Today's Message Index:
----------------------
1. 05:01 AM - Re: Two coms mic switching (Alec Myers)
2. 05:26 AM - Re: Scan Mar 11, 2020 at 9.05 AM (Robert L. Nuckolls, III)
3. 05:58 AM - Re: Scan Mar 11, 2020 at 9.05 AM (Robert L. Nuckolls, III)
4. 06:41 AM - Re: Scan Mar 11, 2020 at 9.05 AM (Bill Boyd)
5. 07:52 AM - Re: Scan Mar 11, 2020 at 9.05 AM (user9253)
6. 08:26 AM - Re: Re: Scan Mar 11, 2020 at 9.05 AM (Bill Boyd)
7. 08:34 AM - Re: Two coms mic switching (Robert L. Nuckolls, III)
8. 08:39 AM - Re: Scan Mar 11, 2020 at 9.05 AM (Robert L. Nuckolls, III)
9. 09:06 AM - Re: Re: Scan Mar 11, 2020 at 9.05 AM (DeWitt Whittington)
10. 09:47 AM - Re: Re: Scan Mar 11, 2020 at 9.05 AM (Charlie England)
11. 10:22 AM - Re: Scan Mar 11, 2020 at 9.05 AM (Bill Boyd)
12. 10:30 AM - Re: Two coms mic switching (cofford)
13. 10:44 AM - Re: Re: Two coms mic switching (Alec)
14. 11:15 AM - Re: Re: Two coms mic switching (Charlie England)
15. 11:36 AM - Re: Re: Two coms mic switching (Alec Myers)
16. 11:37 AM - Re: Re: Two coms mic switching (Carlos Trigo)
17. 01:36 PM - Re: Scan Mar 11, 2020 at 9.05 AM (Robert L. Nuckolls, III)
18. 02:04 PM - Re: Re: Two coms mic switching (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Two coms mic switching |
I dont think you need to switch either side. Run the mic in parallel into both
radios, and allow the appropriate PTT to select which transmits.
> On Mar 11, 2020, at 19:31, cofford <cofford@gmail.com> wrote:
>
Hello all,
I'm sure this has been answered before, but I'm planning to use two com radios
without an audio panel, so I need to switch the mic input. My current plan is
to use two PTT switches on the stick, and tie the COM 2 PTT to a relay to switch
the mic automatically. Does only the "MIC HIGH" side need to be switched,
or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is just
a ground reference for the mic input, but I'm looking for the lowest noise solution.
Thanks,
Casey
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=495242#495242
Message 2
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| Subject: | Re: Scan Mar 11, 2020 at 9.05 AM |
>
>
>To the other questions, I have engaged Advanced
>Flight to build one of their Advanced Quick
>Panels for me, and those are based on their
>Advanced Control=C2 Module just as others
>sometimes build around an Approach Fast Stack
>hub or a Vertical Power ECB box.=C2 I discussed
>getting a legacy ACM with fuses from Rob
>Hickman's inventory, and also having him wire a
>panel without the ACM as a hub and using acres
>of breakers or the modular fuse block bus
>approach, and the ACM with ECB's won the
>day.=C2 My purse, my calendar - my call.
>
>The airplane is an RV-10 with 17 feet of fat
>wire to the starter spinning an IO-540.=C2 The 2AWG seems appropriate to
me.=C2 =C2
>
>The shunt, alternators and regulators are items
>I've already purchased and installed in my
>airframe.=C2 I'm here to make sure I'm about to
>wire the regulators correctly for their intended use.=C2
Okay, plan-C:
Put put a limiter in each b-lead with the
limiters as close as practical to the alternator
end of the shunt. Make shortest practical connection
between battery end of shunt and the contactor.
Agreed . . . 2AWG is a better choice for this
distance.
Sorry for the floobydust . . . I didn't recall
our earlier discussions. I think you're good to
go!
Bob . . .
Message 3
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| Subject: | Re: Scan Mar 11, 2020 at 9.05 AM |
>>>I assume=C3=82 that if sharing a Hall sensor is
>>>permissible it is also permitted to share a 60A shunt.
>>
>>=C2 This is a 'real' shunt . . . not a hall-effect
>>=C2 sensor? Yes, you can tie both b-leads to the
>>=C2 anti-battery end of the shunt.
>
> Can't imagine where my head was at with that . . .
> Obviously, this causes two alternators to share
> a fault protection device at the far end of
> the b-lead . . . a failure in one alternator takes
> down both alternators.
>
> My bad. I owe you a six-pak . . .
On further reflection, why run the aux alternator
through this shunt? You have 'overload' monitoring
with the SB1 controller. An alternator ammeter
is of no value as a flight instrument . . . your
voltmeter(s) tell you everything you need to know
from a pilot's perspective. Besides, you can't
'overload' the aux alternator from the perspective
of damaging it. 'Overloading' it only depresses
bus voltage which is easily detectable on other
instruments. I think I'd let the aux alt b-lead
run right to the contactor and bypass the shunt.
Current values are predictable and accounted for
in your load analysis and plan-b protocols.
Alternator load meters are limited to some
troubleshooting studies on the ground.
Bob . . .
Message 4
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| Subject: | Re: Scan Mar 11, 2020 at 9.05 AM |
I agree, Bob. Never had load meter on the 6A I built and flew for 22
years. Only added this because it was a standard feature on the new glass
EFIS stuff.
I like the idea of moving the standby alternator to the contactor because
it gives me standby power if the shunt were to fail. I must say, the Dynon
shunt appears well-constructed and the terminals and shunt bar beefy enough
to withstand any expected loads "short of a short." In that event we have
other more pressing problems best dealt with by opening the battery
contactor...
I have one other question - well, actually two: first, my original intent
question from yesterday - do I have the wiring for these two regulators
properly crafted as shown, for my goal of auto-switching and annunciation
of standby alternator taking the load (despite this being otherwise
deducible from EFIS voltage readouts and programmable alarms)?
Secondly, what happens it the voltage sense to either regulator (terminal
3) is lost by a wire fault or a breaker trip? Seems like the regulator
would sense an undervolt (namely, zero) and drive its alternator to max
available output voltage. Will the OVP built into these units function off
the other possible voltage sensing pathway (terminal 6 to the switch that
brings power to the regulator circuitry), or will a loss of this voltage to
terminal 3 result in a runaway overvoltage condition that nothing else in
the Z-diagram can mitigate once the battery has soaked up all it can?
I'm pondering the apparent vulnerability of this one wire (bus to sense
terminal 3) to failure, especially adding additional failure points by
running it to a breaker vs. a fusible-link. An inadvertent "open" on this
wire just doesn't sound good. What can you tell me about that?
Thank you for your time and tutelage, Bob.
-Bill
On Thu, Mar 12, 2020 at 9:05 AM Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> I assume=C3=83=9A that if sharing a Hall sensor is permissible it i
s also
> permitted to share a 60A shunt.
>
>
> =C3=82 This is a 'real' shunt . . . not a hall-effect
> =C3=82 sensor? Yes, you can tie both b-leads to the
> =C3=82 anti-battery end of the shunt.
>
>
> Can't imagine where my head was at with that . . .
> Obviously, this causes two alternators to share
> a fault protection device at the far end of
> the b-lead . . . a failure in one alternator takes
> down both alternators.
>
> My bad. I owe you a six-pak . . .
>
>
> On further reflection, why run the aux alternator
> through this shunt? You have 'overload' monitoring
> with the SB1 controller. An alternator ammeter
> is of no value as a flight instrument . . . your
> voltmeter(s) tell you everything you need to know
> from a pilot's perspective. Besides, you can't
> 'overload' the aux alternator from the perspective
> of damaging it. 'Overloading' it only depresses
> bus voltage which is easily detectable on other
> instruments. I think I'd let the aux alt b-lead
> run right to the contactor and bypass the shunt.
>
> Current values are predictable and accounted for
> in your load analysis and plan-b protocols.
> Alternator load meters are limited to some
> troubleshooting studies on the ground.
>
>
> Bob . . .
>
Message 5
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| Subject: | Re: Scan Mar 11, 2020 at 9.05 AM |
Do not forget a fuse or current limiter between the "B" lead and battery contactor.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=495255#495255
Message 6
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| Subject: | Re: Scan Mar 11, 2020 at 9.05 AM |
Good catch. Thanks!
On Thu, Mar 12, 2020 at 10:57 AM user9253 <fransew@gmail.com> wrote:
>
> Do not forget a fuse or current limiter between the "B" lead and battery
> contactor.
>
> --------
> Joe Gores
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=495255#495255
>
>
Message 7
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| Subject: | Re: Two coms mic switching |
At 06:59 AM 3/12/2020, you wrote:
>
>I don=99t think you need to switch either side.
>Run the mic in parallel into both radios, and
>allow the appropriate PTT to select which transmits.
>
> > On Mar 11, 2020, at 19:31, cofford <cofford@gmail.com> wrote:
> >
>
<cofford@gmail.com>
>
>Hello all,
>
>I'm sure this has been answered before, but I'm
>planning to use two com radios without an audio
>panel, so I need to switch the mic input. My
>current plan is to use two PTT switches on the
>stick, and tie the COM 2 PTT to a relay to
>switch the mic automatically. Does only the
>"MIC HIGH" side need to be switched, or do I
>need to switch the "MIC LOW" side as well? I
>think "MIC LOW" is just a ground reference for
>the mic input, but I'm looking for the lowest noise solution.
A DPDT switch routes PTT and MI HI to each radio
independently. An example of this is shown in
Figure 18-11 of the 'Connection
http://www.aeroelectric.com/Books/Connection/18_Audio.pdf
Bob . . .
Message 8
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| Subject: | Re: Scan Mar 11, 2020 at 9.05 AM |
At 08:39 AM 3/12/2020, you wrote:
>I agree, Bob.=C2 Never had load meter on the 6A I
>built and flew for 22 years.=C2 Only=C2 added this
>because it was a standard feature on the new glass EFIS stuff.=C2 =C2
>
>I like the idea of moving the standby alternator
>to the contactor because it gives me standby power=C2 if the shunt were to
fail.
They don't
>=C2 I must say, the Dynon shunt appears
>well-constructed and the terminals and shunt bar
>beefy enough to withstand any expected=C2 loads
>"short of a short."=C2 In that event we have
>other more pressing problems best dealt with by
>opening the battery contactor...
true
>I have one other question - well, actually
>two:=C2 first, my original=C2 intent question from
>yesterday=C2 - do I have the wiring for these two
>regulators properly crafted as shown, for my
>goal of auto-switching and annunciation of
>standby alternator taking the load (despite this
>being otherwise deducible from EFIS voltage=C2 readouts and programmable
alarms)?
yes
>Secondly, what happens it the voltage sense to
>either regulator (terminal 3) is lost by a wire
>fault or a breaker trip?=C2 Seems like the
>regulator would sense an undervolt (namely,
>zero) and drive its alternator to max available
>output voltage.=C2 Will the OVP built into these
>units function off the other possible voltage
>sensing pathway (terminal 6 to the switch that
>brings power to the regulator circuitry), or
>will a loss of this voltage to terminal 3 result
>in a runaway=C2 overvoltage condition that nothing
>else in the Z-diagram can mitigate once the
>battery has soaked up all it can?=C2 =C2
Loss of sense lead shuts the alternator down.
>I'm pondering the apparent vulnerability of this
>one wire (bus to sense terminal 3) to failure,
>especially adding additional failure points by
>running it to a breaker vs. a fusible-link.=C2 An
>inadvertent "open" on this wire just doesn't
>sound good.=C2 What can you=C2 tell me about that?
That was covered in the FMEA for the original design.
Virtually ALL TC qualified alternator controllers
are required to shut the alternator down if
either (+) or (-) sense leads are opened.
Bob . . .
Message 9
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| Subject: | Re: Scan Mar 11, 2020 at 9.05 AM |
And then he shook Pence=99s hand.
Dee
> On Mar 12, 2020, at 11:23 AM, Bill Boyd <sportav8r@gmail.com> wrote:
>
> Good catch. Thanks!
>
> On Thu, Mar 12, 2020 at 10:57 AM user9253 <fransew@gmail.com
<mailto:fransew@gmail.com>> wrote:
<mailto:fransew@gmail.com>>
>
> Do not forget a fuse or current limiter between the "B" lead and
battery contactor.
>
> --------
> Joe Gores
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=495255#495255
<http://forums.matronics.com/viewtopic.php?p=495255#495255>
>
>
>
>
>
>
<http://www.matronics.com/Navigator?AeroElectric-List>
<http://www.matronics.com/contribution>
>
>
>
Message 10
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| Subject: | Re: Scan Mar 11, 2020 at 9.05 AM |
Heh heh heh....
<https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_c
ampaign=sig-email&utm_content=webmail&utm_term=icon>
Virus-free.
www.avast.com
<https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_c
ampaign=sig-email&utm_content=webmail&utm_term=link>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
On Thu, Mar 12, 2020 at 11:20 AM DeWitt Whittington <
dee.whittington@gmail.com> wrote:
> And then he shook Pence=99s hand.
>
> Dee
>
> On Mar 12, 2020, at 11:23 AM, Bill Boyd <sportav8r@gmail.com> wrote:
>
> Good catch. Thanks!
>
> On Thu, Mar 12, 2020 at 10:57 AM user9253 <fransew@gmail.com> wrote:
>
>>
>> Do not forget a fuse or current limiter between the "B" lead and battery
>> contactor.
>>
>> --------
>> Joe Gores
>>
>>
>>
>>
>> Read this topic online here:
>>
>> http://forums.matronics.com/viewtopic.php?p=495255#495255
>>
>>
>>
>>
>>
>>
>> ==========
>> ==========
>> Forum -
>> class=""> href="http://www.matronics.com/Navigator?AeroElectric-List
"
>> rel="noreferrer" target="_blank" class="">
>> http://www.matronics.com/Navigator?AeroElectric-List
>> ==========
>> WEB FORUMS -
>> rel="noreferrer" target="_blank" class="">http://forums.matronics.
com
>> ==========
>> LIST WIKI -
>> rel="noreferrer" target="_blank" class="">http://wiki.matronics.co
m
>> ==========
>> Web Site -
>> -Matt Dralle, List Admin.
>> rel="noreferrer" target="_blank" class="">
>> http://www.matronics.com/contribution
>> ==========
>>
>>
>>
>>
>
Message 11
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| Subject: | Re: Scan Mar 11, 2020 at 9.05 AM |
Very reassuring. Thanks!
On Thu, Mar 12, 2020 at 11:45 AM Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 08:39 AM 3/12/2020, you wrote:
>
> I agree, Bob.=C3=82 Never had load meter on the 6A I built and flew for
22
> years.=C3=82 Only=C3=82 added this because it was a standard feature on
the new
> glass EFIS stuff.=C3=82 =C3=82
>
> I like the idea of moving the standby alternator to the contactor because
> it gives me standby power=C3=82 if the shunt were to fail.
>
>
> They don't
>
> =C3=82 I must say, the Dynon shunt appears well-constructed and the term
inals
> and shunt bar beefy enough to withstand any expected=C3=82 loads "short o
f a
> short."=C3=82 In that event we have other more pressing problems best de
alt
> with by opening the battery contactor...
>
>
> true
>
>
> I have one other question - well, actually two:=C3=82 first, my original
=C3=82
> intent question from yesterday=C3=82 - do I have the wiring for these tw
o
> regulators properly crafted as shown, for my goal of auto-switching and
> annunciation of standby alternator taking the load (despite this being
> otherwise deducible from EFIS voltage=C3=82 readouts and programmable ala
rms)?
>
>
> yes
>
>
> Secondly, what happens it the voltage sense to either regulator (terminal
> 3) is lost by a wire fault or a breaker trip?=C3=82 Seems like the regul
ator
> would sense an undervolt (namely, zero) and drive its alternator to max
> available output voltage.=C3=82 Will the OVP built into these units func
tion
> off the other possible voltage sensing pathway (terminal 6 to the switch
> that brings power to the regulator circuitry), or will a loss of this
> voltage to terminal 3 result in a runaway=C3=82 overvoltage condition tha
t
> nothing else in the Z-diagram can mitigate once the battery has soaked up
> all it can?=C3=82 =C3=82
>
>
> Loss of sense lead shuts the alternator down.
>
>
> I'm pondering the apparent vulnerability of this one wire (bus to sense
> terminal 3) to failure, especially adding additional failure points by
> running it to a breaker vs. a fusible-link.=C3=82 An inadvertent "open"
on this
> wire just doesn't sound good.=C3=82 What can you=C3=82 tell me about tha
t?
>
>
> That was covered in the FMEA for the original design.
> Virtually ALL TC qualified alternator controllers
> are required to shut the alternator down if
> either (+) or (-) sense leads are opened.
>
> Bob . . .
>
Message 12
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| Subject: | Re: Two coms mic switching |
nuckolls.bob(at)aeroelect wrote:
> At 06:59 AM 3/12/2020, you wrote:
>
> >
> > I dont think you need to switch either side. Run the mic in parallel into
both radios, and allow the appropriate PTT to select which transmits.
> >
> > > On Mar 11, 2020, at 19:31, cofford wrote:
> > >
> >
> >
> > Hello all,
> >
> > I'm sure this has been answered before, but I'm planning to use two com radios
without an audio panel, so I need to switch the mic input. My current plan
is to use two PTT switches on the stick, and tie the COM 2 PTT to a relay to
switch the mic automatically. Does only the "MIC HIGH" side need to be switched,
or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is
just a ground reference for the mic input, but I'm looking for the lowest noise
solution.
>
>
> A DPDT switch routes PTT and MI HI to each radio
> independently. An example of this is shown in
> Figure 18-11 of the 'Connection
>
> http://www.aeroelectric.com/Books/Connection/18_Audio.pdf
>
>
>
>
>
> Bob . . .
Thanks for the answers. Not switching at all would cause an impedance mismatch
in my case as both radios have a built-in intercom so the mic input would always
be live. Sounds like switching the MIC HI line is the way to go.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=495264#495264
Message 13
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| Subject: | Re: Two coms mic switching |
Im pretty sure microphones arent impedance matched; a mic input is a high impedance
input and the mic is (?) 600 ohms, so running one into two inputs doesnt
load the source.
Sent from my iPhone
> On Mar 12, 2020, at 1:27 PM, cofford <cofford@gmail.com> wrote:
>
>
>
> nuckolls.bob(at)aeroelect wrote:
>> At 06:59 AM 3/12/2020, you wrote:
>>
>>>
>>> I dont think you need to switch either side. Run the mic in parallel into both
radios, and allow the appropriate PTT to select which transmits.
>>>
>>>> On Mar 11, 2020, at 19:31, cofford wrote:
>>>>
>>>
>>>
>>> Hello all,
>>>
>>> I'm sure this has been answered before, but I'm planning to use two com radios
without an audio panel, so I need to switch the mic input. My current plan
is to use two PTT switches on the stick, and tie the COM 2 PTT to a relay to
switch the mic automatically. Does only the "MIC HIGH" side need to be switched,
or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is
just a ground reference for the mic input, but I'm looking for the lowest noise
solution.
>>
>>
>> A DPDT switch routes PTT and MI HI to each radio
>> independently. An example of this is shown in
>> Figure 18-11 of the 'Connection
>>
>> http://www.aeroelectric.com/Books/Connection/18_Audio.pdf
>>
>>
>>
>>
>>
>> Bob . . .
>
>
> Thanks for the answers. Not switching at all would cause an impedance mismatch
in my case as both radios have a built-in intercom so the mic input would always
be live. Sounds like switching the MIC HI line is the way to go.
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=495264#495264
>
>
>
>
>
>
>
>
>
Message 14
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| Subject: | Re: Two coms mic switching |
That's kinda like adult diapers. (It Depends.)
Most audio circuits are a low impedance feeding a high impedance, but
you can't assume it's true in every case. You may well find high gain
inputs that have their load impedance intentionally kept low, to reduce
noise susceptibility when there's no source connected.
On 3/12/2020 12:40 PM, Alec wrote:
>
> Im pretty sure microphones arent impedance matched; a mic input is a high impedance
input and the mic is (?) 600 ohms, so running one into two inputs doesnt
load the source.
>
>
> Sent from my iPhone
>
>> On Mar 12, 2020, at 1:27 PM, cofford <cofford@gmail.com> wrote:
>>
>>
>>
>> nuckolls.bob(at)aeroelect wrote:
>>> At 06:59 AM 3/12/2020, you wrote:
>>>
>>>>
>>>> I dont think you need to switch either side. Run the mic in parallel into
both radios, and allow the appropriate PTT to select which transmits.
>>>>
>>>>> On Mar 11, 2020, at 19:31, cofford wrote:
>>>>>
>>>>
>>>> Hello all,
>>>>
>>>> I'm sure this has been answered before, but I'm planning to use two com radios
without an audio panel, so I need to switch the mic input. My current plan
is to use two PTT switches on the stick, and tie the COM 2 PTT to a relay to
switch the mic automatically. Does only the "MIC HIGH" side need to be switched,
or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is
just a ground reference for the mic input, but I'm looking for the lowest noise
solution.
>>>
>>> A DPDT switch routes PTT and MI HI to each radio
>>> independently. An example of this is shown in
>>> Figure 18-11 of the 'Connection
>>>
>>> http://www.aeroelectric.com/Books/Connection/18_Audio.pdf
>>>
>>>
>>>
>>>
>>>
>>> Bob . . .
>>
>> Thanks for the answers. Not switching at all would cause an impedance mismatch
in my case as both radios have a built-in intercom so the mic input would
always be live. Sounds like switching the MIC HI line is the way to go.
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| Subject: | Re: Two coms mic switching |
I know. The nerdy part of me really really really wants to try it, to see if it
works.
On Mar 12, 2020, at 2:10 PM, Charlie England <ceengland7@gmail.com> wrote:
That's kinda like adult diapers. (It Depends.)
Most audio circuits are a low impedance feeding a high impedance, but you can't
assume it's true in every case. You may well find high gain inputs that have
their load impedance intentionally kept low, to reduce noise susceptibility when
there's no source connected.
On 3/12/2020 12:40 PM, Alec wrote:
>
> Im pretty sure microphones arent impedance matched; a mic input is a high impedance
input and the mic is (?) 600 ohms, so running one into two inputs doesnt
load the source.
>
>
> Sent from my iPhone
>
>> On Mar 12, 2020, at 1:27 PM, cofford <cofford@gmail.com> wrote:
>>
>>
>>
>> nuckolls.bob(at)aeroelect wrote:
>>> At 06:59 AM 3/12/2020, you wrote:
>>>
>>>>
>>>> I dont think you need to switch either side. Run the mic in parallel into
both radios, and allow the appropriate PTT to select which transmits.
>>>>
>>>>> On Mar 11, 2020, at 19:31, cofford wrote:
>>>>>
>>>>
>>>> Hello all,
>>>>
>>>> I'm sure this has been answered before, but I'm planning to use two com radios
without an audio panel, so I need to switch the mic input. My current plan
is to use two PTT switches on the stick, and tie the COM 2 PTT to a relay to
switch the mic automatically. Does only the "MIC HIGH" side need to be switched,
or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is
just a ground reference for the mic input, but I'm looking for the lowest noise
solution.
>>>
>>> A DPDT switch routes PTT and MI HI to each radio
>>> independently. An example of this is shown in
>>> Figure 18-11 of the 'Connection
>>>
>>> http://www.aeroelectric.com/Books/Connection/18_Audio.pdf
>>>
>>>
>>>
>>>
>>>
>>> Bob . . .
>>
>> Thanks for the answers. Not switching at all would cause an impedance mismatch
in my case as both radios have a built-in intercom so the mic input would
always be live. Sounds like switching the MIC HI line is the way to go.
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| Subject: | Re: Two coms mic switching |
Its kinda cool to assist these technically intrincated discussions
Enviado do meu iPhone
> No dia 12/03/2020, s 18:22, Charlie England <ceengland7@gmail.com> escreveu:
>
>
> That's kinda like adult diapers. (It Depends.)
>
> Most audio circuits are a low impedance feeding a high impedance, but you can't
assume it's true in every case. You may well find high gain inputs that have
their load impedance intentionally kept low, to reduce noise susceptibility
when there's no source connected.
>
>> On 3/12/2020 12:40 PM, Alec wrote:
>>
>> Im pretty sure microphones arent impedance matched; a mic input is a high impedance
input and the mic is (?) 600 ohms, so running one into two inputs doesnt
load the source.
>>
>>
>> Sent from my iPhone
>>
>>>> On Mar 12, 2020, at 1:27 PM, cofford <cofford@gmail.com> wrote:
>>>
>>>
>>>
>>> nuckolls.bob(at)aeroelect wrote:
>>>> At 06:59 AM 3/12/2020, you wrote:
>>>>
>>>>>
>>>>> I dont think you need to switch either side. Run the mic in parallel into
both radios, and allow the appropriate PTT to select which transmits.
>>>>>
>>>>>> On Mar 11, 2020, at 19:31, cofford wrote:
>>>>>>
>>>>>
>>>>> Hello all,
>>>>>
>>>>> I'm sure this has been answered before, but I'm planning to use two com radios
without an audio panel, so I need to switch the mic input. My current plan
is to use two PTT switches on the stick, and tie the COM 2 PTT to a relay
to switch the mic automatically. Does only the "MIC HIGH" side need to be switched,
or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is
just a ground reference for the mic input, but I'm looking for the lowest noise
solution.
>>>>
>>>> A DPDT switch routes PTT and MI HI to each radio
>>>> independently. An example of this is shown in
>>>> Figure 18-11 of the 'Connection
>>>>
>>>> http://www.aeroelectric.com/Books/Connection/18_Audio.pdf
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Bob . . .
>>>
>>> Thanks for the answers. Not switching at all would cause an impedance mismatch
in my case as both radios have a built-in intercom so the mic input would
always be live. Sounds like switching the MIC HI line is the way to go.
>
>
> --
> This email has been checked for viruses by Avast antivirus software.
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>
>
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| Subject: | Re: Scan Mar 11, 2020 at 9.05 AM |
At 08:39 AM 3/12/2020, you wrote:
>I agree, Bob.=C2 Never had load meter on the 6A I
>built and flew for 22 years.=C2 Only=C2 added this
>because it was a standard feature on the new glass EFIS stuff.=C2 =C2
>
>I like the idea of moving the standby alternator
>to the contactor because it gives me standby power=C2 if the shunt were to
fail.
They don't
>=C2 I must say, the Dynon shunt appears
>well-constructed and the terminals and shunt bar
>beefy enough to withstand any expected=C2 loads
>"short of a short."=C2 In that event we have
>other more pressing problems best dealt with by
>opening the battery contactor...
true
>I have one other question - well, actually
>two:=C2 first, my original=C2 intent question from
>yesterday=C2 - do I have the wiring for these two
>regulators properly crafted as shown, for my
>goal of auto-switching and annunciation of
>standby alternator taking the load (despite this
>being otherwise deducible from EFIS voltage=C2 readouts and programmable
alarms)?
yes
>Secondly, what happens it the voltage sense to
>either regulator (terminal 3) is lost by a wire
>fault or a breaker trip?=C2 Seems like the
>regulator would sense an undervolt (namely,
>zero) and drive its alternator to max available
>output voltage.=C2 Will the OVP built into these
>units function off the other possible voltage
>sensing pathway (terminal 6 to the switch that
>brings power to the regulator circuitry), or
>will a loss of this voltage to terminal 3 result
>in a runaway=C2 overvoltage condition that nothing
>else in the Z-diagram can mitigate once the
>battery has soaked up all it can?=C2 =C2
Loss of sense lead shuts the alternator down.
>I'm pondering the apparent vulnerability of this
>one wire (bus to sense terminal 3) to failure,
>especially adding additional failure points by
>running it to a breaker vs. a fusible-link.=C2 An
>inadvertent "open" on this wire just doesn't
>sound good.=C2 What can you=C2 tell me about that?
That was covered in the FMEA for the original design.
Virtually ALL TC qualified alternator controllers
are required to shut the alternator down if
either (+) or (-) sense leads are opened.
Bob . . .
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| Subject: | Re: Two coms mic switching |
>
>Most audio circuits are a low impedance feeding a high impedance,
>but you can't assume it's
>true in every case. You may well find high gain inputs that have
>their load impedance
>intentionally kept low, to reduce noise susceptibility when there's
>no source connected.
Keep in mind that the MIC HI input to an intercom
or transmitter is designed to interface with a
powered, amplified microphone. This is a legacy
hold-over from the days when aircraft microphones
were not unlike those in your telephone . . .
carbon granules behind a foil diaphragm.
https://tinyurl.com/htnn6nq
This microphone is essentially a resistor whose
resistance varies with audio stimulation. Hence
it must first be biased up with some current
so that the electronics can tap the resulting
voltage variances that represent speech.
Here's an exemplar MIC input circuit for a
King transceiver . . .
Emacs!
Looking into the DC power path, the DC source
impedance is on the order of 600 ohms, the AC
load impedance is on the order of 390 ohms
while the load impedance of the first audio
stage is about 48,000 ohms.
So while the voltage INPUT network may indeed
be 'high' impedance, the microphone BIAS network
is not. Further, paralleling two such inputs
doubles the bias to any one microphone.
The using DPDT "TX SELECT" switch for PTT and
MIC HI lines is pretty much mandatory.
Bob . . .
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