Hi > On Aug 4, 2016, at 7:26 PM, Herbert Poetzl <[email protected]> wrote: > > On Thu, Aug 04, 2016 at 06:26:28PM -0400, Bob Camp wrote: >> Hi > > Hey Bob! > >>> On Aug 4, 2016, at 5:29 PM, Herbert Poetzl <[email protected]> wrote: > >>> Dear fellow time-nuts! > >>> I'm currently investigating my options regarding >>> GPS antennae (of course for time related purposes) >>> and I'm really confused by the variety they come >>> in ... (my apologies in advance for the long post). > > >>> Setting: > >>> I'm living in a three storey house with a sloped >>> roof, a covered balcony and a larger garden with >>> huge trees on the Austrian countryside (Europe). > >>> I've walked around with my smartphone (older one) >>> and I get a GPS position fix within 35s in the >>> garden (nine satellites shown), within 100s on >>> the balcony (also nine satellites), and not a >>> single satellite can be seen indoors. > >>> The obvious choice would be to put the antenna on >>> top in the middle of the slanted roof for a perfect >>> sky view, but this brings a number of problems as >>> the roof is very hard to reach and quite high. > >>> I have my 'lab' at the floor where the balcony is, >>> so I'm considering putting an antenna there and >>> run about 5-15m of coax cable to the GPS receiver. >>> The advantage there is that the antenna would be >>> somewhat protected (it still gets very hot during >>> summer and very cold during winter, but no rain >>> and no snow) and easy to reach for maintenance. > >>> The third alternative would be to put the antenna >>> somewhere in the garden and have a rather long >>> cable running to the house and up to my lab. > > >>> Antennae: > >>> Looking on eBay and Amazon shows a huge pricerange >>> for active GPS antennae with and without cable. > >>> It seems to start at about 10 bucks with rather >>> small black boxes [1] designed for cars, probably >>> containing a 25x25 ceramic GPS antenna and an >>> amplifier, progresses over very interesting out- >>> door constructions for boats and whatnot [2] in >>> the 20-100 bucks range and finally tops with high >>> end devices [3] way above 100 bucks. > >>> The information about the cheap devices is usually >>> very scarce, but typically boils down to: > >>> 1575.42 +/- 5MHz >>> 24-28dB LNA Gain with 10-25mA at (3-5V) > >>> 7dB f0 +/- 20MHz >>> 20dB f0 +/- 50MHz >>> 30dB f0 +/- 100MHz > >> That’s the spec on the interference rejection filter. >> Tighter is better as long as it still passes the >> desired signal(s). > > Understood! > >>> They seem to use RG174 and come with SMA as well >>> as BNC connectors (and a number of others as well). > >> The better ones will have a TNC connector on them > > Hmm, I had to google TNC (Threaded Neill-Concelman). > Is it worth the trouble in the < 2GHz range?
It threads on rather than latches on like a BNC. That makes it more water tight in the outdoor environment. > >>> The mid range devices seem to use larger antennae >>> with smaller tolerances (+/- 1MHz) and larger >>> voltage ranges for the amplifier (3-13V). > > >>> Questions: > >>> - What are the key specifications which need to >>> be verified before buying a GPS antenna? > >> You want one that is designed for permanent outdoor >> use. > >> That eliminates the $10 car mounts. > > Even under somewhat protected conditions like on the > covered balcony? You still have fog / condensation / humidity and the other sources of moisture. So not quite so important, but we rule out the balcony below. > > >> These days, I’d get one that does both GPS and GLONASS > > Makes sense. > > >>> - How can they be compared based on incomplete >>> specifications? > >> They can’t. It’s just luck. The ones you see for >> about $40 and up that are designed for mast mounting >> are usually pretty good. > > Okay, thanks! > >>> - Is a place on the roof or in the garden worth >>> the trouble over the covered balcony? > >> The real question is how much of a sky view you get. > >> Ideally you would like a clear view of the sky from >> about NE clear around to NW (270 degrees). > > That would opt for the balcony, as it faces north > and extends the slanted roof, so basically clear > view from NE to NW down to the horizon. It needs to face south and have a clear view over a 270 degree arc. If it faces north …. not going to work very well at all. > >> You also would like to be able to “see” down to within >> 10 degrees of the horizon over that range. > >> The segment from E to W (180 degrees) is pretty >> important. > >> Being able to see to within 30 degrees of the horizon >> is also pretty important. > > >>> - Are there any typical pit-falls or general >>> tips and tricks regarding mounting and cable >>> connection to the receiver? > >> Some receivers put out +12V, most antennas don’t like >> +12 and want +5. > >> Some modern antennas will only handle +3.3V. > >> If you have a long run to the antenna, feed line loss >> is what matters. > >> To some degree you can cope with this by buying an >> antenna that has a higher gain amp in it. > >> They range from about 21 db to about 50 db. > >> You also don’t want to over drive your receiver so >> just getting the 50 db version is not a perfect >> solution. > > Understood! Is there some rule of thumb at what > cable lengths which amplifier gain is best suited? The more money you pay for the cable the lower it’s loss. For $10 a meter you get a lower loss cable than $1 a meter or $0.10 a meter. Figure that anything over about a 30 meter run will require either a high gain antenna or some money invested in LMR-400 cable. > >> Grounding the antenna is always a good idea. > >> A surge suppressor in the line could save you some >> real cost if there is a lightning strike. > > I did a quick search for SMA/BNC/TNC based surge > protectors and not much did come up, any suggestions > what to use there? There are a *lot* of them on eBay. Many of them have N connectors on them. > >> I don’t know about Austria, but here in the US, >> both are required. > > Outside definitely, "inside" I'm not sure, but it > won't hurt to have additional protection for the > receiver(s). It is a good bet that the antenna will be outside. I’d plan it that way. Bob > > Thanks a bunch, > Herbert > >> Bob > > >>> Many thanks in advance and my apologies again for >>> the rather lengthy post. Please feel free to point >>> me to previous discussion regarding this topic. > >>> All the best, >>> Herbert > > >>> [1] >>> http://www.ebay.com/itm/99-Good-GPS-Antenna-SMA-Screw-Needle-10m-Super-Signal-Navigation-DVD-Antenna-/171802461614 >>> https://www.amazon.com/Waterproof-Active-Antenna-28dB-Gain/dp/B00LXRQY9A > >>> [2] >>> http://www.ebay.com/itm/Standard-Horizon-XUCMP0014-GPS-Antenna-f-CP150-CP160-CP170/331364914004 >>> >>> https://www.amazon.com/Garmin-010-12017-00-GPS-GLONASS-Antenna/dp/B00EVT2HSE >>> >>> https://www.amazon.com/SUNDELY®-External-Marine-Antenna-connector/dp/B00D8WAVTC > >>> [3] http://www.ebay.com/itm/NEW-FURUNO-GPA018-Gps-dgps-Antenna-/182223355414 >>> https://www.amazon.com/Garmin-nmea-2000-orders-over/dp/B0089DU96A > >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
