Car roof magnetic antennas

Development Hardware
1

Has anyone found any good magnetic car rooftop application antennas in 915mhz for T-Beam / T-LoRA boards?

Thanks

2

I have these, they’re cheap and seem to work ok. Haven’t tested them on a VNA or anything. Cables are longer than I would like ~9ft according to listing.

https://www.amazon.com/gp/product/B089VSZ61H/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

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3

I got 5-6km with that antenna on the roof of my car with the Long range (but slower) setting. Could have gone further, but a hill got in the way,

VNA shows it’s pretty good.

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4

I just got a pair of them in, and while the VNA shows that they’re not bad for SWR, the performance is underwhelming. I get better range with the stock 915MHz T-Beam antenna sitting on the dash of my car than I do with the mag mount antenna attached to the car roof.

5

I suspect with these low power devices the cable loss is significant.

Have you considered trimming the cable down and retesting it?

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6

I picked up one and noticed that as well. There is a lot of RG-174 between the device and the antenna. I may snip off quite a bit and re-crimp a new SMA on mine.

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7

Hmmm, hadn’t considered that. I did a little bit of searching, and found that RG-174 has around 0.3dB loss per foot at 900MHz. With 9.8 feet of cable, that loss adds up fast! I’m now looking around at mag bases that use RG-316 instead. Guess it’s time to learn how to crimp SMA connectors…

Edit: Just ordered this unit and will give it a try: https://smile.amazon.com/gp/product/B01MZ72P31/

8

I have one of the generic hex die crimpers I got for RG-58 termination a while back. I’ve only done a couple of RG-316 patches for SMA to BNC . I found some SMA crimp connectors I’m gonna pick up to experiment with:

9

I finally tested this unit briefly today, and I don’t know that it’s doing much better than the stock rubber duck. I’ll need to do more experimentation now that I have the range test plugin working. I will say that the base magnet is not strong at all, and the antenna will fall off of your roof at right around 50mph.

This one just arrived today, and has a notably beefier magnet: https://smile.amazon.com/gp/product/B077YB1QNL

Once I do a little more testing with the range testing plugin (which has shown me that I should really test with better GPS), I’ll try to do a bit of a shootout with some of these various options.

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