Trim the Antenna?

Hi everyone,

So I’m brand new at this and just built my PiAware last weekend. I’m using the suggested small magnetic antenna that I bought on Amazon. Since I set it up last weekend I have been receiving pretty good coverage overall – up to 150 miles in certain directions.

I live in west Africa, in a pretty heavily urban environment. My line of sight isn’t the best, and I have the antenna mounted on the outside of a window on the most open-facing side of my apartment, as high as it can be (about 40ft.)

Of course I am like everyone else here trying to maximize my range. So, my question is this – Should I trim the antenna? I have read various places that trimming it to around 67mm will maximize the effectiveness at 1090mhz. Does anyone have any info about this? Is it really worth doing? Do I run the risk of ruining the antenna if I clip it? Finding materials here in west Africa isn’t the easiest task so I don’t want to risk messing anything up.

For reference this is the antenna I am using:

Thanks in advance for your help and support!


I would not clip the particular one you have.
But I would construct one of these, Three Easy DIY Antennas for Beginners and play around with.
lots of fun in it :wink:

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This antenna should be thrown into the garbage.
Trimming should improve the characteristics

Trimming and placing it on top of 2 lb coffee can, or other similar sized metal base like a cookie tray, will increase its effectiveness. That said, if you have minimum building skills, go for the QuickSpider antenna. There is an excellent tutorial on how to build one, just search past posts.

In case you are not into building antennas, and if money is not a problem, purchase the FlightAware antenna. It’s an excellent value.

Thanks for the input, everyone, it’s very helpful!

The advice to trim the small mag mount antennas to 67mm is for the antennas which come with generic digital television USB receiver dongles. Many people use these for ADS-B reception but the antenna is straight and optimised for digital television, not 1090MHz, so in those cases trimming them down to 67mm helps get a bit more from them.

The antenna you’ve linked to is center-loaded and the length is already optimised for 1090MHz reception and should not be trimmed.

These mini antennas can perform really well. I used one for a few months and was getting aircraft over 100NM away. You will get better reception if you put it onto a tin can which has a diameter and height of around 65-70mm. I used to use a Kenco coffee tin and it improved reception a lot.


Very good point. I did not follow the link, and thought it was the antenna that is included with the generic no name dongles.

The QuickSpider is still a better option. The FA antenna still the best option.

Yes I don’t know what magic is inside the FA antenna but its performance is unreal.

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well the metal tubes inside (metal quality), the bottom outer rings and, I believe, they are tuned.
or antenna the upper part and filter the second part.
have tried to replicate one, but, lacking dimensions and tuning eqpt. so …
don’t remember where I saw the yellowish metal, old radios, inside of old antennas …


You’ve let the ADS-B smoke out! It’ll never work again!

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common knowledge.

Thanks a lot, this really helps to clear it up for me. And I agree about the performance of the small antenna, it’s been surprisingly good so far.

The window where I have it mounted has a metal security frame around it, with bars made from rebar and painted black. Do you think this would be a good option or would the can work better?

Thanks again.

The reason for the recommended cans and/or lids have to do with the frequency of ADS-B signals. While metal of any length and shape may ‘improve’ things somewhat, the correct shape and length are important for impedance matching, and maximum signal transfer from the antenna to the receiver.

Very good to know. I’ve got a nearly finished oat can that should match close to the dimensions you mentioned. I’ll give it a try in the next few days and let you know how it goes.

Try them all. Try the antenna on the window frame for a week, then switch to the antenna on the oat can nearby for a week. You can compare each week by looking at your stats page and looking at the numbers and the graphs. Please do followup to say how it went, I’d be interested to see the results from trying both.

I tried my mini mag mount on a large metal frame and it performed worse than without the frame. Then I tried it on the coffee tin and the performance increased a lot, so it looks like having a tin of the right size (~65-70mm diameter and tall) really does help. I’d be interested to see if your results support that too.

Trial Run Results for Four Sizes of Ground Planes

Why Antennas Have Ground Plane?


Well I found a perfectly sized can yesterday and I’ve been seeing a huge performance increase. My number of received positions yesterday was nearly double my previous record. I’m definitely picking up aircraft further away and seeing them longer than before!


Great. Now try different diameter cans. I have done it for Stock Whip (see photos below), but your antenna is different (wire collinear with coil), and optimum can diameter may differ from what I have found for plain 67mm whip.



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Yeah, I’ll keep tinkering with different sizes and see how it goes. What do you use to get the data you shared above? Any advice on real-time signal info from the pi?

My plan to re-site the antenna outdoors did not work out. The places that I’m able and willing to place it cannot handle the weight of the complete assembly (bracket, j-pole extension, fiber glass mast, antenna, etc).

The exercise was not a total loss though. It confirmed that minor changes in antenna siting, specially indoors, can make a big difference.

When I put the antenna back where it was, or as close to where it was, performance dropped substantially. This morning I moved it again, inside the garage, as always. This is the highest and farthest point away from any obstacles possible in the garage.

Performance recovered immediately. Monitoring a little longer to say for sure, but range seems to have increased a little as well.

I can say with certainty now that this is the best/maximum performance I’ll extract from this installation until, and unless, the antenna is moved outdoors. This is not likely to happen anytime soon, if ever.