Looking at my screenshot, you’ll see the noise level exceeding the weakest signal strengths.
My setup is an RPi 4, Nooelec RTL-SDR with RTL820 chipset, homemade dipole antenna going through an ADSB LNA and filter.
Improvements made over time include:
Changing from RG6 to RG58 cabling - not sure if this made any change as it was done in conjunction to moving to the dipole antenna.
Changing from co-colinear antenna to dipole antenna - this resulted in more messages per second and greater average coverage area
Installing LNA and filter - this resulted in significant coverage increase
Reducing cabling length from 20M to 5M - this resulted in me dropping gain from 49 to 38dB
Optimising gain and PPM settings - PPM resulted in slightly more messages / second.
Any ideas on what else I could do to move the noise signal away from the week signals?
You might want to lower your gain with 1 step in order to get below the 5%. The 5% is a generally accepted number for the number of strong mesages.
After lowering monitor the traffic for some hours, up to a day and see if this reduces the noise ratio for you.
Only thing I can think of is using a more sensitive antenna. I have this one:
This improved my numbers ( not much additional range) since it enabled me to get additional weak signals further away that are not catched with a 5.5 dB Flightaware antenna.
Range on this set is around 230 NM, due to the location that is about the maximum I can achieve
Don’t worry too much about this, it’s not a true measure of receiver noise. That figure is an approximation at best, as it includes anything that’s not a decoded message, which will include any garbled or undecodable messages.
If you want to estimate what your receiver noise is like, it’s probably better to run something like sdr# and have a look at the spectrum to make sure there’s nothing egregious.
If you are trying to cover all the bases on Noise, I would consider replacing your 5m length of coax with a well shielded cable such as LMR400. It may not be your noise source but it’s good practice just the same.
If the Nooelec RTL-SDR has plastic case, consider putting it in a metal case to shield it a little from noise.
My location is so noisy, I need to use cavity filters. The FA filter is an alternative and much cheaper.
As @CraigWoodThomas better cabling may provide better shielding in the feed line.
RG58 is not a microwave cable. If you had good quality RG6, that would probably have a lower loss.
Best to to think of noise in two parts: in-band and out-of-band noise.
Out of band noise can be filtered, in-band can’t.
In-band you are stuck with, so all you can do is improve your signal to improve your SNR.
Without a doubt, more antenna gain gives the best return.
While there is nothing wrong with a dipole, if it performs better than a (multi-element) collinear, then the collinear wasn’t very good.
One question - what is “your” greatest interest? By the sounds of it, you are chasing the weak signals / greatest range?
If you want the max range and are prepared to sacrifice some strong local signals, then don’t chase the “5%” target - that’s for people chasing the highest message count, not the greatest range.
I’m not necessarily chasing distance. I’m more interested in quality reception and moving the noise away from the low strength signals. Removing as much of the gaps in the signals I can receive as much as possible, if possible.
My move from collinear to dipole increased my message rate, increasing my overall average distance but maintaining max distance.
I’ve since lowered gain by 2dB and noticed a slight improvement in local coverage with no drop in max range.
The ideal arrangement for low noise would be having the antenna outside, with the LNA/filter immediately below it and before the coax to the receiver. This will give a better signal to noise ratio than having it after the coax. With RG58 this might be noticeable as that’s not ideal frequency use, but with a better coax it might not be significant.
ADS-B is not a protocol that is limited by signal strength normally since the transmitters are quite powerful, so as long as the antenna is in the clear, you should be able to receive out to the horizon excepting any local obstructions.
When you get it right, that antenna works really well, but if you read through these threads, very few perform well.
As discussed elsewhere, one of the greatest obstacles to building a coax collinear is knowing the properties of the coax you are using and how that changes the construction.
CC1090/8-P This one is in stock, has 1 dB less but I think it will be on par to the 11dB model.
Shipping to USA can be calculated on check-out, they also cater express delivery but that can be expensive. I did it once , the express cost was half of the antenna cost
It does deliver to the USA, enconomy schipping, delivery time between 10-40 days depending on customs. I have the day off, have been flying my GA aircraft this afternoon, landed just before the thunderstorms rolled in tomorrow is another busy day for the head of the household, doing chores that need attention from the pilot in command
Curious as to what the “GA aircraft” is. Know what you mean about thunderstorms. Had a serious flash/bang event last evening with a whole lot of rain blowing in at 20mph from our North across the open water. Stay safe with the wheels up.
tomorrow is another busy day for the head of the household, doing chores that need attention from the pilot in command