Narco AR850 to Stratus ESG wiring

[MuseChaser]

Tearing what few hairs I have left out trying to figure this out..

Removed a Narco AT150 transponder, and replacing it with a Stratus ESG. Existing working altitude encoder is a Narco AR850. All quotes and pin numbers below were taken from the AT150, AR850, and ESG manuals, and connectons between the AT150 and AR850 were verified when the AT150 and original harness were removed. Currently building the new harness; the parallel data connections are obvious and no problem.

Here's the specific questions...

1. AR850 Pin 15, "Power Ground," was previously connected to AT150 Pin 2 "Ground." Should it now be connected to...

A. Directly to an aircraft ground point.
B. ESG Pin 37 "Altitude Common (GND)"
C. ESG Pin 1 or 20 "Aircraft Ground" via a jumper/splice between those two. The ESG installation manual specifies "A minimum of 2 ground pins should be tied, and the wiring diagram shows pins 1 and 20 jumpered/spliced with the note "From splice to unit, wire length should not exceed 6 inches." Pin 18 is also listed as "Aux Ground."

2. AR850 Pin 14, "Aircraft Power," was previously connected to AT150 pin 18 "Digitizer Power." Should it now be connected to...

A. ESG pin 2/21 "Aircraft Power" via jumper/splice between those two terminals. The ESG wiring diagram shows those two terminals jumped and connected to aircraft power via a 5A breaker, with the same "6 inch max" from splice to unit caveat.
B. Aircraft Power via it's own new 2A breaker.

3. AR850 Pin 6 "Enable" was previously attached to AT150 Pin 5 "Digitizer Common." Should it now be connected to...

A. ESG pin 37 "Altitude Common."
B. Aircraft Ground.
C. External switch to ground.

I'm not really sure which box (ESG or AR850) is responsible for enabling the Mode C/altitude reporting output. The AR850 manual states..

"Activating the AR850 requires that a ground be applied to P101-6,
the ENABLE input, only when the transponder is placed in the
altitude mode. Normally the transponder would be the ground
source....
If the transponder's internal ENABLE source is a permanent ground
and not altitude mode controlled, the AR850 will be permanently
enabled. When the altitude reporter is permanently enabled, the
companion transponder must have additional internal circuitry
designed to inhibit the transmission of altitude information when
it is operating in other than the altitude mode. If the
transponder cannot meet this requirement, the AR850 ENABLE input
must be controlled by a panel mounted switch."

DOES the ESG handle the Mode A/C/S switching, and AR850 Pin 6 can just be grounded keeping the AR850 active all of the time, or does attaching it to ESG Pin 7 "Altitude Common" take care of this?

Heeellllllppppp......and thank you.

 

[MuseChaser]

@Doug Reid Thanks for the reply. The AR850 in my plane has a 15-pin dsub out, w/ pins 1, 7, and 8 unused; I've attached the relevant page from the manual, printed July 2003, and identified as "MANUAL PART NO. 03753-0623," along with a snip of the actual Dsub pinout pic. This diagram agrees with the installation as I found it in the plane prior to removing the AT150 transponder. The diagram you posted doesn't match the AR850 I have, nor the manual; the revision date on yours is 4/85 and the one I have is revision date 7/03. I didn't realize the same piece of equipment had been made over such a long span of time, and I apologize for not including more specific information.. I do appreciate your reply.

 

[MuseChaser]

Got it sorted out.. a very kind local avionics installer got back to me with crystal clear clarifications and I'm good to go... will complete the installation on Friday!

 

[MuseChaser]

Follow up...

Finished installation today, and the wiring harness worked perfectly. Answers to my questions were to jump pins 1 and 20 together on the ESG, connect them to ground along w/ pin 15 of the AR850, jump pins 2 and 21 on the ESG and join them w/ pin 14 on the AR 850, and connect pin 6 of the AR850 to pin 37 of the ESG. Pressure altitude reporting as it should, power, all configured.. yay!

OK.. one definite NONYAY. The ESG NEVER displayed lat/long info. I tried to be patient... taxi'd out into a clear-view-of-the-sky area and everything... but even after more than 20 minutes never got there. VERY slowly, it got to the point where the GPS diagnostic screen was displaying between six and seven satellites vascillating w/ CN0 values of 32/33 strength (and no others)... but it took forever to get that far, and never got to a point where it displayed lat/long or a NIC value at all. I used RG-174 and mounted the included antenna above the rear-most part of the overhead trim/light/speaker console in a '65 PA28-140 Cherokee, running the cable down the center channel of the windscreen next to another antenna cable, and the total length was probably a tad over five feet, but not a lot. Manual specifies min/max cable loss 2db/7db, so I SHOULD be OK there. Tested cable/terminations for shorts/resistance prior to installation w/ no issues.

Soooo..... ideas?!?!?!? HELP!!! @weirdjim @Jesse Saint ... anyone? Bueller? Just more patience? Manual states that the "initial fix" may take as long as 20 minutes, but I gave it longer than that. Does "initial" mean "very first ever," or "every time unit is powered on?"

 

[Ryan Klems]

I remember when we did @Timbeck2 ESG the first fix did take a very long time (to the point I was a bit concerned). In this case initial does mean the very first time, however, it can continue to take a while if you fly extremely infrequently (say 30 days in between flights) as the satellite position data it has stored will be out of date and it has to wait to recollect all of that. If you fly relatively regularly, TTFF will be pretty quick.

 

[MuseChaser]

I remember when we did @Timbeck2 ESG the first fix did take a very long time (to the point I was a bit concerned). In this case initial does mean the very first time, however, it can continue to take a while if you fly extremely infrequently (say 30 days in between flights) as the satellite position data it has stored will be out of date and it has to wait to recollect all of that. If you fly relatively regularly, TTFF will be pretty quick.

Ryan,

Thanks so much for taking the time to chime in. Today I fabbed a stand-alone 12' cable of RG58 and swapped that out for the approx 6' length of RG174 I had routed as described above... just ran the temp RG58 from the antenna directly to the ESG leaving the extra looped in the cockpit. Worked GREAT. Had a fix in less than five minutes, and all of the satellite CN0 readings were in the low 40s instead of the low 30s, with a NIC of 9 instead of 0. Seems like that min 2db/max 7db loss is etched in stone, and that the RG174 was too close to -2db to work... at least that's my guess. In any case, I'm not thrilled with trying to find someplace to loop a bunch of extra feet of RG58 someplace securely and hide it, but since it worked so well that seems to be the solution. Just for yucks, I swapped the original still-routed RG174 back in, and the results were the same as they had been at first.. no fix, and only a few satellites in the low 30s CN0. Any reason not to just go with the RG58?

 

[Ryan Klems]

Any reason not to just go with the RG58?

I don't see anything in the Appareo manual that specs the actual cable (unlike Garmin), only the db loss. That being said, I do like using RG400. But, if you are getting acceptable db loss, good signal and can pass all the interference tests specified in the manual, there is no reason you couldn't use the RG58.

 

[thomasdr72]

FWIW, you can buy bulk RG400 from various suppliers on eBay for about $1.75 a foot. I stick with RG400 on XPDR/DME and GPS cables, but pretty much stay with RG58 on radios and NAV antennas (mostly because I'm cheap, and they have demonstrated adequate performance for decades and zillions of flight hours). As I recall, RG400 has about half the signal loss of RG58, but it varies a bit depending on the individual cables/frequencies/temperatures/lengths and etc...

 

[weirdjim]

RG-174 has approximately double the loss of RG-58. At 1550 MHz. RG-174 has approximately half (0.5) dB per foot while RG-58 has 0.25 dB per foot. If you need 2-5 dB of loss as per the manual, then the RG-174 needs to be more than 4 feet and less than ten feet. Double those lengths for RG-58.

Why would you buy very expensive low loss coax and then pile up a lot of it getting to a required loss factor? Sounds to me very like the RG-174 cable has a problem ... like a solder joint on the center pin of the connector not being as it should. Just my 8% of two-bits.

JIm

 

[weirdjim]

Any reason not to just go with the RG58?

Yes. RG174 has worked on dozens of our installations over the years without a single problem. 58 needs double the length and 4 times the weight of the 174. Why not find out what is wrong?

Jim

 

[MuseChaser]

Yes. RG174 has worked on dozens of our installations over the years without a single problem. 58 needs double the length and 4 times the weight of the 174. Why not find out what is wrong?

Jim

The embarassing honest answer is, at this point, a lack of patience. I have NO doubt that the RG174 would work very well while saving weight; you know about a gazillion percent more about this stuff than I do and I trust your advice. The RG174 didn't work for me probably because I got heavy/ham-handed w/ the crimps... or didn't get a perfect solder flow on one of the tips.... or did some curves tighter than the minimum radius allowed... or ziptied it a bit too tight somewhere and compressed the dielectric... whatever the reason, I'm sure it's my fault and not the cable's. I wasn't able to find suitable terminations locally to give it another try, (although I think I have enough spare 174 on hand), so I used what was available (RG58), followed your guidelines in terms of required lengths for RG58, and everything's working great except for interference from 121.17-121.22 and 131.27-131.30, due more from the proximity of the Com antenna to the GPS antenna than to cabling issues I could guess, but please let me know if the cable could be a significant part of that issue.

I do NOT like having a big coil of excess cable tied up behind the panel. I've gotten pretty good at snaking/routing the cable and a LOT better at terminating cables properly through my several attempts this week. I'll order some new RG174 terminations and give it another shot in the future after getting some badly desired flying time in again. Thanks for the help, Jim.