Primarily for general aviation discussion, but other aviation topics are also welcome.
#1694540
Straight Level wrote:
gaznav wrote:The problem for 1090 is the overuse of 1030 interrogations by TCAS and SSR and the continued use of Mode 3/A - they are the 1090 big spectrum killers. As the US decided they would continue with Mode 3/A (they even continue to sell brand new ones) they had to go with the 978 fix. Europe is different and Mode S is far more efficient with 1090 - the word ‘Select’ is the clue.


<My bold>
Somewhat of a subjective term :wink:
Have you reference to a 'independent scientific study' to quantify that Gaz?
SL


Lots of research papers on the internet. Here is just one: https://www.researchgate.net/publicatio ... ion_detail

Most studies cite the reduction measures for 1090MHz congestion to include one or all of the following:

1. Use of ACAS X/Hybrid Surveillance (EASA’s SESAR quoted that as much as a 50% reduction).

2. Use of WAM/MLAT in passive mode.

3. Reducing the use of Mode 3/A.

This is what Eurocontrol had to say:

2.1.3.2 1030/1090 MHz Frequency Band

The high number of SSR Mode A/C radars configured with relatively high interrogation rates and interrogator power has, over recent years, lead to congested usage of the 1030/1090 MHz frequency band.

As ACAS and all the cooperative surveillance techniques are dependent upon this frequency band its use is considered to be fundamental to the future of surveillance. Deploying an alternative band would be expensive, time consuming and would introduce technical difficulties. It is preferable to manage, monitor and protect the current frequency assignments in recognition that the 1030/1090MHz as a valuable asset that is to be used with care. The protection of the 1030/1090 MHz frequencies is a key objective of this surveillance roadmap.

Various measures ranging from the removal of spectrally inefficient Mode A/C SSRs (such as promoted through the Implementing Regulation No 1206/2011 Ref Doc 6) through to improvements in ACAS technologies (hybrid surveillance) or the clustering of SSR Mode S ground-stations will lead to improvements in this band and obviate the need for deployment of an alternative frequency band. The deployment of WAM techniques has the potential to reduce excessive transmissions in the 1030/1090 MHz band when compared with conventional SSR systems. However it should be noted that Active Wide Area Multilateration systems configured with broad-beam or omni-directional transmit stations can also place a significant impact upon this frequency band and the surveillance sensors that depend upon it.


Here is another Eurocontrol snippet:
Deployment of ACAS Hybrid Surveillance supports continuing improvements to 1030/1090 occupancy and contributes to a reduction in the need for a second/alternative data link for ADS-B.


https://www.eurocontrol.int/sites/defau ... -2v1.1.pdf

Hence, I’m kind of getting tired with the congestion argument and ADS-B. It’s not ADS-B that causes the 1090 congestion problem (in fact it should help!), it is people using inefficient Mode 3/A transponders, inefficient pre-TCAS 7.1 with Hybrid Surveillance and old bandwidth-hogging Mode 3/A/C Secondary Surveillance RADARs (SSR). :thumright:
#1694542
Hence, I’m kind of getting tired with the congestion argument and ADS-B. It’s not ADS-B that causes the 1090 congestion problem (in fact it should help!), it is people using inefficient Mode 3/A transponders, inefficient pre-TCAS 7.1 with Hybrid Surveillance and old bandwidth-hogging Mode 3/A/C Secondary Surveillance RADARs (SSR).


I certainly do agree with your summation of a significant part of the problem but what happens when we remove all the Mode 3/A/C transponders from the aircraft currently equipped with them and replace those units with ADS-B in EVERYTHING that's in the air, albeit they are low-powered?

I genuinely don't know but if everything is going to have ADS-B fitted then we have to establish if:

High-Powered ADS-B NOW + Few Low-Powered ADS-B NOW + Many Mode 3/A/C NOW

is > or < than

High-Powered ADS-B NOW + Very many Low-Powered ADS-B THEN
#1694586
@PaulSS

As I understand it there are effectively two types of ADS-B:

1. One that transmits at 1090 MHz using the mode-S extended squitter (downlink format (DF) 17) of the SSR transponder, with about 50 kHz of bandwidth.

2. One that transmits at 978 MHz (UAT, Universal Access Transceiver), using a larger bandwidth of about 1.3 MHz for transmitting ADS-B, weather and traffic data.

50kHz = 50,000 Hz
1.3MHz = 1,300,000 Hz (i.e. much, much more)

Now here is the thing. In the USA, due to the congestion caused by the continued use of Mode 3/A by aircraft, also Mode 3/A SSR heads for ATCRUs and also lots of ACAS/TCAS then their congestion problem is bad. In fact, so bad that they had to use UAT on 978MHz for GA. But in Europe, because of the planned phase out of Mode 3/A and the wide-spread use of Mode S for aircraft and ATCRU SSR heads then things are substantially better over here. That is why the use of low-power ADS-B transceivers over here are a possibility but not really in the USA for now whilst they still sell and use the early 1950s tech that is Mode 3/A. So this is the issue, in a densely populated area with multiple ATCRUs with SSR operating within a 100 nautical miles of each other: several SSRs, active multi-lateration systems, and other aircraft-based surveillance systems (such as ACAS/TCAS) will make their own independent requests for transponder replies, resulting in escalating 1090 MHz transmission rates. We are selective in Europe which is what Mode ‘Select’ or Mode S does for us by not asking every transponder that can ‘hear’ us on 1030MHz within say 80 miles and all ‘shouting’ out a reply on 1090MHz. The other problem is that a Mode 3/A reply is about 1/4 of the length in time of a Mode S-ES so it can ‘shout’ many times in a second, due to it being non-selective, to a wide variety of interrogations and effectively swamp the frequency with unwanted replies causing FRUIT and ‘garbling’.
#1694589
gaznav wrote:Hence, I’m kind of getting tired with the congestion argument and ADS-B. It’s not ADS-B that causes the 1090 congestion problem (in fact it should help!), it is people using inefficient Mode 3/A transponders, inefficient pre-TCAS 7.1 with Hybrid Surveillance and old bandwidth-hogging Mode 3/A/C Secondary Surveillance RADARs (SSR). :thumright:


Interesting read Gaz :thumleft:

Both of those papers mention " In addition an increase of the 1090 MHz ES data capacity is being prepared by ICAO. This is to be achieved by adding phase modulations on the same SSR signals.

Oh great! Now our new Mode ES transponders are already obsolete and will require upgrading in addition to everyone else chucking their A/C transponders in the bin. I don't believe of one second that phase (PSK) modulation capability can be added by firmware update.
I'm sure it will all work out in the end as the CAA will pay the VAT on the new transponders which will make the recent 8.33khz costs look like loose change :wink: :wink:
gaznav liked this
#1694602
The chance to use Phase Shift Keying (PSK) for Mode S was missed when the biggest user, the Americans, protested against the increased cost (at the time estimated to be ~20% more). Also, backwards compatibility issues with the older methods of modulation to allow older kit to be modified. They did use differential PSK for the interrogation signal though, which is an odd ‘half way house’!

You’re right, it was a missed opportunity.
#1695703
This just arrived in my inbox from uAvionix. Apologies if covered elsewhere, but no doubt those who understand these issues better than I will be able to comment on the implications of this decision:

"Since the introduction of the uAvionix SkyEcho 2 in late 2018, we have continued to improve the product and provide additional Electronic Conspicuity (EC) functionality to our customers at no extra cost, providing free upgrades whenever a firmware update was available. Most notably, in partnership with SkyDemon, we introduced the lowest cost option for FLARM reception capability available in any EC device on the market. The decision to integrate FLARM aligns with our company’s mission to enable shared airspace awareness for safer skies.

We have also been communicating to customers for some time that we have been working on Mode C/S proximity alert within SkyEcho 2. The intent of this alert is to provide the pilot an indication of a nearby aircraft which is equipped with a Mode C or S non-ADS-B transponder. Such alerts are dependent upon receiving bearing-less signals from nearby aircraft, and estimating the range of such aircraft based on signal strength.

After conducting our beta testing, we do not feel that the experience provided by the SkyEcho 2 will match the high quality and integrity solutions that uAvionix has grown to embrace, and therefore we are discontinuing our intent to implement such a feature. While many of the Electronic Flight Bag (EFB) applications wish to implement a range associated with these alerts, uAvionix does not believe that any range calculation based on received signal strength from a transponder is credible due to varying transponder transmit power levels between aircraft. Providing such a range may mislead the pilot, which could introduce a dangerous sense of false-confidence. Whilst we acknowledge Mode C/S proximity has some utility, it provides no positional reference and is no substitute for maintaining an effective lookout.

In April, we announced we would bring this feature to light with EasyVFR 4. We will gladly provide refunds for any product purchased since making that announcement on April 8.

Thank you for your understanding and continued business with uAvionix. The EC capabilities provided by SkyEcho 2 with ADS-B IN and OUT, FLARM reception, and TSO certified GPS is unparalleled in the quality and capability in an affordable, high quality package. Moreover, ADS-B will become ever more prevalent as the CAA endorsed technology of choice under CAP1391, and as recently communicated by the CAA in its recent “Share the Air” Call for Evidence for Electronic Conspicuity Solutions.

For more information regarding this announcement please contact: support@uavionix.com.

Regards,
uAvionix Corporation"
gaznav liked this
#1695708
I was disappointed to see this, but based on the comments from the SkyDemon folks it's not unexpected. I recently bought a SkyEcho, but mainly in the hope it will help others (airborne and ATC) see me...... Currently the traffic display aspects of SkyEcho do not integrate with my existing Flarm based traffic monitors anyway, so I now would end up having a seperate ADSB-only traffic display and I'm not sure if that is worth the clutter.

I guess at some time I'll end up upgrading the Flarm to a PowerFlarm version so I can see more traffic, as well as be seen. PowerFlarm does bearingless, but I think nowhere near as sophisticated as PAW and the upgrade costs are significant - unfortunately I don't have cockpit space for a third EC system!
#1695725
Personally, I’ve always had mixed views on Mode C/S proximity alerts due to the inexact science of it. We had something similar on the Tornado radar warning and homing receiver that was eventually ditched as it just was not accurate enough as there were just too many variables.

I would far rather have a device that received ADS-B, FLARM and PAW (in that order too) :thumright:
ls8pilot liked this
#1695733
gaznav wrote:...I would far rather have a device that received ADS-B, FLARM and PAW (in that order too) :thumright:

Its your lucky day, I know of just one device that will pick all of those up (in no particular order, other than most threatening !)
In addition to bearingless and ModeS/3D
:D
PaulSS liked this
#1695739
leemoore1966 wrote:
gaznav wrote:...I would far rather have a device that received ADS-B, FLARM and PAW (in that order too) :thumright:

Its your lucky day, I know of just one device that will pick all of those up (in no particular order, other than most threatening !)
In addition to bearingless and ModeS/3D
:D


Yes, but I want a device that also outputs a signal that most can see with theirs! :thumright:
#1695748
Hi Lee

Are you claiming to have sold 4000+ PAW units that are in regular use in the UK? If true then according to the following stats then that would mean better than 1 aircraft in 2 is carrying PAW for aircraft <5.7T with a valid permit or cofa?
https://www.caa.co.uk/uploadedFiles/CAA ... 202019.pdf

Is that really the case? Any chance of a screen shot of the whole of the UK with 4000+ PAW users on it? That would be really interesting to see :thumright:
#1695753
Thanks. How many do you believe you have in the UK? Even at 2,000 or so then that is still pretty significant. I might start asking uAvionix whether their efforts might be better spent receiving PAW now that they have (correctly in my humble opinion) dropped the plan for receiving and displaying vague transponder receptions. :thumright:

If both devices can see and be seen by each other then that has to be a good thing.
#1695755
I find it strange that uAvionix have drawn such a conclusion.
I was, for a long time a Zaon MRX PCAS user (since switched to PilotAware), which also uses signal strength to approximate range for bearingless targets. I always found it worked well. Even for targets I couldn't spot, simply knowing if distance was increasing vs decreasing was a useful piece of information to have. .