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ACK E-04 - High VSWR Error

N130WN

Well Known Member
I armed my ACK E04 ELT for the first time, with the antenna installed in the typical position under the empannage fairing. I got 5 beeps during the self-test indicating a high VSWR condition. :(

IIRC, others with this model ELT have successfully mounted the antenna in the same place. Whats the secret?

If I stand the antenna vertically (further from the surrounding structure) with a temporary mount (pic 2), no more beeps.

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Maybe it's just my computer but I'm not seeing the pictures. What kind of Coax are you using?
 
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I armed my ACK E04 ELT for the first time, with the antenna installed in the typical position under the empannage fairing. I got 5 beeps during the self-test indicating a high VSWR condition. :(

IIRC, others with this model ELT have successfully mounted the antenna in the same place. Whats the secret?

If I stand the antenna vertically (further from the surrounding structure) with a temporary mount (pic 2), no more beeps.

SMXsxp


pCDgGi

Do you have the in-line attenuator installed?

Bevan
 
Got a ham radio friend?

You might try to find a local ham with an antenna analyzer that covers UHF (like this one). With the analyzer and a spare piece of coax with connectors, you should be able to check VSWR of the installed antenna and check for other problems with the antenna or coax.

I've also used multimeters to do a first-principles check for a DC short in the antenna or coax...that would cause a high VSWR fault as well.

Hope this helps,

Dave
N1DLS
 
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...

I've also used multimeters to do a first-principles check for a DC short in the antenna or coax...that would cause a high VSWR fault as well.

Hope this helps,

Dave
N1DLS

...If I stand the antenna vertically (further from the surrounding structure) with a temporary mount (pic 2), no more beeps...

This sort of says the co-ax cable is OK.

I can't see the pictures, but I'm guessing it's the proximity of the antenna to the metal surfaces of the fuselage that is the problem, and probably out of spec. from the installation instructions...
 
Sorry about the original pictures. New links should work.

RG-400 cable is being used. No attenuator. Cable is fine, I think, as things work dandy in picture 2.

I'm pursuing a location in the wingtip for the antenna, leaving the ELT where it is behind the baggage compartment. Additional research indicates this antenna will never work in the tail of an RV -- too much surrounding metal structure.
 
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Oh, promising. Are there any visible differences between my installation and yours?

One additional thought I've had is I have the G3X magnetometer installed on the forward side of the same bulkhead as the antenna. It's not powered during the self test and the test that passes when the antenna is vertical is just as close to the magnetometer, so that doesn't seem to be a factor.
 
Tough location.

You're installing the antenna in a particularly challenging location, with the HS and VS very close by the antenna. All that metal will likely seriously de-tune the antenna (antenna are like tuning forks, they are cut to certain length so that they resonate at the design frequency), and a detuned antenna will exhibit poor SWR. Your test with the antenna standing up seems to indicate this.

You can probably fiddle a bit and find something works, according the ELT beeps, but I'd bet that the radiation pattern would be poor the resulting range of the ELT signal would be compromised. Also, I'd also bet that the resulting radiation pattern would be directed in the quadrant defined the HS and VS ... this install seems to be tossing away signal in perhaps important directions.

Last thing you want is the need for the ELT to work, but the antenna install mutes the signal into uselessness.

My $0.02
 
Measure the VSWR of the antenna as mentioned earlier.

If it's within the manufacturer's specification of <=2.5 at 121.5 MHz or <= 1.5 at 406 MHz then it's an error in the self-test.

If you are outside those numbers then you are in violation of the TSO and have no real recourse to ACK. You probably will also fall in a area were some units may check OK in self-test and others will fail.
 
Sorry about the original pictures. New links should work.

RG-400 cable is being used. No attenuator. Cable is fine, I think, as things work dandy in picture 2.

I'm pursuing a location in the wingtip for the antenna, leaving the ELT where it is behind the baggage compartment. Additional research indicates this antenna will never work in the tail of an RV -- too much surrounding metal structure.

I believe the attenuators are free to owners of Ack (mine was). It may or may not help with VSWR but either way it would be good to have it as it protects the Unit from VHF coming in on the antenna.

Bevan
 
Last thing you want is the need for the ELT to work, but the antenna install mutes the signal into uselessness.

My $0.02

I don't think anyone with any logical reasoning ability could argue with your comment, but there many instances of RV's with ant. under the emp. fairing that had accidental ELT activations that were detected and investigated.

I am comfortable with it installed under the fairing on my airplane because I see it no worse than one mounted on the turtle deck. If the airplane ends up upside down, they are both shielded by the aircraft with tail cone installation possibly even torn off.
If it doesn't end up up side down, the under fairing ant. is protected from being ripped off by flying debris (if you have seen much RV crash wreckage, it is obvious that in most survivable accidents the emp. portion of the airplane survives amazingly well)
A damaged ant. or coax cable is a common cause of ELT's failing to operate in a crash.
 
Oh, promising. Are there any visible differences between my installation and yours?

One additional thought I've had is I have the G3X magnetometer installed on the forward side of the same bulkhead as the antenna. It's not powered during the self test and the test that passes when the antenna is vertical is just as close to the magnetometer, so that doesn't seem to be a factor.

Sorry, I didn't take any photos and it will be a while before I remove the fairing again.
Best I can remember is that I positioned it the same as I always do them... with the fwd end located to keep the ant. centered between the Vert and Horz stabs as much as possible, for as far aft as possible and then secured the aft end to the skin and bottom rib flange of the vertical stab. using a plastic cable clamp, with it positioned to still keep it as far from the vertical stab as possible.
To accomplish this it usually requires making a gentle bend so that it can go up and over the fwd hor. stab. spar.
 
...
A damaged ant. or coax cable is a common cause of ELT's failing to operate in a crash.

And that is the precise reason that your ELT to antenna co-ax run should not be tightly held to the structure of the fuselage.

Don't make it neat and short like your other co-ax/cable runs...:)
 
Mine failed VSWR today

My ACK-04 has been working just fine for over two years but today it failed the VSWR test. After checking the coax connectors with no trouble found, I used a different coax and a different antenna. It still failed. Naturally, ACK is closed today, so I'm screwed. I'll do some more checking tomorrow.

In poking around their website, I noticed that there are a couple of Service Advisories out:

Service Advisory SA E-04.1 Static Suppressor (Applies to serial numbers prior to 9,650)

Service Advisory SA E-04.2 No 406 Self Test (Applies to Serial numbers 12401 through 12524)
 
My experience with antennas - from my broadcast engineering years - is that any irradiating element should not be mounted close to any large metal surface (i.e. fin and stab). The antenna will be detuned with all the big surfaces nearby. You should consider the ground plane into consideration because the whip is half a dipole - and the ground plane (in this case the aircraft skin) - will "mirror" the missing pole of the dipole so I believe that you should mount it vertically in front if the fin, for example.

If you know a ham see if you can get a MFJ-259 antenna analyzer and have your antenna tested. The MFJ-259 won't be able to test it at 406 MHz but you will be able to test it at 121.50 MHz. It will give you a clue on the irradiating system impedance at this frequency.

Ricardo
SBFI/IGU
Brazil
 
check the battery?

In the troubleshooting steps for "five beeps", the fine print says to check the battery. There's a detailed procedure for how to do that. My unit is only 2-1/2 years old and, sadly, the warranty expired after 2 years.
 
Battery failed

I checked the E-04 battery today and it failed the load test, even though it was only 2-1/2 years old. Prior to the test, the open circuit voltage read 11.68 VDC, which was above the 11.5 minimum. I used an automotive type 1156 bulb as a load, and it drew 1.7 amps when placed across the battery terminals. The battery voltage dropped to 8.3 VDC and the procedure calls for at least 10V. Prior to doing all this, I called ACK but, sadly, the technician wasn't much help. So I ordered a new battery from ACS for $170 frikkin' dollars, including "hazardous" shipping. I sure hope that fixes the VSWR problem but I won't know until next week.
 
new battery fixed vswr problem

I replaced the E-04 battery with a factory new battery pack today and it fixed the "five beeps" problem.
 
Cold temps cause self-test fail

Last week I performed my 3-month self test and it failed. I got two beeps <pause> five beeps <pause> five beeps. That translated to "low battery" and high VSWR (or low battery). Since my battery was only one year old, I was suspicious. It was below freezing when I performed the test, so I thought that might be part of the problem.

Today, it was still around freezing, but I used my hair dryer to heat up the battery pack for about 15 minutes. When I re-performed the self test, I got one beep <pause> one beep. Problem solved.

One would think that ACK would add a note in their FAQs that a cold battery will cause a failed self test.
 
Last week I performed my 3-month self test and it failed. I got two beeps <pause> five beeps <pause> five beeps. That translated to "low battery" and high VSWR (or low battery). Since my battery was only one year old, I was suspicious. It was below freezing when I performed the test, so I thought that might be part of the problem.

Today, it was still around freezing, but I used my hair dryer to heat up the battery pack for about 15 minutes. When I re-performed the self test, I got one beep <pause> one beep. Problem solved.

One would think that ACK would add a note in their FAQs that a cold battery will cause a failed self test.

Yep. I experienced the exact same thing just last month. Battery less than 1 year old. As soon as the weather warmed up a little, the self test came back just fine.
 
Thanks for the confirmation. I actually bought a replacement battery last year based upon the self-test failure so, needless to say, I'm not real happy that I wasted almost $200 for something I probably didn't need. I emailed ACK and asked them to add this cold weather information to their FAQs. I'm not holding my breath... As near as I can tell, Li-Ion batteries lose 40% of their capacity at 0*C. That number may be off, but obviously they lose enough capacity to fail the self-test.

From Digi-Key, I just ordered the 7 ohm, 15W resistor that they specify for a battery load test. (Actually, I ordered five 35 ohm, 5W resistors that I will place in parallel.) I still have my old battery pack and will test it right off the bat.
 
Reply from ACK

I just received this response from ACK. Nice of them to tell us:
Yes low temp can be a problem Lithium batteries take a while to warm up even at room temp. If you do several self test in a row at low temp you can usually an OK response. All the TSO and COSPAS testing is done after a 15 minute warm up.
 
It is fairly common knowledge that any battery acts the way you describe, in very cold temperatures. Most of the ELT's I have owned over forty years never reported anything back to the pilot. Today's technology requires more education though. I enjoy reading the manuals and tech forums.
 
I enjoy reading the manuals and tech forums.
Speaking of manuals, yesterday I was reading the installation manual for the Garmin GDL 82. It pointed out that it's possible to have too good of a coax connection to the GPS antenna. In that case, you needed to use a longer coax and coil it up to obtain more loss. The reason I mention this is that when I called ACK last year, the tech mentioned the same thing. Since I only have about an 18" RG-142 coax connecting my ELT to the antenna, he thought I might need a longer coax. This seemed absurd to me at the time, but maybe the circuitry in the E-04 is calibrated to expect a certain range of signal loss in the coax and if your coax is "too good", then the VSRW test fails. Just a theory...
 
I guess I can see the design plan for a box that checks it's own VSWR. I work with police and medical tactical radios and the installers rarely check VSWR after installation.... even though they are told to. It is a good indicator of where the RF power is actually going. Otherwise that and antenna propagation patterns are a complete mystery to most. Having read and experienced crashes where the ELT never even activated, I carry EPIRB and SPOT. My copilot always knows where I am. Right from her smartphone. Having to add coax is interesting, have not heard of that before. Now you have given me something to LEARN about. isn't Van's a cool place to hang out!
 
Speaking of manuals, yesterday I was reading the installation manual for the Garmin GDL 82. It pointed out that it's possible to have too good of a coax connection to the GPS antenna. In that case, you needed to use a longer coax and coil it up to obtain more loss. The reason I mention this is that when I called ACK last year, the tech mentioned the same thing. Since I only have about an 18" RG-142 coax connecting my ELT to the antenna, he thought I might need a longer coax. This seemed absurd to me at the time, but maybe the circuitry in the E-04 is calibrated to expect a certain range of signal loss in the coax and if your coax is "too good", then the VSRW test fails. Just a theory...

I think the Garmin manual is really talking about the transponder antenna co-ax length (loss actually) rather than the GPS antenna line.

This makes sense since the transponder signal strength and sensitivity is defined in the TSO and would affect detection ranges.

http://static.garmin.com/pumac/190-01810-00_03.pdf
 
I think the Garmin manual is really talking about the transponder antenna co-ax length (loss actually) rather than the GPS antenna line.

This makes sense since the transponder signal strength and sensitivity is defined in the TSO and would affect detection ranges.

http://static.garmin.com/pumac/190-01810-00_03.pdf

The Garmin 400W series manual (including 430W, and likely the 500W series as well) requires GPS antenna cable loss to be within a certain minimum and maximum range. In fact, they say that you may have to add additional cable and just coil it up somewhere to get a minimum loss:

333eg04.jpg


The GDL-82 uses the same GA35 antenna and may use similar receive circuitry, necessitating "building in" some additional attenuation through use of a longer-than-necessary cable. I initially had this problem with my GNS480 as well. A very short run of RG400 to the antenna produced lots of drop-outs on position lock. A new 13-foot long RG400 cable was made and coiled up behind the panel. Haven't had a single drop-out in over 300 ours of operation since.

However it is doubtful the same mechanism is in play with the E-04. GPS antennas have internal amplifiers, and the receiver inside the 400W series gets overwhelmed when the signal is too strong. The E-04 is basically just a transmitter with an antenna connected. No receiver to overwhelm, so there's probably no such thing as too little loss in the antenna cable.

edit: snopercod said the ACK tech advised a longer cable to the ELT antenna. Interesting! Does this mean their VSWR self-test is flawed? It would be a shame to attenuate transmitter power on a lifesaving device just to pass a VSWR self-test.
 
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...the ACK tech advised a longer cable to the ELT antenna. Interesting! Does this mean their VSWR self-test is flawed? It would be a shame to attenuate transmitter power on a lifesaving device just to pass a VSWR self-test.
The language you posted from the GPS manual is what I originally saw. Like you, I can't see how that would apply to an ELT. Real VSWR meters use a lot of black magic and voodoo. I seriously doubt that there's a true VSWR meter built into the ELT. Rather, I suspect ACK uses a proxy; I'm guessing they use battery current (or voltage), which is why they say a low battery can give a false "High VSWR" failure. If I understand correctly, a High VSWR would mean there's too much reflected power and not enough being delivered to the antenna. It seems that would manifest itself in lower current draw from the battery, but I could be wrong. Like I say, it's all magic ;)

Anyway, today I tested my 3 year old battery pack - the one that I removed -and it still fails. First, I measured the battery voltage open circuit, and then with a 7 ohm load. At 48 deg. F (the temp in my hangar this morning), O.C. voltage was 12.17, which dropped to 8.23V under load. I waited 20 seconds as they recommend and the voltage increased to 8.60 volts. I assume that's because the batteries are warming up under load. Regardless, ACK says the voltage under load must be >10V so that was a FAIL.

Then I used a hair dryer to heat up the battery pack for 5 minutes and re-performed the test. This time I got only 11.65V open circuit (spec is greater than 11.6V) and 9.19 under load. Better, but no cigar. I measured the current draw and it was 1.29 Amps. Better, but still a FAIL. I have no idea why the O.C. voltage was lower this time.

I plan to run the test one more time by leaving the battery in a 70 deg. F location for several hours. This battery pack should have still been good, since my ELT was never activated (except momentarily for testing) since new. They're supposed to be good for five years, right?
 
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