MGL Avionics User Forum

rainier wrote: ↑Tue Oct 27, 2020 12:23 pm plus mode-A/C receiver and distance estimator.

So a form of TAS? Is it estimating distance based on receive dBm?

Yes - the received signal strength serves as a distance estimator since the propagation loss in free atmospheric space is well known. Variables here are the power of the transmitter, antenna cable length and antenna tune/positioning on both sides. On the SP-14 side the cable attenuation can be compensated for.
Overall we can expect around a +100% to -50% error in distance estimation in real life - but that is still very valuable. We also have the altitude of the intruder from its mode-C transmission. So the SP-14 can tell you to lookout but not in which direction. Of course mode-s and UAT send actual position so that gives us more accurate distance and direction. It is possible for mode-s to not send the ES (i.e. no position) in which case the SP-14 will use the mode-A/C determination here as well.

So Rainier, after a lengthy work-related hiatus from building my helicopter, I'm back at it. During my hiatus I see that you've made progress on both a Mode-S transponder, and a ADS-B/in receiver - the final pieces to my MGL puzzle. To keep moving on this last stage of the project I'm wondering if you have finalized the designs enough to provide some form-factor information that would allow me provide space for the gear, and to lay some wire. Some questions:

1. Is the enclosure of the SP-14 going to be the same as my SP-6, SP-12 and iEFIS Extender?
2. Is the enclosure of the T16 going to be the same as my V16? If not, what will the box look like?
3. Antenna diversity is important to me; I've heard that the T16 will have that capability. True or false? If true, what will be the configuration of the antenna(e) connection(s)?
4. Will the communications protocol for the SP-14 and T16 be CANBUS or RS232?
5. Any chance of diplexing to use a common antenna for the SP-14 and the T16 (one of the T16 antennae, if two are required for diversity)?
6. Apart from coax, power, ground and communications, are there any other anticipated connections for which preparations could be made?

Thanks, Dave Kroontje

Kroontje wrote: ↑Thu Nov 19, 2020 12:19 am So Rainier, after a lengthy work-related hiatus from building my helicopter, I'm back at it. During my hiatus I see that you've made progress on both a Mode-S transponder, and a ADS-B/in receiver - the final pieces to my MGL puzzle. To keep moving on this last stage of the project I'm wondering if you have finalized the designs enough to provide some form-factor information that would allow me provide space for the gear, and to lay some wire. Some questions:

1. Is the enclosure of the SP-14 going to be the same as my SP-6, SP-12 and iEFIS Extender?

Yes.

2. Is the enclosure of the T16 going to be the same as my V16?

Yes.

3. Antenna diversity is important to me; I've heard that the T16 will have that capability. True or false? If true, what will be the configuration of the antenna(e) connection(s)?

There are various ways and they are not completely certain at this stage. The T16 is designed to interface to a smaller transponder (effectively a TSO-C199 device but full power and full compliance) using a high speed link to between them. This however is dependent on the cost of the most expensive part of thetransponder - the final TX power stage transistor which costs much more than everything else put together. This is sadly not helped by the fact that effectively we are left with only a single manufacturer of a transistor directly made for this application.
We are working with a specialized semiconductor manufacturer to try and make something cheaper.
The second option is a dedicated T16D transponder which has the diversity built in - this is very similar to the T16 but has two receivers and uses a single TX stage with an antenna switch. This is fairly cost effective but will only be released after the T16 is well into production.
Finally the third option - as you know one competitor is selling a transponder as "diversity" but it is anything but - they simply use a dipol antenna mounted at the tail of an aircraft. I am watching this with interest as it is not compliant and poses some interesting technical challenges in metal skinned aircraft (effectively your transponder is blocked from transmitting in many forward angles). This kind of thing has been tried before and failed. Anyway - should the authorities allow this (I cannot see how - it's not DO181 diversity compliant in any way) - if it gets the nod - it would mean you can do that with ANY transponder - making up a simple dipol is dead easy.

4. Will the communications protocol for the SP-14 and T16 be CANBUS or RS232?

Both, SP-14 also adds a wifi node so you can use many flight planners on tablets.

5. Any chance of diplexing to use a common antenna for the SP-14 and the T16 (one of the T16 antennae, if two are required for diversity)?

It's possible but generally I do not recommend that if you are using a powerful transponder. There is no way even a good diplexer will not mute the receiver on the 978Mhz UAT feed.

6. Apart from coax, power, ground and communications, are there any other anticipated connections for which preparations could be made?

Nothing for now - wiring is pretty straight forward, like with all our current systems - not much to do and easy to add something afterwards (The joy of CAN bus).

Rainier, will the T16 be able to use a Garmin G430W ADSB+ GPS position RS232 source?

Thanks
Cecil

Rainier,

Two more T16/T16D questions:

1. Am I correct to assume that the T16D will have connections for two antenna cables?

2. Will both transponders have inputs for signaling air/ground state, and if so, what will be the signal (pulling a pin to ground, I hope)?

Although it is my impression that the FAA isn't requiring air/ground differentiation for rotorcraft, I have the transponder wiring plan set up to indicate ground state when the collective is full or nearly-full down, AND there is no engine oil pressure. There's no place for a squat switch.

Thank you!

Dave K

hpmicrowave wrote: ↑Thu Nov 19, 2020 12:45 pm Rainier, will the T16 be able to use a Garmin G430W ADSB+ GPS position RS232 source?

Thanks
Cecil

Garmin does not publish this protocol. I have sent a request for it to them but as expected, I am getting ignored. So for now the answer is NO.
But you can use the SP-12 of course which is equivalent and a whole lot cheaper. You can also use a TN72 from Trig or for that matter any GPS source that is NexNav protocol compliant.
Should Garmin one day make their protocol available I'll add it.

Kroontje wrote: ↑Thu Nov 19, 2020 4:49 pm Rainier,

Two more T16/T16D questions:

1. Am I correct to assume that the T16D will have connections for two antenna cables?

Yes. That is needed as you need to connect two antennas only one of which may transmit at any point in time.

2. Will both transponders have inputs for signaling air/ground state, and if so, what will be the signal (pulling a pin to ground, I hope)?

I assume you are referring to the option of having a T16 transponder slaved to a TSO-C199 transponder to be diversity compliant.
No - you only need to provide power and a high speed datalink cable (Single twisted pair) between the two transponders. The TSO-C199 transponder will be slaved to the T16 and obtain all needed information from it.

Yes I know, IEEE has now mandated we are no longer to use "Master" and "Slave" in our products. Starting to get just a tad ridiculous.

Although it is my impression that the FAA isn't requiring air/ground differentiation for rotorcraft, I have the transponder wiring plan set up to indicate ground state when the collective is full or nearly-full down, AND there is no engine oil pressure. There's no place for a squat switch.

If you are using one of our EFIS systems the state can be transmitted from the flight status of the EFIS - no further wiring required. This is fully compliant as per latest DO181. The EFIS is allowed to make that decision based on its sensor information to detect an active flight.

Rainier,

2. Will both transponders have inputs for signaling air/ground state, and if so, what will be the signal (pulling a pin to ground, I hope)?

I assume you are referring to the option of having a T16 transponder slaved to a TSO-C199 transponder to be diversity compliant.
No - you only need to provide power and a high speed datalink cable (Single twisted pair) between the two transponders. The TSO-C199 transponder will be slaved to the T16 and obtain all needed information from it.

Yes I know, IEEE has now mandated we are no longer to use "Master" and "Slave" in our products. Starting to get just a tad ridiculous.

I was referring to both the T16 and T16D with that question. Trig transponders, for example, have a connector pin which when pulled low sends an “on-ground” signal, typically accomplished by a squat switch. In my case the ground signal would occur when the helicopter has no engine oil pressure and the collective stick is full down (in such a case the copter is either on the ground or, it is in an autorotation and will be on the ground momentarily).

Since a helicopter can hover at considerable altitude, absent an external input, I assume that the EFIS and transponder system would need to consider altitude and underlying terrain elevation to determine if the aircraft is hovering or sitting on the ground.

Will the iEFIS and the T16 or T16D combo be able to correctly provide ADS-B air/ground state signal without an external input?

Although it is my impression that the FAA isn't requiring air/ground differentiation for rotorcraft, I have the transponder wiring plan set up to indicate ground state when the collective is full or nearly-full down, AND there is no engine oil pressure. There's no place for a squat switch.

If you are using one of our EFIS systems the state can be transmitted from the flight status of the EFIS - no further wiring required. This is fully compliant as per latest DO181. The EFIS is allowed to make that decision based on its sensor information to detect an active flight.

Yes, I am using iEFIS Discovery lite.

To clarify, all our transponder models have a squat switch input - this is a simple grounded input (connect to ground to signal ground state - it is also possible to invert the state via setup and you may also use a voltage source (0V / 3V or higher).

You don't have to use it - you can wire the squat switch to the head (it is a Vega head similar to the one used for the V16) or you can wire it to the EFIS or you don't use it at all and use the EFIS to use its sensor logic to determine the status.

The T16/T16D can also be ordered with a built in very high accuracy encoding altimeter for stand alone operations (i.e. where there is no other compliant pressure altitude source available).

The T16/T16D can be selected to operate as a simple mode-A/C transponder, a fully compliant class-1 mode-ACS to level 2 els, you can also select a simple mode-s (without the extended squitter active). You can also select it to be a TSO-C199 compliant beacon transponder (that does not answer to ATC all-call). Finally if you have selected the fully compliant DO181 mode you can select if it should shut up if it is in ground mode (like many transponders do) or if it should answer to ATC using the ground mode transmissions.

It's jack of all trades - and low cost.