Hi,
I am new to this and am trying to tweak my gain to get the best I can. I currently have a PiHut 1090Mhz antenna in my attic, 5m of cable and then a Sawbird+ connected directly to my SDR dongle. I seem to be able to track lots of flights (up to 80) with lots of positions and distance of almost 200nmi but sometimes the message interval varies especially for position. For example a plane can go from updating every few milliseconds to more than a minute and its distance has not changed. I have been looking at the graphs and have noticed that no matter what gain I set my noise is always higher than my weakest signal and after reading other posts on this forum I am not sure if that is correct and if its not what I need to change.
An antenna in the attic (which is also my setup) probably has dead zones due to reflections of the received signal. Tweaking gain won’t help with that.
Is it better to have a higher or lower minus number for weakest signal? Is -34 better than -25 for example. I know -25 means the signal is stronger I am just not sure if not having weaker ones makes a difference or means I am missing stuff or simply the further ones I am picking up are coming through clearer. I only get the higher weaker ones when I decrease gain so I think I know the answer I just want to check.
Yes, -34 would be better than -25 provided the highest value stays the same.
The difference between the highest signal probably around -1 and the lowest is your dynamic range.
You want that difference to be as large as possible.
It will be limited however by the hardware (dongle) you are using.
All the rtl2832U based dongles will have similar dynamic range. They are all 8 bit devices.
There are higher performance devices available such as the AirSpy mini or AirSpy R2 which are 12 bit devices. These give better dynamic range but at a greatly increased price. Unless you are aiming for ultimate performance an rtl2832u based dongle will be fine.
Lots of us started with similar equipment. We learn, tweak, adjust and refine our systems, swapping parts or software settings, hopefully better, and not always. Make a change, see what happens. Wish I had kept a log of my journey through all the changes I made. Have fun, enjoy the successes, learn and understand the why’s where you can. Best Wishes.
Gene
Ok thank you. I was considering the nooelec v5 but if that won’t be much better then I will continue tweaking what I have? Any tips on what to lookout for?
Personally, I prefer the v5 over the mini as it has an sma connector rather than the mcx. It’s a better option when you want to add filters and experiment with different antennas.
The problem you are likely to encounter is the fact that as you improve your antenna setup then the larger all the signals get. The unwanted signals when they exceed a certain threshold start to cause problems in receiving your wanted signal and you start to need to filter them out. That’s part of the fun
Every part in the chain has an influence on how well all our systems work. In general, one wants a high gain antenna mounted as high as we can above things like other buildings and trees. The elusive clear view to the horizon. Very few of us have that. We desire the lowest loss cable to transfer all the signals down to the receiver dongle. The receiver then has the ability to extract the desired ADS-B signals into the digital result and transfer via a direct connection or good USB cable into the appropriate computer, with the Raspberry Pi’s being the common one used by most of us. The software Operating System (OS) and demodulation/display/internet interface all play a part, and there is no perfect combination of the above sadly.
However, you can start with a Raspberry 3b or 3b+, download and install a customized OS from FlightAware or other sources you have a good start. The receivers mentioned above are all good ways to start. Try to get one with an onboard filter and LNA amplifier integrated into the receiver.
Antennas and cables are probably the most important aspect, and probably most of the money spent goes into those components. My system is up at the top in the attic, and yes, I do lose some signals with having the roof over my head. And yes, rain does decrease the range. There are always compromises made in any system. You may need a filter if you are in a noisy RF area.
No specific recommendations. FA has a blue dongle receiver that works very well, and their antenna is used by many of us out here. Keep water out of your cables, a good WiFi or cable connection and you will have a good system. Watch the conversations here and they will give you ideas to follow. Definitely install the Graph1090 package, just put that word in the search up above and it will help you understand how your system is working and point you in the direction of possible improvements. The point is to have fun, improve the system and yourself.
Gene
