Today's Message Index:
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1. 08:03 AM - Re: Re: Antenna grounding (Robert L. Nuckolls, III)
2. 08:21 AM - Re: Re: Antenna grounding (Michael Lazarowicz)
3. 08:23 AM - Re: Antenna grounding (Robert L. Nuckolls, III)
4. 08:33 AM - Re: Review request for RV-9 Electrical System (G3X, GTN, etc) (Robert L. Nuckolls, III)
5. 01:49 PM - Re: Review request for RV-9 Electrical System (G3X, GTN, etc) (gfb)
Message 1
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| Subject: | Re: Antenna grounding |
>
> Bob, how far apart should a 1090 MHz transmitting antenna be from
> a 978 MHz receiving antenna? And how far should a transponder
> antenna be from a com antenna? Thanks
That can only be quantified in the lab and even then, there
are dozens of intertwined variables. The two systems are first
qualified to some agreed upon design goals. Then powers that
be will get their heads together to recommend installation
parameters that are unlikely to exceed limitations identified
in the design goals.
ARC used to want our VHF comm antennas 4 or 5 feet
apart . . . but we stuck pairs of them on top of
the high-wing Cessnas barely 24 inches apart and
similarly spaced from the glide-slope and ADF
sense antennas.
Engineers and marketing people often WISH for
one thing . . . while the folks who have to make
it all fit and work find out what the real limits
are. Recommendations are seldom tucked up tightly
to real lines in the sand . . .
I suspect you're correct in the idea that some committee
of cognizant individuals probably sat down knowing
that 2 feet was enough and then doubled it. I think the
risks to hardware due to proximity are minimal . . . the
biggest concern is for degraded performance. So do the
best you can then try it out.
Bob . . .
Message 2
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| Subject: | Re: Antenna grounding |
When talking of com antennas . How do you deal with a bent whip? Distance
from base or from the tip?
On Sunday, June 12, 2016, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
>
> Bob, how far apart should a 1090 MHz transmitting antenna be from a 978
> MHz receiving antenna? And how far should a transponder antenna be from a
> com antenna? Thanks
>
>
> That can only be quantified in the lab and even then, there
> are dozens of intertwined variables. The two systems are first
> qualified to some agreed upon design goals. Then powers that
> be will get their heads together to recommend installation
> parameters that are unlikely to exceed limitations identified
> in the design goals.
>
> ARC used to want our VHF comm antennas 4 or 5 feet
> apart . . . but we stuck pairs of them on top of
> the high-wing Cessnas barely 24 inches apart and
> similarly spaced from the glide-slope and ADF
> sense antennas.
>
> Engineers and marketing people often WISH for
> one thing . . . while the folks who have to make
> it all fit and work find out what the real limits
> are. Recommendations are seldom tucked up tightly
> to real lines in the sand . . .
>
> I suspect you're correct in the idea that some committee
> of cognizant individuals probably sat down knowing
> that 2 feet was enough and then doubled it. I think the
> risks to hardware due to proximity are minimal . . . the
> biggest concern is for degraded performance. So do the
> best you can then try it out.
>
> Bob . . .
>
Message 3
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| Subject: | Re: Antenna grounding |
>I have it set up so I can switch the cables of
>the ADSB antenna and the Transponder antenna.
>The transponder is no big deal but my ADSB unit
>is up front and I already have it run.=C2 I was
>just=C2 a small amount short if I do the switch,
>so I was wondering if I was stretching the
>limits of the length of the ADSB in.=C2
probably not . . .
>In the End I will just hook it up and do the
>checks .=C2 Just trying to keep the crawling in
>back and re routing of wire to a minimum.=C2
sounds like a plan . . .
Bob . . .
Message 4
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| Subject: | Re: Review request for RV-9 Electrical System (G3X, |
GTN, etc)
At 02:36 AM 6/10/2016, you wrote:
>
>Initial thoughts on electrical system for my
>RV9, hoping to get some feedback from you folks.
>I do have some questions below but please feel
>free to chime in with anything else you feel is valuable.
>
>- On the fence about some sort of avionics
>switch. Most of the big items installed don=99t
>have on-off switches on them so I can=99t keep
>them off during engine start. I understand the
>single point of failure problem so I have been
>avoiding it but it sure would be nice.
What is the foundation for needing one in the first place?
>
>- Safe to put both trim motors on the same
>breaker? The GAD27 install manual recommends 2
>5A breakers but does not indicate why. Seems like a waste of a breaker to
me :)
"Safe" is an un-quantified term in aviation . . . airplanes
are dangerous as @#$$. We design and choose parts that drive
risks lower . . . but they are never zero. So the answer to
your question is, what are additional hazards for having both trims
disabled from the same fault? I suspect they are vanishingly
small. So if you're crowded for breaker space, then drive on.
Remember, 99.99$% of all breakers and fuses in vehicles of
any time sit there for the lifetime of the airplane never having
been called upon to do their job: protect a wire.
>- Any other spots I could save a breaker? I feel
>that I=99m too granular with them but can=99t
>figure out where to trim :) Maybe
>Nav+Strobes, Servos+GMC, AudioPanel+GTR20?
Why not fuse blocks of generous size mounted out of the
way but in sufficient quantity to offer independent
protection for every feeder . . . with unassigned slots
as spares for future expansion?
>- What is the preferred method to set up the
>sd-8 to come on by itself? I have heard setting
>it's regulator voltage low is pretty common? What should that be set to?
Why do this? When the low voltage light comes on
you say, "Aw shucks!". Finish the cup of coffee,
fold up the map, tell the passenger that the
little yellow light is no big deal. Then flip
a few switches to bring your second engine driven
power source into service. The hazards for main
alternator are not grounded in real risk to
comfortable termination of flight. It's the un
founded belief that it's a hazard that drive up
your pucker-factor.
- The e-bus relay should see a peak of 20A with
typical below 15A. I=99m considering the B&C with the 25A heat sink?
20A ebus? How did this get BIGGER than the SD-8 output?
Bob . . .
Message 5
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| Subject: | Re: Review request for RV-9 Electrical System (G3X, |
GTN, etc)
On avionics switch, would be interesting to have most avionics off while cranking
the engine.
For the Trim breaker, Ray Allen indicates that a single 1A would be enough for
both trim motors. This sounds odd considering Garmin recommended a 5A for each.
Yeah, I'm probably going to brake a few items out into fuse blocks. I'm thinking
exterior lights get one, LRUs, Cabin Power, and maybe one other. Is it reasonable
to have these fuse blocks have a pull breaker on the panel?
i.e. Ext Lights panel breaker for 20A goes to a fuse block behind the panel with
fuses for each light.
Is this reasonable?
The e-bus has a peak that exceeds the SD-8. This only happens if everything is
on at once, including the boost pump running, the radio transmitting, both servos
moving and trimming, and a dead ibbs battery charging. This will likely never
happen, definitely not for any amount of time longer than a second or so.
The normal draw for the bus should be about 6A with it maybe going up to 10-15A
on landing. I'm looking at the SD-8 as more of a battery extender than a full
redundant alternator.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=457056#457056
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