SINCE JOINING LATE LAST YEAR AND BEING AN AVID RADIO AMATEUR (G8NLF) a spacecraft engineer by trade (retired now) both ground and space. i started on a quest to get the best results from my system.
first and formost i did absolutely nothing to the downloaded software and the pi aware system, i bought the receiver(rx) and filter FL1) and the pi 3b was a pressy (from a lifelong friend (M1CQU)) so all that out of the way, use the squiggly wire antenna on the magnet and ring of steel just outside the window of the shack about 8 feet off the ground and was pleased to see 10 aircraft and a couple by Mlat. so im up and running… Going via the internet, i found a 4 stage co linear made from copper wire (same as used in household power wire (which is where i got the wire from, aroung 1.8mm dia, and using some 30meters (m) of RG174 i ran the antenna up my transmitter mast (a 28 foot aluminium scaffold pole bought from the scaffold supplier at £26:00 inc vat)ok so now with the 4 section colinear inside plastic conduit (1" in dia) it went around 15 feet off the ground at the gable end of the house and the aircraft live feed jumped to an average of thirty at the 0600 hours run into gatwick and heathrow (i am just south of Aldershot) not bad for a beginner. but i was looking at my position on the global scale of things and not impressed, so back to the internet and the drawing board and i found a 16element coaxial colinear to build (https://www.balarad.net/) a good or dare i say it great design so i made it taking care to do the cutting etc as stated. i didnt want to loose my signals from the current arial so i went to the stockpile of coax for the transmitters and found some RG213 mil spec around 30 m of it terminated in N type connectors so into the junk box to find N to SMA convertor which ended up being N to BNC abd then BNC to SMA but this time the antenna went onto a mast of its own and abobe the gable end of the house, now at a height of 28 feet in the clear , well actually within 12 feet of the feed point to my amateur HF multiband arial (just for completeness, a combination of wire antenna dipoles of 80m down to 6m frequenties.) now the aircraft count shot up to a peak of 96 (best day easter friday) and an average og 70 on the breakfast run (0600) in addition, the range /polar patters improved immensly from 30 mile to around 130 south and 80 to the north (i live in a radio hole surruonded by hills at 200 to 300 m with a 50m peak to the south… One big problem, was that when talking to my amateur friend in the USA, the 100Watts at 14Mhz completely wiped out the ADS B receiver to my surprise, as when using 433 Mhz at 20 watts made no difference(the receiver recovered after some 5 minutes,
I Thought i could do better by moving the antenna to the mast at the end of the HF antenna to avoid it being paralised, but to do that i had to get more coax so i carefully mated a length of rg58 to the rg213 (both 50 ohms but with differing velocity factors and therefore slightly differing characteristics … WOW that killed it my count dropped to 10 to 15 aircraft and the range dropped to 30 miles UGH!! My first thought, i have damaged the antenna in moving it so i built another terminated at the base with an Ntype connector and placed it outside the window on the ground using (a) RG213, 25 to 30 ON THE GROUNG range 30 miles… then (b) RG58 same results. then i tried (c)some new coax i bought at ML&S up london way (this coax is stated to be RG213 look alike) however RG213 has two layers of braided copper whereas the ML&S brand has an inner sheath of copper sheet/Film and an outer layer of braid. and now another revalation, with the new antenna on the ground, up to 50 miles range and up to 40 aircraft. so whats next , up the tree with a completely new run of ML&S coax (c) from the old thought to be defunct antenna back to the receiver in one 45m length and surprise, 150 to 180 miles range and run up to a peak of 80 aircraft .
conclusion,as with amateur raDIO, NOMATTER HOW GOOD THE kit IS, IF YOU HAVE A POOR FEEDER AND ANTENNA SYSTEM IT AINT GONNA WORK. SO I HOPE THIS HELPS A GOOD SINGLE LENGTH OF QUALITY FEEDER AND CAREFULLY BUILT COLINEAR AND HIGH AND CLEAR AS YOU CAN GET IT AND YOU WILL JUMP UP THE LIST … HAPPY HUNTING DE g8nlf (JATENELEF)
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nice write-up - some pictures would have made it even better. but this was the wrong forum you used. better here - this is where all is about feeders and their sites 
ADS-B Flight Tracking - FlightAware Discussions
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I do several things that would mitigate this.
- Cavity filter (I have them for 1090 and 978 Mhz)
- LMR400 (You don’t need to go this far, however, quality coax helps)
- quality USB pigtails( I used a 6"/15cm USB 3.0 pigtail for the dongle) and power cable. Ferrite chokes on both.
I use the USB pigtails to give me room for other dongles. - metal case for dongle and RPI
I do have a professional DPD antenna, however, it probably doesn’t help that much for off band transmissions.
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