OK to use RG-59 (Belden 89259) coax as cable feed between GPSDO and antenna? - Page 1
Forum section: electronics / rf-microwave

author: rbm
author_rank: Regular Contributor
timestamp: November 10, 2018, 12:00:58 am
content: I'm assembling a GPS Disciplined Oscillator based on a Trueposition GPSDO board (late model 111603-type with a Furuno GT-8031F GPS receiver). I've also got a Symmetricon / PCTEL GPS-TMG-26N antenna which I will be locating on the roof of my house. I expect the cable feeding the antenna to be about 20 metres in length, give or take. I've read here that some people have used RG6U coax as antenna feeds. RG6U is 75 Ohm impedance cable, not 50 Ohm as the receiver and antenna expect, yet there's been no reported reception problems by people who have done this.I have a 152 metre (500') reel ofBelden 89259 coaxin the basement which I'm contemplating on using as the antenna feed. This is nice cable in that it is small in diameter and direct burial type. Performance seems to me to be close to RG6U (but I certainly am no ham / radio expert).Will this be OK for my application?

author: TheSteve
author_rank: Unknown
timestamp: November 10, 2018, 02:10:09 am
content: I use RG6 and it works fine. I wouldn't use RG59 for anything other then a short run, it has nearly double the loss of RG6.

author: wraper
author_rank: Unknown
timestamp: November 10, 2018, 02:26:08 am
content: If you place 20m of RG-59 you'll have like 12-15db attenuation at 1.5 GHz, and it's 75 ohm on top of that.QuoteThe only similar thing is impedance.

author: edpalmer42
author_rank: Super Contributor
timestamp: November 10, 2018, 05:04:23 am
content: If you look at the Trimble Thunderbolt, a professional-level GPSDO, the antenna connector is a 75 ohm F connector. In the manual it says that the impedance mismatch is totally irrelevant. They recommend RG-59 because it's readily available, high quality, and lower loss than most RG-58. The manual for the newer Thunderbolt E updates this to recommend RG-6 for basically the same reasons.Ed

author: deBug
author_rank: Contributor
timestamp: November 10, 2018, 05:55:36 am
content: It depends on how much gain there is in the active GPS antenna.They do have a gain margin to compensate for cable loss so I would say that 15 dB of loss (guessing from the data you provided) would be OK.Active GPS antennas has about 20 to 30dB of gain AFAIK so if that is true for your antenna you should be good.//Harry

author: tkamiya
author_rank: Super Contributor
timestamp: November 10, 2018, 06:35:47 am
content: Since you already have the cable, why don't you just try? You don't have to install it. Just put connectors on both side and take the whole assembly outside to test.Many installations use super thin RG174 and have the amplifier to overcome the loss. Compared to that, you have a better solution.

author: hagster
author_rank: Frequent Contributor
timestamp: November 10, 2018, 07:42:00 am
content: Your antenna has a 26dB pre-amp so I doubt it matters much.

author: wraper
author_rank: Unknown
timestamp: November 10, 2018, 10:16:07 am
content: Quote from: tkamiya on November 10, 2018, 06:35:47 amNo people who have any clue use long RG174. A short piece only.

author: rbm
author_rank: Regular Contributor
timestamp: November 10, 2018, 01:01:36 pm
content: Quote from: tkamiya on November 10, 2018, 06:35:47 amYeah, that was my thought as well. Pull off a reasonable length of cable from the reel and just give it a go. If it doesn't work, no tears to shed; I'll just go with the RG6U.

author: cdev
author_rank: Super Contributor
timestamp: November 11, 2018, 12:41:19 am
content: The preamp in the antenna makes it likely the cable won't matter much, unless you have either a very long cable run or use exceptionally thin cable.

author: wolfp
author_rank: Contributor
timestamp: November 12, 2018, 02:52:09 pm
content: I use a 25m satellite-tv cable with 75Ohms between the external active GPS-Antenna and a NEO-8T receiver. The little mismatch does not matter, all GNSS satellites are shown with good level.Wolfgang

author: tkamiya
author_rank: Super Contributor
timestamp: November 14, 2018, 04:55:48 pm
content: Quote from: wraper on November 10, 2018, 10:16:07 amWell, not super long but many puck antennas are sold that way with RG174 permanently attached. RG174 isn't even rated for outdoors use....

author: cdev
author_rank: Super Contributor
timestamp: November 15, 2018, 01:57:35 am
content: The magnetic puck GPS antennas are not meant to be left on the car roof, just slapped there temporarily while you are in the car and driving.