The rule of thumb is that electronic components half their life span for every 10C rise, so with overnight temp not dropping below low 30’s (and this is the cool season), a fan should extend the life of the Pi several years. Like the ferrites, even if is doesn’t help, it won’t hurt.
The planned extension cable is to reduce mechanical strain on the connectors.
so - just your graphs are missing now 
Thanks for doing this!
(and now for the picky questions…)
From your spectrum plots, I’m surprised at the amount of out-of-band energy with the interdigital/cavity filters.
My bet – it’s signal leakage around the filter, such as through the plastic SDR shell. When I’m testing filters, LNAs, other sensitive RF stuff on my bench, I put the mess-to-be-tested in an enclosure made of fine mesh copper cloth. Makes a big difference, particularly with SDRs that have an internal AGC action.
You could try wrapping the RF part of the signal chain (SDR, filters, etc) in aluminum foil (copper would be better) connected to the outer braid of the antenna feed, and the USB shield.
Another approach is to put the whole lot (filters, SDR, Raspberry Pi) in a metal enclosure (metal box or a copper mesh enclosure) with a SMA connector on one end, and Ethernet and power on the other. The rule of thumb is no openings electrically larger than 1/4 wavelength of the highest frequency you’re dealing with. That’s 2.5cm for 3 GHz, pretty big. I like to go as small as I can, with copper mesh that has about 2mm spacing.
cheers
bob k6rtm
pleasure! thanks for reading my post
hello bob,
you are fully right! there must be a little leakage somewhere in the antenna chain - maybe dongle or the tiny cables that connect between filter and dongle. very good idea with the copper mesh or aluminum foil - i will keep that in mind for the future.
on the other hand the test was meant to show the differences in my real world setups that i use to receive ads-b data. as my standard setup is without all this additional shielding - the test shows the behavior of all setups exactly the way i would use them 24/7/365. an additional point is that i used a quite high gain ‘50’ - but this is the gain that is next to ‘-10’ what i’m using to get most aircrafts/messages at my site.
up to now i have zero experience with all these measurings you are doing since a long time. i have no signal-generator, oscilloscope or analyzer 
but i ordered the lime mini sdr and hopefully then can do things like the above mentioned - at least at an amateur level. so all your tips about how to measure will then come handy for me
what do you think about this little thing? LimeSDR all in one lab on Vimeo
cheers
tom
Ok, so I managed to run a small rtl_power script to create a heatmap.
The feeder and FA antenna are located in an attic with a clay tile roof.
The first heatmap shows the FA antenna with the blue dongle and a cavity filter (sold by sysmocom.de)
The second shows the FA atenna with the orange dongle and no filter.
Now I am bit unsure what to make of the results.
E.g, the filter filters out a lot over the whole range, but has that any effect on the 1090 reception? It seems that with the filter, the signals close to 1090 are deeper in color, so does that mean reception is better?
you should have used the opposite configuration: blue dongle standalone vs orange with cavity vs orange standalone!
anyways you see that the cavity wipes out most of the noise and this should result in more messages, slightly more aircrafts and slightly more range. the nearer the noise (at equal power) is to 1090mhz the bigger the problems for the receiver are …
My aim was to find whether my location has a lot of noise or not, thats why I used the orange dongle without any filters.
The first plot is really just a byproduct of seeing if I could get it to work.
Neverteless, I compared them, and stumbled upon the difference in colour intensity around 1090Mhz, wondering whether that means that with the filter the receiver picks up more signals,even though there is little interference in frequencies close to 1090.
The heatmap plot scales the intensities to the strongest signal it sees, so you can’t do a direct comparison.
Ah, and with almost everything filtered out, the 1090Mhz ends up being strongest .
Or almost, there is something around 945M, that does not get filtered out, even with the two-filter-combo.
Anyway thanks a lot for the replies.
the color-intensity does not mean much. but i’d give the orange-dongle/cavity combo a try - maybe it gives better results than with the second filter (blue dongle) in antenna chain …
Yeah, in theory the cavity filter should be enough or even a little better.
I think I’ll give a try, even though the current combination is the result of careful, thorough and extremely unscientific ad hoc testing done a year ago. 
Edit:
To conclude, the results of the following dongle/filter combinations.
There seems to be not much difference between orange + cavity and the blue dongle.
The blue + cavity filter seem to filter out almost everything, but maybe if one increases the gain, those signals
are picked up again? (All measurements had a gain level of 29.7)
really interesting and matches my experience with the sysmocom filter some time ago - it has a little more insertion loss and attenuation is not as good as the jetvision 3-pole @920-960mhz.
because of that behavior it makes sense to use the sysmocom cavity in combination with blue flightaware stick!
would be interesting to see the above 4 plots for 24-1700mhz …
thanx for sharing
Hi biekerc and TomMuc,
I get this error when running heatmap.py. Can you help?
Pi@Test:~ $ ./heatmap.py scan.csv scan.png
Traceback (most recent call last):
File “./heatmap.py”, line 3, in
from PIL import Image, ImageDraw, ImageFont
ImportError: No module named PIL
Pi@Test:~ $
scan.csv is in my Home directory as is Heatmap.py. I have Python 3 installed and rtl-sdr.
maybe???
sudo apt-get install python-imaging
Thanks both, that worked 
interesting to hear … and where are the resulting graphs
cause this was the idea of the thread to see/discuss what results others have - not just mine …
Maybe tomorrow. Now I have it working I need to find some filters I had a couple of years ago
The resulting graphs are here:
hahaha - exactly! i’ve totally forgotten that we already talked about - and that was the starting point for this thread