There is a lot of talk about adding pre-amps to the antenna system, but very little discussion about the reasons why you should or should not use one VS just having very low loss. I was always taught to first use passive amplification(aka antenna gain) along with minimal losses(aka good feed line), and then active amplification as a third option but only if necessary. Since I needed a bit more than 100ft coax run for my setup, even with low loss cable LMR-400, that would have been 5dB loss for the cable assembly plus adapters. I took the minimal loss route and built a tower mounted receiver with just the 6 inch pig-tail from the filter to SDR.
The results show that I now can see ACs pass my radio horizon per heywhatsthat.com. This being microwaves signals what we are dealing with, which strictly require line of sight, I highly doubt that any active amplification will help me further, not even counting the additional noise generated by the pre-amp.
Opinions from the more experienced members is welcome.
I think it depends on what your circumstances are. At the moment I have an antenna in the loft, beneath a roof made of heavy tiles, and between two brick gable ends. I have tried using just the antenna with no amplification and performance is significantly worse than with. In theory, ADS-B transmissions should be easily strong enough to be received from the radio horizon (the minimum transmission power for most airliners is 125W, but the maximum is 500W) without amplification, but local attenuation has a big effect. Having a filter in line also increases loss slightly, but is essential here because of nearby mobile phone towers.
I have a satellite amplifier mounted directly under the antenna, which has proved to be the best configuration for now. I get massively reduced range and message rate without it.
I’ve also tried using a PSA4-5043+ LNA next to the filter but that doesn’t give as quite as good results as having the satellite amp next to the antenna. I did try having both amps in line simultaneously, with the gain on the dongle reduced significantly but it didn’t provide any better (or worse) results as just having the amp at the antenna alone.
I know that the roof is making a big difference to what I can receive because if I move the antenna around inside the loft space, I can modify the footprint of receivable aircraft very noticeably. The two end walls make the biggest difference, so positioning the antenna centrally gives the best all round coverage.
Ideally I would mount the antenna up on the chimney with the TV antenna, but access is difficult.
@bellcontytx
Wow, your stats really shot up around New Years. What did you do then?
I have two setups with the same hardware and antennas.
One is outside, 2 feet above ground with the mag mounted 3.5db antenna on the metal basement window bars. This runs mutability DEV 1.15 over sampling and auto gain.
The other is in our second story bedroom. It run shot std code at the moment.
The outside antenna picks up 50-100% more aircraft. I even saw this when i had the antenna inside the basement window. Outside made a big difference.
I am trying to work out a way to put an antenna on the chimney and the rpi2 in the attic. I just need to run cat5e from the basement to the attic. I have no power in he attic and dislike using wifi unless I really have to. I have a poe switch and Poe to USB micro adapter.
I may be able to use the little antenna on the metal roof vent until I can mount a proper 9db antenna in the chimney.
I have also thought of adding a ~15db yagi pointing south. I am close to sea level and that is the only direction that would work from my location.
That was one of my new year’s resolutions… Not really lol, I just had some free time to do tower work during that time frame. If you compare Jan 02 vs Jan 04, the increase was made by going from 10ft on the fence to 40ft on the tower.
Initially, my Piaware started with a quarter-wave ground plane at about 10ft up on my tower, and 50ft RG-6 with the PiAware inside the house. I then added the bandpass filter due to a 900MHz pager(yeah we still have those around) transmitter that was swamping my SDR. This setup was working OK but the tower itself was blocking the signal to the north, to the point where my range was heart shaped. So to get around this issue I decided to move the antenna to the top of the tower, at about 40ft. I did not want the extra coax attenuation and I wasn’t ready to experiment with amps just yet, so started putting together the parts for an all-in-one outdoor solution.
From top to bottom, Im using the FA antenna directly mounted on outdoor metal enclosure, type-N to SMA adapter, FA BP filter, 6 inch SMA pigtail, SDR, RPi, DC to micro-usb voltage regulator, short shielded Ethernet patch cord, Ethernet surge protector, 75ft CAT6 shielded cable, PoE injector, Internet connection.
I do both, out of necessity. I have a non-ideal setup not only with the antenna in the attic beneath roofing shingles, but also terrain/vegetation issues with a vertical 200’ elevation rise <0.5mi west and tall pines in close proximity to my property.
To minimize the losses in the receive chain from an already challenged setup, I have 50’ of LMR-400 75ohm from antenna to Pi location. My chain is 5dBi antenna > BPF > amplifier > diplexer (ADS-B + OTA UHF antennas) > LMR-400 > diplexer > SDR. Keeping the BPF adjacent to the antenna rather than the SDR makes for one conversion from 50ohm to 75ohm impedance components to further minimize loss (SMA connectors). To the south and north, the VRS range plots are about equivalent to the heywhatsthat range plot, so I figure the setup is optimized the best it’s going to be.
Using the Dump1090 message rate as a rough real time performance metric, I removed first the BPF, then reinserted the BPF and removed the amp. In both cases, the message rate dropped significantly; from 200+ to 150, then to 60, respectively, So for me, I figure amplifier and low-loss cable is the best. The town has a 150’ tower close by my house, each time I drive by I wonder whether I could lease some space on it from them
BellCountyTX,
I can’t imagine a better setup for the money. Any concerns about the Texas heat?
Technically there are better antenna(I doubt you need one), RPIs and filters, but you see aircraft 240+ miles away.
Your location change(10’ to 40’) made a huge difference. From 2% over 120 miles to over 50% over 120 miles away.
I noticed that you are using an old, first edition RPI1(I still have one). Does it have enough memory to work well(I know the stats are great)?
In a few years, adding dump978 and a 978Mhz antenna will allow you to see light/GA aircraft. You may see a few now, given your coverage range.
I have the same nooelec dongle(I found it worked so much better than an old black rtl-sdr unit that I bought last year).
I have mine in the nooelec aluminium case.
Currently my 3ft off the ground setup sees a few more aircraft than you, however, I am in the crowded north east. I barely see anything past 60 miles. You get 2-3 times more position hits than I do. I expect that is due to your excellent coverage. I am hoping a move to my chimney will get me much better results.
I am curious as to how you knew that the pagers were interfering with your ADS-B setup? I have a filter that I have just started to test.
Are the other Antennas on your tower for 2m/70cm or other bands?
Yeah, the heat is a big concern. There are some pre-drilled holes at the bottom of the enclosure. Will get them open when it starts getting hot.
I had to used an old RPi only because thats what I had on hand while building this project. The second it went up to 40ft the CPU alarm went off. It stays between 90 and 99 percent for most of the day and then goes away at night. I already have a RPi2 but want to let the ranking settle first on the RPi to get a good benchmark before replacing anything else. This receiver also uploads to adsbexchange.com so that might be taxing some of the cpu too.
I thought about getting the aluminum case for the SDR but them realized that the metal enclosure provides good isolation from any external RFI.
The pagers are at around 930MHz and will even destroy my scanner’s reception in 850MHz if I use it with an external antenna. Since you asked about the other antennas, the long one is a Comet GP-9 for two RoIP nodes, 2m and 70cm. The shorter one is also a Comet dual-band local comms. Without the BP filter, when my RoIP nodes transmit, my ads-b reception is zero. So this is yet another reason why I need te BPF in place.
