questions: 16 channels plus WAAS

[+AShan]

I been comparing GPS models, and have a couple questions:

 

Lowrance has 16 channels with WAAS.(which I'm guessing

has a built in patch antenna)

 

My ETrex has 12 channels, with a patch antenna, which I sometimes have a problem with

in heavy tree cover, and I'm thinking of upgrading.

 

How about the Garmins with the "high sensitivity receiver", how many channels?

 

Is the quadrahelix model gps's much superior in dense tree cover, compared to a Lowrance

model with 16 satelite reception?

 

What exactly is SIRF? How is it so important?

 

thanks, Anthony

[+briansnat]

Don't get hung up over the 16 channel receivers. They really add little if anything to the reception or accuracy.

 

How about the Garmins with the "high sensitivity receiver", how many channels?

 

The Garmin high sensitivity receivers have outstanding reception in tree cover. They have 12 channels which is all you really need.

 

Is the quadrahelix model gps's much superior in dense tree cover, compared to a Lowrance

model with 16 satelite reception?

 

The antenna has little to do with the reception. Quad helix or patch are both excellent. One is a bit better at some things and the other at other things. The important thing is the internals. It is my understanding that both the newer Lowrance and Garmin units have the SIRF chip set, so both will provide excellent reception under trees.

 

Which leads to:

 

What exactly is SIRF? How is it so important?

SIRF is the kind of chip in the unit. It is what gives you the great reception.

Edited July 4, 2007 by briansnat

[+EraSeek]

Actually if I have it right the Sirf is a 20 channel chip in a 12 channel reciever. It uses every possible signal where others filter out the worst signals. The sirf then does a ton of calculations to figure out where you are. They do about as well as any other unit except that they can grab signals in situations where other units won't or can't. That makes them a worthy unit.

[+trainlove]

Unless the satellites drift there will only be at most 12 above the horizon, and quite a few of those are right near the horizon anyway so as to not normally be seen depending on your antenna type helix vs. patch.

 

But with each WAAS additional satellite taking up a channel having some more than 12 would be useful. At most in the USA 2 or 3 of those are visible but elsewhere up to about 5 might be visible. There is a forum post about this somewhere, perhaps generated by Buggles who works with the GPS system while I have worked with the space sector (satellite hardware).

[+EraSeek]

Unless the satellites drift there will only be at most 12 above the horizon, and quite a few of those are right near the horizon anyway so as to not normally be seen depending on your antenna type helix vs. patch.

 

But with each WAAS additional satellite taking up a channel having some more than 12 would be useful. At most in the USA 2 or 3 of those are visible but elsewhere up to about 5 might be visible. There is a forum post about this somewhere, perhaps generated by Buggles who works with the GPS system while I have worked with the space sector (satellite hardware).

 

If I am correct, this "was" true when we had 24 sats. At current we have 31 sats and 4 Waas sats. So I guess you can get about 15 sats at one time plus 4 waas. By the way I can get all 4 waas sats where I am near Seattle, but my 60cx does only one at a time, which is all you need with waas.

[+trainlove]

If I am correct, this "was" true when we had 24 sats. At current we have 31 sats and 4 Waas sats.

 

Um, of course you are right, I forgot that there are 31 (really 30) satellites now. You DO know that satellite 15 seems to be missing right? If you have a Garmin you can download the Almanac using G7Towin are see all the info. I have recently had my GPS turned on for 48 hours on my roof (powered by a 12V gell cell battery) and nada for #15. As for WAAS I was unsure of how many were visible in the USA but one of these days they will rent transmitter channels on every GeoSynchronous satellite, or at least perhaps every 15 degrees or less along the belt. Well they actually call WAAS something different overseas, EGNOS, and MSAS depending on your location, Europe and Japan in that order.

 

At current we have 31 sats and 4 Waas sats. So I guess you can get about 15 sats at one time plus 4 waas. By the way I can get all 4 waas sats where I am near Seattle, but my 60cx does only one at a time, which is all you need with waas.

 

Well, on every GPS I've read about if you have WAAS on and are receiving one or more of them you have one or more fewer channels for the regular GPS satellites. So if 16 is the design for Lowrance then if you are getting all 4 WAAS satellites in Seattle then you will ONLY get 12 of the other satellites, even if more are visible. That's one reason to occasionally turn WAAS off if you have terrible reception on those sats.

 

Of course since the title of this post is 16 channels plus waas perhaps the Lowrance design is actually 20 channels?

Edited July 5, 2007 by trainlove

[+GOT GPS?]

Most if not all GPS units will take up 2 channels for WAAS, except for SiRF, which only uses one channel, so you don't have to worry about more than 2 channels being used.

[+PDOP's]

Um, of course you are right, I forgot that there are 31 (really 30) satellites now. You DO know that satellite 15 seems to be missing right? If you have a Garmin you can download the Almanac using G7Towin are see all the info. I have recently had my GPS turned on for 48 hours on my roof (powered by a 12V gell cell battery) and nada for #15.

Current GPS Satellite Data

 

Satellite Freq.

PRN/SVN Plane Std # Block Comments

---------+-------+-----+----------+-----------------------------------------------------

 

15/15 D5 Rb1 II Decommissioned 14 March 2007 after 16+ years of service... it is the last Block II satellite...

 

15/55 ?? Rb? IIR-M4 Scheduled launch: September 2007...

 

32/23 E5 Rb2 IIA Old SVN23/PRN23...Currently in non-standard code...

Scheduled for reinstatement on 27 June 2007...note

NANU 2007081...

[+EScout]

The Magellan Explorists with their high sensitivity receivers are 14 channel. I often get 12 plus two WAAS here in So Calif.

I count the constellation and cannot remember seeing more than 12 regular ones on the constellation page at one time. Perhaps it will only show the best 12. The satellite reception programs also usually show less than 12 at a decent elevation, at any one time.

What is more important than 12,14, or 16 channel receiver is the signal processing done by the receiver.