Optimize Gain - which would you chose

Makes sense. Less gain, less data received, less data available and/or valid for MLAT calculations, less common planes seen by nearby receivers, therefore no sync at all, or sync with fewer receivers.

Hi all
Been using optimize-gain.py for few weeks now on n off
but after getting correct figure to use and set it couple days later figures have all changed again as if it is constantly changing the gain setting
is this correct ?

john

You should not use that gain script anymore after finding the optimal values.
Even if that “optimal” might look like it changes, based on your local and far-away traffic.

cool thanks SoNic67

john

I lived in a location where i can barely get aircraft over 120nm and my antennas where 10 metres high since changing location my antennas are actually nearly 9 metres high and the minimum i get is around 240nm and furthest i got so far has been 515nm even when i use to go adsb mobile some locations could get over 100nm but there was one location that i use to get over 300nm with a 5db antenna…

Regards Lino…

@linofalzon

Range mainly depends upon terrain arround antenna location which in turn depends on geographical location. Incresing antenna height also increses range, if antenna is surrounded by tall buildings/trees/hills. Once antenna is above these obstructions and can “see” horizon in all or most directions, any further increase in height brings very little improvement.

You can find your maximum reach at each of different locations (which you have mentioned in your post above) by method described in the FIRST POST of this thread:

What is the Maximum Range I can Get?

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ok, i need some opinions. i have just installed a minicircuits splitter and a second RPI3B and am running a second site in parallel, the antenna is common as are all cables. my hope was to optimize the gain by using a single target and looking at two data sets. (i have a flightaware antenna and a rtlsdr 1090 lna at the antenna (fixed gain of 27dB). this is mounted on the roof. i then have 105 feet of LMR400 (running thru a lightening arrestor (outside) and a minicircuits bias-t (inside the house). the output of the bias-t is feeding the splitter. there are two RTL-SDR v3’s. i estimate about 9dB of loss from cable,lightening arrestor, bias t, splitter etc. the spec for the spliter is -3.6dB, insertion loss and split loss per side)
the “reference” side gain is set to -10. the “experiment” side gain is currently set to 42.1 AND has a 3dB pad between the splitter and dongle. (so, the experiment side has a gain of 13.9dB less than the reference side)

when i get reference side RSSI values of -3dB or less then i see approximately 13.9dB less in the experimental RSSI values than the ref side…so far so good. now (finally) here is my issue and where i need opinions. when the reference side RSSI is, for example -1.9dB i see experimental side RSSI values of -2.3dB. earlier today i had a plane come by at about 2000 feet and only 1/4 mile away (the engines were easily heard). i saw a reference side RSSI of -1.5dB and an experimental side RSSI of -1.6dB
is my antenna over-driving the LNA?
opinions or alternate explanations are very welcomed

I’m running a homemade spider antenna with the rdl-sdr LNA and the rtl v3 dongle.

Gain set at 20.7 so i don’t get overloaded by airplanes flying close by.
Not much cable though. On the quiet end I get messages with RSSI around -34 dBFS.
When i increase the gain to 22.9 the faintest signals i get are around -32 dBFS.
So i figured i’m still receiving mostly everything far out but very rarely get overloaded when small planes come buzzing by close. Back to your setup though.

Setting at -10 means you don’t know what your current gain is as the receiver can switch it around as it chooses. So hard to do comparisons.

Just do the experiments with a gain of 28 on one station and 38 on the other station so you don’t get that close to saturation. Maybe even lower.
If the signal peaks are overloading the dongle the RSSI reading is gonna be off.
I would only compare readings below -3dBFS. Otherwise the receiver with the higher gain may already be losing the stronger messages so the reading will be same while the signal is actually stronger. (You are getting quite a few messages from each plane, some messages will be stronger than others)

You should also really compare the number of messages received from the same target on the different receivers. It will show you much more than the RSSI number, that’s a rough reading anyway and can fluctuate quite a bit.

very true. can you post some comparison charts ? :grinning:

Not sure what you mean? What do you want to see?

something like the following (if you have it) - not a thorough check just a quick one
during high traffic period.

signal%20level

I use a v3 with only the jetvision.de antenna (~70e) elev 350 feet amsl, 4m coax 50ohm
no LNA.
seems with every lower setting there is a significant drop in aircraft count and range
which is not the case with prostick and cantenna on the other rpi same place 4m coax 75ohm sat coax.

Oh sure this is what mine looks like:
dump1090-localhost-signal-24h%20(1)

As you see i keep my peak quite a bit higher. As long as i don’t see dotted lines of low level airplanes buzzing by one or two miles away i won’t decrease the gain. Mind you that is only the occasional GA aircraft mostly on the weekensds or every 3 days or so the police or rescue helicopter.

Which jetvision antenna do you use they sell quite a few?

thanks @wiedehopf

Is the SCO-1090.

Flightaware Antenna (in window) + 30 cm pigtail RG316 + FA Filter + Pro Stick
Gain =48.0

image

thanks @abcd567

what is strange is similar performance between the v3/fa-filter/jetv ant/cable 50ohm and prostick plus/cantenna/cable 75ohms but… with vastly different gain settings.
v3 is set at max and prostick at 37.2. (I try to stay close or on the red 3dbfs line.)
so is cantenna more sensitive or what ?

Please see this also :slightly_smiling_face:

The cantenna is not more sensitive.

The pro stick has a LNA with 17 dB or so gain built in before the actual rtl chipset.

I would use the pro stick with the good antenna to be honest :slight_smile:

After seeing the “blood stained” :slightly_smiling_face: graph, few minutes ago changed gain to 38.6. Will have to wait for an hour to see result.
Please see RSSI column at far-right

That many messages above -3dB is indeed impressive :wink:

@abcd567 If you want to check it out i have pushed a new version of the colorized tracks (signalview) that now clearly shows with a change from violet to red if a plane goes above -2dBFS.

Also changed the message display to Messages per second (averaged over 4 seconds like the RSSI) so that you can see if the msgs/s drop when the gain goes above -2dBFS.

1 Like

yes I tried this and strangely enough results were worst :confused:

@abcd567

I thought - maybe wrongly - the idea was to stay at or below the ‘red line’ to avoid
saturation(?) also the blue and cyan lines seldom match let alone blue over cyan
but in my area can’t get more than 70 aircraft at any given time.