NooElec with small antenna ---> FA Pro Stick + FA 1090 Antenna = worse results?

[klinquist]

Ok, I just *also* ordered a SAW filter from Hong Kong .

[Strix technica]

I ordered the FA 1090MHZ filter to put in front of the stick which should be here on Wed, I will update with those results.

That's a bit of a pity because the bandwidth of that filter seems too wide to exclude GSM signals, which means a negative result won't necessarily prove much. I know they're more expensive, but a SAW or better still a cavity filter would probably have been a better choice. If you have the option of returning the filter and ordering a SAW filter (from China, if you must), that might be a better idea.

On the other hand, if the BP filter in the Pro+ is after the LNA, it might help a bit to filter pre-LNA, even if the bandwidth is too wide.

I do have quite a few Zigbee sensors around the house - 902-928mhz, perhaps those are interfering?

Hard to say. I'm unsure what ZigBee's maximum power output is, but it's probably in in the 50-100 mW range. That's tiny compared with GSM base stations, OTOH, your ZigBee transmitters are that much closer and inside your house, at which point the inverse square law comes into play.

[klinquist]

Thanks for all the replies!

I do have the blue stick - connected directly to the Pi. Pi is powered by a suitable high amperage power supply. The 16" cable between the pi and the antenna is a good quality one.

I ordered the FA 1090MHZ filter to put in front of the stick which should be here on Wed, I will update with those results. I do have quite a few Zigbee sensors around the house - 902-928mhz, perhaps those are interfering?

Anyway, if the FA filter helps out, maybe I'll invest in a better one.

[Strix technica]

TEST-3: Flightaware Antenna and Pro Stick/ProStick Plus with Attenuators
Gain Setting throghout the experiment = 38.6 dB

Adding pads (attenuators) to a system that includes amplifiers (actually two in this case, up to +70 dB or more in aggregate) is counterproductive, to say the very least.

Signal lost in the pads can never be recovered, where injected noise is roughly proportional to the gain you use plus a bit more, therefore all you will accomplish is to decrease your SNR.

If the problem is intermodulation noise, then use a decent, low-insertion loss bandpass filter before the first LNA rather than pads. Then set the gain to avoid overdriving anything.

[Strix technica]

A Cavity filter will sure give precise and narrow band width, but cost $100 to $150

This cavity filter goes for €42 incl. VAT (which you won't pay if you're outside of the EU) so no, they don't all cost thee figures or substantially more than a SAW filter.

Doubtless you can spend hundreds on them, but the same goes for nearly anything.

[abcd567]

TEST-3: Flightaware Antenna and Pro Stick/ProStick Plus with Attenuators
Gain Setting throghout the experiment = 38.6 dB

[abcd567]

Flightaware antenna is a high gain antenna (6 dBi), while mag mount whip antenna supplied with DVB-T is a low gain (1.5 ~ 2 dBi)

The Flightaware antenna therefore picks much more Cell Phone signals, and overloads the rf preamp chip if a filter between antenna and ProStick is not used.

TEST-1: Comparison of Cantenna (Gain ~2 dBi) vs Flightaware Antenna (Gain 6 dBi) WITHOUT FILTER and with Generic DVB-T

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TEST-2: Comparison of a Spider Antenna (Gain ~2 dBi), and Flightaware antenna (Gain 6 dBi) With ProStick/ProStick Plus

[abcd567]

LC FILTER SCHAMETICS

UNBALANCED LC LADDER



BALANCED LC LADDER



FLIGHTAWARE FILTER INSIDE




HUNGARIAN FILTER WITH TAI-SAW CHIP
US $19.99 http://www.ebay.com/itm/112472645896




CHINESE FILTER
US $28.95 http://www.ebay.com/itm/331993013752
Passband : 1086 ~ 1094 MHz (Not mentioned what type of filter is inside. Seems to be a TAI-SAW Chip, but not sure.)






TAI-SAW FILTER CHIP

[Anmer]

Have you tried the Pro Stick with your previous antenna and vice versa? The existing DVB-T "dongle" with the FlightAware antenna?

You don't mention what coax cable you're using?

[abcd567]

The Flightaware stand alone filter is an LC filter.
The Pro Stick + (Blue) has an integral SAW filter.

A Cavity filter will sure give precise and narrow band width, but cost $100 to $150(6 to 10 times the cost of LC or SAW filter).

In my case, Flightaware's $15.50 LC filter did the job well.
In few very severe noisy location, a costly cavity filter may needed. On ebay 1090 Mhz SAW filter are available for around $20, and may be good, but I did not try these.

[Strix technica]

Strange, all I can see is:

Arg. I read what I expected to read, given the following:

Flightaware Pro Stick USB ADS-B receiver dongle which includes an internal 1090 MHZ band pass filter

If it has the bandpass filter, then it's the blue Pro+.

[Anmer]

OP said it was the blue Pro+.

Strange, all I can see is:

I bought a "Flightaware Pro Stick USB ADS-B receiver

[Strix technica]

Or just buy a separate cavity or SAW filter, which you get to choose, that has narrower bandwidth and higher order to knock out adjacent GSM signals.

And I'd say that FA's BP filter is a poor choice, even if it is a SAW filter. If you look at this frequency response plot (bottom of page), you'll see that it has a bandwidth of about 300 MHz beginning somewhere in the range of 930–950 MHz. That's going to pass a lot of GSM, so it's pretty useless.

See also this analysis (scroll to bottom) and this test.

In general, discrete filters cost a lot more, but you get what you pay for.

[abcd567]

I suspected as much (re placement).

Two options:
(1) Adding 2nd SAW filter between antenna input and rf pre-amplifier (extra cost)

(2) Relocating existing SAW filter from current location (between rf pre-amp and tuner), to new location (antenna input connector and rf pre-amp).

I have made these suggestions in Flight aware forums recently.

http://discussions.flightaware.com/post207845.html#p207845

http://discussions.flightaware.com/post208318.html#p208318

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[Strix technica]

The Pro Stick Plus has an integral SAW filter, which is located between front-end rf amplifier chip and the tuner chip.

I suspected as much (re placement).

The solution to this problem is simple: add a filter between antenna and Pro Stick Plus. Flight aware filter is now available at Amazon.com at US $15.50

https://www.amazon.com/gp/aw/d/B010GBQXK8

Though it's "made" (likely re-wrapped) by the same company, that's no guarantee that the linked BP filter is equivalent to the BP filter in the Pro+ stick. That said, it's worth checking whether anybody has measured the actual knee-point and dB-per-decade properties of this before buying it if you suspect intermod noise.

Even taken at face value, 980 MHz is uncomfortably close to the upper edge of the GSM900 band, so it probably isn't adequate for GSM950. I don't know what the actual bandwidth of ADS-B is, but it can't be much more than 1–2 MHz so something with 70 MHz bandwidth is absurdly broad for this application.