FlightAware Discussions

Weird antenna problem - Need advice - Home made was better?

Hi All - I’ve been at this for about two months now. Since I’m impatient I decided to make my own “spider” antenna from parts in the garage (see picture below) - And it worked pretty well! I had a max hit of 255 miles, and seemed to get around +/- 205 miles each day.

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I then decided to pick up my game and order a real antenna - the highly reviewed FA antenna from Amazon. As you can see from the picture I mounted next to my 5m HAM antenna (currently not connected). I also bought a new 25ft cable to match rather than my home made cables. See installation below:

Guess what? My max range is now 155 miles, and I average 30% fewer hits overall. What is going on here? I am NOT using the filter, but thinking perhaps that is my problem? I’m frustrated and stumped, so hopefully somebody has some advice!

Thanks, g-

Step-1: Reduce gain in steps and at each setting watch for a while:
-10 >> 49 >> 45 >> 40 >> 35

Step-2: Add a filter.

 

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Your DIY Spider antenna’s photo proves following:

It is not the beauty or appearance of an antenna which determines it’s performance.

It is how much the antenna conforms to laws of electro-magnetism, plus its location which determines its performance. :slightly_smiling_face:

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Thank you abcd567 - I tried adjusting the gain in the past, albeit not very systematically, and it didn’t seem to make any difference. I will be more systematic this time.

Also, this filter " ADS-B Dual 978 MHz + 1090 MHz Band-Pass SMA Filter" appears to be unavailable. Any other suggestions?

Thanks, g-

How are you feeding the signal to both the 978 mhz and 1090 mhz SDRs? Is it a T type connection? A signal splitter? Something else?

While the 21st harmonic of the 6 meter band does cover 1090 mhz, the nearby antenna should not cause enough parasitic coupling to cost even 3 dB under a worst case scenario.

First diagnostic thing I’d do would be swap the homebrew antenna back in, change nothing else in the system, and observe if the performance improves or gets worse.

If it gets better, then the “new” antenna may either have a defect of some kind, or it could be much broader frequency response than the home brew, so would pick up more strong out of band signals than a true resonant antenna.

I’d first focus on getting the 1090 working well, then run a separate cable and antenna for the 978 mhz receiver.

Another thing I just thought of - moisture. A pinhole in an enclosed antenna can “breathe” in air at night as temperatures fall, then water can condense, and it won’t evaporate and find its way out the next day. The store-bought antenna looks like it has an enclosure or sleeve around the active elements, while the home-brew is fully exposed where any water condensation can easily run off and thus it will dry out quickly.

It can also introduce moisture into a coaxial cable. I once had a 120 foot run of Belden 9913 that ended up with nearly an entire cup of water inside a few years ago. Fortunately the transmitter had proper high SWR final power reduction, but it rendered the installation deaf and mute. The only real immediate clue other than high SWR was the cable felt heavier than it should have.

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