GPS antenna under the window? - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: February 05, 2020, 07:16:13 pm
content: Hi I own a Z3805A GPS controlled 10MHZ, and it has an GPS antenna that only work if it's outside. I live in a rented apartment so it's not so great if I begin to drill holes trough the wall to outside.In a search for an alternative solution, did I stumble upon some flat cables that is made to go under a window, while closed, but do they work, is it possible to use such a thin band without the GPS signal getting unusable?https://www.amazon.com/Maxmoral-Ultra-Thin-Coaxial-Satellite-Connector/dp/B0827KB78D/ref=sr_1_46?keywords=jack+coaxial+window&qid=1580930015&sr=8-46I have no idear on what Z3805A, have as an antenna connection in the back?https://www.ebay.com/itm/HP-Z3805A-10811-DOCXO-16-channel-GPS-Frequency-Time-Receiver-10-MHz-1PPS-ANT/251527236609?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D225074%26meid%3Da903bf2a52c24a60a1931d6d6c319f28%26pid%3D100675%26rk%3D2%26rkt%3D15%26mehot%3Dag%26sd%3D183126224769%26itm%3D251527236609%26pmt%3D0%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A0c2ae985-484a-11ea-afd1-74dbd1801c75%7Cparentrq%3A16bb68651700ac3cf903f02dffea6fe0%7Ciid%3A1

author: hagster
author_rank: Frequent Contributor
timestamp: February 05, 2020, 08:24:21 pm
content: Yes that can work. It's a microstrip transmission line. Never seen a product like that before.

author: FriedMule
author_rank: Frequent Contributor
timestamp: February 05, 2020, 10:30:43 pm
content: Okay thank you.Is the connector correct?What is its name?

author: FriedMule
author_rank: Frequent Contributor
timestamp: February 06, 2020, 08:44:03 am
content: Have to ask how many ohm the GPS antenna has?I can find 50 Ohm type N male cables but it looks like the flat cables is type F and 75 Ohm?

author: thinkfat
author_rank: Unknown
timestamp: February 06, 2020, 09:58:34 am
content: GPS antenna typically is 50\$\Omega\$.PS: these stripline flat flex bridges are typically made for connecting a satellite dish. Therefore, you'll mostly find 75\$\Omega\$, especially if fitted with F connectors.

author: FriedLogic
author_rank: Regular Contributor
timestamp: February 06, 2020, 12:19:42 pm
content: There are small round cables too which might fit, like RG316 or even RG174. They're quite high loss at GPS frequencies, so you would not want a long run of it.75 ohm cable is also often used for GPS antennas.

author: FriedMule
author_rank: Frequent Contributor
timestamp: February 06, 2020, 02:05:45 pm
content: hmm you are both great, is there a way to know the impedance of the antenna, do you know it out from the pictures and model of frequency standard?

author: FriedLogic
author_rank: Regular Contributor
timestamp: February 06, 2020, 09:05:47 pm
content: 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?

author: hagster
author_rank: Frequent Contributor
timestamp: February 07, 2020, 06:35:07 am
content: 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.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 07, 2020, 07:55:30 am
content: 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

author: FriedMule
author_rank: Frequent Contributor
timestamp: February 09, 2020, 05:18:39 am
content: 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

author: FriedMule
author_rank: Frequent Contributor
timestamp: February 09, 2020, 05:22:11 am
content: Quote from: hagster on February 07, 2020, 06:35:07 amI 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.

author: FriedMule
author_rank: Frequent Contributor
timestamp: February 09, 2020, 05:25:23 am
content: Quote from: edpalmer42 on February 07, 2020, 07:55:30 amSorry I do not understand your reply, I think I get the part about the impedance being irrelevant but Trimble, and cable being low cost? :-)

author: edpalmer42
author_rank: Super Contributor
timestamp: February 09, 2020, 07:26:14 am
content: Quote from: FriedMule on February 09, 2020, 05:25:23 amIn 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