Electronics > Beginners
GPS antenna under the window?
FriedMule:
Sorry but I havent got any e-mail about any of you replying.
I think we are talking about max 30 ft, after it gets outside the window,
--- Quote from: FriedLogic on February 06, 2020, 09:05:47 pm ---The antenna and receiver would normally be 50 ohm, but 75 ohm cables tend to have lower loss so are often used for longer runs, and the mismatch appears not to be a big issue. Trimble often use F-connectors on their stuff.
How far is it from the window to where the antenna is going?
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FriedMule:
--- Quote from: hagster on February 07, 2020, 06:35:07 am ---50ohms for GPS. So long as you use an Active antenna with built in LNA you can get away with lossy cable as the noise figure is dominated by the first gain block.
If you are using this for an accurate frequency reference, you want to try and make sure you are as free from multipath reflections as possible. I suspect the reason this receiver won't work being a window is due to it being set to reject weak, inaccurate reflected signals. I.e. it's tuned to be accurate, not highly sensitive.
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I have tried to find out the impedance of the antenna but without luck, and LNA do I not know anything about. In other word, I am unfortunately blank, when its about the antenna.
FriedMule:
--- Quote from: edpalmer42 on February 07, 2020, 07:55:30 am ---The Trimble Thunderbolt GPSDO comes with a 75 ohm F connector even though the input is 50 ohms. In the manual, Trimble basically says that the impedance mismatch is irrelevant, the cable is low cost, easy to get, and good enough to do the job with absolutely no problem.
Ed
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Sorry I do not understand your reply, I think I get the part about the impedance being irrelevant but Trimble, and cable being low cost? :-)
edpalmer42:
--- Quote from: FriedMule on February 09, 2020, 05:25:23 am ---
--- Quote from: edpalmer42 on February 07, 2020, 07:55:30 am ---The Trimble Thunderbolt GPSDO comes with a 75 ohm F connector even though the input is 50 ohms. In the manual, Trimble basically says that the impedance mismatch is irrelevant, the cable is low cost, easy to get, and good enough to do the job with absolutely no problem.
Ed
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Sorry I do not understand your reply, I think I get the part about the impedance being irrelevant but Trimble, and cable being low cost? :-)
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In North America, satellite and cable TV systems are connected to your TV with 75 ohm cable equipped with F connectors. You can buy high quality cable rated for over 2 GHz with 4 seperate shields at any home improvement store. Trimble realized that this cable would work very well to connect their 50 ohm Thunderbolt GPSDO to the antenna, so that's what they specified. They even made it easy by equipping the unit with an F connector instead of the more common BNC, N, SMA, or TNC connector.
So, if a 75 ohm cable is good enough for Trimble, it shouldn't cause you any problems. The biggest nuisance might be having a couple of adapters in the connection to convert between F connectors and whatever else you use. I don't know if F connectors are used in Denmark, but either Amazon or ebay will have whatever adapters you want.
Ed
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