Electrickery

[CID]

But if you think what you're doing with a comm and a gps is an EMC test?? Well............ with only VHF frequencies?

Absolute proof that you don't have a clue. The standards are clear. Even if you are using AC 43.13. (Check 11-107) With respect to VHF COM and GPS, you are truly ignorant. VHF COM interference on GPS is well understood and MUST be explored when certifying them in aircraft.

Refer to AC 20-138D. It's the relevant guidance for installation of GNSS systems.

14-10. Interference - Electromagnetic Compatibility (EMC).

a. The equipment must not be the source of objectionable conducted or radiated interference, or be adversely affected by conducted or radiated interference from other equipment or systems installed in the aircraft.

b. Proper sensor equipment grounding is essential to ensuring EMC.

c. When possible, do not install positioning/navigation sensor(s) near a VHF radio.
d. The following paragraphs identify potential sources of interference and means of mitigating that interference:

(1) VHF communications harmonic, spurious, and local oscillator harmonics can cause interference. VHF interference can be mitigated by:

(a) Installing filters at the output of the VHF transmitter to prevent antenna-to-antenna interference. Such filters should have an insertion loss of 2 dB or less, or the installed VHF transceiver performance will have to be re-evaluated.

(b) Installing the positioning/navigation equipment as far away as feasible from any VHF transmitter equipment (to prevent case-to-case interference).

(c) Replacing the VHF equipment.

(2) An emergency locator transmitter (ELT) can re-radiate DME or VHF signals that can interfere with GNSS. Notch filters on the ELT antenna cable or replacing the ELT can eliminate this problem.

(3) DME has been known to cause interference to GNSS. Replacing the DME transceiver can eliminate the problem for some equipment. 111 3/28/14 AC 20-138D

(4) Direction finding equipment may cause interference. Moving the direction finding antenna to the belly of the aircraft has been found to eliminate this problem.

23-1. Ground Test - GPS, GPS/SBAS, and GPS/GBAS.
21-1.1. Interference.

a. The lack of interference from VHF radios should be demonstrated on the completed
GNSS installation by tuning each VHF transmitter to the frequencies listed below and
transmitting for a period of 30 seconds while observing the signal status of each satellite being
received. Degradation of individually received satellite signals below a point where navigation
is no longer possible is not acceptable and will require that additional isolation measures be
taken. Re-evaluation of installed VHF transceiver performance is not necessary if the filter
insertion loss is 2 dB or less.

b. Evaluate the following VHF frequencies (25 kHz channels):
121.150 MHz 121.175 MHz
121.200 MHz 131.250 MHz
131.275 MHz 131.300 MHz

c. For VHF radios with 8.33 kHz channel spacing, evaluate the following additional
VHF frequencies:
121.185 MHz 121.190 MHz
130.285 MHz 131.290 MHz

d. For installations on rotorcraft, ensure that the rotor blades do not interfere with the
received signals. This problem has been experienced in some rotorcraft and varies with the
rotation rate.

And....if you're interested incoming out of this fog of ignorance you're in, read this:

http://www.tc.gc.ca/eng/civilaviation/o ... 02-123.htm

[NeverBlue]

you aren't reading what I'm writing.

I've moved the alternator feed line on a certified Canadian registered Cessna 150.....

Is it a major mod or not??????????

VHF COM interference on GPS is well understood and MUST be explored when certifying them in aircraft.

....been putting GPS in A/C since 1989...all through their development...S/A...IFR approval...all that... I know what the issues are with EMI and GPS...so what
...we have to do the required post installation performance test according to the STC...which includes yes...the VHF comm interference test...FM comm and SatCom too if installed.

Every current carrying conductor in an aircraft is susceptible to EMI...They are an antenna for EMI.
Every TSO'd box has been tested for EMI through the RTCA MOPS.
Avionics installation standard practices help prevent EMI interference (AC43.13, Boeing ATA 20, AirBus ATA 20, etc)


If you were to perform your VHF radio test/EMI test on the C150 above I've mentioned and it fails the test only after I've moved the feed-line...then the VHF radio or GPS installation is the problem...not the fact that I've moved the feed-line.

The feed-line is in a shielded box called the fuselage.

does Hoptwoit's GPS installation pass the EMI test?

[CID]

Contradict yourself much?

[PilotDAR]

it fails the test only after I've moved the feed-line...then the VHF radio or GPS installation is the problem...not the fact that I've moved the feed-line.

This reminds me of the occasional "reasoning" I've heard at the scene of a car strikes utility pole/tree/parked car etc. collision. The presence of the fixed item was the cause, the driver was not at fault, he was just driving along when he hit it, 'cause it was in the way!

If you move something, you're responsible for any unintended outcome.

[CID]

The feed-line is in a shielded box called the fuselage.

You mean that thing with all the windows? I guess that's why you can NEVER make a cell phone work when you're in a 150 with the doors closed right?

Regardless, Neverblue, you don't seem to have a grasp on what electrical interference is. EMI/RFI are two distinct things. EMC is the activity in determining "compatibility" between systems that have the potential to emit electro-magnetic interference and radio frequency interference. There is "front door" interference which seems to be the type that you are convinced is the only type and "back door" interference which involves waves and fields within the protected areas in the fuselage.

When you move a generator line I would be much more interested in "back door" interference which can be "conducted" or "radiated". More terms that I have a feeling you don't know about.

A cable that carries large currents like a generator cable will have a significant electromagnetic field around it. It will be a varying field so it has the potential to induce current into nearby wiring. Improper separation and/or shielding may result in audio noise, intermittent operation or complete failure of systems.

....been putting GPS in A/C since 1989..

Scary.....

[ourkid2000]

Why do you all continue to engage? You all know how it goes......

[PilotDAR]

Why do you all continue to engage?

It's self serving, I consider it to be an element of my self study recurrent training, 'just keeps the mind working! Perhaps a few others who are keeping their heads down, are benefiting too!

[NeverBlue]

A cable that carries large currents like a generator cable will have a significant electromagnetic field around it.

WTF!!???

A current carrying conductor has a "magnetic" field around it.

Not an electromagnetic field...which propogates...which is RFI...the SAME thing as EMI.

...and I don't know what I'm talking about??

contradict science much CID????

Or maybe it's just self-serving.

[NeverBlue]

.....and all the DC current in the world through a conductor could not produce EMI which is RFI...a frequency....

...I know nothing though.....he he he he he

[NeverBlue]

Oh well...that's it I guess...

Magnetic induction...which can only happen with AC...apparently is the same thing as EMI according to some here and when I question that it's all over...

I can't understand though how originally i was questioning a hand-held non-TSO'd GPS permanently installed onto the primary bus and it not having to be certified as a major mod...

...yet amazingly moving a single DC wire has all kinds of implications..........

ANY avionics technician with half a clue should know that running audio, signal or RF wires with power wires is a NO-NO.

...it says so in your famous AC43.13.....

[PilotDAR]

....and all the DC current in the world through a conductor could not produce EMI which is RFI...a frequency...

Isn't there a conductor in an electomagnet? Doesn't that conductor carry DC current? Doesn't an electromagnet create a magnetic force, when energized? Couldn't that magnetic force interfere with an aircraft compass? Presuming this could all happen as I opine, wouldn't that mean that a DC current was interfering with a compass, because it was creating a magnetic field?

I am certain that this is possible, because I have detected magnetic compass deviation during my EMI tests, which went away, when the DC system was de-energized. Ever watched the compass while you crank an old 172, 150 or 180 series Cessna, whose starter motor is within a foot or two of most of the compass installations?

I know that there are certainly other forms of EMI, with apparently induction being one of them. I was riding jump seat, witnessing an EMI test, as was getting the chirping of the transponder over my headset. Both pilots reported none, which I confirmed happily. As I sat, still hearing the txp chirping, I unplugged the headset to walk back into the cabin. To my surprise, the chirping was still audible in my headset until I got up. I held the plugs up in front of myself, just to be sure. Yup, no electrical connection, and still the interference until I moved away. As it was not too bad, and not at all present in either pilot's headset, the test was a pass.

On another EMI test, out over Inuvik, with no EMI detected, a very pleasant voice came over the intercom, and asked if any of the three of us in the cockpit had our cell phone turned on. We all looked at each other a little sheepishly, as we all did. It seems that the EMI from our phones in the cockpit was not troublesome to the plane, but interfered with more sensitive sensing equipment in the cabin. We all apologized, and turned our phones off!

To me, "EMI" is any interference, which I can attribute to an electrical system, conductor, or component.

[NeverBlue]

To me, "EMI" is any interference, which I can attribute to an electrical system, conductor, or component.

Well YOU are totally wrong.

EMI is RF...

A magnetic field is not an RF field.

An electromagnet does not use induction.

A transformer uses induction....a transformer will not work with DC...well...it can be a light bulb for a few minutes maybe... ...a very stinky one.

And yes...a compass swing is required should I move such a conductor...that's in AC 43.13 and CAR's.

Again, anyone should know that...doesn't make it a major mod........

[NeverBlue]

To me, "EMI" is any interference, which I can attribute to an electrical system, conductor, or component.

Well YOU are totally wrong.

EMI is RF...

A magnetic field is not an RF field.

An electromagnet does not use induction.

A transformer uses induction....a transformer will not work with DC...well...it can be a light bulb for a few minutes maybe... ...a very stinky one.

And yes...a compass swing is required should I move such a conductor...that's in AC 43.13 and CAR's.

Again, anyone should know that...doesn't make it a major mod........

[DonutHole]

Lol. It specifically says that if you want to change the exact conductor you are using in your example it is a major modification.

By omission it states that the GPS install isn't a major modification.

Based on the information we are talking about, any other conclusion is asinine.

If you would like to introduce new information, like say a standard or a car, we might be able to come to a different conclusion. Unfortunately, even if you are right about the interference divergence you are still horribly wrong about your position based on the information we are actually discussing. I know you know that the language Says we are right.

[NeverBlue]

By omission it states that the GPS install isn't a major modification.

What's "it"?

You need to read the TCCA policy letter re gps installation approval.

What the FAA considers minor is not necessarily what TCCA does......

[DonutHole]

By omission it states that the GPS install isn't a major modification.

What's "it"?

You need to read the TCCA policy letter re gps installation approval.

What the FAA considers minor is not necessarily what TCCA does......

What's "it" ?

Holy shit. Whatever man, you're right, the rest of us are wrong. You need it more than we do.

[PilotDAR]

AC500-002 offers a definition:

Electromagnetic Interference (EMI) means the phenomenon occurring when electromagnetic energy present in the intended operational environment interacts with the electrical or electronic equipment causing unacceptable or undesirable responses, malfunctions, interruptions, or degradations in its performance.

'Doesn't mention RF. I entirely agree that RF interference would be classified as "EMI", but obviously TC considers "EMI" to be more broad than simply RF. I'm a little surprised that the AC does not also state "compass" as a victim, but practically a compass must be considered a possible EMI victim, because TC requires an EMI test to include a check for posible affects upon the compass - and I have found them during EMI tests.

If you were to present a mod to TC for an EMI test for design compliance, that test would be incomplete without a compass swing too.

EMI is RF..

Not according to TC's AC, though the reverse is true.

A magnetic field is not an RF field.

Agreed, though it can still be a source of "EMI" (which could result in a failed EMI test.

An electromagnet does not use induction.

Agreed, but it can still be a source of EMI!

Well YOU are totally wrong.

'You know... I have never been told that before! TC has accepted my EMI test plans, delegated me to witness EMI testing, make a finding of compliance for 2X.1301 and 1309, and issue an STC, so they don't think I'm wrong. My clients keep hiring me back, so they don't think I'm wrong... Yet one grumpy, anonymous guy on the internet, whom my peers don't seem to respect, wants me to think I'm wrong? I am unconcerned....

[DonutHole]

It's like he has half a clue.

That policy letter he was referencing says in pretty explicit terms that the type of GPS mod we are talking about is a minor modification.

Props for knowing it existed.

[NeverBlue]

It does not say that donuthole...not at all.

Read the Required Data section at the end.


HOLY COW DAR! You're confused.

EMI is RF..............

And electromagnetic wave is a radio wave...they are one in the same.

[NeverBlue]

And please....

A magnetic field and an EM field are not the same thing at all....and they don't act the same at all.

EMI moves...propagates...

A magnetic field doesn't move...it exists...the lines of flux move but only between magnetic poles of the field.....they do not propagate.

A magnetic field will induce electricity in another conductor but only if the field expands and collapses continually (AC frequency)

That's why we hear inverters all the time in headsets....