[time-nuts] eBay GPS antenna test results.

Bob kb8tq kb8tq at n1k.org
Thu Feb 15 09:41:01 EST 2018


As with any antenna mods, the issue isn’t so much doing them as proving that
what you did had this or that effect. A lot of what you are paying for on the fancy
antennas is the fact that indeed they went through some sort of validation process
on top of the design process. 

An equally valid point is that the standard “telecom” antennas likely are no great
thing for low angle multi path either. That is one of several reasons we tend to 
like cranking up the elevation mask on our TBolts. 

If you are going for the “I want something that does it all” approach. You would want
an antenna that does at least L1 / L2 / L5 and covers the GPS and Glonas parts of 
the bands. So far, those have not shown up as $100 new in box items ….. Given
that the price of gear covering all of that is still “a bit high” (even as a home brew 
SDR), I’m not sure it matters a whole lot at this point. 


> On Feb 15, 2018, at 9:13 AM, jimlux <jimlux at earthlink.net> wrote:
> On 2/15/18 6:04 AM, Bob kb8tq wrote:
>> Hi
>> There are a number of reasons to believe that these antennas are worse
>> than the typical “telecom GPS” antenna for L1 only duty driving a TBolt.
>> If you are going to do L1 / L2 work with something like a NetRS, then indeed
>> you will need a dual band antenna. These (the $99 ones)  are the lowest cost
>> “new in box” L1 / L2 antennas that I have seen. One would *guess* that their
>> close to horizon multi path rejection is not quite as good as a Trimble Zephyr,
>> a Novatel Pinwheel, or a choke ring. The ones from China
>>  also don’t cost $1800 to $6000 when new either …
> one could probably improvise something that serves as a choke ring, or elevation fence.  The infamous JPL Helibowl is pretty simple, and has pretty good rejection of signals near the horizon.
> See, e.g. Page 143 in GPS/GNSS Antennas, by Rao.  (I found it on google
> https://books.google.com/books?id=nL-YFWLQrPIC&pg=PA143&lpg=PA143&dq=helibowl+antenna&source=bl&ots=U-7Y3TMIQw&sig=D4xZVMmv73XkCAH_8KkMegMnxX4&hl=en&sa=X&ved=0ahUKEwjbjLGTjKjZAhVM7WMKHdYPC5sQ6AEIMTAB#v=onepage&q=helibowl%20antenna&f=false
> Oddly, it cites to C.Y Cheng, Numerical Electromagnetic Modeling of a Small Aperture Helical-Fed Reflector Antenna, Masters thesis, Ohio University, Aug 1998.
> Good luck finding that one on-line
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