Today's Message Index:
----------------------
1. 05:02 AM - Re: Re: ELT Antenna (Robert L. Nuckolls, III)
2. 05:09 AM - Re: Re: ELT Antenna (Robert L. Nuckolls, III)
3. 05:44 AM - Re: Re: ELT Antenna (Gerry van Dyk)
4. 06:15 AM - Re: Change to Shottky? (Robert L. Nuckolls, III)
5. 06:21 AM - Re: Wiring Verification (Robert L. Nuckolls, III)
6. 06:36 AM - Re: Re: ELT Antenna (Robert L. Nuckolls, III)
7. 07:11 AM - Re: Re: ELT Antenna (Kelly McMullen)
8. 07:15 AM - Re: Change to Shottky? (Eric M. Jones)
9. 02:10 PM - Re: Re: Change to Shottky? (Thomas Blejwas)
10. 03:11 PM - Re: Z-12 Essential Bus Questions (Robert L. Nuckolls, III)
11. 04:07 PM - Re: ELT Antenna (msmeredith)
Message 1
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At 09:16 PM 1/15/2014, you wrote:
>
>Almost all ELTs, especially the older ones do in fact radiate
>anytime they are near high powered VHF transmitters in the FM, TV, etc bands.
This phenomenon IS demonstrable . . . and rare. The
ELT isn't actually producing any output power unique
to its function. Very strong sources of local radiation
(typically FM stations and the old analog TV stations)
would find its way backwards into the output stage of
the ELT's transmitter (constantly hooked to the antenna -
receiver circuits are not so prone to exhibit this
behavior). If there are two or more strong sources,
then they can MIX or heterodyne against each other
and produce a variety of spurious signals on lots
of frequencies.
Analog TV is gone and about the only source of such
coherent energy would be an FM transmitter but you are unlikely
to spend much time flying around in the FM station's
radiation pattern and in close proximity . . . within
a mile or two.
One might hypothesize that the modern ELT's with
TWO transmitters attached to the antenna are even
more likely to exhibit the behavior . . . but you
still need to be poking around the vicinity of the
strong transmitter at altitudes generally 1000'
AGL or less.
I've heard the rumor that some ELT's were triggered
by local radiation from a comm transmitter . . . but
I've not seen any documentation or FMEA that supported
the assertion. Certainly, modern ELTs are subjected
to the standard DO-160 radiated susceptibility testing
and perhaps even HIRF (high intensity RF) testing.
None of this testing will concern itself with the
intermodulation phenomenon cited above but it would
watch for damage to the ELT and/or false triggering.
Bob . . .
Message 2
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>
>So while you may have valid points about final resting of a crash
>being upside down, during the touchdown, prior to rollout odds are
>very high that any belly antenna will be wiped off the airframe.
>IMHO, with about equal experience between tail wheel(mostly off
>pavement in Alaska) and nose dragging aircraft, in off field landing
>situations of soft surface, nose wheel is far more likely to cause
>flipping than tail wheel.
I don't recall the source now . . . it was many
moons ago . . . but the common wisdom circulated
on the TC side of the house was that on top of
the fuselage, just ahead of the vertical fin, was
the best location for ELT antennas.
If the wreckage did flip over, this location offered
the highest probability for protection by vertical
fin structure.
The 406 mHz signal will be heard nicely even if
the airplane is upside down . . . as long as the
antenna isn't broken off.
Given the magic multi-frequency design of modern
ELTs and their antennas, I suggest the installer
would do well to bite the bullet and strive for
as pristine an installation as possible per the
manufacturer's recommendations.
Hence, bottom side location or bending of the antenna
is discouraged.
Bob . . .
Message 3
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<nuckolls.bob@aeroelectric.com>
At 09:16 PM 1/15/2014, you wrote:
<kellym@aviating.com>
>
>Almost all ELTs, especially the older ones do in fact radiate
>anytime they are near high powered VHF transmitters in the FM, TV, etc
bands.
Analog TV is gone and about the only source of such
coherent energy would be an FM transmitter but you are unlikely
to spend much time flying around in the FM station's
radiation pattern and in close proximity . . . within
a mile or two.
Bob . . .
Just to throw out a thought...
Yesterday the Canadian government opened the bidding to the 700 Mhz spectrum
to cell phone companies. The departure of analog television to digital
freed up the 700 Mhz band. At some point in the future at least in Canada a
smart phone in a pilot's pocket will be communicating on the former analog
TV band. Is this something we should be worrying about this side of the
border? Any thoughts about mitigating such risks?
Gerry van Dyk
Message 4
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| Subject: | Re: Change to Shottky? |
At 03:29 PM 1/15/2014, you wrote:
>Bob: To answer your questions, this is an RV7, all metal
>airplane. The heat sink I used was the 15 watt one, the larger of
>the two offered at B&C. It weighs 7 oz.
>
>I will remove it and install directly to the aluminum subpanel.
>
>Would you change your recommendation if you knew I was in Arizona,
>occasionally flying in 100+ temperatures?
Nope. 100+ isn't 'hot' for a semiconductor.
The it's only 30F or 16C hotter than what
people like to exist in. Most semiconductor
devices are rated to operate up to 175C
AT THE JUNCTIONS . . . that is hot.
The only time your 100F hypothesis would put
a device at risk is if the heat sink were
marginal in the first place. After operating
your system loads for say 30 minutes or so
(time for temps to stabilize) put your fingers
on the device . . . you may find it 'toasty' but
it probably wouldn't 'sizzle spit' . . . most
of the time you'll find it warm but not dangerous
for the epidermis.
If you're really curious, you can put a temp
sensor on the bolt that mounts the device and get
some real numbers . . . good thing to know
and share.
If you don't have a capable remote temperature
measuring instrument, you might consider this
one . . .
http://tinyurl.com/lomcyp3
Comes with two probes and is shipped from US
location . . . fast.
No matter how convincing I might be by offering
advice from experience, there's nothing better
than to go measure it for yourself and then
report the results.
Bob . . .
Message 5
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| Subject: | Re: Wiring Verification |
At 10:19 PM 1/14/2014, you wrote:
Hello again, Bob,
Forgive me for not replying timely; I have had some computer problems
recently and unable to reply. I have stablized my system now so I am
replying before it sleeps again. Hopefully, it won't again soon.
No big deal . . . this IS a hobby . . . other
matters will often prove more pressing . . .
My Luscombe is indeed an all metal airplane. So, the distant grounds
will all be attached at the device location, on the airframe.
Looking over my supply of wire, I find that I have a sufficient
amount of 18 AWG for the power supplies and position lights but no 20
AWG on hand. As I recall from your previous narrative, other than
weight, there is no sin with utilizing a larger wire for this
duty. Since I have the 18 AWG already on hand, I'm theorizing that
would be satisfactory. However, I do have the 16 AWG wire for the
landing lights so that's a no brainer.
I wanted to thank you once again for your assistance. I am moving forward.
Very good. Pleased to hear it. Yes, there's nothing
'wrong' with having wire 'too large' or circuit protection
'too small'. Neither instance elevates risks to the airframe.
Keep us apprised of your progress!
Bob . . .
Message 6
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Just to throw out a thought...
Yesterday the Canadian government opened the bidding to the 700 Mhz spectrum
to cell phone companies. The departure of analog television to digital
freed up the 700 Mhz band. At some point in the future at least in Canada a
smart phone in a pilot's pocket will be communicating on the former analog
TV band. Is this something we should be worrying about this side of the
border? Any thoughts about mitigating such risks?
Good question . . . and far outside my personal
experience history. But then, that's what all this
DO-160/254/178 etc. etc is suppose to explore, identify
and fix. That doesn't mean the occasional 'gotcha' won't
surface in spite of best efforts . . . recent lithium
battery issues are a good example. But that's part
and parcel of any evolving technology.
I'm working on an article for Kitplanes that will attempt
to put some perspective on the lithium battery market as
it relates to our airplanes. I'm not going to suggest
that everybody pry the lead out of their airplanes
and plunk lithium down in the hole . . . but lithium
IS a rising star on the horizon . . . and there are
ways to minimize risks while exploring POTENTIALLY
attractive returns on investment.
There was a similarly bumpy start up for ni-cad batteries
on airplanes too . . . Wwwaaaayyyy back when. They offered
some spectacular performance . . . but we set a few airplanes
on fire with those batteries too. Today, the ni-cad is
still attractive for some operators but it has not displaced
the lead-acid products. Perhaps lithium will evolve to the
same kind of market position . . . perhaps not . . .
I'd say that the risks from the new phones are VERY low.
Consider the actual radiate power of any hand held device,
particularly a telephone. Digital communications technologies
work very hard to maximize performance while minimizing
energy consumption. This tends to make radiators less
hazardous and receivers more resistant to co-located
interference.
Bob . . .
Message 7
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Hmm, I don't know why the switch to digital TV will make much
difference. They are still broadcasting in my area on VHF RF channels 7
and 8 through 13 in my local area. I used to have an antenna
configuration on my Mooney that consisted of VHF com in front of
windshield, top of fuselage behind baggage compartment, Loran about 18
in. behind that, followed by ELT antenna right in front of vertical
stab. When flying VFR transition over Phoenix Sky Harbor I would get bad
squelch break anywhere within 10 nm of the antenna farm located on South
Mountain, approx 8 mi south of Sky Harbor. Made hearing controllers very
difficult.
I isolated it to the ELT by doing a flight with external ELT antenna
disconnected, which completely eliminated problem even within a mile of
the transmitters. This was a 1st generation ELT. Moving 1st com antenna
from in front of windshield to the belly virtually eliminated the
interference. Removing Loran antenna (custom version of Comant CI121)
helped as well.
I understand later versions of ELTs have somewhat better isolation of
the transmit oscillator, but doesn't completely eliminate. Good
separation between ELT and com antennas is probably best defense.
Kelly
On 1/16/2014 6:01 AM, Robert L. Nuckolls, III wrote:
> <nuckolls.bob@aeroelectric.com>
>
> At 09:16 PM 1/15/2014, you wrote:
>> <kellym@aviating.com>
>>
>> Almost all ELTs, especially the older ones do in fact radiate anytime
>> they are near high powered VHF transmitters in the FM, TV, etc bands.
>
> This phenomenon IS demonstrable . . . and rare. The
> ELT isn't actually producing any output power unique
> to its function. Very strong sources of local radiation
> (typically FM stations and the old analog TV stations)
> would find its way backwards into the output stage of
> the ELT's transmitter (constantly hooked to the antenna -
> receiver circuits are not so prone to exhibit this
> behavior). If there are two or more strong sources,
> then they can MIX or heterodyne against each other
> and produce a variety of spurious signals on lots
> of frequencies.
>
> Analog TV is gone and about the only source of such
> coherent energy would be an FM transmitter but you are unlikely
> to spend much time flying around in the FM station's
> radiation pattern and in close proximity . . . within
> a mile or two.
>
> One might hypothesize that the modern ELT's with
> TWO transmitters attached to the antenna are even
> more likely to exhibit the behavior . . . but you
> still need to be poking around the vicinity of the
> strong transmitter at altitudes generally 1000'
> AGL or less.
>
> I've heard the rumor that some ELT's were triggered
> by local radiation from a comm transmitter . . . but
> I've not seen any documentation or FMEA that supported
> the assertion. Certainly, modern ELTs are subjected
> to the standard DO-160 radiated susceptibility testing
> and perhaps even HIRF (high intensity RF) testing.
> None of this testing will concern itself with the
> intermodulation phenomenon cited above but it would
> watch for damage to the ELT and/or false triggering.
>
>
> Bob . . .
>
>
Message 8
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| Subject: | Re: Change to Shottky? |
The calculation here on the dissipation and voltage drops of Schottkys and P/N
diodes are simply being pulled out of the air. What diodes are you referring to?
You show me yours and I'll show you mine.
A "standard" 15A 50V P/N diode is 1.5 Volts Vf like 1N3208. So at 13V you get
11.5V out.
I use and sell IXYS DSSX61-0045A. Power_Deuce_Schottkys. At 15A they are 0.45Volts
Vf. So at 13VDC you get 12.55VDC out.
I supply these on heatsink. They are isolated and paired so they can be used in
Y-configurations or separate or paired.
I've looked and don't see any better diodes for general aircraft purposes. If the
difference was as small as some here have erroneously stated, we wouldn't be
having this conversation. Most modern battery operated equipment have no p/n
diodes. They waste too much power.
Remember: With diodes the measurements are often at 50% duty cycle. Also remember
that Vf is not reduced when diodes are in placed parallel (unlike R for resistors).
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=417007#417007
Attachments:
http://forums.matronics.com//files/power_deuce_schottky_manual_109.pdf
Message 9
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| Subject: | Re: Change to Shottky? |
-Eric,=0A=0AI think that I misinterpreted the use of the word "average."
- (My-aero, mechanical, and civil engineering degrees were not big on d
iodes.) -Say, for the specific diode STPS60L30CW: http://www.st.com/en/re
sources/technical/document/cd00001857.pdf- ,=0AFig. 1 provides "average f
orward power dissipation versus average forward current (per diode)."- I
now understand that the term "average" is the average for-the cycle (not
the average between the two diodes), i.e., the average amperage for a squar
e-wave cycle with a delta of 0.5 would be half the peak to peak amperage.
- So, if I understand you correctly, the voltage drop with both diodes co
nnected to the same source-should be calculated using the total current,
as if there were only one diode connected. For this particular diode assemb
ly-and my system (14A max.-at 13V), the voltage drop from Fig. 9 at a T
j of 125 degC is 0.31 to 0.32, for a power dissipation of-slightly more t
han 4W.- I would only use this diode if I were confident that I could kee
p the Tj low, because it has high leakage at high temperature and because t
his diode is only rated to 150 degC.- But the leakage versus voltage drop
is the tradeoff I see in the selection process.-
Not clear to me that we need extremely low leakage.=0A=0AI don't understan
d-why the voltage drop should be calculated as if all the current goes th
rough only one diode.- This implies that the current doesn't substantivel
y split, because if it did, the voltage drop in each diode would be lower.
- If there is a good authoritative-reference that you can suggest, I wo
uld appreciate it.- I've Googled and found different views and opinions.
=0A=0AThanks.=0A=0ATom=0A=0A=0A=0A-=0A=0A=0A>____________________________
____=0A> From: Eric M. Jones <emjones@charter.net>=0A>To: aeroelectric-list
@matronics.com =0A>Sent: Thursday, January 16, 2014 8:14 AM=0A>Subject: Aer
oElectric-List: Re: Change to Shottky?=0A> =0A>=0A>--> AeroElectric-List m
essage posted by: "Eric M. Jones" <emjones@charter.net>=0A>=0A>The calculat
ion here on the dissipation and voltage drops of Schottkys and P/N diodes a
re simply being pulled out of the air. What diodes are you referring to? Yo
u show me yours and I'll show you mine.=0A>=0A>A "standard" 15A 50V P/N dio
de is- 1.5 Volts Vf like 1N3208. So at 13V you get 11.5V out.=0A>=0A>I us
e and sell IXYS- DSSX61-0045A. Power_Deuce_Schottkys. At 15A they are 0.4
5Volts Vf. So at 13VDC you get 12.55VDC out.=0A>=0A>I supply these on heats
ink. They are isolated and paired so they can be used in Y-configurations o
r separate or paired. =0A>=0A>I've looked and don't see any better diodes f
or general aircraft purposes. If the difference was as small as some here h
ave erroneously stated, we wouldn't be having this conversation. Most moder
n battery operated equipment have no p/n diodes. They waste too much power.
=0A>=0A>Remember: With diodes the measurements are often at 50% duty cycle.
Also remember that Vf is not reduced when diodes are in placed parallel (u
nlike R for resistors).=0A>=0A>--------=0A>Eric M. Jones=0A>http://www.peri
heliondesign.com/=0A>113 Brentwood Drive=0A>Southbridge, MA 01550=0A>(508)
764-2072=0A>emjones(at)charter.net=0A>=0A>=0A>=0A>=0A>Read this topic onlin
e here:=0A>=0A>http://forums.matronics.com/viewtopic.php?p=417007#417007
=0A>=0A>=0A>=0A>=0A>Attachments: =0A>=0A>http://forums.matronics.com//files
======================0A>=0A>=0A>
=0A>=0A>=0A>
Message 10
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| Subject: | Z-12 Essential Bus Questions |
At 11:39 AM 1/11/2014, you wrote:
>Thanks Bob. I read your recent, excellent article on DO-160
>testing. With EAB airplanes, can we count on all the devices
>installed having seen the same testing? I'm planning on a bunch of
>Garmin's experimental avionics offerings and I'm not sure those
>boxes see the same testing as their certified hardware. I've
>Googled it a few times but can't find anything. I need to ask
>Garmin's Team X about it. So that's why I'm a bit shy to risk
>putting all the avionics through engine start power cycling.
Garmin doesn't have a dual-path set of products.
Everything they build for the panel has roots
in TC aircraft. DO-160 has become the 'design
bible' for any/all devices attached to a vehicular
DC power system. Except for issues of lightning
strike, gizmos that go into cars and trucks are
just as vulnerable to 'gremlins' as the
stuff that goes onto airplanes.
Garmin's "experimental specific" products are
essentially identical to their TC counterparts.
Bob . . .
Message 11
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All,
After digesting everyone's points, I decided I better pay attention to function
over beauty...I'm going to mount the ELT antenna on top of the turtleback. It'll
be a foot or so forward of the fin - can't reach inside much farther than
that anyway to beef it up and install hardware. Ordered a longer coax today.
Thanks much for all your inputs and ideas!
--------
Mark Meredith
Super Chipmunk N7DW
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=417043#417043
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