FlightAware Pro Plus + External Filter in San Francisco?

Hey there everyone! I’m new to the PiAware ‘scene’, but so far I’m really enjoying the results, however I’m almost fixated on a issue I see which leads me to my question:

I cannot seem to pick up anything further than about 110 - 120mi north of me. South is limited to about 20mi.

SFO and OAK are about 20miles south and east, SJC is 50miles south. I’m seeing the same results with the official FlightAware antenna as I was with my pigtail (Nooelec) cantenna, which is mildly annoying. I’m running the new FlightAwarePro Plus stick with the built-in filter.
As I’m located in San Francisco proper, I’m wondering if I would see any benefit from using an external 1090 filter even though the FA Plus stick already has one built in. Wanted this communities thoughts.

My Antenna is located in a window on the top floor (3rd floor) of our building with line of sight in three directions. I’m using a 9ft. cable to connect. We’re about 40 feet up with mostly unobstructed views North and West.

Any help would be appreciated!

The short answer is yes, the filter will help. It’s better at blocking strong interference from other transmitters like cell towers, tv and radio broadcasts, etc.

YES. In my setup, adding an FA filter to ProStick+ (blue) did improve performance.
The improvement is significant where strong RF Interfering signals (such as Cell phone) are present.
The improvement is negligible where RF Interfering signals are absent or weak.
Improvement is therefore location dependent.

However as FA filter is not costly ($15.50 only), it is worth trying.

Good deal. Thanks everyone; the filter is super cheap, so I’ll just try it out and report back. I was afraid of causing more problems doubling up, but it sounds like it’s all good.

How close are you to the (estimated) 2MW of RF coming off Sutro tower? Yes, the FlightAware filter will help. Probably, a cavity filter would help more.

Let us know what happens–

bob k6rtm

Sutro tower is about 2 - 2.5 miles away to the south west. Any recommendations on a cavity filter? Haven’t heard of this before.

Look around on the forums for informaton on cavity filters – the FlightAware filter uses more or less standard components, things you can identify as inductors and capacitors. It does a good job, but the “skirts” on the filter, how steep it attenuates signals away from the passband of interest, in our case 1090 MHz, aren’t very steep.

Cavity filters, on the other hand, are plumbing voodoo with rods and wires in a very sturdy metal enclosure using cavities of particular sizes as filter elements. Skirts on cavity filters are very steep. Cavity filters are also more expensive, but if you have a lot of RF close by, they can be about the only answer. In comparison to other filter types, cavity filters have low insertion loss and steep skirts. SAW filters have pretty steep skirts, but much higher insertion loss.

See, for example, http://www.radioforeveryone.com/p/test-ads-b-cavity-filter.html for some pictures of a very nice commercially available cavity filter for ADS-B. Shiny metal, bits of teflon, screws and rods that don’t seem to do anything, but they do… The person who put up that page didn’t really need what a cavity had to offer. Usually when you decide you need a cavity filter you’re at the tearing-hair-out stage (or thinking of ways to disable that GSM tower 400 meters from your house, while making it look like an accident).


bob k6rtm