MGL Avionics User Forum

The signal strength is regulated basically between that of a class A and class B device. While this does make a difference to the range estimate (as you do not know the TX power of the source - you only know it is between X and Y), it still provides great value - the received signal strength drops by the square of the distance (so 4 times as much power for twice the distance). So given that, you could estimate a source say 5 miles or 10 miles away - in either case not much of an issue - but if 1 or 2 miles you may want to notify the pilot.
Sadly the mode-A and mode-C transmissions are identical in format so you cannot tell which is which - the mode-C is the more useful as it has altitude. And of course you can receive these things from a large number of aircraft and you don't have a clue if this is one or 100 aircraft. But you do have the signal strength - if it gets close it will be getting very strong - so you can warn. This is done by means of a "Ghost aircraft" that is shown with a unique call sign at the estimated distance to your right on the screen (rather than straight ahead). We don't know the direction so we put it at a known position relative to your own aircraft with a unique identifier. This way it is also compatible with other EFIS systems.

It does not work like that - transponder emissions are strictly controlled as part of the certification and the difference in signal strength between the airliner and your cessna has a fairly small bearing on the actual strength of the signal received due to the way energy dissipates in free space - with both at same distance.

Bigger effects are related to antenna placement on both emitter and receiver.

The distance estimate can typically be off by +/-50% taking all factors into account. However that is still very valuable. You can certainly distinguish easily between "about to ram you" and "no threat".

rainier wrote: Thu Feb 25, 2021 9:41 am I am busy working on our prototype ADS-B/UAT/1090ES receiver. It's the size of a SP-7 and uses the same housing. It's a true dual receiver but uses only a single antenna via a diplexer. It's a real designed for purpose system complete with SAW filters, RF preamps etc - not a repurposed satellite TV receiver. It should be quite price competitive with the DIY solutions out there. It can also evaluate ordinary mode-A and mode-C transmissions from older transponders and estimate how far the aircraft if from you based on the received signal strength which it can measure accurately. So it can be used as an early warning device even for older transponder equipped aircraft - as long as that aircraft is being interrogated by a radar or other aircraft's TCAS system.

Any idea when we might see this? It's really the only significant drawback to MGL for me right now.

It's ready but not in production and no idea when it will be.

The so called "chip shortage". It's not a shortage. It's ZERO. We cannot get some of the required chips (processors) and no indication when these will be available from the chip manufacturers. We have orders in the pipeline for quite a while but no known lead times. This particular manufacturer ST Microsystems is in fact not even taking new orders. Unfortunately others are no better so it does not even help to redesign.

We can only hope...

It's bad - really bad. The light we saw at the end of the tunnel is actually a train coming towards you...