Electronics > Projects, Designs, and Technical Stuff
Roof mounted GPS for positioning only
Rerouter:
For an upcoming project, I will need to have 4-6 GPS feeds run into a building from the roof down 2 stories into an equipment room (for testing)
I can see suggestions about mainly lightning protection appearing in similar threads, but nothing about recommended antennas, or if there are preferred methods to distribute this signal to 4-6 devices, for positioning only, most where focused on timing. this does not mean where in the building, only that they correctly lock to the place the outdoor antenna is set up.
The devices under test could be hooked up to any given port, so it currently seems I would need an external power brick or similar to power the roof antennas LNA at my best guess? If this means I loose a port and have it hooked up to a plug pack that is fine aswell,
Or to throw the distribution side of things to the wind, would it be possible to rebroadcast the GPS signal to this room (zero reception with many current gen devices) using an amplifier and low gain antenna in the room? At the end of the day, the devices only need to get lock and test OK, where they are in the room or building does not matter.
Fraser:
Treat the situation as similar to a cell phone tower as they use a GPS receiver in their installations.
I suggest buying a commercial grade ex cellphone tower high gain GPS antenna. Common models look like an ice cream cone and contain a 36dB amplifier. You want the gain at the antenna and not at the base station (apartment). The actual antenna element is an efficient QFH. Power for the preamplifier is via the coaxial cable so a power inserted is used at the base end of the coax feed (in your apartment) For coax you could try using decent quality satellite TV coax like CT100 as that is low loss at GPS frequencies. Distribution of the signal in your apartment requires a decent splitter that contains amplification to compensate for the spitting and associated losses. You could look at common amplified splitters for satellite TV as a cost effective solution. They are more common and cheaper than dedicated GPS distribution splitters. Satellite TV splitters also offer the DC bypass that is needed for the LNB power so such accessories lend themselves to your scenario. In the UK our satellite TV IF from the LNB covers 950MHz to 2000MHz.
Fraser
Fraser:
Professional GPS antennas with decent low noise gain often look very different to consumer grade antennas as they use more robust housings and may not use the ceramic patch type antenna element. My antennas came in different amplifier gain versions to match the losses in the coaxial feeder. In general, you want the amplification to just compensate for the cable losses by the time the signal gets to the receiver. A bit of extra gain does no harm though. Be careful not to over drive the amplifier in the amplified splitter however. The losses can be calculated from the coaxial cable specification and expected length of feeder run.
Used or surplus Cellphone tower GPS antennas are relatively common and inexpensive :)
The units that I bought fir use with my Thunderbolt GPSDO units is the first one in the attached pictures. You can see why it is called an ‘ice cream cone’ !
Fraser
edpalmer42:
The other category of GPS antennas to consider would be marine (mounted on a boat) antennas. They're obviously waterproof. Timing antennas typically include narrow-band filtering that navigation antennas don't. For navigation purposes I don't think the filters make any difference.
To distribute the signal, there are dedicated GPS splitter/amplifiers that provide power to the LNA from the connected receivers. Some have one port that provides power, but many provide power from all ports via coupling diodes so that the LNA will stay powered if any of the GPS receivers are powered. Don't try to rebroadcast the GPS signal. Too many things could go wrong with such a plan - starting with the police knocking on your door!
Ed
mjs:
I've designed such systems and commercial GPS amplifiers/splitters/repeaters.
That's quite easy setup, a good quality outdoor antenna, cable, bias-T for power feed from +5V supply and suitable signal splitter for 1575Mhz should be enough. Possibly add an additional 10-15dB amplifier between cable and bias-T.
There's no difference between location and timing until you get into Metrology side of the forum.
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