[time-nuts] Anyone have experience with this antenna?

Bob kb8tq kb8tq at n1k.org
Tue Feb 6 12:14:07 EST 2018


There are “cell site” specific GPS antennas on the market. Panasonic has had one out 
for quite a while. I’m sure there are several others. 

One issue with doing any sort of “cover” for a precision antenna is distorting it’s pattern. 
Plastic (or whatever you use) will have different properties than air. A path through a blob
of “not air” will change the effective path length. That impacts the timing and thus the 
navigation solution. If you are worried about 2mm sort of pattern accuracy, things get 
tricky. Early on, there was a big “throw out the radomes push when this was first noticed.


> On Feb 6, 2018, at 6:15 AM, Bo Hansen <timenuts at rudius.net> wrote:
> Hi
> Besides the RF characteristics it may also be worth considering the quality of the plastics used. Over time water ingress may become an issue. Fours years after the installation of a CN brand antenna, sourced locally so probably not counterfeit either, we had to replace it at OZ7IGY www.oz7igy.dk
> RF wise 42 dB of gain IS an issue. Again at OZ7IGY, with 12 carriers in the air especially 13 cm and 23 cm, blocking and IMD were an issue before we mounted a BPF. I have taken apart the above mentioned antenna, a Motorola antenna and an eBay "hockey puck" antenna. The best design was clearly the Motorola one because it had a BPF after the pre-amp - probably because it was designed by RF competent people too. Each of the other ones had two FETs/MMICs in series and then a BPF. Of cause if no nearby carriers are in the air it may be less of an issue.
> So designing a really good antenna and pre-amp may be a business opportunity. There are many hi IP3 MMICs available designed for GPS and the like purposes. SAW BPFs with <1 dB loss are available fairly cheap so one before the FET/MMIC with a 1 dB NF is the way to go. A DIY radome using standard materials from any hardware shop is attached.
> Bo, OZ2M
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