Roof mounted GPS for positioning only - Page 1
Forum section: electronics / projects

author: Rerouter
author_rank: Super Contributor
timestamp: February 22, 2020, 11:50:09 am
content: 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.

author: Fraser
author_rank: Super Contributor
timestamp: February 22, 2020, 12:14:39 pm
content: 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

author: Fraser
author_rank: Super Contributor
timestamp: February 22, 2020, 12:30:02 pm
content: 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 inexpensiveThe 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

author: edpalmer42
author_rank: Super Contributor
timestamp: February 22, 2020, 05:00:49 pm
content: 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

author: mjs
author_rank: Regular Contributor
timestamp: February 22, 2020, 06:34:18 pm
content: 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.

author: BravoV
author_rank: Super Contributor
timestamp: February 22, 2020, 07:13:38 pm
content: These are what I used, the antenna Huber+Suhner (SPA 1500/110/5/0/RCP_RX40_C1) with integrated lightning protector and gain LNA = 40dB ->Datasheet (PDF)Took photo with few Rosenberger N connectors to company it, when I acquired it while ago before installation.For distribution, I used Symmetricom 58535A 2 ports spliter for my 2 GPSDOs, also in the photo there is a Symmetricom 58529A, an inline LNA & GPS L1 band pass filter which was came at the same time with the 58535A, but I don't use it as the antenna's gain is enough.Even though the antenna manufacturer claimed it has the integrated lightning protector, and so far Thor has not strike yet or not sure, still feeling not safe, and add more layer of protection, just bought recently PolyPhaser DGXZ-06NFNF-A, RF DC pass surge arrestor, that claimed it can withstand multi-strikes, without the need of replacing the GDT as in conventional RF lightning protectors.

author: awallin
author_rank: Frequent Contributor
timestamp: February 23, 2020, 07:24:22 am
content: digikey lists a decent selection of e.g. Tallysman antennas.high-end would be multi-frequency 'geodetic' like 1526-1063-ND for around 1500eursmall single-frequency ones are around 100eur like 1526-1054-ND

author: Rerouter
author_rank: Super Contributor
timestamp: February 23, 2020, 08:07:49 am
content: awallin, for a fixed mount to a building roof, and not a time based application that seems a little excessive?As second hand is not an option, currently looking at possibly this, It ends up on the pricier side of what they have correctly entered in the parametrics, but its not overkill expensive. with the built in band filtering it removes the need for an external one.https://www.tallysman.com/app/uploads/2019/06/TW3740_TW3742_Datasheet_rev2_9.pdfThank yo bravo, will add an external lightning arrestor to what I will need to get.So seems I am covered for the fixed wiring distribution, as the signal strength will be quite hot coming out of the antenna, this just leaves the idea of the rebroadcast (some devices needing testing do not actually have an external connector on reflection)As the legality side of things seems to be don't rebroadcast cellphone bands / don't jam GPS as 2 seperate points, So my twisted thinking is it would appear an antenna like above with a decent filter to remove all non navigation bands, and with some attenuators inline to keep the broadcast power low enough to be comparable to mid-poor reception outside for the GPS should allow re-broadcast with a passive antennaedpalmer42 I hold no issue if the signal is very weak to ensure It cannot jam (already cant pass through the building to get in, so a weak signal should be swamped getting out is my thoughts) If there are specific amplitudes or similar I need to meet, more than willing to accommodate

author: Miti
author_rank: Super Contributor
timestamp: February 23, 2020, 09:45:09 am
content: Take a look at this:https://www.gps-repeaters.com/I don’t know what your budget is but I installed one of this at work for functional test and it works well.

author: Rerouter
author_rank: Super Contributor
timestamp: February 23, 2020, 09:54:42 am
content: Miti, what did it end up costing you, would prefer a rough price before having to deal with chasing blind quotes,

author: Miti
author_rank: Super Contributor
timestamp: February 23, 2020, 11:57:00 am
content: Don’t remember exactly but somewhere under a thousand quids.

author: Fraser
author_rank: Super Contributor
timestamp: February 23, 2020, 12:40:18 pm
content: GPS rebro units are not uncommon. They comprise a decent external GPS antenna with good gain of around 30dB to 40dB. The low loss coaxial cable feeds into the rebro location and is either distributed by an amplified splitter or directly feeds the rebro antenna unit. The rebro antenna unit contains a tuned amplifier with a gain set for the coverage area required. The antenna tends to be a gain type where a coverage area is a long open plan area. A flat patch antenna is common. Omni directional antennas can be used but tend to be for smaller area coverage. A simple dipole is used for a test bench setup for instance.It should be noted that these systems are anything but efficient but they get the job done. Buying a proven complete system would save a lot of time and experimentation. Hobbyists have the free time and can purchase surplus amplifiers etc. For a professional commercial grade installation, companies produce complete kits of parts as has already been stated. DIY systems can suffer self oscillation related issues and even professional installations need to be wary of too much amplifier gain leading to self oscillation through coupling of the rebro antenna with leaky feeder coax or even the main antenna input, if not far away.Fraser

author: edpalmer42
author_rank: Super Contributor
timestamp: February 23, 2020, 04:34:41 pm
content: Quote from: Miti on February 23, 2020, 09:45:09 amAt the bottom of the page on this site, there's a link to a page on licensing. To summarize: U.S. and U.K. - a license is required, Canada - a license is required but they probably won't give you one.Ed