Community Forums

Share:

Looking for technical details of RMT target: What is the IR carrier signal? (Trimble/Geodimeter)  

Page 2 / 4

Richard Imrie
Posts: 1163
Member
(@richard-imrie)
1,000+ posts
Joined: 4 years ago

I haven't looked at that one for a year or so, but if the 606/604 IR frequencies are not in there, I'm fairly sure I have a slightly different/older version that stated the frequency. She's been a long road, but when 4 years ago I got my Geodimeter 650 ex USA (from someone who posted a couple of times on this Forum), then acquired (at high price, the RMT, ex USA also) and saw that thing spin and track, well ... Added my own homebrew radios ... SurvCE ... .RTK is the king, and we try and use it exclusively, but robotic TS is more satisfying. 

Reply
chris mills
Posts: 430
Member
(@chris-mills)
250+ posts
Joined: 7 years ago

Better than gold!

That's going to be a good evenings reading! Well done.

Reply
1 Reply
Richard Imrie
Member
(@richard-imrie)
Joined: 4 years ago

1,000+ posts
Posts: 1163

There was a guy around offering for sale a full GDM/5600 maintenance manual, for around $1000 ... My one remaining issue is alignment of the tracker to the optical scope. On the GDM 650 that we use, it is off about 25mm at 200m, but I also have an equivalent 5601 that is off about 300mm at 200m, which must affect distance measurement (angle diff is taken care of by the in built calibration procedures). There are shops around, nowadays exclusively USA, that say they can align the tracker as part of their routine calibration suite, but for me at the edge of the earth, per instrument that's $300 each way shipping plus $700 shop ... I can see why S'series combined the tracker with the scope, but the manuals for that do indicate a misalignment as being normal (and if it's outside tolerances - send it to the shop, too), so maybe the issue wasn't resolved.

Reply
chris mills
Posts: 430
Member
(@chris-mills)
250+ posts
Joined: 7 years ago

That misalignment is more than you would expect, but it isn't really going to make any difference to the measured distance UNLESS you are getting a very weak signal due to range or obstructions/atmosphere. As long as the instrument locks on OK there shouldn't be a problem. In my experience the 600 series never reached the range abilities for finding the target that the 4400 used to have - generally the 4400 used to get at least an extra 50 metres.

Reply
Richard Imrie
Posts: 1163
Member
(@richard-imrie)
1,000+ posts
Joined: 4 years ago

Yep. The GDM manual does say (from memory) that for accurate distance measurement, one of the 360 degree RMT mini prisms must be aligned to the instrument.  (We wont be doing that for each topo shot, and probably wont check that when doing control). So presumably with a 300mm tracker misalignment at 200m, if you rotated the RMT it would give different distance readings. We have 1 arc second GDM and 5600's, so for angle that's 1mm at 206m, so maybe with a 300mm tracker misalignment that's going to "add" maybe 5mm to that.  

Reply
1 Reply
chris mills
Member
(@chris-mills)
Joined: 7 years ago

250+ posts
Posts: 430

My comment referred to the "block" target rather then the 360 prism. With the 360 prism then rotating it will change the actual physical length of the measured line by 1-2mm. as the observed line moves from the centrally facing prism position to mid-way between two adjacent prisms.

With a misalignment measure, the actual distance doesn't change, just that the "pointing" is offset from the prism centre. The effect then is only noticeable if the signal strength drops sufficiently to affect the accuracy.

After all, for accurate non-contact shots into a corner you would probably point onto the solid face near the corner, take the distance and then swing across to point at the exact corner for the angle. The instrument is designed to "hold" the distance over a 30cm. swing.

If you apply pythagoras to a triangle 200m by 0.3m the change is well smaller than the measuring ability of the instrument; for closer distances the misalignment is still the same angle difference, so proportionately the error would become smaller still.

Reply
Norm Larson
Posts: 894
Member
(@norm-larson)
500+ posts
Joined: 6 years ago

Oscilloscope ordered and I have to stay off my knee for a while according to the doc, so, sitting by the lake learning electronics ...   This is going to be interesting

Reply
Page 2 / 4