Mode C/S

[the_top_pilot]

Lee,

I know this has been discussed before and I know the reasons why not..
I think PAW is fantastic and am promoting it with all my might, the question I then get asked from pilots is does it do mode C (1090mhz tx's). When I say No because of the technical reasons the aircraft  only TX's Ident and Altitude they all say ok but a rough proximity and a height would be great.

The question I ask is are you further investigating a Signal Strength altitude alert?

As for calibrating the signal strength? Do we know the position of your furthest ADS-B signal and where it is in relation us, do we know the signal strength of that input? If that is the case could we not set a percentage of that signal strength to determine other risks?

Steve

[Admin]

Hi Steve,

This is definitely still a todo, but need to do some research first I think.

The real spanner in the works with the strength vs distance approach is that not all transponders use the same transmit power, this was highlighted by one of the forum members.

A little busy on other things at the moment, but will revisit this, I may put it in as some experimental code that users can decide to enable if they wish

Thx
Lee

[the_top_pilot]

Lee,

That would be fantastic I think a warning that prompts us to look for an aircraft if it near us on a similar level in our proximity is a possible life saver.

I would be happy  to help flight test this.

If there was an option on the config page that allowed the user to dial in signal strengths in % for proximity warning to allow for flight tests. I understand the differences in output power of transponders. Is it the airlines have one power and GA have lower output? I am sure to miss Airliners but it is us users in class G I want warning about.

Steve

[tfede]

I Agree with Steeve, here in Italy most of the ULM are euipped with a C mode trasp and it would be a great aid for our flight safety to be at least aware that someone is flying around us.
Please keep me posted, i will be a good tester in case you want to develop something.

Federico

[Moffrestorer]

Of course the better solution would be for all those with only Mode C to carry PAW also, so they can see and be seen via the P3i part of the unit!

[Admin]

Hi All

I mentioned a while back I had some thoughts about using ADS-B transmissions to calibrate the possible mode C/S bearingless target warnings. The table below indicates the signal strength versus vertical difference, and the actual distance

The horizontal axis across the top is the vertical difference in metres at the receiver relative to the transmitter
The vertical axis on the left is the received signa strength.
The table values are the horizontal distance to the transmitter, the value in the brackets is the number of samples (saturated to 999)
So for the actual distance you would use a simple bit of pythagoras using the vertical separation and the horizontal separation.

A pattern clearly emerges regarding the vertical separation, the signal strength, and the resultant horizontal separation.
I can foresee the possibility to generate bearingless target warnings based upon this data, although I am still not convinced on the accuracy, and hence more analysis needs to be done.
Also there are some strange effects which I think are actually due to the surrouinding buildings and trees attenuating certain paths.

By the way the column and row figures of -1 effectively means infinity, so any value between the previous column and infinity.

Code: [Select]

VMETRES 200         400        1000        2000        4000        8000       10000       15000          -1
SIG
  1:      0(  0)      0(  0)  18125( 71)  32466( 74)  34808(156)  49805(857)  58745(591)  71097(500)  38237(  2)
  2:      0(  0)      0(  0)  16902( 42)  26133( 27)  30916( 85)  47134(448)  57822(324)  69916(259)      0(  0)
  5:      0(  0)      0(  0)  16555(104)  22370( 55)  31177(312)  45729(999)  57966(999)  73682(999)  62019(  3)
 10:      0(  0)      0(  0)  16412(340)  17160(961)  27501(999)  34092(999)  49510(999)  62203(999)  37522( 28)
 20:      0(  0)      0(  0)  15878(137)  13577(999)  16069(999)  20867(999)  40066(999)  53633(999)  29838( 36)
 30:      0(  0)      0(  0)      0(  0)  10357(258)  11649(999)  15654(999)  28654(999)  33443(999)  20596( 13)
 40:      0(  0)      0(  0)      0(  0)   9277(147)  10868(999)  12932(999)  19876(442)  19101(524)  10168(  9)
 50:      0(  0)      0(  0)      0(  0)   9246( 41)  10847(563)  12348(999)  16545(218)  15005(186)  11590(  6)
 60:      0(  0)      0(  0)      0(  0)   6812(  7)  10514(236)  11612(999)  14928( 75)  16131( 30)   9851(  1)
 80:      0(  0)      0(  0)      0(  0)   6857(  1)   8637(290)  10498(744)  20155( 13)  12789( 11)  11294(  2)
100:      0(  0)      0(  0)      0(  0)      0(  0)   6247(232)   9106(204)      0(  0)      0(  0)      0(  0)
 -1:      0(  0)      0(  0)      0(  0)      0(  0)   5695(116)   7767( 50)      0(  0)      0(  0)      0(  0)

[the_top_pilot]

Lee

That looks very encouraging.

Steve

[rodent0_2]

Don't want to stand on any ones toes here, but I don't see how signal strength can be reliable, as being a radio ham I know that atmospheric conditions affect radio propagation greatly, just a thought.

[Admin]

Don't want to stand on any ones toes here, but I don't see how signal strength can be reliable, as being a radio ham I know that atmospheric conditions affect radio propagation greatly, just a thought.

Quite right, I think this is the whole problem with relying on signal strength, but this is what the ZAON tools were using, and people claim they were useful, I am not convinced - hence the ongoing analysis.
I think I would look to add this as an experimental feature, and also have this enabled by a flag

I would hope that we see signal strengths go 'ballistic' at close ranges, and hence mitigating some of the other issues

[rg]

are you able to read the ALT info from the transponder response to the ground stations or are you just trying to work it out?

[the_top_pilot]

A warning is a warning this is not to replace the Mk1 eyeball, but if something gives  a warning and you lookout see and avoid then it has done it's job.
In practice I would set to where an alarm was close(ish) for a non bearing contact.

I am aware of signal strengths from my previous Job as a BBC Engineer (33years).

Steve

[Admin]

are you able to read the ALT info from the transponder response to the ground stations or are you just trying to work it out?

The information I have available from Mode C/S is signal-strength and pressure-altitude.
For ADS-B I also have the position Lat/Long

The table I created is information gathered from ADS-B data received by PAW, loading up the values of horizontal difference.

The question is whether this can be used as a lookup table for mode C/S where all you have available is signal-strength and pressure-altitude

[JCurtis]

are you able to read the ALT info from the transponder response to the ground stations or are you just trying to work it out?

The information I have available from Mode C/S is signal-strength and pressure-altitude.
For ADS-B I also have the position Lat/Long

The table I created is information gathered from ADS-B data received by PAW, loading up the values of horizontal difference.

The question is whether this can be used as a lookup table for mode C/S where all you have available is signal-strength and pressure-altitude

The FA document for testing ADS-B Out installations has acceptable peak power to be +21dBW to +27dBW, in each quadrant - so it could be different in each quadrant just as long as all four are within the limits above.  That is quite some potential difference to contend with just there, let alone the variance in Mode C transponder output in the GA fleet too.  Throw partial antenna shielding as the relative axis of the aircraft change over time and it all gets very fuzzy very quickly.

Also Mode C returns require triggering via an active radar ping, so depending on altitude there may also be poor coverage to even trigger the transponder in the first place. 

My fear would be too many false positives and it will be start to be ignored, too few and it could be considered useless and also ignored.  But how do you know what are true alerts or not unless you visually confirm each one?  There is a potential here for technology to be a hinderance rather than a help IMHO.

Some of the reviews of the, now defunct, ZAON units highlight the unpredictability of the results.  There must be a reason why they folded?

[Admin]

My fear would be too many false positives and it will be start to be ignored, too few and it could be considered useless and also ignored.  But how do you know what are true alerts or not unless you visually confirm each one?  There is a potential here for technology to be a hinderance rather than a help IMHO.

Some of the reviews of the, now defunct, ZAON units highlight the unpredictability of the results.  There must be a reason why they folded?

Yes I am not convinced either, but I am prepared to do some more analysis to see what I can find.

[tfede]

It sounds anyhow encouraging, if you will include the function as a "testing the beta of the beta" i will test it for sure.

Trying also to spread the infos in the Italian VFR forum, more and more people getting interested there in the wole system.

Thaank you vor your work !

Federico