Gps cable

Has anyone tried to use LMR 400 cable as the GPS cable instead of the LMR 200, and if so how long could the cable be for the GPS cable?

Ever dance with the devil in the pail moonlight?

We used LMR400 on our GPS antenna, but we weren’t going that far with it. That’s just what we carry in our shop, so instead of special ordering LMR200…

Just out of curiosity, why do you need to have a long run on the GPS cable?


The LMR400 cable has lower loss than the LMR200, so you’d think you could use a longer cable. But maybe not. There are likely three issues to consider:

1. Voltage drop on the 5VDC supply to the active antenna.

2. Signal strength to the CMM.

3. Signal delay to the CMM.

The 1 pulse-per-second signal supplied by the CMM synchronizes all attached APs and BHs. The CMM generates the 1 pps signal by using the GPS receiver as its source to be able to also synchronize physically separated APs and BHs. These separate timing signals must be identical, within some margin of error or variation, to permit the Canopy network to operate reliably.

It’s conceivable the 100-foot limitation specified by Motorola is based on the signal delay, not cable losses. LMR200 cable may be specified simply because it produces an acceptable loss at that length. If this is the case, LMR400 cable may also be limited to 100 feet.

Hopefully, Canopy Tech Support will comment on this issue.

We were thinkin about putting all our canopies closer to the grougn so climbing a tower would not be necessary to perform work on the CMM but the tallest tower is 120ft.

The length of the GPS antenna cable should then not be an issue for you. Mount the CMM at ground level, mount the GPS antenna within 100 feet of the CMM, and mount the APs and BHs up to 330 feet (100 meters) from the CMM. Even the 330-foot limitation on the Ethernet cables can be exceeded when using Cat5e or better cable. The GPS antenna needs a clear view of the southern sky, but not the horizon; it likely doesn’t need to be at the top of the tower.

Just to reinforce much of what was said here…

I used LMR400 for my GPS link and it works fine. It does provide less power loss than LMR200 of course.

My LMR400 run is only about 50 feet, so I cannot speak for the cable limitation. I mounted the CMM on the ground and ran the cable up the tower to the GPS. That way, all work on the CMM can be done while standing on ground :slight_smile:

Your best bet is to do what Teknix said and be sure you have a clear view of the sky, but do not mount it at the top of the tower. LMR400 should extend the GPS cable limitation from LMR200, but I’d rather be safe. If you were to go over the allowed length, it may be fine for a while, but the GPS could suffer later.

The main concern is to use as little connectors as possible to avoid power loss and weatherproof them as well.