Avionics wiring question
Michael Lester
I am wiring in a King KX-155 Nav/Com. I don't want to use a mixer
panel – I want to have both the Nav and Com run to the intercom (and
thus to the headphones) and just control the radios with their volume
control. (There is only one radio input on the intercom.)
The installation manual shows two audio connections for each of the
Nav and Com radios, a "Hi" and a "Low".
Question:
1) What does the "Hi" and "Low" refer to? (impedance?
Amplitude?)
2) Can I connect one of these pair together? i.e. is there some
sort of diode type relay that will prevent output from one source
flowing back into the other?
3) Has anyone done something like this before?
Thanks.
Michael
N116GT
Dave O
>Question:
>
>1) What does the "Hi" and "Low" refer to? (impedance?
>Amplitude?)
Impedance. HI for headsets, LO for speakers.
>2) Can I connect one of these pair together? i.e. is there some
>sort of diode type relay that will prevent output from one source
>flowing back into the other?
They are designed to connect directly together, HI to HI or LO to LO.
>3) Has anyone done something like this before?
Yes. :)
On my Long EZ's KX-155A, the COMM AUDIO HI (pin 9 on the tray) is
connected directly to the NAV AUDIO HI (pin 10 on the tray) and then
via shielded cable directly to the headset jacks.
Cheers,
Dave O
Dave O
>maux_...@maux.net (Michael Lester) wrote:
>
>>Question:
>>
>>1) What does the "Hi" and "Low" refer to? (impedance?
>>Amplitude?)
>
>Impedance. HI for headsets, LO for speakers.
Whoops, I have another document that conflicts with this answer. All
I have are a couple of rather aged photocopies from the KX-155 manual.
One suggests ('suggests' because the photocopy is cropped right in the
middle of the info) that LO is for connection to an audio panel while
the the other one has a hand written note that the LO is for a speaker
connection. I guess you'll have to wait for someone with more info on
the LO to respond. The HI works just fine for directly driving my two
headsets as noted in my prior post.
Cheers,
Dave O
MikeM
Michael Lester wrote:
>
> Any Avionics Gurus out there?
>
> I am wiring in a King KX-155 Nav/Com. I don't want to use a mixer
> panel – I want to have both the Nav and Com run to the intercom (and
> thus to the headphones) and just control the radios with their volume
> control. (There is only one radio input on the intercom.)
>
> The installation manual shows two audio connections for each of the
> Nav and Com radios, a "Hi" and a "Low".
>
> Question:
>
> 1) What does the "Hi" and "Low" refer to? (impedance?
> Amplitude?)
Hi means that this pin is the audio output, while Low is the
signal return (ground) for that audio. If you were running
a shielded wire to your intercom, connect the center conductor
to HI, and the shield to Low. If you check with an ohmmeter,
you will find that all the Low pins are common to the Power
ground pin (and maybe the case). As far as I remember, all
of the Low pins on a KX155 are common to the chassis...
Sometimes, the Hi/Low designation refers to a "floating" output,
such as a transformer coupled output where neither end of the
output winding is grounded inside the radio. In this case,
there would no dc continuity from either hi to chassis ground,
or low to chassis ground....
> 2) Can I connect one of these pair together? i.e. is there some
> sort of diode type relay that will prevent output from one source
> flowing back into the other?
Try connecting Com Hi to Nav Hi to the intercom headphone input.
> 3) Has anyone done something like this before?
Haven't tried it cause I use a RST audio panel which keeps the
two outputs isolated. I have a KX155 service and installation manual,
if you me to look something up.
MikeM
Skylane '1MM
JG
at least have a means to isolate these audio outputs before feeding to the
intercom (they are 'unbalanced' lines)
snip ---------------
>
> Michael Lester wrote:
> >
> > Any Avionics Gurus out there?
> >
> > 2) Can I connect one of these pair together? i.e. is there some
> > sort of diode type relay that will prevent output from one source
> > flowing back into the other?
>
> Try connecting Com Hi to Nav Hi to the intercom headphone input.
>
> MikeM
> Skylane '1MM
snip---------------
Jim Weir
shared these priceless pearls of wisdom:
>
->1) What does the "Hi" and "Low" refer to? (impedance?
->Amplitude?)
The installation manual should show three outputs -- "low level audio",
"phones", and "speaker (if this unit has the optional power speaker amplifier)".
Low level audio (sometimes called "emergency phones") is intended to be used if
and when the internal phones/speaker power amplifier craps out. It is an output
directly from the detector with a low-power audio amplifier output of about 10
to 30 mW into a single 150 ohm headset (1 to 2 volts RMS into 150 ohms). The
power phones amp, by comparison, will give you 300 to 800 mW (3 to 5 volts RMS)
into four 150 ohm headsets in parallel (38 ohms).
>
->
->2) Can I connect one of these pair together? i.e. is there some
->sort of diode type relay that will prevent output from one source
->flowing back into the other?
Not directly. However, one resistor of about 470 ohms (anywhere from 220 to
1000 will work just fine) in series with each low-level output run to the 600
ohm input of your intercom/audio panel will work just dandy.
>
->
->3) Has anyone done something like this before?
No more than half a million times in the last 60 years.
Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com j...@rst-engr.com
MikeM
>
> If you want to feed both Com and Nav audio to the same input, you should
> at least have a means to isolate these audio outputs before feeding to the
> intercom (they are 'unbalanced' lines)
Yes, they are 'unbalanced', but that has nothing to do with bridging
the COM and NAV audio outputs together.
There are separate COM headphone and NAV headphone
amplifiers inside the KX155. If the designer of the KX155 purposely
designed-in some series output impedance into those amplifiers, then
the two outputs can simply be shorted together, and a single wire
can be run to the ship's failsafe HEADPHONE jack, (and to the
intercom input).
If the two headphone amplifiers have a low output impedance, then
just bridging them together with a jumper is a bad idea. In this
case, connect two 220 Ohm, 1/4W resistors in series. Connect one
end of the series pair to COM, and the other end to NAV. Connect
the wire going to the ship's failsafe HEADPHONE jack and intercom
input to the junction between the two resistors. This puts 220 Ohms
in series with each output...
MikeM