How many channels do I need for my receivers

However many channels on offer or in use, selecting Channel 13 is always a good choice, since few people seem to want to use it. Even when there are a lot of users in an area it is nearly always the last choice for others to switch to. (If you have to choose by frequency rather than the manufacturer's number, then picking one with 13 in it, say xxx.13xx is the next best choice.)

Realistically, except in an area where there is a huge amount of construction work going on there are rarely that many units trying to talk to talk to other.

Actually the new Javads have over 800.

The Javads -- at least the newer units -- assign multiple channels to each SV for reliability. Whether or not this makes any significant difference, I can't say.

And dedicate some to interference monitoring.

You do not need even 120 for now...or in the near future. 440 channels is way off in the future and 800 is a marketing tactic.

Dogmatic much, CW?

Each GPS satellite broadcasts as many as 5 signals presently: L1 (divided into C/A and P1), P2, L2C and L5. GLONASS presently has as many as three signals (L1, L2, L3) and Galileo will offer as many as 3 free signals (L1, Ea5 and Ea6). It is possible to have as many as 20 satellites available at times today. If each of those is broadcasting all those signals you would have need for perhaps 80 channels if only one channel is assigned per signal, but this could all change in the near future. As Jim points out, Javad assigns multiple channels to a single signal, so it's like five ears listening to the same whisper in a noisy room, and as Plumb Bill points out, Javad also uses 100 of those 864 channels for monitoring interference. From a purely technical standpoint, I cannot say whether it makes a difference. I'm a surveyor, not an Electrical Engineer. I can say that the LS appears to track more aggressively in certain types of canopy than other receivers I've previously used. And as Gavin mentions, there are existing supplementary signals from correction services like SBAS, OmniStar, StarFire, and TerraStar, not to mention Beidou. Also, who knows what will be around in a few years? Of course, then the question is,"will the new receivers actually be able to receive those future signals?" Who knows? I do know that at just the right time of day I can see Beidou satellites with the LS as well as Galileo satellites. If you have a tendency to keep equipment for a while, it makes sense to get the most future proof receiver you can find in anticipation of what may or may not be around the corner. If you tend to trade in often, it's not near as much a concern in my opinion and you can wait until the need is really there. We still have receivers that are 10 years old in the field, so I tend to think long term.

:good:

Just didn't have time to type all of that. 🙂

I would love to see some tests performed with an LS when Beidou and Galileo are both in view (if that happens, haven't checked planning software).

I've got an old RTK receiver. 36 channels. Still works great.

If you're only using GPS, which is perfectly fine in many cases, you just need to be able to track 12 GPS satellites at one time. 24 for L1 and 12 for L2. That would be the minimum.

From there on out, it's options. Glonass, sbas, etc.

> Looking at Geomax zenith 25 (120 channels), but Javad has 200+, then trimble r10 has 440. I'm new to this, so be gentle.

120 channels is far more than you need now.

> Dogmatic much, CW?
>
> Each GPS satellite broadcasts as many as 5 signals presently: L1 (divided into C/A and P1), P2, L2C and L5. GLONASS presently has as many as three signals (L1, L2, L3) and Galileo will offer as many as 3 free signals (L1, Ea5 and Ea6). It is possible to have as many as 20 satellites available at times today. If each of those is broadcasting all those signals you would have need for perhaps 80 channels if only one channel is assigned per signal, but this could all change in the near future. As Jim points out, Javad assigns multiple channels to a single signal, so it's like five ears listening to the same whisper in a noisy room, and as Plumb Bill points out, Javad also uses 100 of those 864 channels for monitoring interference. From a purely technical standpoint, I cannot say whether it makes a difference. I'm a surveyor, not an Electrical Engineer. I can say that the LS appears to track more aggressively in certain types of canopy than other receivers I've previously used. And as Gavin mentions, there are existing supplementary signals from correction services like SBAS, OmniStar, StarFire, and TerraStar, not to mention Beidou. Also, who knows what will be around in a few years? Of course, then the question is,"will the new receivers actually be able to receive those future signals?" Who knows? I do know that at just the right time of day I can see Beidou satellites with the LS as well as Galileo satellites. If you have a tendency to keep equipment for a while, it makes sense to get the most future proof receiver you can find in anticipation of what may or may not be around the corner. If you tend to trade in often, it's not near as much a concern in my opinion and you can wait until the need is really there. We still have receivers that are 10 years old in the field, so I tend to think long term.

So basically... 😉

I'm not in disagreement with you on that. Outside of firmware issues for little things (with big effects) like week rollovers and leap seconds, there is no reason that a receiver from ten years ago shouldn't operate as well or better than it did 10 years ago (from a technology standpoint). The other side to that is that it will continue to operate just like it did ten years ago. As I said before, we have equipment that is that old and we keep using it because it keeps working.

Mark Silver's X90-OPUS receivers are a great example of old technology still finding a place in today's positioning world. Those receivers are 24 channel dual frequency GPS only receivers. And they are great for OPUS. I would not want an RTK system based on that, personally, because I would give up a lot of capability that I enjoy with newer equipment (more channels and more signals).

The point of my post was to give him a baseline number since none was provided by anyone else.

The only difference I've noticed over the years is the fix times of newer rtk equipment is faster, maybe 20 or 30 seconds different and the support for current data formats is outdated.

I guess by more signals you mean glonass, but glonass isn't always good. If I want the best elevations, I generally turn glonass off.

> I'm not in disagreement with you on that. Outside of firmware issues for little things (with big effects) like week rollovers and leap seconds, there is no reason that a receiver from ten years ago shouldn't operate as well or better than it did 10 years ago (from a technology standpoint). The other side to that is that it will continue to operate just like it did ten years ago. As I said before, we have equipment that is that old and we keep using it because it keeps working.
>
> Mark Silver's X90-OPUS receivers are a great example of old technology still finding a place in today's positioning world. Those receivers are 24 channel dual frequency GPS only receivers. And they are great for OPUS. I would not want an RTK system based on that, personally, because I would give up a lot of capability that I enjoy with newer equipment (more channels and more signals).

> Mark Silver's X90-OPUS receivers are a great example of old technology still finding a place in today's positioning world. Those receivers are 24 channel dual frequency GPS only receivers. And they are great for OPUS. I would not want an RTK system based on that, personally, because I would give up a lot of capability that I enjoy with newer equipment (more channels and more signals).

Well for me, the x90+(?) as a CORS network RTK unit is new to me and I am thrilled with its improved success for my business over the old Topcon Hiper units I have been using as CORS network RTK units for years.

I could not tell you how many channels I have or what they would be used for anyway.

Are you guys saying that I could be tuning in to Woody Woodpecker while out surveying? Wow, we live in modern times.

> Well for me, the x90+(?) as a CORS network RTK unit is new to me

The CHC x90+ is static only (according to their website) so no RTK, but the 24 channels are plenty for GPS-only OPUS processing. Could it be something else? Mark sells x91+ and x900+, one has 120 channels, the other 220. I don't know how CHC (actually Trimble and Novatel boards) use all of the channels. For the money, you'd think they'd be able to pick up your favorite re-runs.

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.