Today's Message Index:
----------------------
1. 07:01 AM - Re: what is the truth about gps antennas? (user9253)
2. 08:56 AM - Re: what is the truth about gps antennas? (Robert L. Nuckolls, III)
3. 11:23 AM - Fuse-able link (John Morgensen)
4. 01:15 PM - Re: Fuse-able link (Robert L. Nuckolls, III)
5. 02:10 PM - Re: Fuse-able link (Charlie England)
6. 04:00 PM - Re: Fuse-able link (John Morgensen)
7. 04:05 PM - Re: Fuse-able link (John Morgensen)
Message 1
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Subject: | Re: what is the truth about gps antennas? |
Read this thread:
http://forum.matronics.com/viewtopic.php?t=16766060&start=0&postdays=0&postorder=asc&highlight=&sid=4eec20ad70d380aa54524dd467494a91
While none of the postings were by engineers, their replies are based on experience.
Stein owns an avionics company. He is the expert. Follow his recommendations.
If shorter cable must be used, consider RG-58.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=486456#486456
Message 2
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Subject: | Re: what is the truth about gps antennas? |
At 09:23 PM 12/19/2018, you wrote:
>
>I'm interested in hearing from an engineer who
>might know about what really goes on with my
>stratus esg gps antenna. they say to use RG400
>cable, 10' minimum, and never paint the antenna.
>they also told me the strength ratings should
>run in the 30's. I have 3' of RG400 with a
>mechanical 90=C2=B0 elbow, I spray painted the
>antenna flat black and mounted it on the
>glareshield of my RV. my readings are all in the
>40's. they told me this shows an overdriven condition.
>so why use low impedance cable then need 10'? my
>iFly740 and Lowrance 1000 gps's have antennas
>with much smaller cables. the iFly shows WAAS
>grade accuracy, using an antenna 1/4 the size of the stratus RAMI antenna.
>when does being overdriven prove to be a
>problem? is this a situation where I could add
>more mechanical connectors to increase impedance
>rather than more cable length?
>I get the feeling things get written and then
>forever repeated, such as never paint an
>antenna, without asking any questions. could I
>use a different antenna than the RAMI brand?
>should I not worry about any of this and just go fly?
Paint MIGHT degrade antenna performance
but without laboratory grade testing, you
don't know about YOUR paint. Hence, easiest
way to deal with it is never paint. Now,
if you have a painted antenna and the receiver
is still got good signal numbers, then
the 99% sure THAT paint is not an issue.
OVER-DRIVEN? Never heard of such a thing
in GPS receivers. RG400 has an attenuation
figure on the order of 16db typical to 20 db
maximum PER 100 FEET at GPS frequencies.
Assume worst at 20db/100' for a 10' feeder cable,
shortening it to ZERO feet would raise the
signal by 2db Maximum, probably less. This
is trivial.
Color be skeptical . . .
Antenna dimensions are only
loosely related to performance. Physical
and electrical things INSIDE make the
difference . . . and the technology
is now so old that manufacturing a good
antenna is child's play.
You certainly want to minimize connections
but don't loose any sleep over it if you've
added one for enhanced maintenance.
I've got a GPS cable on my bench signal generator
that is 20' long and RG174 style (relatively
high attenuation) that drives the GPS disciplined
reference oscillator . . . it gets stood up
in less than 2 minutes even after being off
for weeks.
There's been a lot of hangar-lore floating
around the aviation environs concerning
things technical for over a century. Sadly,
many 'field representatives' of major
suppliers are not all that cognizant of
foundations in physics for the products
they sell. Stories not backed up by
measurement and/or demonstration are
suspect. GPS is no exception.
If anyone encounters a 'factory representative'
who offers less than comfortable advice,
shoot me their name and phone number.
The proof of the pudding is in the flying.
You'll be getting error messages when an
if the receiver is being improperly serviced
by what's coming down the coax.
Bob . . .
Message 3
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Two years ago I had an over-voltage event and the crowbar protection
behaved as expected. It popped the 5amp breaker. I had the alternator
(Plane Power 60amp internal) repaired and it has behaved normally since
then. The alternator stopped working this Sunday. The crimp had failed
on the 18ga to 22ga fuse-link. Closer inspection revealed that the
insulation under the heat shield on the fuse-link was almost completely
gone.
Questions:
1. Should I have inspected the fuse-link after the over-voltage incident
before putting the plane back in service?
2. Is it acceptable to solder the joint between the 18ga and the 22ga or
is a crimp connector required?
Thanks,
john
Message 4
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Subject: | Re: Fuse-able link |
At 01:23 PM 12/20/2018, you wrote:
>
>Two years ago I had an over-voltage event and the crowbar protection
>behaved as expected. It popped the 5amp breaker. I had the
>alternator (Plane Power 60amp internal) repaired and it has behaved
>normally since then. The alternator stopped working this Sunday. The
>crimp had failed on the 18ga to 22ga fuse-link. Closer inspection
>revealed that the insulation under the heat shield on the fuse-link
>was almost completely gone.
>
>Questions:
>
>1. Should I have inspected the fuse-link after the over-voltage
>incident before putting the plane back in service?
>
>2. Is it acceptable to solder the joint between the 18ga and the
>22ga or is a crimp connector required?
I would really like to have that fusible link
assembly. Can you cut it out and fabricate
a new one?
When you say "gone" . . . is it melted, charred,
evaporated? Was it Tefzel wire?
That link normally carries 3A or less. I've
demonstrated that 22AWG Tefzel will carry
20A indefinitely in the open air.
Some combination of factors stacked up to
cause this particular link to suffer
damage. A good place to start is careful
examination of the link.
Bob . . .
Message 5
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Subject: | Re: Fuse-able link |
On 12/20/2018 3:14 PM, Robert L. Nuckolls, III wrote:
> At 01:23 PM 12/20/2018, you wrote:
>> <john@morgensen.com>
>>
>> Two years ago I had an over-voltage event and the crowbar protection
>> behaved as expected. It popped the 5amp breaker. I had the alternator
>> (Plane Power 60amp internal) repaired and it has behaved normally
>> since then. The alternator stopped working this Sunday. The crimp had
>> failed on the 18ga to 22ga fuse-link. Closer inspection revealed that
>> the insulation under the heat shield on the fuse-link was almost
>> completely gone.
>>
>> Questions:
>>
>> 1. Should I have inspected the fuse-link after the over-voltage
>> incident before putting the plane back in service?
>>
>> 2. Is it acceptable to solder the joint between the 18ga and the 22ga
>> or is a crimp connector required?
>
> I would really like to have that fusible link
> assembly. Can you cut it out and fabricate
> a new one?
>
> When you say "gone" . . . is it melted, charred,
> evaporated? Was it Tefzel wire?
>
> That link normally carries 3A or less. I've
> demonstrated that 22AWG Tefzel will carry
> 20A indefinitely in the open air.
>
> Some combination of factors stacked up to
> cause this particular link to suffer
> damage. A good place to start is careful
> examination of the link.
>
>
> Bob . . .
>
Sounds like the failure was in the joint, so... Less than perfect crimp,
followed by years of increasing corrosion in the joint, causing
resistance heating in the joint?
I solder/heatshrink my fuselinks, but I trust my soldering skills (a
couple of careers that required a decent skillset).
Charlie
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Message 6
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Subject: | Re: Fuse-able link |
I'll fish it out of the trash and send it to you.
john
On 12/20/2018 2:14 PM, Robert L. Nuckolls, III wrote:
> At 01:23 PM 12/20/2018, you wrote:
>> <john@morgensen.com>
>>
>> Two years ago I had an over-voltage event and the crowbar protection
>> behaved as expected. It popped the 5amp breaker. I had the alternator
>> (Plane Power 60amp internal) repaired and it has behaved normally
>> since then. The alternator stopped working this Sunday. The crimp had
>> failed on the 18ga to 22ga fuse-link. Closer inspection revealed that
>> the insulation under the heat shield on the fuse-link was almost
>> completely gone.
>>
>> Questions:
>>
>> 1. Should I have inspected the fuse-link after the over-voltage
>> incident before putting the plane back in service?
>>
>> 2. Is it acceptable to solder the joint between the 18ga and the 22ga
>> or is a crimp connector required?
>
> I would really like to have that fusible link
> assembly. Can you cut it out and fabricate
> a new one?
>
> When you say "gone" . . . is it melted, charred,
> evaporated? Was it Tefzel wire?
>
> That link normally carries 3A or less. I've
> demonstrated that 22AWG Tefzel will carry
> 20A indefinitely in the open air.
>
> Some combination of factors stacked up to
> cause this particular link to suffer
> damage. A good place to start is careful
> examination of the link.
>
>
> Bob . . .
>
Message 7
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Subject: | Re: Fuse-able link |
I forgot to mention that this is a pretty faithful Z13/8 with dual pmags
and an S700-2-10 for off/battery/alternator.
john
On 12/20/2018 3:11 PM, Charlie England wrote:
> On 12/20/2018 3:14 PM, Robert L. Nuckolls, III wrote:
>> At 01:23 PM 12/20/2018, you wrote:
>>> <john@morgensen.com>
>>>
>>> Two years ago I had an over-voltage event and the crowbar protection
>>> behaved as expected. It popped the 5amp breaker. I had the
>>> alternator (Plane Power 60amp internal) repaired and it has behaved
>>> normally since then. The alternator stopped working this Sunday. The
>>> crimp had failed on the 18ga to 22ga fuse-link. Closer inspection
>>> revealed that the insulation under the heat shield on the fuse-link
>>> was almost completely gone.
>>>
>>> Questions:
>>>
>>> 1. Should I have inspected the fuse-link after the over-voltage
>>> incident before putting the plane back in service?
>>>
>>> 2. Is it acceptable to solder the joint between the 18ga and the
>>> 22ga or is a crimp connector required?
>>
>> I would really like to have that fusible link
>> assembly. Can you cut it out and fabricate
>> a new one?
>>
>> When you say "gone" . . . is it melted, charred,
>> evaporated? Was it Tefzel wire?
>>
>> That link normally carries 3A or less. I've
>> demonstrated that 22AWG Tefzel will carry
>> 20A indefinitely in the open air.
>>
>> Some combination of factors stacked up to
>> cause this particular link to suffer
>> damage. A good place to start is careful
>> examination of the link.
>>
>>
>> Bob . . .
>>
> Sounds like the failure was in the joint, so... Less than perfect
> crimp, followed by years of increasing corrosion in the joint, causing
> resistance heating in the joint?
>
> I solder/heatshrink my fuselinks, but I trust my soldering skills (a
> couple of careers that required a decent skillset).
>
> Charlie
>
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