So when the technical specs say the Proflex 500 tracks 75 channels, what exactly does that mean? How do the different constellations, signal types, and physical number of satellites equate to that 75 channel limit. My Z-Extreme is advertised as being a 12 channel "all in view" receiver. What does the term all in view mean, and how does it related to the Proflex 500 which has many more channels listed, but all in view is not mentioned? I am guessing at some point manufacturers started changing what their definition of a "channel" was, but I'd like to hear some sort of informed response from those who are in the know.

Sometimes it might be handy if I was more of a high tech redneck. That is probably not going to happen.

I listened to the speech without complete understanding. I really do not care about some things like that. It is probably good to remember that I care more about what happens at the tip of the pole and comprehension of my work environment than I do about the technology of the GPS receiver. I do not have much control over the technology of the receiver but I know how to make measurements with it.

The measurements are what matters to me. I know that I can do RTK work with the ProMark500 and ProFlex500 that was not possible with the ZXtreme. I still have to double check it when experience tells me I am standing in a challenging environment.

But I will share what I think I know.

There are now several kinds of satellites in space that can be used by the ProFlex500 with more planned for the future. New space vehicles, more signals, & more kinds of signals translate to a need for enough channels to receive data from what is in view.

The ZXtreme was designed at a time when there was less in view but it was capable of using all of the GPS SVs that were in view. I suspect it will still do that unless somebody has experience with more than 12 GPS above the horizon. The MobileMapper CX beside me reports 13 satellites in view but two of them are WAAS.

i.e., Javad is selling a 216 channel receiver... This seems like many more than 75...

The system architecture of our new products: ProMark 500 and ProFlex 500 allow for easy chip "stacking" which can offer HUNDREDS of channels.

The last I was told, there are ~ 55 potentially available signals from space today, so 75 channels is more than accommodating. 216 is a fine number that is fun to put on bid specs, but it doesn't mean shinola in the DIRT today...

As well, being "GALILEO READY..." is like saying we're Windows 9 ready, it's all marketing smoke and mirrors. Magellan's business and engineering model is to offer strong, reliable solutions making the most in accuracy and affordability in SV's available today and in the near-term future.

When GALILEO is operational and offers a true technical asset to the person in the field we'll have a simple upgrade path to add that to currently available products, no need to toss and write another fat check.

Friday's nickel's worth...

-Ben
Modified By Ben Sullivan on 9/4/2009 at 3:13 PM

So you are saying a channel is what then? A decode-able signal? IE, my Z-Extreme will give me output for L1, L2, P1, P2 and C1. Is that 5 channels or only 2 (2 frequencies)? The number of satellites being tracked has nothing to do with available channels? IE, 10 GPS sats x L1 + L2 frequency = 20 channels. Or 10 GPS sat x (L1 + L2 + P1 + P2 + C1) = 50 channels?
Modified By Joe M on 9/4/2009 at 3:27 PM

It takes 1 channel to tune in 1 frequency. Following are the frequencies that any GNSS receiver has to deal with now and in the near future.

GPS L1 1575.42 MHz
GPS L2 1227.6 MHz
GPS L5 1176.45 MHz

GLONASS L1 1598.0625-1609.3125 MHz
GLONASS L2 1242.9375-1251.6875 MHz

Galileo L1/E1/E2 1559-1592 MHz
Galileo E6 1215-1300 MHz
Galileo E5 1164-1215 MHz

WAAS L1 1575.42 MHz (I believe all other SBAS use the same frequency). Future addition to WAAS will be L5 1176.45 MHz. L1/L5 on WAAS will give atmospheric corrections and make WAAS ranging (Blade Technology) much more precise.

Assuming you are only using GPS and WAAS you would currently be utilzing 12 L1, 12 L2 and 2 WAAS channels, 26 Total.

Early GLONASS were L1 only now all satellites are L2 capable. R09 has a problem with it's L2 signal and is broadcasting L1 only. A few years ago Ashtech had a receiver that could receive L1/L2 GPS and L1 GLONASS. It was called the Z-18 and I saw one a year or 2 ago on ebay. Ashtech also had the GG24 (24 channels L1 GPS/GLONASS) in a Super CA box. Still listed on the Magellan site is the GG24E. It is the GG24 on a Eurocard, about 1/4" longer than the GG24 card, so it won't fit in a Super CA box. I would say there are still a lot of ship and aircraft navigation systems happy to still use this card.

All GPS satellites broadcast L1 and L2 at the exact same frequencies, differentiation being through decoding the satellite PRN number. I would say this makes it easy for a GPS to filter out more noise than a GPS/GLONASS antenna that must accept a wider band width. Note that GLONASS and Galileo broadcast over a wider frequency. I assume Galileo will be like GLONASS in that each satelite will have it's own specific wavelengths within the allowed ranges.

From reading the Magellan specs the newest receivers are able to receive any selected signal on a given channel, i.e. a channel could collect L1 GPS one day and L2 GLONASS the next, utilizing different filtering techniques.

One question not yet answered is if the current 500 antenna is capable of receiving the L5/E5 frequency of signals. I am assuming that they do receive the wider range of L1/L2 GLONASS now.

Assuming you have a fully capable antenna, let's look 3-4 years in the future. Assume at least 8 L5 GPS satellites in Orbit, at least 18 GLONASS and 16 Galileo. Your 500 might be receiving the following.

12 L1, 12 L2, 4 L5 GPS (28 channels)
2 L1, 2 L5 WAAS (4 channels)
8 L1, 8 L2 GLONASS (16 channels)
6 L1, 6 E6, 6 E5 Galileo (18 channels)

That is 66 out of your 75 availablr channels.

It may be that more than 1 channel may be needed to receive an L1/E1/E2 signal even at the same frequency. L1 Galileo will be free, and some or all the E frequencies will cost you money, so you may not want to use them.

As to the JAVAD with 216 channels one must look at one of their unique features. That receiver can be hooked up to a 4 antenna array on a single pole. That would give you 54 frequncies per antenna which should cover all the GPS GLONASS satellites or whatever combination you prefer. With a 4 antenna array receiver on base and a 4 antenna array receiver as rover, you would have 16 base to rover vectors solved every epoch. The point of that is in that each antenna may have 1 or 2 different satellites blocked from the other antennas. The subsequent meaned position can make up for canopy caused problems but at what cost?

JAVAD also has receiver software that can lock on the same satellite with more than one channel. In that way several satellites can be used as reference satellites with severa positions being calculated and the best combination gets saved.

Multiple antennas to a single receiver is not new. In the past Magellan sold the ADU5 reciever for Marine applications. The ADU5 connected to 4 different L1 antennas on a ship and at any time could give Heading, Pitch and Roll information as well as using Beacon correction. Today Magellan lists the Aquarius 2, L1/L2 receiver connected to 2 antennas. I assume that for roll information a second Aquarius 2 would be interconnected thus giving a completely independant and redundant system. Considering the value of a ship, redundancy is cheap.

I believe the LIDAR and newer aerial photography planes have similar, heading, roll and pitch systems.

By the time you get to be able to use all 75 channels your 500s will be old and gray, rather than new and gray.

Paul in PA

Modified By Lawrence Paul Lopresti on 9/5/2009 at 3:34 PM

Thanks for the response.