Cavity type resonator bandpass filters typically have lower insertion loss compared to ceramic loaded resonator or SAW filters. The cavity filters have better selectivity than lower Q types.
I’m using a homemade 3 resonator interdigital “cavity” BPF which has a measured 0.5 dB loss at 1090. It has 55 dB loss at 1030 MHz, and over 80 dB rejection at 960 MHz.
The MCL ceramic loaded filter I’ve tried has over 1.2 dB loss including a board and two SMA connectors. The FA filter loss is around 1.5 to 2 dB. Either is a fine value for the money.
I bought mine from sysmocom.de, they have 2 versions for ADS-B, a 40MHz wide version (€23.80) and a 8MHz wide 7-pole version (€41.65). The gsm-900 band signals at my home are so strong that my spectrum anaIyzer detects them even without a probe connected to it.
This looks very interesting. I did not want to go through the ordering process just to find out the shipping cost. I also could not find a way to remove the VAT, as I’m not ‘blessed’ by that.
Oh, well… nobody uses the ceramic filters “naked”. A LNA stage is used in front of them, which makes the insertion loss moot. Like I said that is relevant on the emitter antennas.
And no, the fist stage in a LNA won’t be overloaded, not unless you are at couple feet away from the GSM antenna.
Those of us in high signal areas don’t go “naked.” My cavity filter is between the antenna and the LNA.
In that configuration the filter loss adds directly to the Noise Figure.
As is typical of resonator filters the RF connectors are at DC ground which certainly helps keep the LNA “alive” here in thunderstorm country.
When I started with the hobby about 3 years ago I ranked about #450 globally, after having added the cavity filter I ended up around #200. Switching to a Pi4 with an Airspy mini and LNA earlier this year had an even bigger impact…
I’m taking single steps ~ monthly to judge the results.
Last incremental upgrade was in September when I lowered the system NF from 5 to 2 dB.
Next steps will be to a Pi 4 and then a 20 MHz sample rate on the AirSpy.
After that…?
This might do the trick.
Has built in LNAs, so combined with 6 airspys and several pi 4s to handle them, you could have quite a nice system. Not sure it would be cost effective though.
It doesn’t have a price on the website, though it’s probably not cheap being aimed at the professional market. It might attract a bit of attention putting that on the roof.
Adding 24MHz should be very easy. Let me prototype the code. @wiedehopf: Would you like to do some testing/adjustment? I don’t have the required setup now.
Update: I pushed a new version with a few optimizations and the new -m 24 for Airspy R2. The other options should work exactly as before.
Please test and report. Thanks!
I don’t have a Pi4.
But i will test with my Pi3 and the airspy mini that is connected.
Oh which Pi are you compiling on?
When i tried compiling with the default gcc on Buster, the performance of the resulting binary was terrible on the Pi3.
Using gcc6 fixed that problem.
Just as a heads up.
Edit: Just trying the new binary, seems to run fine.
