Trasponder C mode

[The Westmorland Flyer]

On filtering ADS-B: That might be a good option but at the moment it would result in almost all traffic being filtered out.

On Transponders: I fitted a GTX328 Mode-S transponder to my aircraft during build in 2009. Unfortunately I took what was, with the 20:20 vision of hindsight, probably the wrong decision to not go for the more expensive GTX330. At the time I saw no prospect of non certified GPS equipment being permitted to provide ADS-B out data. A decision I am now coming to regret!

[Moffrestorer]

Hi Lee,

The Manual for our Becker Mode S box, states antenna output powers as follows (presumably same spec for all makes);

Class 1 (useable above 15,000'); 125W (21dBw)
Class 2 ( GA useable to 1500'); 70W (18.5 dBw)

You indicate that with mode S targets you can interrogate position and height, and measure signal strength, so far so good. Presumably there will be an output power spec that applies to Mode C transponders, also, plus height info can presumably be decoded off the transmission. So perhaps you will be able to obtain some kind of distance comparison, factoring in inverse square law power reduction?

Mode C was always going to be difficult owing to the lack of position info. I would hope that owners with this type of transponder would carry PAW also, due to its low cost and be conspicuous to other GA via the P3i transmissions. As noted in a previous post, the Zaon units will detect Mode A and C  transponders by cleverly timing the transponder transmissions and appling various algorithms to give range and relative height.

To answer Rob's post, I believe my Mode S is ES capable, but it is not yet enabled. I intend applying for the LAA minor mod asap, once Easy VFR is compatible with PAW,(and I am actually able to see  traffic) to enable me to use ADSB-Out via the PAW USB/RS232 output. ADS-B IN will be courtesy of PAW!

[SteveN]

Caution Becker..  See my post here:

http://forums.flyer.co.uk/viewtopic.php?f=1&t=93283&p=1341692&hilit=becker#p1341692

[The Westmorland Flyer]

On power, most standard form factor transponders output around 200W peak power (the RMS power is tiny, perhaps 5W max). The Trig TT31 is slightly unusual in that it is 250W peak power. I think the big boys run about 400W peak. Although it sounds like a big difference, it's only about 7dB between the lowest and the highest power and much less than that between commonly used units, which won't make a lot of difference to close-in signal strength.

On Mode-S, no positional information is sent from the aircraft in any of Modes A, C or S. Positional information is only available when Extended Squitter is supported in the transponder and ADSB out data are sent to it.

[scsirob]

The free air path loss increases about 6dB going from 1km to 2km distance. That makes 7dB difference in signal strength quite important for distance estimation. When you look at Mode-C and Mode-S transponders in the field, there are some with low output of <100W, others produce around 250W. Becker has the ATC4401 in low and high power versions.

Another issue for field strength is the antenna installation. The difference between a short run of good quality cable and a decent antenna, or a long run of cheap RG-58 with a poorly matched antenna can easily mean 4 times stronger signals from the same transponder. Certified planes will have more repeatable signal strengths when things are properly installed. With experimentals your mileage may vary (for real this time).

[the_top_pilot]

Maybe a simple answer would be just to set an alarm when a signal strength is received over a trigger threshold level. Although if you suddenly get an alarm and not knowing where to look may cause a distraction?

Steve

[Paul_Sengupta]

On Transponders: I fitted a GTX328 Mode-S transponder to my aircraft during build in 2009. Unfortunately I took what was, with the 20:20 vision of hindsight, probably the wrong decision to not go for the more expensive GTX330. At the time I saw no prospect of non certified GPS equipment being permitted to provide ADS-B out data. A decision I am now coming to regret!

Problem is, Garmin "sold" us the idea of the 330 at the time as being ES capable. Now they want another huge chunk of money to upgrage them to ES. I think all 330 (non ES) owners in Europe should get together to have a class action against Garmin for mis-selling the transponders. Maybe we could get 330s upgraded to ES for free, how they should have been in the first place.

[The Westmorland Flyer]

I *think* that when I was looking at the GTX330 back in 2009 it did include ES. At least there was no indication anywhere that this was an option that had to be bought separately. Perhaps they changed that somewhere along the line? Or maybe I just didn't investigate sufficiently. Whatever, Garmin seems to have seriously lost the plot on transponders and, I might add, Nav/Com transceivers. If 8.33 ever happens then I'll be replacing my SL30+SL40 combination with something Trig-like I expect.