Author Topic: Using PAW to test own Transponder  (Read 2637 times)

rwheeler

Using PAW to test own Transponder
« on: November 08, 2020, 11:07:16 am »
Hi,

We have a Garmin GTX 35R connected to and controlled by a Garmin G3X in our Sling 4. We also have a G5 with own GPS antenna on the same CANBUS

Following the recent article in the LAA Mag on EC I wanted to use our PAW to test the output and specifically confirm the SIL code being output.

I had previously done this during the build stage with an older version of PAW sw on the bench, and whilst the airframe was in a barn in Suffolk -  the hex code appeared as expected in the Traffic table.

Whilst testing yesterday in a hangar at Denham, I did not see our hex code in the table, but did see 15+ targets of various types.

I even tried changing the HEX code in PAW (different profile) temporarily to avoid it being filtered out but still nothing. Not sure when the filtering of own Hex code takes place?

My question is therefore, should I be seeing our own TXPDNR whilst stationary in a hangar if it set to ON and 7000? And if so what set up do I need to make this happen.

The advice in LAA TL3.03 seems to imply this should work - so what was i doing wrong!

Cheers Rod

Admin

Re: Using PAW to test own Transponder
« Reply #1 on: November 08, 2020, 11:26:33 am »
Hi Rod
I can think of two things here

1. The transponder is not emitting
2. The proximity is too close saturating the receiver front end

Btw, the GRID network of receivers is capable of reporting SIL SDA VERSION and NACP
I have proposed using this in the past as a simple automated system of detection
Thx
Lee

PaulSS

Re: Using PAW to test own Transponder
« Reply #2 on: November 08, 2020, 01:21:29 pm »
The transponder may not be emitting because it’s not being interrogated. Even if it is ‘on’ that doesn’t necessarily mean it is transmitting anything.

Is there an ATC unit nearby where interrogation ‘signals’ can be received by your transponder while it’s on the ground?
« Last Edit: November 08, 2020, 01:23:14 pm by PaulSS »

grahambaker

Re: Using PAW to test own Transponder
« Reply #3 on: November 08, 2020, 02:16:11 pm »
Parking it outside and waiting for it to be pinged by TCAS from a passing airliner (not a given these days) may be all it takes but:

- does it automatically enable ‘Ground’ mode now it’s in the aircraft?
- is ‘ON’ the right setting? On most conventional transponders, that will emit Mode A only, and you’d need to select ALT for modes C and S to be emitted.

Wadoadi

Re: Using PAW to test own Transponder
« Reply #4 on: November 08, 2020, 07:43:16 pm »
specs for modes S means it will transmit without needing to be pinged! I can't remember without fishing the spec out if it twice a second or once every 2 seconds, but either way no ping required!  auto ground mode may be a factor!

PaulSS

Re: Using PAW to test own Transponder
« Reply #5 on: November 09, 2020, 06:28:32 am »
I know that I could very well be wrong but, as I understand it, Mode S transponders will continuously transmit their address but the extended squitter doesn't reply with all the other Mode S information until the address is received by the ground station (for instance) and THEN that address it is interrogated for the other stuff. So it blasts away an address but that is not the information that we need from the Mode S information or the extended squitter data for ADSB nor to test if the transponder is working properly. You might get the HEX address of the aircraft but nothing about its altitude etc, nor about the other data that is 'selected'.

grahambaker

Re: Using PAW to test own Transponder
« Reply #6 on: November 09, 2020, 07:28:53 am »
I know that I could very well be wrong but, as I understand it, Mode S transponders will continuously transmit their address but the extended squitter doesn't reply with all the other Mode S information until the address is received by the ground station (for instance) and THEN that address it is interrogated for the other stuff. So it blasts away an address but that is not the information that we need from the Mode S information or the extended squitter data for ADSB nor to test if the transponder is working properly. You might get the HEX address of the aircraft but nothing about its altitude etc, nor about the other data that is 'selected'.
My point is that with a conventional transponder set to 'ON' it won't transmit Mode S nor Mode C, just the squawk; you need to set them to 'ALT'. I'm not familiar with the 35R but would assume the same applies, so that you can de-select squawking the altitude if requested by ATC.

PaulSS

Re: Using PAW to test own Transponder
« Reply #7 on: November 09, 2020, 08:04:15 am »
You are correct, Graham; I was replying to Wadoadi with the address musings.

I have a ground/air switch through my EFIS to the transponder so it selects ground mode, unsurprisingly, when it's on terra firma. In order to test it I need to pretend it's in the air by over-riding that ground/air logic or it will never give airbourne returns, only the Mode S ground returns. Perhaps the transponder in question has a similar switch fitted, however, I still do not believe you would get the Mode S data transmission (apart from the address) until it is interrogated by ATC/TCAS. I am more than happy to continue my education and be proved wrong  :)

mariko

Re: Using PAW to test own Transponder
« Reply #8 on: November 09, 2020, 12:11:40 pm »
I know that I could very well be wrong but, as I understand it, Mode S transponders will continuously transmit their address but the extended squitter doesn't reply with all the other Mode S information until the address is received by the ground station (for instance) and THEN that address it is interrogated for the other stuff. So it blasts away an address but that is not the information that we need from the Mode S information or the extended squitter data for ADSB nor to test if the transponder is working properly. You might get the HEX address of the aircraft but nothing about its altitude etc, nor about the other data that is 'selected'.
My point is that with a conventional transponder set to 'ON' it won't transmit Mode S nor Mode C, just the squawk; you need to set them to 'ALT'. I'm not familiar with the 35R but would assume the same applies, so that you can de-select squawking the altitude if requested by ATC.
If I'm not wrong, my trasponder can switch between "Standby" "ACS" or "AS"
Ciao
  Mariko

grahambaker

Re: Using PAW to test own Transponder
« Reply #9 on: November 09, 2020, 02:55:56 pm »
The installation manual for the 35R may provide a clue:
Quote
The GTX 35R/45R transponders are compliant with RTCA/DO-181D, which specifies that the selection of transponder ALT and GND modes may not be controlled by the pilot. To allow the transponder to beoperated in ALT mode while on the ground, for the purposes of performing periodic testing in accordancewith the requirements of 14 CFR Part 91.413, the G3X system provides a special transponder ground maintenance test mode. Refer to the G3X installation manual (190-01115-01) for information

rwheeler

Re: Using PAW to test own Transponder
« Reply #10 on: November 09, 2020, 03:46:27 pm »
Thanks Graham.
I did spot this and had tried Enabling the maintenance mode for a short time.

Still nothing showed on the PAW traffic screen but perhaps I also need to press the ALT mode key to actually activate it? It is not clear from the manual

I hope to get up to Denham this week so will do more testing and let you all know
Thanks again for all your helpful input!
Rod

exfirepro

Re: Using PAW to test own Transponder
« Reply #11 on: November 12, 2020, 11:04:48 am »
Rod,

Have you read this previous thread, which clarifies some of the issues with using your ‘ownship’ PilotAware to monitor and report on your own Mode-S / ES ADSB-Out installation?

http://forum.pilotaware.com/index.php/topic,1778.msg19225.html#msg19225

In accordance with the LAA and BMAA procedures, the test should in any case be carried out using a separate PilotAware located away from the aircraft (not least to remove the likelihood of receiver saturation). An alternative if you are still having problems is to use the detection and reporting software from the ‘Get Your Wings’ website, which can be run on a laptop. You will need a ‘spare’ SDR and antenna (which could perhaps be borrowed from another PilotAware) to connect to the laptop as the detector. I have used this system successfully on a couple of installations when a second PilotAware wasn’t available and the paperwork was accepted by the authorities.

https://getyourwings.co.uk/uncertified-gps-testing-or-just-checking-the-output-from-your-transponder/

Hope this helps.

Regards

Peter