Flightaware pro stick plus refusing to outperform cheap DTV dongle


#1

G’day guys,

YES I HAVE PLAYED WITH GAIN

Hoping someone with some experience with this product confirm what I think might be causing my problems.

Current hardware layout is:

Flightaware 66cm antenna mounted on a 3 meter metal antenna mast ontop of my tin roof in Sydney Australia, total elevation of antenna is 33M above sea level. Flightaware 66cm -> N Type -> BNC -> 5 meters of RG6 Coax (75ohm) -> F Type -> SMA -> Flightaware Pro Plus.

When I use the Flightaware Pro Plus I see 200+ messages per second with range maxing out at 100km. When I swap to a cheapy Rafael Micro R820T tuner with gain at ‘-10’ ill see 120+ messages with range maxing out at 350km.

Ive used a script to cycle through different gain levels (across -10 to 50) with both dongles and sweet spot for the FA seems to be around 33 and the Rafael seems to be -10.

On the FA dongle I seem to lose contact with planes with reported RSSI of -6. on the Rafael they drop out at around -30. That seems weird for the FA to drop out so early.

My thinking is either the filter in the pro plus is squashing out something it shouldnt be, or the amp is over powering the receiver and even with the software gain turned all the way down cant get this under control. I dont believe my hardware setup is causing problems as a straight swap between dongles changes the results so drastically (im aware the coax isnt idea with the impidence mismatch and length)

Thoughts?


#2

your settings sound reasonable -10 for the dongle without amp and 33 for dongle with amp.

i’d try first the simplest possible setup and connect antenna with the shortest possible 50ohm coax you have -> then test both dongles-> then both with the 5m 75ohm. the problem with the fa-dongle is that the amp is at the end of the antenna-run an not in front where the best place for filter/amp is …

my thoughts after years of testing lots of antennas/amps/filters/receivers :smiley:


#3

The FlightAware Pro Plus has a LNA – BEFORE the filter.

My bet is you’re saturating/overloading that LNA, which results in reasonable traffic close in, but nothing at distance (those signals swallowed up by intermod/noise/crap from an overloaded LNA).

I know that if I remove the FlightAware filter between my external antenna and the Pro Plus LNA, the numbers on that system go down.

You can also do a spectral sweep (rtl power) using the R280T to see how nasty your RF environment is. My bet is the LNA in the Pro Plus is choking on the RF equivalent of cane toads.

Have fun – let us know what you find out, as it helps the next poor bloke traveling this path.

bob k6rtm


#4

Most likely you need to add an external filter, as I had to.

44


New setup (FA New Dongle + FA Antenna) worse than old setup (Old SDR + Stock Antenna)
#5

Aaaah!

Thanks guys. I didn’t realise the order of the filter and LNA was this way. Sounds like this explains the signal loss as such a relatively high RSSI.

I’ll grab a filter and report back. Thanks for the help.


#6

don’t you koalas have gsm 900 too - if so the flightaware-filter probably isn’t the best idea …
like bob k6rtm already wrote it’s a good idea to first make a short test (using the standard dongle) what frequencies with what power are around your site. here’s a short howto from obj: Filter not producing desired result


#7

Please see my Jun 2017 post below. Scroll right to see complete image


#8

Thanks everyone for the help. 1090mhz filter installed today and the receive range is just edging out the Rafael dongle, with message per second at around 350m/s!

With some gain tweaking we should be in business!

@abcd567 - Agreed, we need one with two filters.


#9

is that a fancy photoshop effort or is someone making this?


#10

Filter near sma connector was added to ProStickPlus pcb by me using flow soldering PHOTOSHOP :smile:


#11

Dam. Would happy pay for a run of the PCB if we could get the blueprints. CBF starting from scratch!