Transponder recommendations

[denverpilot]

Follow-up, DME is fixed and was apparently something relatively simple... no details yet, but the comment "It wasn't the display, so that saved you a bunch..." was good to hear.

We probably don't have time at this point to get the new coax installed to the tail and the DME back on board prior to departing for Gastons... so we'll be there with a temporary W&B change form in hand, and a hole in the panel.

There's a weak chance we'll get 'er done tomorrow, but very weak and requires more schedule juggling than it's probably worth.

 

[murphey]

Excellent suggestion! Local shop will take a look on Monday, so no flying this weekend for me. I may go out during the weekend and see if something's come loose or the tubing is bad.

rats.

Nope - shop says nothing wrong with the static line or system. Mobil avionics truck is due out early next week. Rats. Another weekend with no flying.

 

[denverpilot]

Nope - shop says nothing wrong with the static line or system. Mobil avionics truck is due out early next week. Rats. Another weekend with no flying.

Bummer. Well, here's both hoping the test gear finds something concrete and condolences if it's the transponder.

I went /U to Gaston's and now we're working with the avionics shop to probably get the antenna coax work and the DME reinstall done. Then we can file away our 2.6 pound temporary weight and balance change document.

The avionics shop says they've had some extra business from all the massive fleet of firefighting aircraft at BJC this week and last, but they think they can squeeze us in later this week. Personally if a firefighting aircraft is down due to an avionics issue, we can be bumped around the schedule a bit. Bigger overall social priorities if you ask me.

If your airplane, my airplane, and Clark's airplane were a flying club's fleet, we'd have some really POed members right about now. Haha.

Speaking of that, I wonder what rental schedules look like at APA these days with all the hail damage. Wow.

Or the shop schedule at Arapahoe Aero or the others. Probably booked solid right up and through Oshkosh next month. Anyone not paying attention who calls to do something last-minute before a planned trip to OSH is probably going to be disappointed around here.

Bet Beegles will be busy for a while too. Hmm. Wonder if anyone's 182 got trashed. Maybe Beegles will have new plastic parts in stock soon. Sad way of thinking, I know. But they're close and they did have our instrument panel covers a couple years ago, after all.

 

[denverpilot]

DME fixed. We're a /A again.

The culprit... A $27 dollar internal fuse. Odd-ball sized and FAA approved.

And the new transponder cable was run back to the tail...

Total shop bill, $430 to test both units on the bench, replace a fuse, and run some coax. Almost all labor.

I need to get into avionics. Sheesh.

 

[murphey]

Bummer. Well, here's both hoping the test gear finds something concrete and condolences if it's the transponder.

I went /U to Gaston's and now we're working with the avionics shop to probably get the antenna coax work and the DME reinstall done. Then we can file away our 2.6 pound temporary weight and balance change document.

The avionics shop says they've had some extra business from all the massive fleet of firefighting aircraft at BJC this week and last, but they think they can squeeze us in later this week. Personally if a firefighting aircraft is down due to an avionics issue, we can be bumped around the schedule a bit. Bigger overall social priorities if you ask me.

If your airplane, my airplane, and Clark's airplane were a flying club's fleet, we'd have some really POed members right about now. Haha.

Speaking of that, I wonder what rental schedules look like at APA these days with all the hail damage. Wow.

Or the shop schedule at Arapahoe Aero or the others. Probably booked solid right up and through Oshkosh next month. Anyone not paying attention who calls to do something last-minute before a planned trip to OSH is probably going to be disappointed around here.

Bet Beegles will be busy for a while too. Hmm. Wonder if anyone's 182 got trashed. Maybe Beegles will have new plastic parts in stock soon. Sad way of thinking, I know. But they're close and they did have our instrument panel covers a couple years ago, after all.

eBay and look for "basaviationsales"

 

[denverpilot]

eBay and look for "basaviationsales"

Bunch of junk under that username right now. A lovely Northstar M3 LORAN for $12.

 

[kontiki]

ADSB rules require 1090Mhz Mode S ADSB Extended squitter above Fl 24

Below Fl24 you can use UAT.

Mode S format is necessary for AC Equipped with TCAS II. TCAS II is not the Zaxon gear, TCAS II interrogates on 1030 and listens on 1090 to detect intruders using an RF based methods with some data exchange. Transponders listen on 1030 and talk on 1090.

UAT Universal Access Transciever takes GA ADSB to 978 MHz.

UAT Aircraft under FL24 will be able to uplink 1090 traffic: iike you can with TIS now using ADS-R (repeater).


I believe they took GA to 978Mhz because they didn't want to saturate 1090 MHz.

TCAS II needs 1090 Mode S to work properly, there is probably no alternate that could be developed and deployed before 2020.

Ive seen a spec for hybrid TCAS that uses gps positions instead of RF methods but for intruder azimuth and ranging, but it's only been out there a year or so. I doubt anyone has approval for one yet.

 

[denverpilot]

Is the DME antenna cut for the same frequency range as the transponder?

I am unsure as to where they live in the spectrum , and my google FU is lacking the results...

I ASSumed DME is within the nav vhf portion of the band split and the transponders were upward of 900 mhz based on the antenna length....
The RF side has peaked my curiosity.

DME, from Wikipedia...

"An airplane’s DME interrogator uses frequencies from 1025 to 1150 MHz. DME transponders transmit on a channel in the 962 to 1150 MHz range and receive on a corresponding channel between 962 to 1213 MHz. The band is divided into 126 channels for interrogation and 126 channels for reply. The interrogation and reply frequencies always differ by 63 MHz. The spacing of all channels is 1 MHz with a signal spectrum width of 100 kHz."

The DME channels are "paired" with VHF counterparts so when you switch your Nav radio, the DME follows along.

There's usually a cable between the two for "remote" setting of the DME. My DME also has a switch to manually set the DME frequency but you set the VHF Navaid frequency you want the DME to base itself off of, and it internally selects the correct DME frequency, since DME frequencies aren't published on charts.

We also have a switch that selects whether the Nav 1 receiver or Nav 2 receiver remote is active, so you can flip it to have the DME reading off of either tuned Nav source.

Transponder receives primary radar sweep at 1030 MHz and transmits back at 1090 MHZ. Transponder is right in the middle of the DME band. Works out good for swapping antennas.

http://en.wikipedia.org/wiki/Secondary_surveillance_radar

I was Googling for a channel chart to show the gap in the DME channel assignments around the radar transponder, but can't find it right now.

If you think about it, DME is just "backwards" secondary surveillance radar without any azimuth information. The DME ground station is just a transponder. Signal from the airborne DME is received on one frequency and bent-piped back out on another. Time measured and distance known.

Add a little math to the DME receiver and it could provide a ground track. Add more ground DME stations and a frequency hopping DME systems, and...using this knowledge, it's possible (easily) with today's high speed CPUs and Nav data information storage that a navigation device could be built that could range to multiple DME stations and determine the aircraft's location as long as more than one were in range.

It'd need two stations for finding two possible locations on a map (the distance curves cross at two points) and a third to remove the ambiguity and determine which of those two crossing points the aircraft is at. Cheap and easy. How's that for cool? (And the exact same principal as GPS, but GPS uses a clocked signal for range instead of the aircraft measuring round-trip time to the birds.)

Nifty huh? All sorts of neat Nav stuff possible with all those ground based systems that folks haven't built. DME-RNAV. Could be done. You'd probably want the box to do auto-Ident. Indenting multiple DME stations would be a bugger.

 

[Everskyward]

DME-RNAV. Could be done.

It already is.

3. Navigation Issues. Pilots should be aware of their navigation system inputs, alerts, and annunciations in order to make better-informed decisions. In addition, the availability and suitability of particular sensors/systems should be considered.

(a) GPS. Operators using TSO-C129 systems should ensure departure and arrival airports are entered to ensure proper RAIM availability and CDI sensitivity.

(b) DME/DME. Operators should be aware that DME/DME position updating is dependent on FMS logic and DME facility proximity, availability, geometry, and signal masking.

(c) VOR/DME. Unique VOR characteristics may result in less accurate values from VOR/DME position updating than from GPS or DME/DME position updating.

(d) Inertial Navigation. Inertial reference units and inertial navigation systems are often coupled with other types of navigation inputs, e.g., DME/DME or GPS, to improve overall navigation system performance.

http://www.faa.gov/air_traffic/publications/atpubs/aim/aim0102.html

I guess that's what you were getting at, anyway.

 

[denverpilot]

Yeah, but I've never seen DME/DME standalone. It's usually just another input to a complex system with INS. Not really going to either, with the low prices of GPS. It's just a neat by-product of the system that can be exploited if desired for very little cost.

 

[Everskyward]

Yeah, but I've never seen DME/DME standalone. It's usually just another input to a complex system with INS.

You don't need INS to have DME-DME. That was just a list of possible sensors you could have in your FMS. We have DME-DME but no INS. It comes in handy if you lose GPS signal. You can't do a GPS approach but you can still use the FMS for enroute navigation. It's true, though, that I have never heard of standalone DME-DME either.

 

[denverpilot]

Right, I should've said I've never seen one not feeding an FMS.

Most FMS user interfaces seriously blow and they should die. Heh. Like plugging four digit codes into the freaking Lunar Lander.

 

[Everskyward]

Right, I should've said I've never seen one not feeding an FMS. Most FMS user interfaces seriously blow and they should die. Heh. Like plugging four digit codes into the freaking Lunar Lander.

The one in our airplane is not what I would call user-friendly although it's light-years better than that old Trimble 2101 I/O.

 

[cavmedic]

DME, from Wikipedia...

"An airplane’s DME interrogator uses frequencies from 1025 to 1150 MHz. DME transponders transmit on a channel in the 962 to 1150 MHz range and receive on a corresponding channel between 962 to 1213 MHz. The band is divided into 126 channels for interrogation and 126 channels for reply. The interrogation and reply frequencies always differ by 63 MHz. The spacing of all channels is 1 MHz with a signal spectrum width of 100 kHz."

The DME channels are "paired" with VHF counterparts so when you switch your Nav radio, the DME follows along.

There's usually a cable between the two for "remote" setting of the DME. My DME also has a switch to manually set the DME frequency but you set the VHF Navaid frequency you want the DME to base itself off of, and it internally selects the correct DME frequency, since DME frequencies aren't published on charts.

We also have a switch that selects whether the Nav 1 receiver or Nav 2 receiver remote is active, so you can flip it to have the DME reading off of either tuned Nav source.

Transponder receives primary radar sweep at 1030 MHz and transmits back at 1090 MHZ. Transponder is right in the middle of the DME band. Works out good for swapping antennas.

http://en.wikipedia.org/wiki/Secondary_surveillance_radar

I was Googling for a channel chart to show the gap in the DME channel assignments around the radar transponder, but can't find it right now.

If you think about it, DME is just "backwards" secondary surveillance radar without any azimuth information. The DME ground station is just a transponder. Signal from the airborne DME is received on one frequency and bent-piped back out on another. Time measured and distance known.

Add a little math to the DME receiver and it could provide a ground track. Add more ground DME stations and a frequency hopping DME systems, and...using this knowledge, it's possible (easily) with today's high speed CPUs and Nav data information storage that a navigation device could be built that could range to multiple DME stations and determine the aircraft's location as long as more than one were in range.

It'd need two stations for finding two possible locations on a map (the distance curves cross at two points) and a third to remove the ambiguity and determine which of those two crossing points the aircraft is at. Cheap and easy. How's that for cool? (And the exact same principal as GPS, but GPS uses a clocked signal for range instead of the aircraft measuring round-trip time to the birds.)

Nifty huh? All sorts of neat Nav stuff possible with all those ground based systems that folks haven't built. DME-RNAV. Could be done. You'd probably want the box to do auto-Ident. Indenting multiple DME stations would be a bugger.

Thanks, my search string was not triggering any decent results.

 

[kontiki]

DME, XPDRS, TCAS, & some Satcom systems all play in the L band. On large jets with TCAS, XPDRS, DME installations there is usually a suppression bus that connects the three.

It keeps TCAS from treating own ship XPDRS like an intruder. Failure of the suppression bus was a real concern in earlier days. Crews would see an intruder right on top of own ship that followed on all path and Alt changes.

The suppression bus also inhibits each of the 3 systems from stepping on each others transmissions.

Satcom came along much later. Supposedly modern software is now smart enough to obviate the suppression bus, but it's still the standard.

Again, I'm talking about TCAS II to DO 185 standards.

 

[denverpilot]

Yeah, if you look real carefully at the aviation portion of the NTIA allocations and correlate them to what's on board a typical AWACS, you'll notice there's a reason for the frequency allocations of almost all of the avionics out there.

Setting up AWACS and ELINT birds in the beginning days of transistorized radio and poorly understood and/or older RF filtering technology was difficult. Frequency separation was employed heavily.

It also drove almost all of the ground-based allocations. Interference coordination in limited spectrum and spectrum management is a Big Deal(TM).

People are always wanting to ask for more spectrum at NTIA meetings. It's regularly the military who says, "Ummm... No..." due to the way things are laid out to keep various transmitters out of other receivers in aircraft.

Aircraft are a tough RF systems environment. Not enough antenna separation to get out of near-field effects, floating "ground" and ground loops, all sorts of interesting challenges.

 

[Jim_R]

Aircraft are a tough RF systems environment. Not enough antenna separation to get out of near-field effects, floating "ground" and ground loops, all sorts of interesting challenges.

Aww, BS. Lightsquared says all it takes is a $5 filter and everything's hunky-dory!

 

[wsuffa]

Nifty huh? All sorts of neat Nav stuff possible with all those ground based systems that folks haven't built. DME-RNAV. Could be done. You'd probably want the box to do auto-Ident. Indenting multiple DME stations would be a bugger.

It's been done. (Edit: note that Mari already said that).

Perhaps you mean something like MLS.

BTW, there are plenty of KNS-80 RNAVs for sale these days.

 

[Anthony]

Just one word............NARCO.


You won't (will) regret it.

Yeah, go the cheap ARC route, and just hold your nose.