goTenna Mesh External Antenna

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PBF
Operator
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Joined:Fri Sep 01, 2017 4:51 am
goTenna Mesh External Antenna

Post by PBF » Sat Nov 04, 2017 12:05 am

I'm trying to deploy a goTenna mesh network with my CERT team leaders all focused around a central node.
The mesh units run 1watt on 900mhz ISM.

Someone soldered on an SMA antenna jack for me and I hooked it up to 40' of LMR-400 via a 3" SMA-to-N-Type jumper. I know, significant amount of loss but the 20' I had bought for this project was too short. It's then connected to a 6dbi gain antenna and mounted directly under my GMRS antenna on a PVC antenna mast.

From what I can tell, I'm not getting any better range than if I had just hung a stock goTenna mesh in my front window....in fact, it might be worse. The person helping test was able to hit it from Eagle Rock Park when it was in my front window and now cannot.

My GMRS repeater has amazing range.

Any ideas?

Is this a signal loss issue related to the 40' LMR-400?

Would it be better to get the 900mhz antenna above the 450mhz antenna? Can I safely mount it on the opposite side of the PVC from my GMRS antenna just to get a few more feet up?

How difficult is it to cut 10' off my LMR-400 and re-terminate a Type-N connector on it just to shorten it up?

Or is it just a problem with 900mhz really being strictly line of sight?

Patrick

opfor
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Re: goTenna Mesh External Antenna

Post by opfor » Sat Nov 04, 2017 10:10 pm

So you need to figure out what the radiation pattern is of your antenna... a 900mhz with 6db of gain is going to be fairly flat. If you're looking at vertical isolation, there are calculators out there... Since you're running antennas on different bands (but they are ~multiples) you may want to look for a better calculator than this: http://www.commscope.com/calculators/qvisolation.aspx

Given a 1-watt output I'm guessing you are probably getting more feed-line loss than you would just having the antenna at a lower position. Chances are good, what you probably need to do is actually get an antenna tester out (ask toolbox) and actually make sure the whole system is tuned. This can actually be a pretty serious issue if you have an antenna system mis-match that's serious enough that you're just not getting power out. I don't really have good equipment for this. The other option would be to use a BIRD wattmeter with a 900mhz slug and see what your tx vs reflected power is. Another possibility here is the antenna that's built into the device just can't support the larger load and that's causing the issue.

There's a lot that can happen with systems like this, and debugging them can be complicated.
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PBF
Operator
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Re: goTenna Mesh External Antenna

Post by PBF » Wed Nov 08, 2017 11:50 pm

I'm going to yank the unit and swap it for an un-modified one. If I run it naked out in a weather proof bag mounted on the antenna mast I should get a good baseline for what I should get line of sight before adding an antenna.

Is PVC enough of an RF block that I need to be concerned about it having the antenna mounted directly to the PVC below my GMRS antenna?

opfor
tactical nylon fetishist
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Re: goTenna Mesh External Antenna

Post by opfor » Fri Nov 10, 2017 10:15 am

unless it's aluminized or has some other property that allows it to conduct electricity this should not be an issue. Also in theory you could just have a short length of PVC tube, with an end cap to act as a cover for your device.
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nacho
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Re: goTenna Mesh External Antenna

Post by nacho » Thu Jan 18, 2018 4:53 am

Off the top of my head the loss of 40ft of LMR 400 at 900MHz should be way less than the 6dB of gain.

nacho
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Re: goTenna Mesh External Antenna

Post by nacho » Thu Jan 18, 2018 4:56 am

Yeah, -3.9dB at 100ft on 900Mhz. Something is wrong with your setup. Unfortunately the only line / antenna analyzer I have tops out at 600MHz

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