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?
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.
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
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.
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....
2a. https://web.archive.org/web/20231104153359/https://i.ebayimg...
(Adding because of how many broken eBay links I've encountered on forums over the years.. it's always frustrating, haha.)
https://web.archive.org/web/20231104153749/http://retro-gps....
> 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.