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GPS antenna
Hi,
I've just set up a KiwiSDR in Cha-Am, Thailand, but I am not satisfied with my GPS coverage. I have placed the GPS antenna outside, but under a sun-shade ceiling. That is the best I can do with that short cable. I am thinking about buying a better GPS antenna, with at least 5m or longer cable. I gather the GPS antenna which came with the Kiwu is a passive antenna.
Do any of you have recommendations (links if possible) for a good (better) and sensitive GPS antenna to buy as a replacement for the original GPS antenna which came my Kiwi?
Thanks...😊
Geir, LA6LU
Thailand
Comments
The supplied antenna is an active one, just not that great. Definitely do not attempt to extend the length of its high-loss rg174.
Many installations use those NOS Lucent/Alcatel "bullet" shaped antennas from Ebay etc. Here is a long thread about someone who fixed their reception using one of those, and most importantly, using a low-loss coax run: https://forum.kiwisdr.com/discussion/1658/more-gps-problems-damaged-hardware/p1
For the best results the supplied GPS antenna should be sitting on a metal surface, as it needs some sort of 'ground plane' to function to it's full ability.
I have one on a metal plate, inside a waterproof box, mounted outside, feeding two KiWi's, via 10m of satellite tv coax and a two way passive splitter, and it functions just as well a a cheap Chinese 'Bullet' shaped antenna used under the same circumstances. So I know that under the the correct conditions, it can function more than adequately.
However that being said, some 'Bullet' antenna's are better than others, especially the ones made by named companies such as Trimble. I have my suspicions that many of the Chinese ones have the same electronics as the cheap 'Puck' types, the sort supplied with the KiWi, inside a 'Bullet' shaped housing, so as to make them look like a much more expensive, properly filtered design using a different form of antenna, rather than the standard 'patch' type on a ceramic substrate, that most cheap versions use.
There are other factors though, such as the RF transparency of some materials and your surroundings, such as high rise buildings or vegetation, which may block the antennas view of the sky. Some types of glass also have a very thin metal coating to control heat loss / gain, and these pretty much block all of the GPS signal, and many other similar things, such as WiFi and cellular phones.
Leave it running for a while, and take a look at the coverage 'map' on the GPS admin page, to figure out which bits of the sky it can actually 'see'. This may help you find a better location to put it in.
Good Luck,
Martin
Thanks Guys, I really appreciates your great feedback. :)
My antenna is stretched out as far as the cable length allows it via a hole in the concrete wall, to under the ceiling of our terrace. The antenna is attached to the ceiling with some strong doble sided tape. Since the antenna is magnetic, I also stuck the botton of a tuna fish can to it as a groundplane. However, my house (but not the terrace) is of concrete so only around half of the sky is visible for the GPS antenna and there is no way around that. The half sky which is left sometime gives 5 or 6 good satellites in the Kiwi's admin screen, but sometimes there are none.
I agree fully on what is said about the chinese antennas. They're notorius copycats and one can never be sure if what is bought is of good quality or just garbage. But I know Chris Smolinski from before as I have bought many of his decoders earlier. I think I am dropping him an email and ask what 40 dB antenna he bought and where. I rather check this first, so the chance of getting a quality antenna is better.
Thanks again for your help. :)
Yes I can see the problem you have.
The top side of the antenna needs to be facing upwards with a clear view of the sky.
In your case I think it would be worthwhile trying to extend the GPS cable.
Either with a purpose bought male to male SMA cable and a 'bullet' female to female adaptor for one end to allow connection to the existing GPS cable.
Alternatively us a good quality satellite tv cable, with F connectors on the ends. Then use a female F to male SMA adaptor at each end and an additional female to female SMA as before.
Ideally the antenna needs to sit on a metal plate at the outside edge of your terrace. Maybe you could make a metal bracket to allow it to be mounted somewhere neatly outside.
Your terrace looks really nice, especially as it's still quite cold here in the UK :-)
Regards.
Martin
a few of us use a variant of these. They used to be on eBay for <$75
but that feeds multiple Kiwi through splitters. One of these would suffice for you
Either of those might be overkill but you'll never visit a GPS problem again with one of those probably installed. The excess gain will overcome any feedline loss.
"In your case I think it would be worthwhile trying to extend the GPS cable."
Yes, at least the cheapest way. :) If I just could get the (original) antenna out and on top of the terrrace roof, I think it would change to the better. The drawbackof course is the added cable loss, but perhaps worth a try.
Tomorrow, when it's light, I will measure how much cable I'll need and possibly order something from ebay. At home in Norway, I have all I need, incl. different types of coax, plugs and crimp tools, but not here, so I'll just try to find something finished with about the right length.
Perhaps I also order a PCTEL antenna too, just to be safe. :)
73s
Geir, LA6LU
"Either of those might be overkill but you'll never visit a GPS problem again with one of those probably installed. The excess gain will overcome any feedline loss."
Thanks for the link, that got me started on ebay. As mentioned above, I think I'll order a PCTEL, plus some cable, both for the existing antenna and what's needed for the PCTEL.
73s
Geir, LA6LU
Update: I just bought a PCTEL 40dB GPS antenna from the US and 10m coax from China, all on ebay. The cable is fitted with a TNC male and SMA male which will fit the PCTEL and the Kiwi.
Thanks again guys. Your help is very much appreciated. :)
73's
Geir, LA6LU
http://la6lukiwisdrth.ddns.net:8073/