Primarily for general aviation discussion, but other aviation topics are also welcome.
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User avatar
By gaznav
#1803799
@leemoore1966

In the very unlikely event of a 112 microsecond extended squitter transmission arriving at exactly the same time and the same received strength, then both signals would be garbled. However, as you know, ADS-B transmits at least every second or so, so the receiver should get it second time around.

It’s the same reason why air traffic ask us all, apart from the leader, to squawk standby when in close formation of more than one aircraft. The replies would garble each other coming from the same close proximity that reply to the same interrogation pulse. It also looks messy on an air trafficker’s RADAR display!
#1803802
gaznav wrote:@leemoore1966

In the very unlikely event of a 112 microsecond extended squitter transmission arriving at exactly the same time and the same received strength, then both signals would be garbled.


Hi Gaz
Please read my question again, I said one signal arrives -3db relative to the other, ie half the power. I am specifically debating your low power assertion

If one signal is half the power of the other, but sufficient for the receiver sensitivity, are the emissions garbled, or decoded ?

Thx
Lee
#1803803
I'm late to this thread, sorry, but there's an increasing level of misinformation appearing, so I'll join in.

Just to be clear on this particular question, there is a requirement in the standards for 1090 ADS-B receivers which describe exactly that circumstance Lee describes. When a second overlapping frame arrives that is 3 dB louder than the current frame, the receiver MUST receive the second frame. That is required for all TCAS processors, and all certified 1090 ADS-B receivers other than the lowest compliance level. It is optional whether an airborne receiver also successfully receives and decodes the first frame, but some will. Most ground based equipment (Mode S radars and proper ADS-B receivers) will do so. In case that sounds like magic, it is a straightforward digital signal processing problem with solutions that have been done to death in the international standards committees.

On the other hand, few, if any, of the hobbyist receivers correctly implement this and therefore will receive neither of the transmissions.

I might have thought Lee would have known this.

Andy
Flying_john, Cub, ls8pilot and 2 others liked this
#1803805
Thanks for the clarification on certified ADSB receiver @Trig Andy
So back to the original question, @gaznav
So using your analogy, if I have a 500W emitter at 2nm, at what distance will a 20W emitter need to be, in order to be visible ?


Thx
Lee
By Crash one
#1803809
This is becoming a techno babble bun fight between techno nerds and is impossible to make head nor tail of.
There are three contestants in this race.
Flarm
Paw
Se2.
Flarm is far more expensive than the other two, has a shorter range and it’s protocol is exclusive.
Se2 transmits and receives only ADSB which may or may not become the future for everyone.
Paw transmits only P3i but receives everything except Flarm (unless you buy something else from Flarm).
So as a stand alone unit Paw comes out on top every time.
The more Paw units there are the more useful it becomes.
Se2 seems to be having drop out problems (unreliable I am led to believe so don’t kick me to death if I’m wrong).
This is all I needed to know! :D
#1803810
SE2 wins IMHO, once you've hacked out £250 runs without any fancy installation and can be used absolutely free of any more kit except a mobile 'phone screen, all warnings are relayed it by WiFi using Easy VFR Basic charts and free download at NO more cost.
No annual fees or anything.
So as an incentive to show where you are to others and SEE the increasingly larger no. of ADSB senders it presents a truly inexpensive solution, ie free. (And FLARM for £30 per annum)
Last edited by mikehallam on Sun Oct 18, 2020 5:09 pm, edited 1 time in total.
gaznav, Miscellaneous liked this
User avatar
By Cub
#1803812
Crash one wrote:Se2 seems to be having drop out problems (unreliable I am led to believe so don’t kick me to death if I’m wrong).


I have read a single, apparently unresolved, first hand report in this thread, of an SE2 ‘dropping out’. If anyone experiences such issues then please contact uAvionix customer support and the issue will be properly and professionally dealt with.

Please rest assured there are hundreds of satisfied customers integrating their SE2 with their chosen EFB application and definitely not experiencing any issues.
Last edited by Cub on Sun Oct 18, 2020 4:08 pm, edited 1 time in total.
Rob L, gaznav liked this
#1803815
leemoore1966 wrote:I am sorry Gaz but I am not sure you have an understanding of what is happening here
1090mhz does not emit a modulated carrier, allowing corruptions due to overlaps.


This is not correct. Most modern ADS-B receivers can certainly resolve collisions using both power and phase.
If a higher power squitter collides then the receiver can land it simultaneously. The phase of the carrier is coherent along the pulse transmissions, so corruptions can be resolved even when the colliding squitter is lower power. Another technique is used to correlate the manchester coded symbols in sample blocks and use an array of matched filters: https://patents.google.com/patent/US9906265B1/en
gaznav liked this
#1803822
The biggest problem I see at the moment is to get an SE2 as most places state they are sold out.

Does anyone have any availability?
gaznav liked this
#1803823
mikehallam wrote:SE2 wins IMHO, once you've hacked out £250 runs without any fancy installation and can be used absolutely free of any more kit except a mobile 'phone screen, all warnings are relayed it by WiFi using Easy VFR Basic charts and free download at NO more cost.
No annual fees or anything.
So as an incentive to show where you are to others and SEE the increasingly larger no. of ADSB and FLARM senders it presents a truly inexpensive solution.


You do realise I hope that you won't receive Flarm on SE2 without paying the £30 p.a subs to either Skydemon or Easyvfr.
#1803824
TheFarmer wrote:I agree FD, but I’ve decided to wait until there’s a standardised system where the hardware works reliably, and the traffic info is not just a random and minimal selection.


That would not be the way forward I think.

How about you take delivery of the SkyEcho2 and try it; if you don't like it I will pay what you paid for it, minus the rebate you got from the CAA.

I want one but cannot find a source to buy one from and I know you would take care of sending it to me.
gaznav liked this
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