3 ms·

Which model was yours? This page appears to show every model of handheld GPS ever made, and Lowrance has 4 entries. Thanks for sharing this, I never had the ch

Which model was yours? This page appears to show every model of handheld GPS ever made, and Lowrance has 4 entries. Thanks for sharing this, I never had the chance to see one of these units. It's so weird now to imagine GPS with no map! P.s. What does a six-channel GPS receiver even mean? Is more channels more better?

TedDoesntTalk 3y ago
Here's a better picture of what I owned. It had a huge hard-plastic case: https://www.ebay.com/itm/314936082464 https://www.ebay.com/itm/314936082464 The antenna flipped up and doubled as a screen protector: http://retro-gps.info/photos/files/page2-1023-full.jpg http://retro-gps.info/photos/files/page2-1023-full.jpg https://i.ebayimg.com/images/g/zxUAAOSwDspimA3F/s-l1600.jpg https://i.ebayimg.com/images/g/zxUAAOSwDspimA3F/s-l1600.jpg Sorry, I don't remember what 6-channel means. I would guess it could receive data from up to 6 satellites? Don't know. IIRC, this cost about $700 but cartridges were extra. Very expensive for the time. It worked without the cartridges, but I think it only displayed lat/long then, or in any case much more limited info. The carts added more info like town/city/state. Unfortunately, I could not find any YouTube videos of early GPS receivers.
- metadat 3y ago
  Thanks @TDT for your prompt and rapid reply, always nice to connect with such a generous person who indulges me :D. What a spiffy looking unit, it looks like belongs mounted in the dash of a 198x Mercedes, Porsche, Corvette, Bronco, or similar alongside one of those old school built-in car phones. Archive links of the eBay resources: 1a. https://web.archive.org/web/20231104152903/https://www.ebay.com/itm/314936082464 https://web.archive.org/web/20231104152903/https://www.ebay.... 1b. https://archive.ph/QxwrN https://archive.ph/QxwrN 2a. https://web.archive.org/web/20231104153359/https://i.ebayimg.com/images/g/zxUAAOSwDspimA3F/s-l1600.jpg https://web.archive.org/web/20231104153359/https://i.ebayimg... 2b. https://archive.ph/crpGm https://archive.ph/crpGm (Adding because of how many broken eBay links I've encountered on forums over the years.. it's always frustrating, haha.)
  - TedDoesntTalk 3y ago
    You're welcome! This is the best photo in my opinion -- shows the antenna up (not covering screen), unit is powered on, and the unit itself is in excellent condition: https://web.archive.org/web/20231104153749/http://retro-gps.info/photos/files/page2-1023-full.jpg https://web.archive.org/web/20231104153749/http://retro-gps....
skhr0680 3y ago
https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2841&context=smallsat https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2... > The receiver has six channels that continuously track four primary GPS satellites and sequentially acquire and track all other visible and healthy satellites on the fifth and sixth channels.
jdietrich 3y ago
>What does a six-channel GPS receiver even mean? Is more channels more better? The operating principle of GPS is more complex than I can usefully summarise in a comment, but essentially the satellites are continuously broadcasting an extremely accurate time signal that the receiver uses to calculate the time-of-flight to each satellite. GPS receivers need signals from a minimum of four satellites to provide a location fix. There are usually more than four satellites visible, so additional channels allow for more than the minimum number of signals to be received. this can provide improved accuracy, faster time-to-first-fix and better resilience to interference. If you're receiving five or six signals, you don't lose your positioning fix when one of the satellites moves below the horizon or is obstructed by terrain. Reflected signals can cause error, because the time-of-flight of the signal will be greater than the actual distance to the satellite; extra channels allow these errors to be compensated for. For a long time, GPS receivers typically had no more than 12 channels, which was the maximum number that would actually be useful given the limited number of satellites in the original GPS constellation. Since then, many other navigation satellite constellations have launched, so between 40 and 60 navigation satellites are typically visible at any moment. Receivers have commensurately improved, with even basic receivers often having upwards of 48 channels.
- eastbound 3y ago
  How does encryption work on GPS signals? Since it seems the military have access to better accuracy, it’s not just a wavelength that is broadcasted.
  - jdietrich 3y ago
    Prior to 2000, the civilian signal (C/A code) was deliberately degraded by the addition of small random variations in the time signal, but this is no longer the case. A separate military signal (P-code) still exists, which is encrypted in order to prevent spoofing; to my knowledge, the encryption scheme used for the military signal is still classified.

TedDoesntTalk 3y ago

Here's a better picture of what I owned. It had a huge hard-plastic case: https://www.ebay.com/itm/314936082464 https://www.ebay.com/itm/314936082464 The antenna flipped up and doubled as a screen protector: http://retro-gps.info/photos/files/page2-1023-full.jpg http://retro-gps.info/photos/files/page2-1023-full.jpg https://i.ebayimg.com/images/g/zxUAAOSwDspimA3F/s-l1600.jpg https://i.ebayimg.com/images/g/zxUAAOSwDspimA3F/s-l1600.jpg Sorry, I don't remember what 6-channel means. I would guess it could receive data from up to 6 satellites? Don't know. IIRC, this cost about $700 but cartridges were extra. Very expensive for the time. It worked without the cartridges, but I think it only displayed lat/long then, or in any case much more limited info. The carts added more info like town/city/state. Unfortunately, I could not find any YouTube videos of early GPS receivers.

metadat 3y ago
Thanks @TDT for your prompt and rapid reply, always nice to connect with such a generous person who indulges me :D. What a spiffy looking unit, it looks like belongs mounted in the dash of a 198x Mercedes, Porsche, Corvette, Bronco, or similar alongside one of those old school built-in car phones. Archive links of the eBay resources: 1a. https://web.archive.org/web/20231104152903/https://www.ebay.com/itm/314936082464 https://web.archive.org/web/20231104152903/https://www.ebay.... 1b. https://archive.ph/QxwrN https://archive.ph/QxwrN 2a. https://web.archive.org/web/20231104153359/https://i.ebayimg.com/images/g/zxUAAOSwDspimA3F/s-l1600.jpg https://web.archive.org/web/20231104153359/https://i.ebayimg... 2b. https://archive.ph/crpGm https://archive.ph/crpGm (Adding because of how many broken eBay links I've encountered on forums over the years.. it's always frustrating, haha.)
- TedDoesntTalk 3y ago
  You're welcome! This is the best photo in my opinion -- shows the antenna up (not covering screen), unit is powered on, and the unit itself is in excellent condition: https://web.archive.org/web/20231104153749/http://retro-gps.info/photos/files/page2-1023-full.jpg https://web.archive.org/web/20231104153749/http://retro-gps....

skhr0680 3y ago

https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2841&context=smallsat https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2... > The receiver has six channels that continuously track four primary GPS satellites and sequentially acquire and track all other visible and healthy satellites on the fifth and sixth channels.

jdietrich 3y ago

>What does a six-channel GPS receiver even mean? Is more channels more better? The operating principle of GPS is more complex than I can usefully summarise in a comment, but essentially the satellites are continuously broadcasting an extremely accurate time signal that the receiver uses to calculate the time-of-flight to each satellite. GPS receivers need signals from a minimum of four satellites to provide a location fix. There are usually more than four satellites visible, so additional channels allow for more than the minimum number of signals to be received. this can provide improved accuracy, faster time-to-first-fix and better resilience to interference. If you're receiving five or six signals, you don't lose your positioning fix when one of the satellites moves below the horizon or is obstructed by terrain. Reflected signals can cause error, because the time-of-flight of the signal will be greater than the actual distance to the satellite; extra channels allow these errors to be compensated for. For a long time, GPS receivers typically had no more than 12 channels, which was the maximum number that would actually be useful given the limited number of satellites in the original GPS constellation. Since then, many other navigation satellite constellations have launched, so between 40 and 60 navigation satellites are typically visible at any moment. Receivers have commensurately improved, with even basic receivers often having upwards of 48 channels.

eastbound 3y ago
How does encryption work on GPS signals? Since it seems the military have access to better accuracy, it’s not just a wavelength that is broadcasted.
- jdietrich 3y ago
  Prior to 2000, the civilian signal (C/A code) was deliberately degraded by the addition of small random variations in the time signal, but this is no longer the case. A separate military signal (P-code) still exists, which is encrypted in order to prevent spoofing; to my knowledge, the encryption scheme used for the military signal is still classified.