[time-nuts] Req: Decent GPS Antenna Active/Passive Recommendation

[Bob Camp]

Hi

All of the ones I've opened up or seen dis-assembled have had the ceramic plate antennas in them. That very much surprised me early on, since I *assumed* they had something fancy inside based on their shape.

No argument about the filtering, I'm not sure if the temp-co of filter delay on an exposed antenna makes it a plus or a minus….

Bob

On Sep 15, 2013, at 5:48 PM, Robert Atkinson <robert8rpi at yahoo.co.uk> wrote:

> Hi Bob,
> Many of the midrange antennas have one or more significant differences from the cheap "pucks". Firstly they generally have better filtering, many pucks have none. This is important if you are co-located with transmitters.  Secondly many use quad-helix antenna elements rather than the off-set feed ceramic patches in the pucks. The heical elements have better control of the radiation pattern and along with a larger radome are less likely to be affected by external contamination. I also wonder how the tuning of a cheap ceramic patch holds up over the range of temperatures seen by a fixed antenna. Modern receivers compensate well for poor antennas, try using an early receiver on an internal patch and you won't get great results.
> 
> Robert G8RPI.
> 
> 
> 
> 
> ________________________________
> From: Bob Camp <lists at rtty.us>
> To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
> Sent: Sunday, 15 September 2013, 22:19
> Subject: Re: [time-nuts] Req: Decent GPS Antenna Active/Passive	Recommendation
> 
> 
> Hi
> 
> Worth noting: 
> 
> The "mid class" antennas are not a lot different electrically than the "low end" antennas. The main differences are mechanical:
> 
> 1) You get a much more weather tight housing
> 2) You get a rational way to mount the antenna 
> 3) There's a connector on it so you can put a good piece of coax on it
> 4) The housing *may* be more immune to snow / ice buildup and bird nests
> 
> RDR Electronics on the usual auction site appears to be selling some nice ones at the moment.
> 
> Bob
> 
> On Sep 15, 2013, at 4:36 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
>> 
>> john at westmorelandengineering.com said:
>>> Well, I need something that I can put outside, in the weather, with my
>>> verticals, and other antennas.  I am a Ham radio enthusiast, and I want
>>> something I can properly mount and can be an all-weather device and can live
>>> happily 'in the farm' so to speak. 
>> 
>> I split GPS antennas into 3 clumps.
>> 
>> At the low cost end are the small "mouse" or "hockey-puck" type units, 
>> usually with a magnetic mount.  They typically come with 10 or 15 feet of 
>> thin (lossy) cable.  Ballpark price is $10.
>> 
>> In the middle are the typical cones that you see on cell phone stations.  The 
>> Lucent 26 dB ones are common on eBay.  Ballpark price is $50.  The same or 
>> very similar thing is also available with different brand names.  Some of 
>> them come with a pipe mounting setup such that the coax and connector is 
>> inside the pipe and out of the weather.
>> http://www.megapathdsl.net/~hmurray/time-nuts/Lucent-Antenna.jpg
>> 
>> At the top end are the choke ring antennas intended for surveying.  They are 
>> mostly out of my price range so I haven't looked carefully.
>> 
>> ----------
>> 
>> I haven't seen a GPS antenna without an amplifier, but I haven't been 
>> looking.  They also include a filter.  See the LightSquared flame-wars for a 
>> discussion of filters.
>> 
>> I think the choke ring antennas usually let L1 and L2 through while most 
>> others are L1 only.
>> 
>> The other important consideration is the sensitivity of your receiver.  Every 
>> couple of years a new generation comes out that is a few dB better than the 
>> previous ones.  (Has anybody seen a Moore's Law type graph?)
>> 
>> Modern receivers are sensitive enough to work indoors with a non-fancy 
>> antenna, at least most of the time.  YMMV etc, and "indoors" probably doesn't 
>> include buildings with a lot of steel.  It doesn't cost much to try.
>> 
>> If you have an old recycled GPSDO such as a TBolt or Z3801A, the receiver is 
>> much less sensitive and a good antenna position helps a lot.  Of course, it 
>> also depends upon what you want to do and/or how nutty you are feeling.
>> 
>> There is yet another dimension.  GPS receivers come in two modes: navigation 
>> and timing.  Navigation units need 3 or 4 satellites to figure out where (and 
>> when) they are located.  The timing units assume they are not moving and that 
>> they know their location.  They should be able to maintain timing with only 1 
>> satellite.
>> 
>> 
>> -- 
>> These are my opinions.  I hate spam.
>> 
>> 
>> 
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