Printable View
I know the Lowrance Point 1 GPS uses the L1, L2 frequencies for better accuracy. Therefore, the Point 1 should have military accuracy (excluding military encryption).
Does the internal Lowrance GPS use L1,L2? Does the HB internal use L1,L2? Does the External HB GPS use L1,L2?
The answers seem not to be on tech support line cards.
Anyone know?
:dono
As far as the Lowrance products, the Point1 is the only L2 or Glonass receiver.
Some real world clear sky EPE data:
HDS Internal: 30-40ft. (~10ft accuracy)
LGC-4000: 20-30ft (~6-8ft accuracy)
Point 1: 8-18ft (almost dead on)
My guess is any receiver that used L2 would feature it in their advertising somewhere.
The GPS Receivers that Humminbird uses are for the L1 frequency only.
Little more information for you CP:Quote:
Originally Posted by Humminbird_Greg
We only use the L1, C/A code, 1.575 GHz frequency, not the L1 C/A code, 1.602 GHz frequency.
Thanks all.
Each GPS satellite transmits signals on two frequencies: L1 (1575.42 MHz) and L2 (1227.60 MHz). The L1 frequency contains the civilian Coarse Acquisition (C/A) Code as well as the military Precise (P) Code. The L2 frequency contains only the P code. The P code is encrypted by the military—using a technique known as anti-spoofing—and is only available to authorized personnel. The encrypted P code is referred to as the Y Code. Civilian GPS receivers use the C/A Code on the L1 frequency to compute positions—although high-end survey grade civilian receivers use the L1 and L2 frequencies’ carrier waves directly. Military GPS receivers use the P (Y) Code on both L1 and L2 frequencies to compute positions.
New GPS satellites also transmit on the L5 (1176.45 MHz) frequency. However it will be some time before there are sufficient GPS satellites transmitting the L5 frequency and before there are readily available GPS receivers that are capable of receiving the L5 frequency.
You understand all this stuff there Kosmo? You know what a carrier is? I believer the P is just heavy duty encryption for MilSpecs. Nothing to do with accuracy.
For some reason, the L2 frequencies you (Kosmo) posted don't match what Greg Posted?:scratchhead:scratchhead:scratchhead:scratc hhead:scratchhead
Lowrance L1/L2 : Same as Greg posted
Type L1, C/A code, 1.575 GHz Frequency/ L2 C/A code, 1.602 GHz Frequency
No its all beyond me but I thought id post what I found.yes I see frequency is differ ent but thats probably just and era that been posted.i figer your trying to work out some kind of hack so you can get the military accuracy.
The P code was intended to restrict access to the L2 data. People have figured out how to mathematically recreate the L2 signal without doing the decryption, so it is available to civilian receivers now. Newer satellites put the C/A on the L2 as well, but that isn't on all birds.
OK. I haven't kept up with much in GPS technical advancements since I retired. I knew the L2 was protected mil access at one time.
Not quite CP.Quote:
Originally Posted by Cane Pole
I stated that we did not use 1.602 GHz for the L1 C/A code. I read in a manual where it was stated that the L2 frequency was 1.602 GHz frequency. According to the GPS.gov web site; the L2 signal is (1227 MHz) 1.227 GHz (the L1 signal is 1575 MHz or 1.575 GHz, so that may be within the bandwidth of the L1 signal).
While I was looking, I found that there are some additional frequencies they are looking at employing that will give added accuracy for civilian GPS Receivers but they won’t happen anytime soon. The L2C (civilian use) signal should be available around 2018 and allow military (or better) accuracy. The L5 (for aviation safety services) signal around 2021 may allow sub-meter accuracies. The L1C signal (civilian use) will be available around 2026 and will use the same L1 1.575 GHz frequency as the current L1 signal. The same L1C signal is a “future standard” frequency being developed by other countries in their own GPS systems.
You have to watch those EPE (Estimated Position Error) numbers as these are generated by the company who produces the products and not all may be based on real-world data. The better measurement would be the HDOP (or PDOP) numbers as these are based on the locations of the GPS satellites used.
You also have to watch accuracy statements as these are usually expressed in either a 50% (often called CEP or Circular Error Probable) rate which means at least 50% of the time the position accuracy will be within the distance stated, or a 95% rate. Example: a GPS Receiver that has a CEP rating of 13 feet could also have a 95% rating of less than 5 feet – which would you use in your advertisement?
Ok. Like I said, I'm retired and don't keep up with it anymore. However, 2 frequencies must be better than one or the military wouldn't be using it.
ok,I see were your going with this now:RoflQuote:
Originally Posted by Cane Pole
The P-code is much longer than the C/A code which gives you gain and accuracy improvements. For non-engineers, you get the extra gain because the receiver actually knows what pattern it is looking for and the longer pattern makes it easier for the processing software in the receiver to see the data. In a way it is like looking for a canoe or a supertanker in a dense fog.
When a GPS doesn't know where it is or doesn't have current ephemeris data, it can take a while to acquire a position fix. Because the P-code is much, much longer than the C/A code, it takes much longer to synchronize to the code and acquire position. Going back to the canoe, once you find a canoe it's much quicker to see if it is the right canoe than it is to verify that a supertanker is the one you are looking for.
The original concept was that receivers would synchronize to the C/A, find out what time it was, about where they were and get the ephemeris data. Once they had that they would be able to synchronize to the P-code relatively quickly. The C/A sequence is a kilobit long while the P-code's sequence is something like 3/4 of a terabit long. Military and high accuracy receivers use both the L1 and L2 to correct for atmospheric errors, which is a major advantage of being dual frequency.
Technology has changed since the original design that first went active almost 20 years ago. Hardware got faster, decoding techniques got much better and people figured out how to use the P-code without knowing the encryption code.
Changes are coming to GPS, with the addition of the civilian data on the L2 frequency and increases in sequence length on the C/A signal, civilian receivers will soon have two frequencies to use so they have the ability to correct for atmospheric errors internally and both codes will be substantially longer giving significant increases in decoding gain.
Probably more info than anybody wanted, but I find the system amazing. We have a high accuracy receiver at work. When it is mounted on a vehicle, you can actually see the wiggle caused by opening and closing doors.
I taught GPS before/during intiail WAAS. I took a course at Trimble Instruments and used there course ware (with permission) for my class course outline.
I can't remember much, and don't have enough interest anymore, so I ask questions. At one point im my life, I was very thorough. Don't know what happened.
it's called C.R.S. and it's a symptom of old age, so they tell me :Rofl
(can't remember sh..er I mean stuff.)
Ok. But, I still member lots of insignificant stuff.Quote:
Originally Posted by wannabe fisherman