Here's one for all the experts.

EdFred

EdFred

Taxi to Parking
Joined
Feb 25, 2005
Messages
31,402
Location
Michigan
Display Name
The Ed
Home Airfield
9D9 / 6Y9 / 88TN
Flying along fat dumb and happy, and static (as if someone else has a stuck mic) will start on COM1, when either at the end of a transmission another aircraft or ATC makes, or just at a completely random time - when no (audible) transmission is made. If I switch frequencies on COM1 the static goes away. If I put that same frequency on COM2, I get static. It has happened on an ATC frequency, so I double checked with ATC that someone didn't have a stuck mic, and they reported everything normal. This has happened from 118.0 into the 130's. Sometimes it lasts 5 minutes, sometimes it lasts 15 minutes. Then last week Thursday I was Tx/Rx on 128.4 on COM1, Rx on 123.075 on COM2, and monitoring 121.5 on COM2, and I had the anomaly happen on both 128.4 and 123.075. I changed freqs on each radio, static gone. I swapped .075 and .4 between 1 and 2 and the static was there.

I shut off each radio, static on those specific frequencies persisted

I turned off everything in the plane except the audio panel, and transponder and the static persisted on those two frequencies.

Landed the plane, shut EVERYTHING off, turned the radios back on - the static persisted on those specific frequencies.

It's happened on 118.0 120.85(I think) 121.5 123.075 128.4 124.6, and at least one frequency in the 130's.

COM1 is a 430W
COM2 is a SL40
Audio Panel is a 340
 
Pull the antenna connector off of the ELT to see if that makes the noise go away. DON'T simply turn the ELT off, pull the antenna connector off.

Thanks,

JIm
 
weirdjim said:
Pull the antenna connector off of the ELT to see if that makes the noise go away. DON'T simply turn the ELT off, pull the antenna connector off.

Thanks,

JIm
Click to expand...
IME, A good pair of side cutters fixes a lot of static issues. Seems like at least half of the "new" airplanes to the area that I fly in have issues with static on the important frequencies around Lincoln all the way down to about 200 ft. Airline pilot friend confirmed that their jet does the same thing coming into Lincoln.

Measure the ELT antenna on an airplane that isn't doing the static ****, then cut the one on the problem airplane down to the same length. Problem solved. Not that I'd ever do such a thing...

Care to spend a little time teaching and tell me why shortening the ELT antenna reduces problems with static overwhelming the squelch on many different airplanes I've seen? Genuinely wanting to know.
 
jesse said:
IME, A good pair of side cutters fixes a lot of static issues. Seems like at least half of the "new" airplanes to the area that I fly in have issues with static on the important frequencies around Lincoln all the way down to about 200 ft. Airline pilot friend confirmed that their jet does the same thing coming into Lincoln.

Measure the ELT antenna on an airplane that isn't doing the static ****, then cut the one on the problem airplane down to the same length. Problem solved. Not that I'd ever do such a thing...

Care to spend a little time teaching and tell me why shortening the ELT antenna reduces problems with static overwhelming the squelch on many different airplanes I've seen? Genuinely wanting to know.
Click to expand...

Output transistor of the ELT Collector-Base diode is acting as a varactor, taking in as much power as it can get (from the local oscillators of the radios) and spewing it out as trash all over the band. Shortening the antenna changes the resonant frequency of the output circuit and may just take the trash and move it out of the aircraft band. You might be able to do the same thing by changing the length of the coax, but that is a hell of a lot more work. And, it might move it into another section of the aircraft band. ELT manufacturers never had to worry about this as the idiots that wrote the TSO never had a CLUE about RF reradiation.

Jim

.
 
jesse said:
IME, A good pair of side cutters fixes a lot of static issues. Seems like at least half of the "new" airplanes to the area that I fly in have issues with static on the important frequencies around Lincoln all the way down to about 200 ft. Airline pilot friend confirmed that their jet does the same thing coming into Lincoln.

Measure the ELT antenna on an airplane that isn't doing the static ****, then cut the one on the problem airplane down to the same length. Problem solved. Not that I'd ever do such a thing...

Care to spend a little time teaching and tell me why shortening the ELT antenna reduces problems with static overwhelming the squelch on many different airplanes I've seen? Genuinely wanting to know.
Click to expand...

Buy different ELTs. My old ACK is fine around here. The yellow 172 had an older Ameriking pos that was terrible.
 
Id like to know what transmitter in the Lincoln area is causing it because thee aircraft & ELTs having problems dont do it in the other cities I've flown them to.
 
Years ago, we had a mercury vapor light that generated static on the local CTAF freq. I forgot who tracked it down with directional antenna. shut it off.
The next day it was back on, the following night it was shot out.
 
The ELT hasn't changed in the 7 years I've owned the plane, and I've had the SL40 in there for a few years as well. This only started happening after the 430 got upgraded to WAAS. And it's not every flight, and there's no rhyme or reason as to when it will happen. I could disconnect the ELT as suggested, but if it doesn't happen, it's not necessarily that the ELT is the problem as I've had static free flights since the upgrade as well.
 
EdFred said:
The ELT hasn't changed in the 7 years I've owned the plane, and I've had the SL40 in there for a few years as well. This only started happening after the 430 got upgraded to WAAS. And it's not every flight, and there's no rhyme or reason as to when it will happen. I could disconnect the ELT as suggested, but if it doesn't happen, it's not necessarily that the ELT is the problem as I've had static free flights since the upgrade as well.
Click to expand...


Don't ask questions if you don't want answers.


Jim
 
weirdjim said:
Output transistor of the ELT Collector-Base diode is acting as a varactor, taking in as much power as it can get (from the local oscillators of the radios) and spewing it out as trash all over the band. Shortening the antenna changes the resonant frequency of the output circuit and may just take the trash and move it out of the aircraft band. You might be able to do the same thing by changing the length of the coax, but that is a hell of a lot more work. And, it might move it into another section of the aircraft band. ELT manufacturers never had to worry about this as the idiots that wrote the TSO never had a CLUE about RF reradiation.

Jim

.
Click to expand...

Damn, never thought of that. Makes sense. Explains why @jesse snipping ELT antennas helps sometimes too.

bnt83 said:
Id like to know what transmitter in the Lincoln area is causing it because thee aircraft & ELTs having problems dont do it in the other cities I've flown them to.
Click to expand...

My airplane did it there also. Whatever the mix is, it's freaking strong. Which would hint at broadcast transmitters, also by how widespread it is.

Smashes the standard Omaha Approach frequency with noise but not enough to cover up Omaha, just enough to make it impossible to close the squelch. Very annoying.
 
bnt83 said:
Id like to know what transmitter in the Lincoln area is causing it because thee aircraft & ELTs having problems dont do it in the other cities I've flown them to.
Click to expand...

Always seems to me like it's coming from these pair (located 9.7nm SE of the airport). The closer you get to these set the worse it gets. It goes from just keeping your static open to starting to stomp on the controllers. However it won't completely overwhelm your ability to hear ATC unless you get within a mile of it, and horizontal to it (same altitude).

First one standing at 639 ft:
http://wireless2.fcc.gov/UlsApp/AsrSearch/asrRegistration.jsp?regKey=2617129

Second one at 513 ft:
http://wireless2.fcc.gov/UlsApp/AsrSearch/asrRegistration.jsp?regKey=2627668

There are two broadcast microwave stations on it.

And three FM stations:
KFRX, 106.3 MHz, 100,000 watts erp
KBBK, 107.3 MHz, 100,000 watts erp
KLNC, 105.3 Mhz, 3,200 watts erp

118.5 and 124.0 take a beating. Maybe other frequencies as well.
 
Last edited:
EdFred said:
The ELT hasn't changed in the 7 years I've owned the plane, and I've had the SL40 in there for a few years as well. This only started happening after the 430 got upgraded to WAAS. And it's not every flight, and there's no rhyme or reason as to when it will happen. I could disconnect the ELT as suggested, but if it doesn't happen, it's not necessarily that the ELT is the problem as I've had static free flights since the upgrade as well.
Click to expand...


Remove the ELT for 90 days, go fly...

91.207,
(e) Notwithstanding paragraph (a) of this section, a person may—
(1) Ferry a newly acquired airplane from the place where possession of it was taken to a place where the emergency locator transmitter is to be installed; and
(2) Ferry an airplane with an inoperative emergency locator transmitter from a place where repairs or replacements cannot be made to a place where they can be made.
No person other than required crewmembers may be carried aboard an airplane being ferried under paragraph (e) of this section.
(f) Paragraph (a) of this section does not apply to—
(1) Before January 1, 2004, turbojet-powered aircraft;
(2) Aircraft while engaged in scheduled flights by scheduled air carriers;
(3) Aircraft while engaged in training operations conducted entirely within a 50-nautical mile radius of the airport from which such local flight operations began;
(4) Aircraft while engaged in flight operations incident to design and testing;
(5) New aircraft while engaged in flight operations incident to their manufacture, preparation, and delivery;
(6) Aircraft while engaged in flight operations incident to the aerial application of chemicals and other substances for agricultural purposes;
(7) Aircraft certificated by the Administrator for research and development purposes;
(8) Aircraft while used for showing compliance with regulations, crew training, exhibition, air racing, or market surveys;
(9) Aircraft equipped to carry not more than one person.
(10) An aircraft during any period for which the transmitter has been temporarily removed for inspection, repair, modification, or replacement, subject to the following:
(i) No person may operate the aircraft unless the aircraft records contain an entry which includes the date of initial removal, the make, model, serial number, and reason for removing the transmitter, and a placard located in view of the pilot to show “ELT not installed.”
(ii) No person may operate the aircraft more than 90 days after the ELT is initially removed from the aircraft; and
(11) On and after January 1, 2004, aircraft with a maximum payload capacity of more than 18,000 pounds when used in air transportation.
 
Yeah, I knew about the 91.207 thing.
 
The ELT varactor thing does the same thing around a strong external transmitter ... like an FM radio transmitter putting out dozens/hundreds of kilowatts.

Jim
 
weirdjim said:
The ELT varactor thing does the same thing around a strong external transmitter ... like an FM radio transmitter putting out dozens/hundreds of kilowatts.

Jim
Click to expand...

Any way a notch filter would work?
 
bnt83 said:
Any way a notch filter would work?
Click to expand...

Not really. It works something like a laser ... it takes broadband energy (anything from DC to daylight) and converts it to a spot frequency or band depending on the parameters of the individual device doing the masering (spelling ok). Jim
 
EdFred said:
Flying along fat dumb and happy, and static (as if someone else has a stuck mic) will start on COM1, when either at the end of a transmission another aircraft or ATC makes, or just at a completely random time - when no (audible) transmission is made. If I switch frequencies on COM1 the static goes away. If I put that same frequency on COM2, I get static. It has happened on an ATC frequency, so I double checked with ATC that someone didn't have a stuck mic, and they reported everything normal. This has happened from 118.0 into the 130's. Sometimes it lasts 5 minutes, sometimes it lasts 15 minutes. Then last week Thursday I was Tx/Rx on 128.4 on COM1, Rx on 123.075 on COM2, and monitoring 121.5 on COM2, and I had the anomaly happen on both 128.4 and 123.075. I changed freqs on each radio, static gone. I swapped .075 and .4 between 1 and 2 and the static was there.

I shut off each radio, static on those specific frequencies persisted

I turned off everything in the plane except the audio panel, and transponder and the static persisted on those two frequencies.

Landed the plane, shut EVERYTHING off, turned the radios back on - the static persisted on those specific frequencies.

It's happened on 118.0 120.85(I think) 121.5 123.075 128.4 124.6, and at least one frequency in the 130's.

COM1 is a 430W
COM2 is a SL40
Audio Panel is a 340
Click to expand...

One of the few occasions on which I declared an emergency was similar. I was taking a prospect up for a demo in a Cessna 320 from sea-level Boeing Field. As soon as we got up to about 500 feet (msl elevation of Sea-Tac airport) the whole cabin filled with static. I tried everything short of turning off the master (which I should have tried, in retrospect) and couldn't make it quit. So I broadcast in the blind to Seattle Approach that I was going straight out to an initial approach fix and shooting the ILS back into Boeing. Noise ended as we descended through 500 feet on final. Landed, shut down, turned it over to the maintenance folks. Didn't even get a "call this number." I think the problem was with the DME portion of the SEA VORTAC because it is UHF.

Bob Gardner
 
Last edited:
I'm scratching my head trying to figure out how the ELT could have anything to do with it unless it's on and transmitting. Is it the Opera singer and the wineglass thing?
 
luvflyin said:
I'm scratching my head trying to figure out how the ELT could have anything to do with it unless it's on and transmitting. Is it the Opera singer and the wineglass thing?
Click to expand...

But it happens on different freq' which is what makes it even more odd. I've pulled the ELT, but haven't had a chance to get out and test.
 
It's not too odd. Most ELTs since they are transmitters only and normally not used for anything are pretty simple (and crappy) radios. Theres a nice tuned circuit connected to the antenna that opens up the possibility for other signals (especially locally strong ones from adjacent antennas transmitting) to get in there and mix with other signals and cause spurious products.
 
EdFred said:
But it happens on different freq' which is what makes it even more odd. I've pulled the ELT, but haven't had a chance to get out and test.
Click to expand...

Most of this is way over my head. But I did see "RF reradiation" somewhere, that got me thinking along with the get the wire cutters and shorten the antennae, about the wineglass thing. It'll be interesting to see if pulling the ELT out changes anything. Is it an old 121.5 ELT? One of the new 406 ones?
 
luvflyin said:
I'm scratching my head trying to figure out how the ELT could have anything to do with it unless it's on and transmitting. Is it the Opera singer and the wineglass thing?
Click to expand...

You have a tuned VHF-ish antenna connected to a circuit that can mix RF frequencies that has no proper bandpass filtering on the "output" of the transmitter.

If a strong external signal (typically going to require a broadcast power level to do this) enters the ELT and is mixed with another frequency and the resulting mathematical harmonic "hits" the frequency you're attempting to receive on the Comm radio, you receive the noise from your ELT antenna.

Nearly every radio design out there in common practice uses a "mixer stage" in the circuit to mix an intermediate frequency with another and also uses mixers to multiply the relatively low frequencies inside the radio up to generate the final operating frequency.

Good quality radios include bandpass filters on that final circuit so harmonic frequencies outside of the chosen frequency range of the radio are lowered significantly in power level or essentially wiped out completely.

ELTs are not high quality radios and as @weirdjim has pointed out, output filtering is not required by the ELT verification standards -- a significant oversight for a transmitter designed to be installed in or very close to the near-field of multiple other radios on multiple bands. When you stuff RF into a transmitter from an external source like that, with no filters, it's likely to be mixed and re-radiated in enough strength to bother nearby receivers. It won't be super strong, but plenty strong enough to mess up sensitive receivers on a typical light aircraft sized object.

If you take a careful look at the bands the military operates on in the NTIA documents -- you'll notice something interesting. The bands are all harmonic relatives and can easily be filtered from other nearby radios operating on harmonically related frequencies. As one person who sat on the NTIA board in the 70s and 80s said, not joking that hard... (Paraphrased...) "The military band plan below the upper microwaves is basically what engineers could get to work on early AWACS and ELINT aircraft with tube radios and not wipe out all of the other receivers on the aircraft."

Aircraft are one of the hardest places to design radios to stay out of each other.
 
A lot of older aircraft didn't have squat for planned antenna spacing. Since more and more antennas are being installed these days we find that may times an existing antenna or two must be relocated.
 
EdFred said:
Flying along fat dumb and happy, and static (as if someone else has a stuck mic) will start on COM1, when either at the end of a transmission another aircraft or ATC makes, or just at a completely random time - when no (audible) transmission is made. If I switch frequencies on COM1 the static goes away. If I put that same frequency on COM2, I get static. It has happened on an ATC frequency, so I double checked with ATC that someone didn't have a stuck mic, and they reported everything normal. This has happened from 118.0 into the 130's. Sometimes it lasts 5 minutes, sometimes it lasts 15 minutes. Then last week Thursday I was Tx/Rx on 128.4 on COM1, Rx on 123.075 on COM2, and monitoring 121.5 on COM2, and I had the anomaly happen on both 128.4 and 123.075. I changed freqs on each radio, static gone. I swapped .075 and .4 between 1 and 2 and the static was there.

I shut off each radio, static on those specific frequencies persisted

I turned off everything in the plane except the audio panel, and transponder and the static persisted on those two frequencies.

Landed the plane, shut EVERYTHING off, turned the radios back on - the static persisted on those specific frequencies.

It's happened on 118.0 120.85(I think) 121.5 123.075 128.4 124.6, and at least one frequency in the 130's.

COM1 is a 430W
COM2 is a SL40
Audio Panel is a 340
Click to expand...
Ok Ed
This might be a little strange or even unconventional in thinking but I have had this happen in 3 different airplanes including my current new one (to me).
I will be flying along and one out of 5 flights (cross country over a few hours) my radios do the same thing, or they just go quiet.

I have proven that my 12v usb charger plugs cause this and when I un plug them it all goes back to normal. Then I can plug them back in on the next flight and something resets.

Been through 3 different usb chargers and 3 different airplanes and its all random. But when I have problems or stop hearing ATC I immediately unplug those chargers and life goes back to normal.

Always with Com1 being a Garmin GNS and com 2 being something more classic........ took a few months for the bonanza to do it but it finally did 2 weeks ago...
 
MyassisDragon said:
Ok Ed
This might be a little strange or even unconventional in thinking but I have had this happen in 3 different airplanes including my current new one (to me).
I will be flying along and one out of 5 flights (cross country over a few hours) my radios do the same thing, or they just go quiet.

I have proven that my 12v usb charger plugs cause this and when I un plug them it all goes back to normal. Then I can plug them back in on the next flight and something resets.

Been through 3 different usb chargers and 3 different airplanes and its all random. But when I have problems or stop hearing ATC I immediately unplug those chargers and life goes back to normal.

Always with Com1 being a Garmin GNS and com 2 being something more classic........ took a few months for the bonanza to do it but it finally did 2 weeks ago...
Click to expand...

Cheap USB chargers are almost always switch-mode power supplies and notorious for creating broadband RF noise. Usually a MC34063 inside them or similar.

The best option if you're experiencing it from a phone or device charger is simply to try a different brand of charger. No guarantees it won't be built the same way, and very unlikely that anything in the price range of these chargers will have any proper RF shielding, filtering, or bypassing.

Switching power supplies are just RF noisy and it has to be dealt with properly. It's rarely done in a $5 device from the Dollar Store or direct from China. The bigger name brands may or may not do a better job of it.

There's ways to use a linear voltage regulator and they're much quieter at RF, but at the cost of a LOT of heat generated when stepping down voltage. Big heat sinks and a need to get all that heat transferred to the air.

There's also ways to make a switcher that can have the switching frequency adjusted so at least all the noise it's making doesn't "hit" the RF spectrum you're trying to receive on.

I noticed a large number of certified and uncertified USB panel mount plugs at OSH for sale this year.

None had schematics or information on how they were handling a) stepping down 12/28VDC to 5V for USB, nor b) whether or not they properly handle both of the non-standard high-rate charging schemes (for lack of a better way to differentiate them, Apple's and Samsung's/Everyone Else's) for power hungry USB devices.

Assuming they do, and aren't just the standard 0.5A for USB, they're likely switchers and hopefully the manufacturer of the panel mount has tweaked the switching speed to something that won't blast VHF/UHF and GPS frequencies and properly bypassed the input and output and shielded the snot out of the things. Judging by their size though, no way.

Didn't see any USB-C ones. At least not in the brochures or on display anywhere. And the phones and phablets and tablets that need that are coming and being released now...

The "best" 12-28 VDC to 5 VDC RF quiet power supply would be a linear voltage regulator driving a few beefy transistors with negative feedback resistors on them to balance the load, mounted on big old heat sinks, or even a solid chunk of aluminum, but it would be huge and heavy and would get real warm. A nice space heater, but very RF quiet.

Until someone makes one of those in a decent but huge package, you just have to play around with different cheap switchers and try to quiet them down. And you have to test under different loads, and see what they do across the entire spectrum of VHF (and if you value things like ILS and DME and GPS you'll want to see what they do on UHF and L1 also) which is probably the real "randomness" in your scenario. Received frequency and changing loads (iPad already charged vs iPad needing a big charge at 2.1A, etc.)...

Fun stuff. Kinda. Somewhat of a PITA to make a nice RF-clean USB charger for aircraft use in both "12 Volt" and "28 Volt" systems.
 
PS: You'll get all of that cleaned up and the switch mode supplies INSIDE the phone or tablet will then make noise. Good luck quieting those down! Hehehe.
 
denverpilot said:
Cheap USB chargers are almost always switch-mode power supplies and notorious for creating broadband RF noise. Usually a MC34063 inside them or similar.

The best option if you're experiencing it from a phone or device charger is simply to try a different brand of charger. No guarantees it won't be built the same way, and very unlikely that anything in the price range of these chargers will have any proper RF shielding, filtering, or bypassing.

Switching power supplies are just RF noisy and it has to be dealt with properly. It's rarely done in a $5 device from the Dollar Store or direct from China. The bigger name brands may or may not do a better job of it.
Click to expand...

Couldn't some physical shielding inside the case be done, like a copper mesh, or something like that?
 
sferguson524 said:
Couldn't some physical shielding inside the case be done, like a copper mesh, or something like that?
Click to expand...

Yes but RF noise generated inside the charger will radiate out via the external cables. Those also need chokes or appropriate decoupling at RF frequencies. But you could stuff the entire charger inside a metal box and see if it helps. (Note: Careful of power dissipation... No airflow means it'll get a lot warmer than it was designed to get.)

And then there's still this...

denverpilot said:
PS: You'll get all of that cleaned up and the switch mode supplies INSIDE the phone or tablet will then make noise. Good luck quieting those down! Hehehe.
Click to expand...

The devices plugged into said 5V USB charger are also often RF noise radiators. Usually better designed and built than the charger by a long shot, but just turning up or down the backlight on them changes the switching frequency of a PWM circuit usually for driving the backlight LEDs, for one example, and most of them need a switch mode supply to drop everything inside down from the battery voltage to 3.3V for most mobile device components.

The usual design criteria of mobile devices is to keep the noise the device's components make, away from the frequencies (and multiples) of whatever cellular bands are being received by the device, and little effort is given to protect say, the much lower VHF spectrum.

You just can't tell where it's coming from with mobile devices and their chargers without actually sniffing it out and eliminating it. While keeping in mind that different charge rates, different screen brightness, and even "sleep" mode all may change the switching frequencies going on inside the device.

As with the power supply, the RF noise assisted in becoming stronger outside of the mobile device itself via that same USB cable, again acting as an antenna. Same problem in reverse.

There's some fascinating articles on the web about radio amateurs with RF engineering backgrounds working really hard to eliminate USB charger noise when attempting mobile weak-signal work at VHF, 220 MHz, and UHF.

Most folks who work on RF sites near large cities agree, the overall noise floor across all RF spectrum caused by so many electronic devices in densely populated areas, has risen significantly (measured in many dB and remember dB is logarithmic) over the last few decades. It's way way above the solar noise naturally seen from space.

Frankly trash like that can contribute to "static in the aircraft" too... A nice high noise floor to almost open the squelch circuit and then add garbage from an onboard mobile device and charger... It all compounds. Add I'm that inside an aircraft there's no real "ground" (although done right, some things can at least behave like a proper RF ground) to use to tie shielding to, and it's just a total pain in the butt environment for radios.
 
bnt83 said:
Installed around a 100 of them this year.

https://www.mcico.com/assets/products/ProductFliers/Flier_TA102_TrueBluePower.pdf

These seem to be popular too.

http://dacint.com/wp-content/uploads/2015/06/DAC-GDC64-flyer-03-17-15.pdf
Click to expand...

Cool. Curiosity killed the cat so I had to go read the TSOs those things claim. Boy was TSO-C71's section on RF emissions quite a laugh... 200 microvolts of RF between 90 KHz and 1500 MHz?!

And then a little disclaimer from FAA that RF levels that high WILL interfere with other onboard systems but they'll leave it up to the operator to figure it out because in the 1960s when that TSO was published, "large and expensive filters are required". Hahaha. Wow does that thing need an update...

200 frigging microvolts! Wow. That's huge.

http://rgl.faa.gov/Regulatory_and_G...a6e1e82905b86256dc1005a3ff2/$FILE/TSO-C71.pdf
 
Nate,

Thanks for the well written reply. Makes sense to me. What a PITA.
 
So, I put in a 406 ELT, got rid of the old clunker strobe, and flew it around without much issue. And then the problem returned recently. The culprit from the best I can tell....portable ADS-B in position on the glareshield. The static started twice recently, I look at the receiver, and thought what the hell...moved it. Static went away. I can put it back after the static ceases, and it won't come back. But for some reason, jut happens to be where it was sitting.
 
EdFred said:
So, I put in a 406 ELT, got rid of the old clunker strobe, and flew it around without much issue. And then the problem returned recently. The culprit from the best I can tell....portable ADS-B in position on the glareshield. The static started twice recently, I look at the receiver, and thought what the hell...moved it. Static went away. I can put it back after the static ceases, and it won't come back. But for some reason, jut happens to be where it was sitting.
Click to expand...

Stratux with the cheap SDRs? They throw off so much noise that a small GPS placed next to them won’t lock on enough satellites for a position solution.
 
Another thread resurrection..

Plane: 172
Garmin 430 (waas), Artex ELT (not sure of model)

Scenario:
ELT went off randomly at airport while plane sitting for about 5 days.
Mechanic removes ELT, sends in for testing. Placards the plane- NO ELT
I've flown the plane several times since, and so far there has been about 5 times I've lost GPS signal.
Twice on departure, then 3 times on RNAV approaches. All 3 were different approaches, (2 different at same airport, 1 at another)
Signal comes back after about 15-45 sec. typically, but the glideslope remains flagged. Horizontal guidance returns.

Only other oddity, is yesterday at yet another airport, the GNS430 radio had intermittent static, only on Tower freq. and only until about 200 ft. AGL.
Also during those static 'blips' the GNS430 showed Rx (receive).

After reading the above thread, what are possibilities?
1. Loose connection to GPS antenna due to mechanic fumbling with wires removing the ELT?
2. Interference from ELT wiring or laying across other wiring?
3. Stratux on top of panel?... but is always there and never an issue before.
4. Aliens conducting tests in area?
5. 430 has COVID-19?

??
 
Artex have a serial cable running to it from the 430? Is it just dangling somewhere now?

I’m more with your theory they knocked something loose or busted an already fragile connection but you also have that cable if your ELT was 406 with GPS input which may have created a shared ground between the devices, or been shielded cable keeping noise in when they were connected depending on which end was tied to a device’s frame ground.

Royal conjecture but you forgot about that cable if it exists as another possible source of changes. Stupid thing could be just the right length to be an antenna at some noise frequency too. Things are supposed to have RF decoupling caps in the designs and such, but a nice static buildup zap from an airframe antenna can destroy those.

And of course if no cable then disregard.

Also was the ELT activation truly unknown? Someone whack the airplane hard and not say anything? Hate to be a pessimist but... is there a shiny new antenna housing that isn’t as dirty as the rest of the airplane? Ha.

Any lightning close by on ELT day?

Totally spitballing here to show there’s more variables maybe. I’d want to get the ELT back in and properly installed before troubleshooting the Garmin. Revert all changed things first.
 
You must log in or register to reply here.
Back
Top