We're about to start a job staking new power poles for a 19 mile transmission line. The accuracy is +/- 3" (6" circle). Seems like RTK (either network or base station) will be the fastest choice but I have two questions. We're in an area where we generally have good CORS network coverage but portions of this will be well outside of cell range so I'll have to use a base/rover setup which is not something I have had to do in a very long time. What kind of range can I expect with decent accuracy with a base/rover setup? Also will the existing transmission lines interfere with the radio or the GPS?
Thanks
Your range will mostly be affected by the topography, usually around transmission lines your range is around 5 miles. You will run into some multipath issues depending on the KV of the existing lines and your proximity to existing structures. Hope this helps.
fattiretom, post: 356074, member: 6039 wrote: We're about to start a job staking new power poles for a 19 mile transmission line. The accuracy is +/- 3" (6" circle). Seems like RTK (either network or base station) will be the fastest choice but I have two questions. We're in an area where we generally have good CORS network coverage but portions of this will be well outside of cell range so I'll have to use a base/rover setup which is not something I have had to do in a very long time. What kind of range can I expect with decent accuracy with a base/rover setup? Also will the existing transmission lines interfere with the radio or the GPS?
Thanks
Your range will probably be a function of the equipment you're using. My Topcons have a range of six or seven miles in open country, but that doesn't mean that's a good idea. For transmission corridors I like to have a good OPUS control point every two or three miles, with intermediate base control points no more than 3000' apart. I have no scientific reasoning for this, it is just what has worked out for us over the years.
Noisy transmission lines don't usually bother the equipment's ability to hear the SVs. I think the difference in the frequencies is the reason for that. But I have had times in the past the rover's ability to hear the base has been compromised. It usually isn't a problem; I believe our data link is 900 mHz.
On hot and dry days (when you can hear the conductors "frying") I have had a problem with static electricity. We zapped an LCD screen on a DC a few years ago..on such a day when you draw sparks on metal fence posts near the lines.
You can really overcome a lot of topographic and poor correction signal problems with savvy placement of a repeater or repeaters. It won't solve the problems associated with change in the ionosphere or other distance related degradation of function but it can solve many problems related to ridges, hills, etc. Heck, depending on the terrain, it might be worth your while to have a person dedicated to actively moving the repeater(s) up to advantageous locations.
I would try not to have my RTK base points under the power lines; they do create electromagnetic interference and it does result in higher "noise" on the satellite signals. It is always a good practice to relegate the entirety of your error budget to the rover.
Regarding range, that is strictly a function of the terrain and your radios. RTK accuracy does not significantly degrade due to the length of the baseline until you exceed 10Km (6.2 miles), which is probably farther than your radios will take you in most conditions.
fattiretom, post: 356074, member: 6039 wrote: We're about to start a job staking new power poles for a 19 mile transmission line. The accuracy is +/- 3" (6" circle). Seems like RTK (either network or base station) will be the fastest choice but I have two questions. We're in an area where we generally have good CORS network coverage but portions of this will be well outside of cell range so I'll have to use a base/rover setup which is not something I have had to do in a very long time. What kind of range can I expect with decent accuracy with a base/rover setup? Also will the existing transmission lines interfere with the radio or the GPS?
Thanks
It depends on the terrain, but no more than 5 with the new narrowbanding and no repeaters. If you have to be in a hole, probably about a mile.
I've not had transmission lines affect our positions and sometimes it's the only place we could set control and loop into. That being said, even though we always hit well, I never stacked the control in the dead center as I remember the static electricity biting me with an old 2B running long transmission lines when I was 16. Jesus that was 22 years ago as I type this. Ugh.
fattiretom, post: 356074, member: 6039 wrote: We're about to start a job staking new power poles for a 19 mile transmission line. The accuracy is +/- 3" (6" circle). Seems like RTK (either network or base station) will be the fastest choice but I have two questions. We're in an area where we generally have good CORS network coverage but portions of this will be well outside of cell range so I'll have to use a base/rover setup which is not something I have had to do in a very long time. What kind of range can I expect with decent accuracy with a base/rover setup? Also will the existing transmission lines interfere with the radio or the GPS?
Thanks
I have had some surveys where overhead transmission lines gave us to problems whatsoever. I have had a couple where the completely busted our positions, mostly in the elevation. As was said, having the base somewhere other than under the lines is a good idea if you can do it. And, just like in all cases, having good satellite coverage is helpful. I don't know where you'll be, but you might review the ephemeris to see when your best times of day for satellites will be at the various locations.
I don't know if it is possible, but I know that the load on transmission lines varies throughout the day. If the power company has information as to when they expect peaks of usage, you might be able to incorporate that into your schedule, specifically avoiding being under the lines during peak times when the EM interference is greatest.
