GPS Antenna - Looking For Recommendations - Page 1
Forum section: electronics / general

author: German_EE
author_rank: Super Contributor
timestamp: August 13, 2019, 06:40:58 pm
content: I have a limited view of the sky from my workshop window and because if this my GPSDO sometimes loses lock as less than four birds are visible using the supplied puck antenna which sits on the window frame. Adding a 40cm x 40cm ground plane using a sheet of PCB material brought a slight improvement but I was looking for more so I purchased off EBay a GPS antenna meant for boatshttps://www.ebay.com/itm/New-Marine-GPS-Active-Navigation-Antenna-10-meter-with-SMA-Connector-for-Navman/162304912373?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649The coverage graph from Lady Heather shows that this marine antenna is about as good as the puck (and that 10m cable will not be helping) but I might try modifying the GPSDO for a 5V feed to see if signal levels go up.Does anyone know of a decent GPS antenna? I don't mind spending a reasonable sum, say up to $100, providing it actually works from a window location. Please note that it is NOT possible to run a coax up the side of our building to the roof, the owner of the building has forbidden this option.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 13, 2019, 07:49:03 pm
content: Quote from: German_EE on August 13, 2019, 06:40:58 pmWhich GPSDO do you have? Many of them have a 'position hold' mode which should maintain lock with only one satellite. Performance with only one satellite will probably be degraded, but it will stay locked.What direction does your window face? Since you're in Germany, South is best, East or West should be adequate. If North, put your money into a Rb standard!QuoteHigher voltage will probably give higher gain, but it might not matter. Does your GPSDO report signal strengths? I'm at a similar latitude to you. I have a 38 dBi timing antenna with ~35 m. (100 feet) of RG-59 coax (10 - 12 dB loss @ 1.5 GHz). My Thunderbolt (old and somewhat deaf by modern standards) occasionally reports signal strengths of > 50 dBc which is almost ridiculously high. If you have enough signal, more won't help.Ed

author: German_EE
author_rank: Super Contributor
timestamp: August 14, 2019, 06:14:40 pm
content: The signal levels change way too fast to give anything useful but the plot in Lady Heather reports signal to noise ratios where (I presume) higher is better.From 0 degrees to 30 degrees I get 41 dB SNR but this area is a sort of cartoid shape similar to the response of a microphone,From 45 degrees to 100 degrees I get 32 dB SNR, there is a large patch of colors on the chart and a good view of the sky to the east.From 100 degrees to 340 degrees signal levels are very low because I am blocked by the building but there is SOMETHING because I see patches of red and gray which means 15-20dB SNRFrom 340 degrees to 0 see nothing, zeroNote that various parts of the horizon are also blocked by other buildings.The receiver in use is one of the BG7TBL units but I exchanged the provided wall wart for a low noise linear supply.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 14, 2019, 06:27:26 pm
content: Quote from: German_EE on August 13, 2019, 06:40:58 pmNo vent shafts/air ducts running up to the roof?

author: edpalmer42
author_rank: Super Contributor
timestamp: August 14, 2019, 08:04:46 pm
content: Quote from: German_EE on August 14, 2019, 06:14:40 pmA 'challenging' location at best. Your 41 dB SNR for 0 to 30 degrees sounds good, but there isn't much coverage at that angle. It's limited to very high azimuth values. 32 dB for 45 to 100 degrees is reasonable. The rest is trash. I don't think a higher signal level will help. It might even hurt by trying to include distorted signals that you really don't want to use.QuoteIs that one of the ones he created or one where he did a 'wrapper' around a commercial unit (i.e. Trimble, Symmetricom, etc.)? I seem to remember that at least some of the units he built himself were based on navigation rather than timing receivers. If so, you may not have a position hold mode and so, will certainly have trouble maintaining lock. You'll have to talk directly to the GPS receiver and see what it has to say. Since he's done so many types of units I can't offer any specific suggestions.I suspect that any GPSDO will struggle to give good performance at your location. In situations like this, I recommend that a Rb standard be used as your house standard and occasionally compare it to GPS. I have good visibility of the sky and that's what I do.Ed