PilotAware
British Forum => General Discussion => Topic started by: the_top_pilot on October 31, 2015, 08:16:44 am
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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
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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
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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
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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
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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!
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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.
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)
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Lee
That looks very encouraging.
Steve
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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.
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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
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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?
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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
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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
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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?
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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.
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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
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Please don't give up the mode C detection without sufficient trialling. Although PAW may be superior we need to work with the existing environment which is still predominantly mode C I think.
I have used TCAS on the A320, MD902 helicopter & Zaon PCAS on light aircraft. Each system has it's own benefits and limitations which I'm happy to discus.
The Zaon (which measures range using signal strength) is very useable and has regularly altered me to nearby traffic which I then spotted.
Lee, you are welcome to borrow my Zaon to assist in calibration & comparison.
Roger
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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.
The XRX appears to have multiple small antenna's under its dome. This allows directional detection. I'm not sure how they determine distance.
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[snip] 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.
The advantage that the PAW has over the older Zaon products is that it can automatically calibrate the sensitivity dynamically based upon current known ADS-B target geometry. Such an auto-cal won't be perfect, and obviously won't take into account antenna shielding or transmit power variations, but it'll be a whole lot better than the nothing we currently have.
Some of the reviews of the, now defunct, ZAON units highlight the unpredictability of the results. There must be a reason why they folded?
I suspect a large part of the commercial failure of Zaon was the very high price (around £800 IIRC) compared to the functionality. The work Lee and the team have done to bring about the PAW reverses that equation, giving us a lot of functionality for a very low price.
Another very willing Mode-C/S trialist/guinea-pig here, Lee.
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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.
The XRX appears to have multiple small antenna's under its dome. This allows directional detection. I'm not sure how they determine distance.
As far as I am aware, on the XRX the minor variation in difference of time of signal reception gave an indication as to which sector the intruding aircraft was in as the connectors between aerial and receiver were standardised.... even with such a small distance between the antennae, the delays in signal reception was apparently sufficient to calculate where the signal was coming from. Strength only gave approximate distance.
For info, I still use my Zaon MRX on every flight, what amazes me is that even with just one antenna, somehow it can still work out whether the intruder is climbing, descending, above or below me - and for me, collision avoidance means ALTITUDE, after all, I'm only going to hit an aircraft which is at the same altitude I'm flying, and that's how to optimally use the MRX.
Look to see what height the intruder is at, is it climbing or descending. Using this info, increase the vertical separation and problem sorted. If Lee could work out how Zaon established the aircraft height and whether it was climbing / descending using just Mode C, that would be a major step forward.....
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Well, that's easy, altitude is part of the Mode C transmission which can be decoded.
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What's depressing is the number of people who fly Mode A when they have Mode C.
I hear some people do not understand that "Alt" = Mode C !!! ::) :o
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I hear some people do not understand that "Alt" = Mode C !!! ::) :o
Not too surprising, considering "alt" stands for "alternate" on just about everything else in aircraft.
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Hi,
any news about C mode detection ?
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Hi all,
I'm new to this forum, and am playing catch-up while I wait for the bits to build a PAW - ADSB only at first, though I have ordered a 'shield' from Jeremy Curtiss to add baro input so can easily add ARF (or whatever) later. In the absence of anything better over the years, I have been using a Zaon MRX in my flex wing since 2009. Despite its limitations I can vouch for the fact that it can be a life saver as an extra pair of eyes. Ok it doesn't provide any directional info on the contact, but a contact with rapidly decreasing range or altitude separation really focuses the mind and at least in the case of altitude points to which way you need to look and whether to climb or descend to maintain separation!
I certainly would appreciate the addition of any Mode C /S alerting to the PAW system even if the range is a bit 'iffy'. Let's face it the number of aircraft flying at our level with ADS-B out (which I have) is much smaller than those with Mode C/S so let's not reject any opportunity to 'see' the mode C or S aircraft that are about!
Previous comments about how the two Zaons work is pretty much spot on by the way, range is estimated from signal strength with altitude being decoded from the transponders signal.
Best Regards to all
Peter
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Federico,
I think the PAW unit would be a superb Traffic Avoidance system for the Italian ULM users as you have to endure the crazy altitude restrictions that Air Traffic Control & AeCi put upon you.
I have never understood the reason behind the ULM Low level level restrictions?
With such a enthusiastic ULM environment in Italy where virtually every ULM is at the same level buzzing around like firecrackers I would find the PAW extremely useful if the ULM fraternity employed this system.
On a personal note : Whilst you have Pilots like Crono campaigning for better conditions for Italian ULM users I would imagine that he will have opinions on PAW 😊
Crono is an Electronic genius who would alongside yourself make a great pair of users to test the PAW units.
Advertising the PAW unit on the VFR Forum is a great idea as I have to admit that the enthusiasm of VFR Forum users is very positive & I think the uptake of PAW users in Italy would be far more than it is in the UK.
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.
Thank you for your work !
Federico
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I have an update regarding Mode C/S bearingless targets
http://forum.pilotaware.com/index.php/topic,304.0.html
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Lee, as you know, I'm a strong believer in the significant potential benefits of incorporating Mode C/S detection into PAW in some form or other, so it's great to hear that you have made further progress on this front.
I will PM/e-mail you about possible testing of your 'prototype' against my ZAON MRX.
Regards
Peter
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Don't forget, it will not only be a function of the transponding aircraft's antenna performance, but also the performance of the PAW antenna.
There are so many variables.
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Regarding Mode C and bearingless targets, have you looked at the Free Path Loss equation, or FRISS Transmission formula? If you Google for FRISS you will see how it may be possible to determine the approximate range of a transmitting target. Okay, it won't be very accurate or tell you where the target is in relation to a PAW device but may be of use in filtering out Mode C at FL200?
This url has a very good simple(ish) description): http://www.antenna-theory.com/basics/friis.php
TonyN
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Regarding Mode C and bearingless targets, have you looked at the Free Path Loss equation, or FRISS Transmission formula? If you Google for FRISS you will see how it may be possible to determine the approximate range of a transmitting target. Okay, it won't be very accurate or tell you where the target is in relation to a PAW device but may be of use in filtering out Mode C at FL200?
This url has a very good simple(ish) description): http://www.antenna-theory.com/basics/friis.php
TonyN
Hi Tony,
Actually filtering based upon altitude is not an issue, we are looking at mode C/S, so we already have the Altitude of the targets. So we can filter any signal between +/- Nft, whatever we decide N to be, lets say 1000ft for arguments sake. So now all we have to contend with, is the signal level of all Transponder returns at +/- 1000ft.
The reality is that we are not dealing with a 'perfect' environment, as mentioned in many earlier posts,
we have losses at the transmitting end(s) and losses at the receiveing end, and these losses are not uniform in all directions, or across all installations.
So +200ft from target A could give a different totally different signal strength to +200ft from target B.
That is the reality because I have analysed in detail, ADS-B signals of corresponding traffic at equivalent distance/altitude
I see this approach as complimentary to the far more accurate ADS-B/P3I transmissions, but clearly quite vague in its nature, and possibly providing only a short window of warning, in order to ignore many of the potential false positives.
Not giving up yet, and still pursuing this as an additional safety net to what we have already accomplished.
As I mentioned in another thread, I sometimes think our efforts may be better spent convincing our fellow Pilots to adopt PilotAware and/or ADS-B (out).
Thx
Lee
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Hi Lee,
I was thinking Mode A and forgetting Mode C! Yes, of course you have altitude information....
I wonder if it will be possible to determine (by in-flight testing) a band of received signal levels that are most likely to indicate a potential close encounter?
For example, is there likely to be much difference in received signal levels between an aircraft transmitting at 1, 2, 5 and 10 miles away? My thinking is that you could ignore Mode C signals until they got to a level typical of, say 2 miles away.
Yes, there will be all the PAW variables you mentioned but perhaps a good starting point to possibly refine upon as more data becomes available?
As all Mode C transponders are built and tested to certified levels (I assume they are?), and most installations use standard transponder antennas, I wonder if there is really a significant difference in transmitted power from different aircraft/installations?
Tony
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The problems:
1) there are different powers of transponders for commercial and non-commercial
2) every transponder installation will be subject to vagaries of time and corroded connectors, antennae, etc.
3) every receive setup will be different
4) shielding of one antenna from the other will depend on individual aircraft, both on the transmit and receive side, and where they are relative to the sticking out bits
The best we can hope for is an approximation but at least there'll be an alert.
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An alert is whats important until everyone has a Pilotaware.
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The counter argument is that you create too many false alerts, then people will no longer trust it. At least with PAW and Mode S you know if you get an alert then it's accurate.
The Zaon devices lost credibility pretty fast, for alerting to traffic that wasn't there or vice versa. So, people don't trust them. It actually creates MORE pilot workload, because now you have to actually take time to verify the alert, thereby diverting attention from what the pilot should be doing.. BAD! and goes against the ethos of a device that doesn't impair pilot workload and cockpit efficiency.
Wouldn't want PAW to be tarred with the same brush, by giving bad alerts.... the majority of alerts would come from ModeC and would be very unreliable. The PAW system would then very quickly gain a bad reputation.
Needs to be carefully considered, in my opinion :-)
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As I mentioned in another thread, I sometimes think our efforts may be better spent convincing our fellow Pilots to adopt PilotAware and/or ADS-B (out).
What he said.
Also an affordable, low power ads-b out transmitter (I.e. not a full mode S transponder) would be nice! ;)
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Also an affordable, low power ads-b out transmitter (I.e. not a full mode S transponder) would be nice! ;)
I'm afraid dedicated ADS-B out is only any use if you don't have any sort of transponder.
CAA/NATS will not permit more than one 1090Mhz transmission device in an aircraft.
That us the main driver behind Le'e's P3I initiative of course. :)
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I wonder if it will be possible to determine (by in-flight testing) a band of received signal levels that are most likely to indicate a potential close encounter?
For example, is there likely to be much difference in received signal levels between an aircraft transmitting at 1, 2, 5 and 10 miles away? My thinking is that you could ignore Mode C signals until they got to a level typical of, say 2 miles away.
Yes, there will be all the PAW variables you mentioned but perhaps a good starting point to possibly refine upon as more data becomes available?
As all Mode C transponders are built and tested to certified levels (I assume they are?), and most installations use standard transponder antennas, I wonder if there is really a significant difference in transmitted power from different aircraft/installations?
Tony
Tony, that's what Lee has asked the 'engineering group' to help him with (though due to family commitments, weather and a back problem I've yet to contribute my share). We fully acknowledge the difficulty of determining accurate range to raw transponders solely from signal strength, especially given the many variables of transmission / reception as referred to by Paul above, but feel it's really important not to simply disregard such a large group of aircraft without giving the problem due investigation.
The counter argument is that you create too many false alerts, then people will no longer trust it. At least with PAW and Mode S you know if you get an alert then it's accurate.
The Zaon devices lost credibility pretty fast, for alerting to traffic that wasn't there or vice versa. So, people don't trust them. It actually creates MORE pilot workload, because now you have to actually take time to verify the alert, thereby diverting attention from what the pilot should be doing.. BAD! and goes against the ethos of a device that doesn't impair pilot workload and cockpit efficiency.
Wouldn't want PAW to be tarred with the same brush, by giving bad alerts.... the majority of alerts would come from ModeC and would be very unreliable. The PAW system would then very quickly gain a bad reputation.
Needs to be carefully considered, in my opinion :-)
Wobble wing,
I fully agree, which is why I volunteered to help Lee with the testing. As a long term ZAON MRX PCAS user, (since 2009 including trips abroad) I am fully aware of the issues.
Yes it does give alerts for which you can't find the aircraft - generally due to a CAT with it's higher power transponder, but these are not in reality 'false' alerts and once you get used to the system can be quickly disregarded.
My real worry is that without raw transponder detection, PAW users may get lulled into a false sense of security and allow lookout to become lax. Especially bearing in mind that GA traffic - which is what we are most at risk from - which wants to fly in controlled airspace will happily fit a transponder (lots already have), but are unlikely to go down the ADSB route unless it becomes easier /cheaper (viz. the recent uncertified ADSB trials and the potential for PAW to provide the 'uncertified' GPS source if this goes ahead).
As has been said earlier, until ALL GA and commercial helicopters (very unlikely) can be persuaded to adopt PAW, raw transponder detection is the best route we have to a very significant proportion of the aircraft likely to fly into us!
Please bear with us and let us give it a fair trial. If it can't be done to an acceptable level of reliability, I know Lee won't roll it out.
Best regards meantime
Peter
p.s. In my experience, When the ZAON 'fails' to alert me to a nearby aircraft, the most likely scenario is that it is NOT transponder equipped. Don't be too quick to 'blame' the ZAON - PAW won't 'see' aircraft not broadcasting any form of alert either!!
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The difference between the Zaon and this of course is that this can differentiate between bearingless (Mode C or Mode S with no ADS-B) contacts and those with ADS-B, so wouldn't alert to all the commercial traffic. There are suggestions in the pipeline for various switches and filters so that you can choose to only display the contacts likely to cause conflict.
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Exactly Paul,
I personally would limit bearingless targets to say <5 miles ( or even <2) and +/- 1,500 feet max - i.e. the immediate danger zone and the distance you can reasonably see. The general principle I apply with the ZAON is anything I can't see after an alert and a good look round is a CAT outside this range (due to its much higher power transponder swamping the ZAON) which I can therefore disregard and move on. If it gets any closer, the ZAON soon tells me and I look again, with no harm done and no great increase in my workload.
Peter
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Also an affordable, low power ads-b out transmitter (I.e. not a full mode S transponder) would be nice! ;)
I'm afraid dedicated ADS-B out is only any use if you don't have any sort of transponder.
CAA/NATS will not permit more than one 1090Mhz transmission device in an aircraft.
That us the main driver behind Le'e's P3I initiative of course. :)
I realise this is what P3I is for.
Hadn't realised one could only have one 1090 tx from an aircraft. Thanks for that.
I was thinking more of 'ads-b out only' for aircraft with no electrics. Transponders are really hungry, as well as expensive.
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I'm afraid dedicated ADS-B out is only any use if you don't have any sort of transponder.
CAA/NATS will not permit more than one 1090Mhz transmission device in an aircraft.
That's actually not quite correct. Most CAT and quite a lot of high end GA carries more than one transponder for redundancy, however only one can be in use at a time. One reason for this is that the transmitter of transponder 1 would blow up the receiver of transponder 2 and vice-versa, since they are operating on exactly the same frequency. Another issue is having two transponders both squawking the same aircraft ID, squawk code, etc. from the same position. Jolly confusing to radars and their controllers!
Transponders are really hungry, as well as expensive.
Modern Mode S transponders aren't particularly greedy. Typical average power consumption is well under 1A at 12V which is easily within the capabilities of a small battery to provide for a few hours of flight. A non-squawking ADS-B out transmitter would require much the same power budget.
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One reason for this is that the transmitter of transponder 1 would blow up the receiver of transponder 2 and vice-versa, since they are operating on exactly the same frequency
Mmmm. Transponders transmit on 1090Mhz but receive on 1030Mhz so can't see any blow up caused by that.
Anyway our £5 dongles that do listen on 1090 seem to cope just fine :)
I think NAT's issue re LPAT is garbling though that happens to some degree anyway. I wish they would at least try both transponder and LPAT ADS-B out together in their ongoing trail and see if it 'just works' in real life. . It would save a lot of us shelling out to upgrade our MODE S to add ADS-B.
I'd like to understand how NATS can tell if it is one of two devices transmitting anyway.
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One reason for this is that the transmitter of transponder 1 would blow up the receiver of transponder 2 and vice-versa, since they are operating on exactly the same frequency
Mmmm. Transponders transmit on 1090Mhz but receive on 1030Mhz so can't see any blow up caused by that.
Anyway our £5 dongles that do listen on 1090 seem to cope just fine :)
I think NAT's issue re LPAT is garbling though that happens to some degree anyway. I wish they would at least try both transponder and LPAT ADS-B out together in their ongoing trail and see if it 'just works' in real life. . It would save a lot of us shelling out to upgrade our MODE S to add ADS-B.
I'd like to understand how NATS can tell if it is one of two devices transmitting anyway.
As Ive done quite a lot of the Flying with LPAT on behalf of AOPA and NATS perhaps I can input some thoughts.
Not using the Aircraft Transponder during flying of the LPAT was defined by the CAA to avoid interference, garble and FRUIT, from the LPAT with the conventional Mode-S and A/C Transponder. It has not been determined scientifically that the LPAT would cause problems with the conventional ground interrogations/response but a precaution that was implemented as part of the CAA authorisation to conduct the trials.
In my particular case the need to switch of my Transponder is a more of a practical issue with that fact that I also have an ADS-B enabled transponder hence during the flying trails we needed to be confident that the ground tracking of the LPAT and receipt by an LPAT in another aircraft was from the LPAT transmissions. In addition we needed to be certain that any onboard transponder was not flooding the Rx of the LPAT and affecting range performance of the LPAT Rx.
Overall the trials of the LPAT are being done in an environment to determine the performance of the LPAT and therefore eliminate any possible effect of a working transponder in the same aircraft. In addition the CAA authorisation for the LPAT is for only one working transponder in the aircraft undertaking the trials.
Having said all that Im sure I have had both operating together, pure accident, and not had any reports from ATC that I have disappeared from their radar :-) but nothing formally tried and perhaps we need to include an LPAT flight with an active transponder to determine if LPAT performance is affected on the RX side. As you suggest a well designed Rx should be able to cope with a nearby Tx on the same frequency within limits as my onboard PCAS as well as other existing traffic warning devices demonstrate.
Ref the discussion on the use of two active Transponders in the same aircraft i.e. Conventional and/or LPAT. This would produce interesting results if they both would respond to ground interrogations, the LPAT does not respond to conventional Ground Interrogations, as the Radar Display Trackers would see two response from a target. At the moment the ADS-B position data from the Uncertified GPS enable Transponders and LPAT, is not sent to any of the Radar Tracking software but only recorded so in this safety conscious environment it can be determine if the accuracy, reliability and integrity of the ADS-B transmissions from uncertified GPS is sufficient for presentation to ATC either on its own or as part of a combined Conventional Transponder, ADS-B enable environment. In the future - lots of work still to do and part of the overall European Trials of uncertified ADS-B enabled transponders, including LPAT, I'm sure this is the direction that it will go in Europe and is already part of the overall surveillance environment in other countries where conventional SSR ground Stations are challenged by terrain and other factors.
All of this is part of a European Project EVA which is looking at the use of Electronic Conspicuity devices to assist the VFR pilot. You can read more of this in the AOPA magazine.
Merry Christmas and a Happy New Year..
Alan
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Transponders transmit on 1090Mhz but receive on 1030Mhz so can't see any blow up caused by that.
Yes, you're right of course, although 60MHz separation at 1GHz is not a lot for the front end filtering to work on. I have a feeling that if our ADS-B in dongles had their antennas mounted on the underside of the aircraft in the line of fire from the transponder antenna then they would be less than happy!
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Interesting Alan, thanks for that.
Yes, I agree there should be no great difficulty with mixing ADS-B out squitter from an ADS-B out device with Mode-S radar replies from a separate transponder, with the proviso of receiver front end protection/blocking/recovery times for the transponder. I guess the ADS-B transmitter could also operate at significantly lower peak power than the transponder, as we're not looking for vast range.
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Hi Rod -
I have moved this post to the Engineering thread
Thx
Lee
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Hi Fellow Forumites
I have decided to resurrect this thread to post these results as it gives the reader some background into the thinking behind what we have been trying to achieve.
What follows is largely the text from an email message to Lee regarding the testing of Mode S alerts based on the signal strength as discussed earlier in this thread which Exfirepro and myself have been conducting in Scotland using an engineering version of the software provided by Lee some time ago. This software has gone through several changes as we have progressed these trials. Some of these changes are reflected in the current software version as the pre-selectable Mode S alert levels and these are what I am referring to in this email. The settings in the current public release of the software had already undergone quite a lot of testing but as has been commented about in various threads on the forum they were still a work in progress. It has always been recognised that because of the variations in equipment between CAT transponders and GA transponders, the variations of installations and the vagaries of RF propagation that Mode S acquisition could never be an exact science, but in order to make PilotAware as multi-functional as possible it was worth the effort to give this our best shot
I have always stated from the start of my involvement with this project that there is no such thing as a false alert. Sometimes the target may be further away and not an immediate threat but increased vigilance in lookout for a few seconds never killed a pilot yet, but not knowing something is out there could. Read on:-
Hi Lee
The new trigger levels for the Mode S alerts are looking good from my perspective on a flight yesterday. Whilst circumstances plotted against me to achieve the original objective of a flight with Peter (Exfirepro) our separation proved useful in that I picked up a mode S alert for a well know PA28 aircraft that is based the opposite side of the Forth from us.
When I got home I managed to download the Trk file and using “Notepad”, trawled through until I found the start of the alert for G-EVIE and using the time stamp from the $GPRMC message and tracking his recorded flight path in FR24 and my own one, and cross referencing my position from the $GPGGA message to plot the position in Google Earth. I was then able to approximate his position on Google Earth from his track on FR24 using the same time frame and came up with an estimate of our separation distances.
I first saw him on a Green flag in EVFR and then in a few seconds this was Amber. There were some fluctuations between green & Amber before it then became Red.
I hasten to add that I was giving the sky the “big eyeball” trying to find him but failed to get a visual on him. The alert, again after a few fluctuations reverted to Amber and then Green and then disappeared.
My finding from all this were that:-- We were flying a more or less parallel course and he was 1100’ below me hence the reason I probably couldn’t find him visually against the background.
At the initial Amber alert he was appox. 4.5 statute miles behind in my 7 o’clock.
At the initial Red alert he was approx. 2.7 sm in my 9 o’clock which was the nearest we got.
He then proceeded to pull ahead of me on a very slight diverging course.
His speed according to FR24 was about double mine. The whole alert period from first contact to last contact (Green, Amber, Red, Amber, Green) was about 3 minutes.
This was all carried out with the “Short” setting of the Mode S detection range.
As far as I’m concerned if we can replicate this a few more times I would find this level of warning completely adequate. It’s never going to be foolproof as this shows with the fluctuation of signal strength from what was essentially a fairly straight forward overtake manoeuvre which all things being equal should result in a gradual increase in signal received through a peak and then a gradual decrease but as can be determined from the fluctuations we are not operating in an ideal environment
This is the best result for me so far in this testing as with a bit of, (make that a lot of,) faffing and switching between programmes I have managed to take some of the guesswork out of the equation.
Hope this helps.
Alan