreams. Contract with a surveyor that has the correct equipment and experience. GNSS recivers to establish a Geodetic Baseline, apply Leplace correction for True or Astrnomic North. Then a good Total Station to set control points and use reflectorless shots for checks. Then a high density scan with a Terrestrial Laser Scanner. Create point cloud and transfer to CAD.
We used to (attempt to) sell the Ashtech AD4 in a package that did exactly this. There was a 1 meter bar that had an L1 only GPS at each end that were synced to comput a rtk vector from one to the other.
Now, any of the dual input receivers will do the same with full constellation speed and accuracy.
This is a similar application to the heading sensors deployed on ships.
There is typically a direct readout of heading with respect to True North.
The application never took off as far as I could tell for path alignment. The ship application saves enough $ in fuel in one voyage to pay for itself many times over reducing the small angular tacks that add up. So boatloads of them were sold.
The heading solutions are available in complete packages for reasonable prices today. I am out of town this week, but if you DM me I will send you more information. I am actually getting trained on them this Wed.
Mark
Id guess mark silver is on a good track there...
Now, my idea.
Get a nice aluminum concrete screed, and install a laser sight on top of it.
Place it on the base of the tower, on one side. Usually a triangular 3 leg tower.
Then, set a nail, at the extension of the screed, maybe 100' from tower. Go both ways. Shoot the nails with GPS.
Climb the tower with a large speed square, and a field book.
Measure the angles of the antennas, off a flat side of the tower.
Nate
Is it possible to see this back plate and bar from the ground with a total station by chance or any other 2 points that you could derive the azimuth from? If so set 3 points on the ground with gnss that you can either triangulate or direct reflex the distance in. Next question which is more of a non issue but What is defined as TRUE NORTH. Astronomic or geodetic and if geodetic the datum in which it is derived from.
I have had a but tighter tolerances to do what you are doing but for other reasons. I transferred the alignment of antenna to the ground with a laser tracker then used other tools. GPS or astro shits depending on what the environment was like. I had a vertical requirement as well. Might could design a bracket template to set on the tower and perform a astro from the tower as well and place a point azimuth mark onto the ground. Perform that in reverse back to template as ck. But thats a lot of climbing.
The application never took off as far as I could tell for path alignment. The ship application saves enough $ in fuel in one voyage to pay for itself many times over reducing the small angular tacks that add up. So boatloads of them were sold.
Mark
You had me with the pun "So boatloads of them were sold." Great info and serendipitous timing with your upcoming training for this specific technology. Thank you for the information and I look forward to your private reply.
Then, set a nail, at the extension of the screed, maybe 100' from tower. Go both ways. Shoot the nails with GPS.
Is it possible to see this back plate and bar from the ground with a total station by chance or any other 2 points that you could derive the azimuth from?
Thank you both for your input. The towers are quite varied in build and location; for instance one is self-supporting with a wide base (36'). At 270' it has tapered to only 32", then for the final 40' it is a round monopole affixed to the top of the lattice self-supporting tower. Another is only 40' tall, but just a few yards from a steep precipice into a gorge. And finally another is a 16-sided monopole in a metro area where the surrounding area is limited access.
Many of the antennas are not visible from the ground because the tower tapers inward too much, or there are other lower antennas that obstruct clear sight from the ground.
No such device exists, only in your dreams.
Based upon the reply from @mark-silver I found this product by Sunsight: https://www.sunsight.com/ This fits Mark's description of a dual GPS bar capable to measuring azimuth. This device displays data by Wi-Fi connection to a tablet or mobile device. I would prefer a digital display on the unit itself, but this is very close to perfect. Thank you for your time and reply.
Scott
@nate-the-surveyor I think I remember a job similar. We located the tower base and measured up the antenna plate to compute the azimuth.
True or Astrnomic North
I would expect that the users of this information want azimuths with respect to geodetic north. We had a thread recently where I think a majority considered that to be "true" north.
I certainly would want a solution that did not involve placing myself near antennas operating at microwave frequencies and significant power levels.
ChapGPT says:
Should the azimuth of a radio tower be measured as astronomic or geographic direction?
The azimuth of a radio tower is typically measured as a geographic direction rather than an astronomic direction.
In the context of radio tower installations, the azimuth refers to the horizontal angle or bearing from a reference point (usually north) to the direction in which the antenna is pointing. It is used to determine the direction of maximum signal transmission or reception.
When measuring the azimuth of a radio tower, it is more practical and convenient to use geographic directions. Geographic directions are based on the Earth's geographic coordinate system, which uses fixed points such as true north, south, east, and west as references. These directions are more relevant for practical purposes and align with commonly used maps, charts, and navigation systems.
On the other hand, astronomic directions are based on celestial coordinates and can change over time due to factors like Earth's rotation and precession. Astronomic directions are more commonly used in astronomical observations or celestial navigation.
To accurately determine the azimuth of a radio tower, a compass or a digital instrument like a theodolite or surveying equipment can be used. These tools are calibrated to measure geographic directions, providing reliable and consistent results for radio tower installations and alignments.
I apologize for any confusion caused. Compasses are not calibrated to measure geographic directions directly. They are calibrated to measure magnetic directions, specifically the Earth's magnetic field.
A compass works based on the principle of a magnetic needle aligning with the Earth's magnetic field. The needle of a compass is magnetized and free to rotate, aligning itself with the magnetic field lines. The direction the needle points is the magnetic north.
To convert the magnetic direction to a geographic direction, you need to account for the declination, which is the angular difference between magnetic north and true north (geographic north). This declination varies based on your location on the Earth's surface and can change over time.
To obtain a geographic direction from a compass reading, you would need to apply the appropriate declination correction. This correction can be found on charts or obtained from reliable sources such as the National Geophysical Data Center (NGDC) or other mapping agencies. By adding or subtracting the declination to the compass reading, you can determine the corresponding geographic direction.
So, to clarify, compasses are primarily calibrated to measure magnetic directions, and conversion to geographic directions involves considering the declination specific to your location.
Hi Scott, I can't reply to your DM (but I got it). I figured it was because of where I am, but now see that it is the DM system completely broken. Could you drop me an email at mark at igage dot com and I will just email you directly?
The Sunsight device is exactly like what we were trying to sell years ago. My initial recollection was that it was an Ashtech product, but it was actually way before that and was branded 'Thales'. I found my notes from doing demos at ATT, Verizon and T-Mobile. Nobody in the biz was interested in such a device at the time. I was successful in doing a demo for the US Air Force at Hill AFB on the 'GPS Blackout' phased array, but Thales took that sale direct once I did the demo.
At the time, the cell carriers were deploying microwave backhauls for towers and I thought it was a killer application. But they all had sighting tube attachments and were very comfortable using the sights to get close to top mounted strobes, then fine tune the positions with signal strength feedback. All of the carrier demos I did went no where. The feedback was they just needed to get close, then they were always going to hand tune the alignment by signal strength. There was also a concern that the electrical and physical alignment were not colinear.
The AFB application was really nifty and we were able to check the alignment using an emitter placed 20 miles from the antenna, by switching the antenna to a field strength meter and then rotating the antenna (it was servo controlled on a 10 meter diameter round base) to a maximum. The GPS measurement was amazingly close and repeatable.
Mark
I've done a couple of antenna orientations to FCC specs (1° of arc), but both antennas were visible from the ground, so my approach isn't applicable to the matter at hand. But FWIW:
My task in both cases was to locate the tower base and submit to the antenna manufacturer for design of the mount. On install day I assisted the steeplejacks, in one case (adjustable mount) by guiding the install via handheld radio, in the other case (fixed mount) by checking (fingers crossed!) alignment. I then issued a certification for submittal to the FCC.
Both antennas were located roughly 200' above ground. I established 3 control points around each tower and occupied them with GPS receivers and ran static sessions, then occupied the control with a total station and located the tower legs. Once the design was finalized I staked out a ground point on the desired alignment line and checked to another control point to verify the stakeout. On install day I set up a 1" instrument on the staked out point and turned the calculated angle. That allowed me to sight along the antenna beam to guide/verify alignment.
At the time, the cell carriers were deploying microwave backhauls for towers and I thought it was a killer application. But they all had sighting tube attachments and were very comfortable using the sights to get close to top mounted strobes, then fine tune the positions with signal strength feedback. All of the carrier demos I did went no where. The feedback was they just needed to get close, then they were always going to hand tune the alignment by signal strength. There was also a concern that the electrical and physical alignment were not colinear.
Thanks again Mark for all the great info! After emailing you I received your hilarious out of office reply. I sent it to a few colleagues and it was voted "Best Out Of Office Reply" ever.
Pretty wild that the major carriers weren't interested in the automatic antenna alignment technology at the time. The scope alignment method works fine for lower frequency backhauls (24 GHz and lower) but up into the E-Band frequencies of 60 GHz and 80 GHz it's extremely difficult to align at 4+ miles. At these higher frequencies the discrepancy between a perfectly aligned path and something that won't even register is incredibly minute. Interesting comment about the electrical and physical alignment, I would concede that there likely is some discrepancy between the two.
My particular project is mostly panel antennas using unlicensed 3-6 GHz frequencies. The company is improving documentation of their deployments of Point to Multi-Point services in preparation for engineering upgraded services. Looking forward to your email, thanks.
Scott
My task in both cases was to locate the tower base and submit to the antenna manufacturer for design of the mount. On install day I assisted the steeplejacks, in one case (adjustable mount) by guiding the install via handheld radio, in the other case (fixed mount) by checking (fingers crossed!) alignment. I then issued a certification for submittal to the FCC.
Great photo, Jim. From what I can tell that's a FM antenna (sometimes referred to a FM horn) on the leg of the tower between the two climbers; if not then something similar of relatively low frequency. I've never worked with anything quite like that, all my experience has been in microwave networking using 3-80 GHz equipment. I enjoyed the photo and description of your work, thank you for sharing. I see you're in Davis. I live in Santa Cruz but the tower work I'm describing is just south of you in the Stockton/Modesto area.
Scott
