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Fred Klein
Joined: 26 Mar 2012 Posts: 503
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Posted: Fri Oct 18, 2013 10:04 am Post subject: elec. noise in antennas |
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All,
I have been diligent in separating antenna wiring from power wiring...in my fiberglass airframe, I molded in conduits along the sides of the fuselage...all power wiring on the port side...antenna wiring and pneumatics on starboard.
My port conduit is getting pretty filled, and I have ample space in the stbd conduit.
With my batteries mounted aft, I have 2AWG feed to the starter and a 2 AWG ground wire from battery to engine.
So here's a question:
Since the feed to the starter is only passing current when the starter contactor is closed, can I run its feed along w/ my RG58 com and xpndr antenna wires?...or will the mere presence of the starter feed (all that metal!) alongside the antenna wires degrade my reception and transmissions?
And...am I correct in reasoning that the 2AWG ground wire definitely needs to stay away from those antenna wires?
thanks for your insights,
Fred
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tim2542(at)sbcglobal.net Guest
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Posted: Fri Oct 18, 2013 11:19 am Post subject: elec. noise in antennas |
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Is this a pusher with the engine and battery aft?
In either case, some separation is good insurance, more is better where possible. Less so if your using good coax like RG 400.
I'd suggest just do the best you can to keep them apart at least a couple of inches. The 2AWG ground will be busy when you crank like you said, but if you have an alternator or electronic ignition or engine monitoring system it could have 30-40 amps on it at times after start, probably 8-12 or so on it after the battery is charged. I'd still keep apart as far as is reasonably possible.
Just one opinion...
Tim
All spelling errors are Apples responsibility.
Quote: | On Oct 18, 2013, at 11:04 AM, Fred Klein <fklein(at)orcasonline.com> wrote:
All,
I have been diligent in separating antenna wiring from power wiring...in my fiberglass airframe, I molded in conduits along the sides of the fuselage...all power wiring on the port side...antenna wiring and pneumatics on starboard.
My port conduit is getting pretty filled, and I have ample space in the stbd conduit.
With my batteries mounted aft, I have 2AWG feed to the starter and a 2 AWG ground wire from battery to engine.
So here's a question:
Since the feed to the starter is only passing current when the starter contactor is closed, can I run its feed along w/ my RG58 com and xpndr antenna wires?...or will the mere presence of the starter feed (all that metal!) alongside the antenna wires degrade my reception and transmissions?
And...am I correct in reasoning that the 2AWG ground wire definitely needs to stay away from those antenna wires?
thanks for your insights,
Fred
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Fred Klein
Joined: 26 Mar 2012 Posts: 503
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Posted: Fri Oct 18, 2013 1:08 pm Post subject: elec. noise in antennas |
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On Oct 18, 2013, at 12:19 PM, Tim Andres wrote:
Quote: | Is this a pusher with the engine and battery aft? |
Tim...to clarify, my engine is a tractor (forward) w/ battery aft...Fred
[quote][b]
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nuckolls.bob(at)aeroelect Guest
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Posted: Fri Oct 18, 2013 3:41 pm Post subject: elec. noise in antennas |
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At 01:04 PM 10/18/2013, you wrote:
Quote: |
All,
I have been diligent in separating antenna wiring from power
wiring...in my fiberglass airframe, I molded in conduits along the
sides of the fuselage...all power wiring on the port side...antenna
wiring and pneumatics on starboard.
My port conduit is getting pretty filled, and I have ample space in
the stbd conduit.
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There is no demonstrable value in separating antenna
coax wires and other ship's wiring. The idea that
'noise' escapes ships wiring to invade the inner-sanctum
of your coax is a poplar myth morphed into sage advice.
Quote: | With my batteries mounted aft, I have 2AWG feed to the starter and a
2 AWG ground wire from battery to engine.
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How do you know htat you need 2AWG feeders?
How long are your battery-to-firewall runs?
Bob . . .
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Fred Klein
Joined: 26 Mar 2012 Posts: 503
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Posted: Fri Oct 18, 2013 5:08 pm Post subject: elec. noise in antennas |
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On Oct 18, 2013, at 4:40 PM, Robert L. Nuckolls, III wrote:
Quote: | Quote: | With my batteries mounted aft, I have 2AWG feed to the starter and a 2 AWG ground wire from battery to engine.
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How do you know htat you need 2AWG feeders?
How long are your battery-to-firewall runs? |
Bob...thanks for asking...
I don't in fact "know" that I need 2 AWG feeders...I used that size solely for the purpose of emphasizing that the problem I was facing was caused by some VERY large wires; I note however that Z-19RB calls for 2AWG feeder from battery contactor to starter contactor.
My "battery-to-firewall runs" are exactly 9 feet; firewall to starter is another 3 to 4 feet.
Fred
PS: Thanks for dispelling one more myth!
[quote][b]
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nuckolls.bob(at)aeroelect Guest
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Posted: Sat Oct 19, 2013 6:03 am Post subject: elec. noise in antennas |
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Quote: | I don't in fact "know" that I need 2 AWG feeders...I used that size
solely for the purpose of emphasizing that the problem I was facing
was caused by some VERY large wires; I note however that Z-19RB
calls for 2AWG feeder from battery contactor to starter contactor.
My "battery-to-firewall runs" are exactly 9 feet; firewall to
starter is another 3 to 4 feet.
Fred
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Understand. Recall that the Z-Figures are ARCHITECTURE drawings
and that wire gauge callouts need to be validated against
the real needs of your proposed system. Let's do a little
sharp pencil work with your FAT wires:
4AWG wire has a resistance of 300 micro-ohms per foot. Your
FAT wire engine cranking loop is 24 feet log. This means
that the loop resistance in wire is on the order of 300 x
24 = 7200 micro ohms or 7.2 milli ohms. Assume a difficult
cranking event at 200A for your proposed engine. 200 x .0072
= 1.4 volts drop. You've got 2 RG batteries in parallel with
something on the order of 7 milliohms each or 3.5 milliohms
paralleled for cranking. 200A tosses off an additional 0.7
volts at the battery terminals.
A rule of thumb target for terminal voltage at the starter
is 9.0 volts. Starting with 12.5 volt battery
we give up 1.4 volts in wire at 0.7 volts at the batteries
This says we can toss off another 1.4 volts in contactors,
terminals and bolted joints. Seems like ample head-room.
Your FAT wire runs are analogous to cranking somebody else's
car on a cold morning with a 12' long set of jumper cables
fabricated from 4AWG wire. The first hi-performance set
of jumper cables I built were made of 2AWG welding cable . . .
got the cue from a service truck operator who's jumper
cables were obviously ROBUST. In subsequent years and
repeats of the jumper-cable fabrication task, I deduced
that the AAA Truck was rigged for worst case situations
involving vehicles a lot larger than aunt Minnie's
Dodge Dart. A little sharp pencil work deduced that
for us little guys, 4AWG offers adequate performance
with some left over.
Suggest you can re-size your deliberations about
space in your wiring conduits assuming the smaller
wire.
Bob . . .
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Fred Klein
Joined: 26 Mar 2012 Posts: 503
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Posted: Sat Oct 19, 2013 8:23 am Post subject: elec. noise in antennas |
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On Oct 19, 2013, at 7:03 AM, Robert L. Nuckolls, III wrote:
Quote: |
Understand. Recall that the Z-Figures are ARCHITECTURE drawings
and that wire gauge callouts need to be validated against
the real needs of your proposed system. Let's do a little
sharp pencil work with your FAT wires:
4AWG wire has a resistance of 300 micro-ohms per foot. Your
FAT wire engine cranking loop is 24 feet log. |
Bob,
Yes...being an architect, I do keep in mind that your Z-xx diagrams are conceptual frameworks subject to computation for sizing.
I humbly bow...no joke...to the knowledge and experience embedded in your "sharp pencil work"...case in point...while I'm aware of the fact that calculating resistance in the length of wire is a critical factor when sizing wires, I would not have used the "loop" dimension...rather, I would have used the distance from battery to starter. (
A question:
In your "sharp pencil work", you used 200 amps as a load for cranking..I'm astonished that the load could be so high...even on a cold morning. At the moment, I'm seeking the rating of my starter motor, and have been anticipating to use that rating to determine the max. current flow in order to size the wire to it.
Is that not the way to do it?
Fred
[quote][b]
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Fred Klein
Joined: 26 Mar 2012 Posts: 503
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Posted: Mon Oct 21, 2013 12:46 pm Post subject: elec. noise in antennas |
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Last week I wrote:
Quote: | Quote: | I have been diligent in separating antenna wiring from power wiring...in my fiberglass airframe, I molded in conduits along the sides of the fuselage...all power wiring on the port side...antenna wiring and pneumatics on starboard.
My port conduit is getting pretty filled, and I have ample space in the stbd conduit.
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...and Bob N. responded by writing:
Quote: | There is no demonstrable value in separating antenna
coax wires and other ship's wiring. The idea that
'noise' escapes ships wiring to invade the inner-sanctum
of your coax is a poplar myth morphed into sage advice.
|
This leads me to another question:
With my battery aft of the cabin, if I put my starter feeder in my starboard conduit and my battery ground wire in my port conduit, will the SEPARATION of these two (most probably 4AWG) wires cause any problems?
(I have one "advisor", a marine electrician, who is adamant that separating those feeders will cause all manner of hurt in the form of magnetic fields)
(I know nothing about magnetic fields, but it would seem to me that separation of those wires would have zero consequences when the starter is NOT engaged.)
Fred
[quote][b]
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nuckolls.bob(at)aeroelect Guest
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Posted: Mon Oct 21, 2013 3:35 pm Post subject: elec. noise in antennas |
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Quote: | With my battery aft of the cabin, if I put my starter feeder in my
starboard conduit and my battery ground wire in my port conduit,
will the SEPARATION of these two (most probably 4AWG) wires cause any problems?
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Quote: | (I have one "advisor", a marine electrician, who is adamant that
separating those feeders will cause all manner of hurt in the form
of magnetic fields)
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He is correct. Magnetic fields formed by OUTBOUND
electron flow in a wire is best managed by bringing
the INBOUND electrons on an adjacent wire . . . twisted
with it if practical but just getting the close an a
parallel as practical is good.
Quote: | (I know nothing about magnetic fields, but it would seem to me that
separation of those wires would have zero consequences when the
starter is NOT engaged.)
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Alternator currents flow on those wires too during
recharge. About 20 years ago I talked with a guy
at OSH who had one of the Rutan Ez models. Seems
hitting starter spun his compass like a top and
turning the alternator on and off would swing
the compass to the tune of 20 degrees or more.
This has been a problem in steel tube aircraft
but especially composites. Do what you can to keep
these two conductors as parallel and adjacent
as practical.
Bob . . .
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