Same Setup/location total different results

[flieger28]

Hi, i have 2 Pi setup on my roof. Maybe 7 meters apart. They both have an Flightaware Pro (orange) stick and both have the same typ of antenna.
Right now one shows me 45 Aircraft (33 with positions). This Raspi runs dump mutability (Gain35)
The second one shows only 14 Aircraft ( 8 with positions) This Raspi is running dump_fa (already used the Test scipt, the lowest Gain, 20,7 had the best result)

How can it be that there is such a huge difference? I Also tried a different Antenna from the same type, as i had one in spare. Same Result.
Is there something i oversee?
Before the Pi also had dump_mutability running with the same bad result.

[flieger28]

Here is one of the Test-Script results

gain= 49.6 messages= 5 positions= 0 planes= 1
gain= 48.0 messages= 3 positions= 0 planes= 0
gain= 44.5 messages= 3 positions= 0 planes= 0
gain= 43.9 messages= 3 positions= 0 planes= 0
gain= 43.4 messages= 54 positions= 1 planes= 1
gain= 42.1 messages= 213 positions= 3 planes= 1
gain= 40.2 messages= 189 positions= 6 planes= 2
gain= 38.6 messages= 204 positions= 7 planes= 2
gain= 37.2 messages= 54 positions= 0 planes= 4
gain= 36.4 messages= 246 positions= 13 planes= 3
gain= 33.8 messages= 122 positions= 2 planes= 3
gain= 32.8 messages= 4 positions= 0 planes= 1
gain= 29.7 messages= 492 positions= 17 planes= 7
gain= 28.0 messages= 475 positions= 23 planes= 5
gain= 25.4 messages= 2457 positions= 148 planes= 14
gain= 22.9 messages= 3446 positions= 224 planes= 15
gain= 20.7 messages= 6602 positions= 483 planes= 19

[abcd567]

Swap the 2 Pis and see what happens.

Current:
Location1+antenna1+cable1+dongle1+pi1
Location2+antenna2+cable2+dongle2+pi2

After swap:
Location1+antenna1+cable1+dongle1+pi2
Location2+antenna2+cable2+dongle2+pi1

[flieger28]

Could have figured that out for myself
Will try that tomorrow

[jonhawkes2030]

Have you looked at the “do I need a filter posts”?
The gain setting looks pretty low.

[flieger28]

@jonhawkes2030

Have you looked at the “do I need a filter posts”?

The gain setting looks pretty low.

But shouldn’t that belong to both installations? The other one on the same roof works fine, also without filter and with a gain setting of 35

[jonhawkes2030]

Correct. The filter is something to look at later.

Are the RPIs or dongles close to each other? They both generate noise. I have my RPIs and dongles in metal cases. I found it reduced noise.

I am curious as to why you stopped the gain testing at 20db. I would have continued until the reception dropped.

[flieger28]

I used one of the scripts provided here in the forum. And that one stopped at 20.7
Optimize-Gain-dump-fa-on-Raspbian-Jessie

Starts like this, and as I’m not a Linux “pro” i decided better not to mess with the script

  #!/usr/bin/python2
import time, socket, subprocess, fileinput, os

measure_duration = 62  #duration of one pass, seconds
ntests = 5   #number of tests
gains = "20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6".split()
#gains = "20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4".split()
#gains = "36.4 38.6 40.2 42.1 44.5 48.0 49.6".split()

[abcd567]

@flieger28

FULL RANGE of gain (0.0 to 49.6) in the top gain line. All partial gain lines are commented out.

#!/usr/bin/python2
import time, socket, subprocess, fileinput, os

measure_duration = 62  #duration of one pass, seconds
ntests = 5   #number of tests
gains = "0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6".split()      
#gains = "20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6".split()
#gains = "20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4".split()
#gains = "36.4 38.6 40.2 42.1 44.5 48.0 49.6".split()

[flieger28]

Will try that.
I just put the better performing Pi to the position of the bad one.
He performs better. The bad one received 12 planes. The one i put now on the same antenna and FA Stick get’s 55

[flieger28]

I guess i figured it out. In one of the Topics here i found out that it would be smart to enlarge the base of the antenna. Because the Antenna is on the chimney and that part is out of metal, that should be the reason for the better results. Just running the test script for the other pi, to see which gain ist best for that one.

For Pi (bad) 20.7 seems best

gain	Messages	positions	planes
49,6	2	0	1
48	2	0	1
44,5	318	0	2
43,9	330	0	3
43,4	380	0	4
42,1	300	4	3
40,2	55	1	4
38,6	23	3	2
37,2	54	9	1
36,4	9	0	2
33,8	308	0	4
32,8	259	0	4
29,7	1819	30	10
28	1318	13	8
25,4	2392	60	12
22,9	3270	154	13
20,7	4114	168	17
19,7	2903	100	15
16,6	3128	103	13
15,7	4001	128	13
14,4	3283	101	10
12,5	2341	77	9
8,7	1111	26	10
7,7	628	16	5
3,7	157	2	3
2,7	132	4	3
1,4	13	0	1
0,9	90	0	1
0	54	0	1

[flieger28]

After i put the “bad” Pi also on the chimney

[evangelyul]

regarding the gain test.

1. pick the time with most traffic for your area eg day/noon with more that 10 aircraft.
2. remember to re-run the test with ANY change in configuration receiver, dongle, antenna, software.

[flieger28]

I’ll tried to improve the receiver further.
Cost 2€

[flieger28]

Also the range is greatly improved

[jonhawkes2030]

Consider @abcd567 's post on tuning the antenna length for better reception

Episode 2 of Improving DVB-T Magmount Antenna.

I have been using the DVB-T’s magmount whip antenna after trimming its removeable part to 67mm length as shown in the image 1. Recently I opened the base of the magmount antenna (images 2, 3 & 4). I noted that there is about 15 mm of vertical metal part between screwable whip and feed coax. This hidden vertical metal is part of antenna, and hence antenna length should be measured from the bottom of this part where coax is soldered to it. Since this part is 15 mm long in my antenna, my magmount…

A tuned antenna is similar to adding a band pass filter without adding any loss.

Be aware of electrical interference. I have one device in our bedroom, behind a dresser with a TV on it. When the TV is on, reception noticeably decreases. This is with a cavity filter on the coax too.

[flieger28]

Would be not so smart to cut this antenna. It is one that is allready made für 1090 Mhz and it performs well

https://www.ebay.de/itm/ADS-B-Mini-Magnet-Antenne-1090-Mhz-mit-SMA-Stecker-und-3m-RG174-Kabel-ADSB/202212013318?hash=item2f14c67506:g:e9gAAOSwOdpXzDcL

[jonhawkes2030]

I would not believe them. I have seen hundreds of the same exact antenna advertised for particular frequencies.
It looks exactly like a few I have.
I did a quick search on RG174 and the specs, on two sites, say Maximum frequency 1Ghz.
How does it look on an antenna analyser?

[flieger28]

Maybe you are right.
But i also have a regular DVB-T Antenna which came with one of my first sticks. Also i cut this one to 6,9cm it comes nothing near to the results of the antennas which i posted.

This is the Data of one of my Pi with the Antenna from the Ebay Link
I’m pretty satisfied with that results.

Unfortunately i don’t have the knowledge nor the equipment to check if the Antenna works like advertised.

[jonhawkes2030]

If it works well then stick with it.

Your recent upgrades seem to have made significant improvements.

Are you using Mutability dump1090 1.15?
The newer FA version seems to get more aircraft, from memory.
It also has more aircraft image types.