I assume you mean this setting:
This is indeed disabled by default. Never tried activating it.
There isn’t much point unless you use planeplotter. That has a couple of interesting features like the beamfinder thing that uses the locations of radar heads and their rotation rates to work out a position using timing. They’ve also added a form of mlat for mode a/c aircraft, but I’ve not tried it out to see how useful it is since I find using planeplotter not worth the hassle.
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Radarcape/AirSquitter can feed to PlanePlotter, but i do not have it installed
To compare apples to apples, note that the rate of messages in Europe is much higher than the one in US, because of different interrogation rates.
The EU uses more “ATCRBS/Mode S all call” while US uses “Mode S discrete interrogation” (directed at a specific Mode S transponder equipped aircraft).
Mode A/C raises the number of msg/s in a useless way, since it is not useful for MLAT. Mode S interrogations are generated at a rate of 50 times per second or 50 Hz pulse repetition frequency (PRF) and approximately 230 Hz for Mode A and C interrogations.
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As far as i see most of the users replying to that thread are in Europe, aren’t they?
I think @SoNic67 's contribution is useful to those of us reading in other parts of the world. When I first read the earlier comments about seeing message rates around 1200 a second with around 60-70 aircraft, my first thought was “what’s wrong with my setup?” - in the last seven days, the highest message rate I’ve seen was 600/sec with 100 aircraft.
After thinking about it I remembered this thread: https://discussions.flightaware.com/t/overload-on-the-use-of-surveillance-radar/76593
Clearly, the message rate is significantly influenced by the number and operating mode of the SSRs interrogating aircraft visible from any particular location, so it isn’t a particularly useful parameter for comparing setups unless they are looking at the same patch of sky.
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I did not want to say his contribution is not usesfull. I am sorry if my statement could be misunderstood
Are you using a Radarcape device or an airspy?
With a general stick (e.g. the Flightaware stick) the rate is lower and it can be seeing 600 with 100 aircraft. It highly depends on your location.
As far as i know you cannot add the MLAT aircraft from the map but count ADS-B only.
The Radarcape devices do have a significant number of MLAT aircraft once they are connected to the Jetvision network
Friend of mine is using a regular Raspberry with the blue FA stick
He does have higher message and position rates, but a significant lower number of aircraft.
EDIT: My current view. There are 65 aircraft with ADS-B positions, but 81 with MLAT positions. So 16 aircraft are on the map coming from MLAT only, i would assume these are not counted in the messages/frames
Average rate is at approx 950 with peaks up to 1300:
Highest rate i’ve seen so far was around 1100 with peaks to 1400 while 92 ADS-B aircraft in range.
Another interesting thing is that the usage of the Radarcape devices does not have that significant impact to the positions reported on Flightaware. The difference is less than 10%
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Sorry if I sounded annoyed - I sometimes forget that many of the contributors here don’t have English as their first language 
I’m using an Airspy mini - the 100 aircraft I quoted included MLAT (to be more precise 17 MLAT, 82 ADSB and 620 messages/sec). The point I was trying to make is that most of us shouldn’t be worried if we aren’t seeing peaks around 20 messages per aircraft per second (assuming 1200 messages/sec and 60 aircraft) - in a lot of environments, aircraft just don’t transmit at that rate.
I’m sure someone will tell us if MLAT aircraft need to be included.
I’ve realised that I need to do a lot more reading to understand how ADSB transmissions and SSR interact here in Australia. From what I’ve read so far, I think an aircraft transmitting just ADSB messages, with no SSR interrogation, transmits at an average rate of 5.6 messages per second.
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I am not the expert in that, but from my understanding MLAT are coming from an MLAT server which collected the information across multiple receivers.
I don’t think these are counted in the messages. I would assume these are already decoded and coming via network.
Maybe an expert (@wiedehopf ?) can bring some light in that topic.
This is a long term graph with of 24 hours an sample average on frames of 60 seconds. Peaks are not shown. Below the ADS-B aircraft.
EDIT: Currently i have 85 ADS-B and 114 MLAT on the screen.
Frame Rate is at 1000 with peaks to 1500
So i am coming more and more to the conclusion that MLAT is not counted in the frames.
Looking at OpenSky-Network the frames and messages do match and there are also no MLAT counted.
MLAT is displaying also aircraft which are far beyond my range for this direction, like these two. 250 km distance, but i do have a range of 200 km only to the north due to obstacles.
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Guess you are right. Seeing all these numbers make me worry that something is wrong with my settings. I think especially newbies like me are always comparing the messages rate/ planes etc with the top. I have to admit it is hard not to 
As for me I am trying to have the best results and always struggling what I can do more/better. Next week I will be mounting my antenna (at least) and thinking about buying an airspy.
I think it’s really important to understand that the different numbers cannot be compared to a different station not beeing on the same location.
All locations are individual with different conditions.
I am playing around sometimes with heywhatsthat on my location. Moving by 500 Meter can result in a complete different range ring (and therefore different results).
That is my second device, a Raspberry with 3 dB Antenna, FA Stick and Piaware operated Indoor with priority to the north. Now you could think by simply doubling the numbers you can reach the Radarcape performance (70/1000), but that is not working that way
I know that as well. And I also know that just changing to a Radarcape would improve my reception. My range to the north is obstructed ort better I hardly see anything 
It may or may not. As stated several times here it depends on your environment.
Pretty likely, but not guaranteed, at least from the message rate (however important that is)
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oeps, sorry typo, should have been I know changing to Radacape might improve my reception.
Sorry for misleading you.
Here we are again with the non-native speakers.
I am struggling also pretty often.
So looking at the graphs… why do you have such a high value for tracks with single messages?
Message rate for the last 48 hours
A Radarcape is not a guaranty for a better range or message rate
Dark grey is Radarcape, light grey is Airspy R2
@EmilK
are you talking about my graphs? If yes I don’t know
@Dutchyb
Not really your graphics, those from @foxhunter.
Anyway, looking at them it seems to me that the gain is too high or some interferences are playing a role and are interpreted as single messages.
Do you have the possibility to install a cavity filter? A spectrum analysis would be helpful to see if you have some “bugs” that are ruining your recepe 
(Spektrum with an rtl-sdr receiver as example).
These are from my indoor Raspberry with FA stick, not the Jetvision device. I did not look at it further. It’s just my backup receiver for these sites not covered by AirSquitter.
Changing the gain does not have any impact on these.
That’s exactly a statement i made earlier. If you are limited based on location these devices can’t produce “miracles”.
Even the blue FA stick deliver the same range (at least at my location)
Your ADS-B Tracks seen with these peaks are looking strange to me.
@foxhunter
Those peaks are the adbs service restarts or unit reboots. I settled down at a gain of 14 but I tried to play with different gains a different voltages to see where is to sweet point. Actually the gain of 14 is just under the optimum (from my observations) and a value of 15 a just a little too high so I tried to work at 4 to 5V to see if I can hit the jackpot but I believe that the LNA isnt that linear… so gain of 14 will stay until I get the new LNA.
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