Advice on what to buy

I’m not interested in georeferencing surveys.

I only need to measure distances and height-differences between points.
On X,Y and Z I could easily accept a (relative) error of about 10 cm.

In 90% of cases I can pull out the measurements in the studio but in some cases (rare) I need to read the measurement immediately in the field.

At about 250 km and 300 km I have two fixed public GNSS stations.

With what minimum configuration can I get what interests me ? Could I use only ONE receiver ?

What kind of distance do you need to measure? 1m or 10km?
But in my ears it sound like you need two units and use e.g mobile topographer to get the live distance. A fairly simple setup but gets the job done.
The gnss station (distance to station is too long) for this setup would not perform well enough.

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The area inside which I take the measurements is never more than 100,000 square meters.
The maximum height differences will be a few hundred meters.

Considering that I am not interested in georeferencing, considering the 10 cm error, is totally impossible with just one station (even with multiple frequencies) and with the corrections of a station at 250 Km ?

You would probably struggle to get fix with baseline over 200km and if you did get fix, the error would be to much. If you have VRS service, then one reciver is enough.
And PPK is not an option as you need live readings, right?

For some services you can get almost live readings with only one RS2 and upload data to e.g NrCan for a rapid solution. But then you need cell coverage in the field too.

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What if I gave up on live readings (I rarely need them) and only operated in PPK mode ?

It would be possible ? With what times of observation ?

Its doable but it seems like the baseline length is eating up your time. A 15 min observation time should be enough for RS and even shorter for RS2.
But i think two RS units is the fastes and cheapest solution, because of the short baseline.
You just dump the base where ever you start and just use the rover like it was the only one you had, you could also select between PPK and RTK too. I also think its more robust. My 2 cents

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15 minutes to measure a point, risking mistakes, doesn’t make much sense.

Ok. I definitely need 2 receivers.

I was thinking I could even use 2 Reach M+ with 2 Tallysman multi-GNSS antenna for like $ 650.00… possibile ?

Possible yes.
Still, you might find a RS duo combo cheap now that RS2 is on its way, people are trading in or up.
Then you dont need the antenna, battery fuzz.

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In the Reach RS the battery is included and not removable. Perhaps using a simple external power bank to power the M+ is not a bad idea…

What does having one frequency mean instead of a multi-band receiver ?
Are the measurements “more precise” ? How much time does a fix take ?

For short baseline, not so much difference only faster fix and possible more reliable fix in noisy enviroment. For longer baseline with RS2 you gain more accurate fix and it handle really long baseline very well. And then there is the PPP option with RS2 that is not possible with RS.
Time to fix somewhat dependent on the situation, from few seconds to minutes

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In my case the distance between base and rover will never be more than a few hundred meters. So the advantages of multiband technology would be limited. But it happens that I find myself working inside excavations with high and reflective walls (white stone) and this could cause “noise”.

Does PPP mean that you can get the solution of a single point with a single receiver ? In what time ?

The ppp feature is an absolute position thing, not necessarily wanted for your relative measure.

You need (2) LoRa (LongRange) add on radios also for the M+ receivers.

The new RS2 would be ideal here. Looks like u have a lot to think of and tradeoffs to weigh.

Ok… I understand that I got these options…

A) 2 M + with 2 antennas, 2 radios and 2 power bank for 900 $
B) 2 RS for 1600 $
C) 2 RS+ for 3800 $

With your areas of work, the M+ and the RS+ might not be right for your needs, as you will have limited skyview of lots of multipathing. Here the multifrequency RS2 will shine!

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Its what I fear.

The base can always be placed in a point with the whole sky at sight (the top of the pit).

The rover, however, could find itself measuring points at the base of the pit and therefore have portions of the sky not visible and reflective walls around. Anyway I did tests and in the most disadvantaged points, at least a good dozen satellites are seen.

Try using this utility: http://gnssmissionplanning.com/App/Settings

It is a GNSS predictor, with the added ability to create crude obstructions. Look at your PDOP values after, they should be under 2.0.

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Now that is an awesome little tool!

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It is pretty dang powerful :smiley:

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