How many channels do I need for my receivers? A Boat-Load!
I hate to throw this out there, but ...
[ X90 as RTK ]
It would be a shame to do this in 2014, but it does work and it would be as good as any other 12-SV GPS only autonomous base.
I will now add fuel to the channel fire:
Channels does not equal Satellites
Different brands require a different number of channels per SV. For example, with Ashtech equipment, in general, you get three observables for each channel.
The X90-OPUS uses a BD-950 engine which is advertised as 24-channels on the [ data sheet ], and you get 8-observables for 2-channels (in other words 2-channels will produce C1 L1 D1 S1 P2 L2 D2 S2.) That means the X90 will track 12 US Satellites (GPS) at a time. Works great for OPUS, which is the point.
I have never seen a definitive list that says how many channels are required to track a single SV for each of the major manufacturers. One would need a specification for each brand and for each type of SV. (For example it may take more channels to track a Block IIIA SV than for a Block II or Block I.)
For all of the ink that has been spilled advertising how many channels different receivers have, there is little to indicate how many SV's a given receiver can fully track. I suspect that the answer depends on SV type, constellation type...not a simple sound bite for a magazine advertisement.
If a channel is required for every observable, and your receiver is tracking 12 observables per SV, then you will need a boat-load of channels. A couple of weeks ago in front of our office I was provisioning a SP80 and noticed that it was tracking 9 GPS, 8 GLO, 3 SBAS, 3 GAL and 2 BDU. That is 25 SV's. (12 x 25 = 300)
But that pales in comparison to what is going on in Asia, every single day.
Earlier this year (Feb 24, 2014; 9:30 am) I was on the roof of [a major manufacturer] in Shanghai China and I kid you not, we were tracking over 37 satellites! If you don't believe me, here is mission planning:
and a sky plot:
(12 x 37 = 444)
The GNSS performance was of a caliber that we will not see here in the USA for a while. I was allowed to do 100+ dumps and all elevation changes were within 3 mm of the first observation.
One last thing, you can not compare a 8-year old receiver to a new receiver. The time to fix is now a fraction (2-4 seconds) of what it was, the ability to hold a fix under moderate canopy is amazing, the ability to hold a fix when you trip or stub the rod into the ground is amazing, the ability to survey 24-7-365 is amazing.
Most importantly, the quality of the fixed solution on most modern receivers is far superior to those produced even two years ago.
If you choose to compare brands, make sure you have the latest device from both manufacturers. It is not a fair comparison otherwise.
We may be entering a period where it makes sense to replace GNSS receivers every 3-years or so. The idea of a future proof device has not weathered reality well--yet.
Mark
How many channels do I need for my receivers? A Boat-Load!
Great info Mark, thanks! 3mm!? I can't describe on this forum what that does to me for fear of being banned. 😉 😛
Tell me more, tell me more, did she put up a fight? 😀
How many channels do I need for my receivers? A Boat-Load!
Good stuff, Mark. That's truly amazing.
