GPS inline amp needed? - Page 1
Forum section: electronics / general

author: jailbird
author_rank: Newbie
timestamp: March 30, 2019, 12:32:50 am
content: Sorry for the stupid question as I'm definitely not a RF guy! I went through and replaced my old 58532A and 58536A (with its nasty 40ns group delay) with one of the TOPGNSS GN-GGB0710 RTK/CORS antennas and a GPS Networking NALDCBS1X8 in order to add L2, GLONASS, and Beidou support to my setup.My question is about signal levels. In this house I'm having to use "what I have" (definitely going to make sure that the next house is wired better). What that means is I have ~163ft of 75Ohm builders-grade RG6 from inside to outside (TDRd using a Fluke. There's currently a barrel connector probably about 1/3rd of the way, so that 163 is two lines connected together). On the outside, the RG6 is connected to a grounding block, and then there's 7ft of RG11 between the grounding block and the antenna. On the inside, there's 13ft of RG11 going from the wall plate to the splitter, and then roughly 3ft (each) of LMR400 from the splitter to the various devices.I'm driving a mix of "old" things (a Thunderbolt-E, a TrueTime XL-DC, a Motorola M12+ powered CNS Clock, and some Chinese Trimble clone), "new" things (a Ublox-based LeoNTP & a Ublox NEO-M8T), and some that are in-between (a Samsung UCCM & a Geppetto FE-5680A GPS Discipline module).If I'm doing my math right , that's ~21.1 dB for the RG-6, ~0.2 dB for the LMR-400, and ~2.3 dB for the RG-11. Add the 1 dB for the impedance mismatch, and I'm looking at 24.6 dB for the run (+ the loss from the grounding block, adapters, and 2 barrels).The antenna says 5.5 dBi + 40 dB LNA gain. The splitter says 14 dBi gain (I'm not sure how that's split across the 8 ports?).So my (long, sorry!) question is: Am I going to have enough gain left? I picked up a Chinese 27 dB GPS/Beidou/GLONASS inline amp that I can swap out in place of the one barrel connection on the RG-6 lines if needed, but I don't want to overpower the receivers.If it helps at all, right now with *just* the CNS Clock plugged in to the splitter, Lady Heather is reporting the dBc for the 6 tracked sats anywhere from 38.3 - 40.3 dBc. My "gut feeling" is that's a tad low, but that the 27 dB from the amp would probably be way too much?Again, sorry for the newbness, one of these days I'll figure out RF.

author: tkamiya
author_rank: Super Contributor
timestamp: March 30, 2019, 03:33:40 am
content: You might be better off by just sticking out an antenna outside the window. (or just inside it).Or else, just try and see if you can maintain a lock. If you are going to connect inline amp, you will have to place it before most signals already gone. I'm not sure if you can do that or not.I have seen all sorts of weird and incorrect terminations of 75 ohm stuff. Also, spliter is a TV grade stuff isn't it? So the loss may be far greater. Now, why would anyone mix long RG6 followed by short RG11 then to LMR400??Very weird.

author: jailbird
author_rank: Newbie
timestamp: March 30, 2019, 03:46:16 pm
content: The CORS antenna is outside. The newer receivers like the U-Blox with their sensitivity work fine with a puck antenna inside the window. The older units though have problems maintain a 3D fix like that. At least in my North-facing window.I’m using a GPS Networks distribution amp, not a DBS splitter, although I should have since they’re a lot cheaper!Since I was stuck with 75 Ohm RG-6 for the antenna run, I wanted to keep the number of impedance mismatches at a minimum, as well as losses. So 75 Ohm RG-6 & RG-11 from the antenna to the distribution amp, which is 50 Ohm. Since the amp and receivers are both 50, I went with LME-400 on that side.

author: tkamiya
author_rank: Super Contributor
timestamp: March 31, 2019, 12:26:58 pm
content: You have similar setup to mine, except mine is not TV coax and the entire length is a lot shorter. I also have a distribution amp / splitter in the middle.You have 160 feet of RG6. Putting inline amp is not going to over-drive the receivers. I'd try it. If you are using HP/Symetricon distribution amp / splitter, net gain on that is zero.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: April 01, 2019, 04:37:30 am
content: Well you must know more than I do about the 40ns group delay on the HP/Symmetricom splitters.What is the problem you are experiencing with those? Mine seem fine. Is it just a matter of dialing out the delay, like cable delay?Maybe I need to adjust my cable delay an additional 40ns?

author: jailbird
author_rank: Newbie
timestamp: April 01, 2019, 06:16:54 am
content: Quote from: SoundTech-LG on April 01, 2019, 04:37:30 amI was mostly joking about the “nasty” part.. I was mainly replacing it as it’s bandwidth is around the GPS L1 band only, while newer receivers support L2, GLONASS, and BeiDou also. I was modernizing my antenna/dist amp setup for that reason.As for the 40ns figure, it’s not on the main page, sadly, but they do list it on page 11 of:https://www.microsemi.com/document-portal/doc_download/135738-datasheet-syncserver-s6xx-optionsAnd yes, adding it to the cable delay is what I did!

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: April 01, 2019, 02:08:01 pm
content: The specific data sheets for 58532A and 58536A show the 40ns delay on pg. 1 / pg. 2I use Beidou and Glonass sats in my LEA-M8T based setup in Spectracom Securesyncs. There does not seem to be any issue using the splitters for those sats. Plenty of signal strength, plenty of tracked sats. Maybe location? I'm very near the West Coast shore.