Today's Message Index:
----------------------
1. 06:33 AM - Re: Mixing together two mics (Robert L. Nuckolls, III)
2. 10:00 AM - Re: Starter wiring (Franz Fux)
3. 01:04 PM - Re: Starter wiring (Robert L. Nuckolls, III)
4. 02:16 PM - Re: Mixing together two mics (Radioflyer)
5. 04:18 PM - Re: Re: Mixing together two mics (Robert L. Nuckolls, III)
6. 04:52 PM - Re: Mixing together two mics (Radioflyer)
7. 05:16 PM - Re: Re: Mixing together two mics (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Mixing together two mics |
At 11:46 PM 6/11/2011, you wrote:
>
>Is it workable to mix two mics together for input into a Com's mike
>jack by using impedance matching resistors? Here' my situation...
>
>My two place aircraft is fitted with one headphone jack and one mic
>jack. The mic is keyed via SPST PTT switches in the control sticks.
>The intercom I have is a portable unit that inconveniently gives me
>two mic output plugs: one for pilot and one for copilot.
>
>Ostensibly, the two mic ouputs are to allow use of external DPDT PTT
>switches and a "Y" harness which would then plug into the aircraft's
>one mic jack. I understand that the normally open DPDT switches
>essentially shield one mic from the other and allow the "Y" cord to
>"mix" the mics into one output. However, I want to avoid the
>resulting cabling mess if I were to do this. So, I'm looking for a
>good way to combine the mic outputs into one output without causing
>too much signal deterioration.
Not enough information to offer cogent advice.
I've not encountered this kind of intercom before
and it's difficult to deduce the rationale behind
its design.
Are you planning to permanently install this
intercom? If so, it seems practical to eliminate
the y-cable and simply hardwire the harness
to emulate the 'portable' wiring configuration.
Without seeing internal schematics for the intercom,
we have no way of knowing how the push to talk
switches influence connection of the microphones.
A simple y-cable can do no more than parallel
the three conductors. It's a low risk experiment.
Bob . . .
Message 2
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| Subject: | Re: Starter wiring |
It is wired per Z-27 with one non impulse coupler magneto and the Lazar
ignition. Starter is a simple push button switch. In order to engage the
starter, magneto switch is in the on position and ignition in the off as per
drawing
Franz
On 10/06/11 4:21 PM, "Robert L. Nuckolls, III"
<nuckolls.bob@aeroelectric.com> wrote:
> <nuckolls.bob@aeroelectric.com>
>
>
>> I would like to change over to either start on both or the electronic
>> ignition
>> only for better starting.
>
> Is the mag impulse coupled?
>
>> Could you let me know how I would go about
>> accomplishing that task.
>
>
> What are you using for an ignition switch?
>
>
> Bob . . .
>
>
>
>
>
Franz Fux
Director of Operations
Last Frontier Heliskiing Ltd.
Bell 2 Lodge
P.O. Box 1237
Vernon, BC, V1T 6N6
CANADA
Office Contact
T: (250) 558-7980
F: (250) 558-7981
Lodge Contact
T: (250) 275-4770
F: (250) 275-4912
http://www.bell2lodge.com
---
LAST FRONTIER Heliskiing
www.lastfrontierheli.com
---
And for some of the best Steelhead Fishing in the world at Bell 2 Lodge
www.steelhead-fishing.net
Message 3
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| Subject: | Re: Starter wiring |
At 12:56 PM 6/12/2011, you wrote:
><franz@lastfrontierheli.com>
>
>It is wired per Z-27 with one non impulse coupler magneto and the Lazar
>ignition. Starter is a simple push button switch. In order to engage the
>starter, magneto switch is in the on position and ignition in the off as per
>drawing
Okay. I presume your ignition switch is not the
OFF-R-L-BOTH-START functionality offered by the
legacy key-switch described . . .
If your magneto is not impulse coupled, then you
would want it to be OFF during all cranking operations.
Starting would be accomplished with the electronic
ignition only.
If you were using the A510 style switch magneto would
be treated as if it were the classic RIGHT magneto.
The electronic ignition would be LEFT. The R to GRD
jumper would be left in place to disable the right mag
during cranking.
In your case, there is no START function on the ignition
switch with which to effect an auto-disable of the
right mag. Therefore, you would want to start the
engine with the ignition switch in the LEFT position.
Once the engine is started, the switch may be freely
manipulated between R-L-BOTH for the purpose of
pre-flight run-up testing and flight ops.
Bob . . .
Message 4
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| Subject: | Re: Mixing together two mics |
The Intercom is an RST 442B. Old stuff, but it works well and I can't afford a
replacement right now. So, I'm planning to install it as a permanent intercom
and am trying to hardwire the "portable harness" as you suggest. The only problem
is how to make the two output mic signals as one. If I follow to the letter
the way the two mic outputs are to be used with a DPDT PTT switch and Y-cable,
I wind up with
I think the rationale was to allow each pilot to install his own PTT switch without
involving the aircraft wiring and to allow easy portability to any other
aircraft.
Each mic that plugs into the intercom sees a resistor network that eventually sums
all inputs into an LM386. Before each mic signal gets very far into the network
it is looped back via a 27 Ohm resistor as a mic output. I can send a schematic.
My assumption is that it is not OK to simply tie the two mics together to make
one mic output. I'm hoping some simple resistors can be used to mix the two mic
outputs. I f I picked up a "mixed signal" after the LM386, then I would get
all audio (music, nav, marker beacon, etc) possibly into the COM and I think I
want to avoid this.
--Jose
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=342805#342805
Message 5
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| Subject: | Re: Mixing together two mics |
At 05:12 PM 6/12/2011, you wrote:
>
>The Intercom is an RST 442B. Old stuff,
I found the schematic in my archives . . .
>Each mic that plugs into the intercom sees a resistor network that
>eventually sums all inputs into an LM386. Before each mic signal
>gets very far into the network it is looped back via a 27 Ohm
>resistor as a mic output. I can send a schematic.
>
>My assumption is that it is not OK to simply tie the two mics
>together to make one mic output. I'm hoping some simple resistors
>can be used to mix the two mic outputs. I f I picked up a "mixed
>signal" after the LM386, then I would get all audio (music, nav,
>marker beacon, etc) possibly into the COM and I think I want to avoid this.
Yup. But as a permanent installation, you could do something
like the 'relay' version of PTT and mount the relays in an enclosure
along with the intercom board. A sort of re-packaging effort
that would meed Jim's design goals while keeping all
the mickey-mouse wiring corralled in one enclosure.
Bob . . .
Message 6
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| Subject: | Re: Mixing together two mics |
Bob, Thanks for taking the time to look at the schematic. I guess you're right
and that I should just implement a relay. I was hoping to avoid yet another device,
but it is probably the path of least resistance given the situation.
Or....maybe I could install a 2 channel isolation op-amp (unity gain) in the intercom
to combine the pilot copilot mics lines. Hmmmm. Decisions, decisions.
--Jose
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=342820#342820
Message 7
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| Subject: | Re: Mixing together two mics |
At 07:49 PM 6/12/2011, you wrote:
>
>Bob, Thanks for taking the time to look at the schematic. I guess
>you're right and that I should just implement a relay. I was hoping
>to avoid yet another device, but it is probably the path of least
>resistance given the situation.
>
>Or....maybe I could install a 2 channel isolation op-amp (unity
>gain) in the intercom to combine the pilot copilot mics lines.
But that would put both mics into the keyed
radio at the same time . . probably not good.
> Hmmmm. Decisions, decisions.
There's a host of useful experiments that would
probably lead to a useful configuration. It's all
a matter of time and return on investment. I can't
count how many times I would have been better off
just following the instructions . . . or pitching
the thing and starting from scratch.
Nobody ever said that education was cheap.
Bob . . .
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