Transmit power and range

[JCurtis]

...the ISM band the duty cycle can be no more than 10% (per hour) so that shouldn't be an issue.  A device can transmit for a total of no more than 36 seconds in any given hour.

10% would be 360 seconds but perhaps there is an overarching limit of 36s/hour as well, effectively making the long term maximum duty cycle 1%?

The rules give a maximum single length of a transmission to be 36 seconds, with a min 3.6 second gap between.  There are various tables around with all this stuff in.

I was wondering about "interference " from other ISM sources. Am I being overly simplistic in my thoughts that when PAW receives transmissions from non-PAW sources, data will be unrecognisable as not conforming to PAW protocols, therefore nothing is output to display or otherwise?

The ARF will ignore transmissions if they are not on its 'net', in the ARF setup there is a PANID setting - unless it gets the same ID it simply throws the packet away and Lee never even sees it.  I believe they also throw the packet away if it fails a CRC check too, again before Lee even sees it in PAW.  Current this is set to the default of 5AA5 so it's possible if someone else is using an ARF with the default too Lee may see some packets that don't relate to P3i.

[Moffrestorer]

Yes, it is, the CC1190 on the ARF flips between Tx and Rx based on a signal received from the small SRF board on the ARF module.  When in Rx is operates as a high gain receiver, when in Tx a power amp.  If you add anything external to the ARF to try and boost things etc. it would also need to 'see' these control signals to be able to switch the amp on and off.


I've not seen that admission, but would not be surprised if production variances caused enough of a problem to explain some of the oddities.
[/quote)

1) I'm not sure why one would need to switch the amplifier on and off. During Rx cycle there would be no TX signal at amplifier input as CC1190 has flipped away from TX mode, therefore no TX carrier.
Amplifier input correctly terminated, so presumably no transmission or spurious output to TX antenna.

2) worth looking at openmicros.org webpage concerning ARF/SRF. Looked it up when Lee pointed to it concerning PAW master slave RSSI tests. The transceivers can act in very odd ways, largely inhibited by Wirelessthings firmware update, but sometimes requiring re-flashing of memory by WT.

[Ian Melville]

If we accept that most risks come from straight ahead give or take 30 degrees then we can get away with something in the cockpit, e.g. on the coaming, but that will be severely compromised in other directions, especially behind and below. It is something of an intractable problem and not something we have had to worry about in the past with other types of avionics. If this was a simple problem we'd have fixed it by now!

Not convinced the threat is from 30 degree either side of dead-ahead. I would hope that most pilots would spot something in this area sooner or later. Under noses, above high wings and below low wings, I would consider the greatest threat due to not being spotted? A vertical dipole would be blind to an aircraft directly above or below e.g. on approach.

[Ian Melville]

How do you graft on of these onto a PA28?
 

[stephenmelody]

It never comes from dead ahead...

https://www.youtube.com/watch?v=H4TuJM3uuzY

[rwheeler]

HI All, I have successfully built two units at the weekend. Thanks to excellent documentation and advice on the forum both fired up first time with just the ADS-B In fitted. I did some initial testing in an RV9 over East Anglia and was gaily spotting the big jets heading into and out of Stansted, Norwich and even London at 2000' over Diss - see pic.

https://www.dropbox.com/s/u0g2dnujcchezk4/IMG_0164.PNG?dl=0

Later when back on the ground I was still picking up a/c over Belgium - seems extraodinary - is that norm

https://www.dropbox.com/s/mhqfuo3ofgh102l/IMG_0165.PNG?dl=0

When my ARF and Jeremy's shield arrived I fitted and again fired up great. First test was at my desk in Fulham and again good results with ADS-B In.

I was interested to see one a/c turning onto finals at LCY (2000') and it had a course marker attached

https://www.dropbox.com/s/2sd8cp085egm4m5/IMG_0166.PNG?dl=0

 - does that mean I was receiving Mode S data? I understand that Mode-S on its own only transmits Reg and Height info on the ES - what should I expect to see on Skydemon for an a/c in that mode only (i.e no connection to a GPS source)

Keep up the good work

Cheers, Rod

[The Westmorland Flyer]

Good stuff Rod. It makes me realise just how much busier upper airspace is down in your neck of the woods - around here I might see as many as six ADS-B aircraft at at any one time between, say, Manchester and Glasgow!

ADS-B uses the Mode-S transponder transmitter, which is quite high power and is intended to give a range of up to 200 miles, albeit to a high gain radar head, so yes, what you're seeing is to be expected.

An aircraft squawking Mode-S without extended squitter will not show at all on the current PAW system because there is no positional information available for PAW to plot where it is. The identity and altitude are actually transmitted as part of the Mode-S response, not in the extended squitter. With ADS-B out, GPS position data are provided to the transponder and it is that information that is broadcast in the extended squitter.

I don't know why SD sometimes attaches a velocity vector (track marker) to aircraft. I too have seen it occasionally. Perhaps it's to do with being at low altitude or lower speed? Does anyone know?

[Admin]

Hi Rod,

That has got to be one of the busiest screenshots I have seen so far

Thx
Lee

[rwheeler]

Thanks John - so it seems to Squitter or to Extended Squitter that is the question!

I am fortunate enough to have access to a nice Cardinal with a Mode-S Transponder and G430 for further testing but it has not yet undergone the upgrade to connect the two together (for fear the avionics chaps will mess up both!) so not sure how useful that will be at the moment.

One more question - am I  correct in assuming that PAW even with an ARF will also not pick up true F****M traffic as that has a different transmit protocol? Lee has just been very clever in utilising the existing SD F*****M interface to enable PAW to show ADS-B and (when available) ARF contacts? Or am I missing something?

Hope the weather clears and everyone can get some flying this weekend

[ianfallon]

One more question - am I  correct in assuming that PAW even with an ARF will also not pick up true F****M traffic as that has a different transmit protocol?

Correct

[ianfallon]

An aircraft squawking Mode-S without extended squitter will not show at all on the current PAW system

I don't know why SD sometimes attaches a velocity vector (track marker) to aircraft. I too have seen it occasionally. Perhaps it's to do with being at low altitude or lower speed? Does anyone know?

Kind of. If you have vanilla S mode S AND a PilotAware with the same hex code configured being picked up by a 2nd PAW, your reg (from the Mode S) will be used in preference to the hex code when displayed in SD! A neat side effect of Lee's s/w implementation. It takes the reg from the mode S and position from the PAW. My testing with a Funkwerk shows that this happens even if the transponder is in STBY mode.

I think it shows the vector if the aircraft in question is a potential conflict e.g. similar altitude (?)

[The Westmorland Flyer]

My testing with a Funkwerk shows that this happens even if the transponder is in STBY mode.

That's curious and I don't understand how it can work, as on standby the transponder is not squawking and should be producing no RF output at all. I'd like to hear more! 

I just thought - it's probably because you were squawking earlier and PAW has remembered the ICAO code to callsign pairing from then.

I do agree it's a very handy facility. Of course it relies on Mode-S interrogation from the ground, which means there aren't so many places up here where it'll work!

I think it shows the vector if the aircraft in question is a potential conflict e.g. similar altitude (?)

Ah yes, that makes sense.

[ianfallon]

My testing with a Funkwerk shows that this happens even if the transponder is in STBY mode.

That's curious and I don't understand how it can work, as on standby the transponder is not squawking and should be producing no RF output at all. I'd like to hear more! 

I just thought - it's probably because you were squawking earlier and PAW has remembered the ICAO code to callsign pairing from then.

It may be a bug in the transponder s/w but I think STBY just means it's not transmitting a squawk not that it's not transmitting ADS-B messages. It was a surprise to me too!