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airlincoln(at)sbcglobal.n
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 Posted: Thu Dec 20, 2007 12:11 pm Post subject: swapping two radios using 3P/DT switch? |
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Bob and/or other electronics gurus--
I'm using revision 11 and looking at chapter 11 (switches) and also the FAQ's...I have attached an excerpt from the FAQ's that I think applies to my question as well...it's a gentleman inquiring about using either a "3PDT" switch (I think numerically this is a "3-3 switch"?) to change between two comm radios.
If I have a panel mount comm radio (with it's own antenna) and a portable comm radio (an SP-200 with it's own antenna) and a simple two-place intercom system (i.e. PM 3000), I believe I need the above referenced three-pole double-throw (3-3) switch to swap between the two radios: a pole for the wire going to the headset earphones, a pole for the wire coming from the headset microphone, and a pole to swap the PTT line. By doing this, I can swap radios without having to go through the intercom system which is in-line with your philosophy (which I agree with) of minimizing knob-twisting distractions. I don't see any examples of triple pole switches in the book and I can't find any in the Spruce catalog, but if I'm thinking correctly, do you have a suggested resource for obtaining one? Otherwise is there another switching logic I should consider? Once again, everyone please feel free to shoot holes in my ideas. Thanks.
Lincoln Keill
Sacramento, CA
My plane is equipped with an old King KX170B, Microair 720, with a Sigtronics SPA 400<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
intercom. I have interconnected them with a simple switching arrangement that allows selecting
comm1 (King), comm 2, (MicroAir), both (audio only), nav (audio for ident). My problem is, I've
describe my circuitry to a good A&P, and I think I've improperly wired the switches for comm
selection. I've used a DPDT miniature toggle to switch the Mic audio and Headset audio to
either comm1, or comm 2, with a SPST miniature toggle to either connect or remain open
across the headset audio switch lugs of the DPDT switch. The configuration works, and
communications are clear, according to all reports I've received during the last year. My A&P
tells me that I should have also included the transmitter key line in the switch, using a 3PDT
switch, so as to key up the proper transmitter. My gut tells me he's right, but now I'm curious to
know why the simpler circuit I've used hasn't caused problems during the last year. Many times
I've had both radios tuned to the same frequency, and keying the mike has never created the
squeal normally associated with two transmitters using the same frequency at the same time. In
fact, the radio not selected will receive the information transmitted by the other. I've used a
hand-held radio to double check, and can not detect any keying of the transmitter section of the
non-selected radio when the PTT switch is keyed, and I know that the transmit key line is
connected to both radios directly. What am I missing?
A If you have confirmed that the non-selected transmitter is indeed passive then you're
probably okay. I'm at a loss to explain why you are not having problems . . . the standard
practice since day one has been to switch both mic-audio and PTT lines for the selected
transmitter. The only thing I can think of is that some modern transmitters I've seen don't need
the PTT line to make the transfer from receive to transmit. Microphones should break both the
PTT and Mic-Audio lines when the PTT button is relaxed. This allows different microphones to
share the same input to the transmitter without interfering with each other.
Many modern amateur transmitters sense the microphone power current draw when a
microphone is connected to the audio circuit via the PTT switch and use this to deduce the need
to transfer from receive to transmit.
[quote][b]
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matronics(at)rtist.nl
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| Posted: Thu Dec 20, 2007 12:48 pm Post subject: swapping two radios using 3P/DT switch? |
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3PDT and 4PDT switches are easy to get at online electronics stores like Digikey.
[quote] ---
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rlborger(at)mac.com
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| Posted: Thu Dec 20, 2007 12:48 pm Post subject: swapping two radios using 3P/DT switch? |
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Lincoln,
Check ebay Item number: 180195626322
They seem to be primarily used in audio (musical instruments, guitar parts) circuits. It's a push-button (foot operated) switch but might could be adapted to your use.
I just found a 3PDT toggle switch available from MPJA (Marlin P. Jones & Associates) online
http://www.MPJA.com/ ( http://www.mpja.com/prodinfo.asp?number=16075+SW )
Try to search 3PDT switch in Google for more options.
Good building and great flying,
Bob Borger
On Thursday, December 20, 2007, at 02:26PM, "Lincoln Keill" <airlincoln(at)sbcglobal.net> wrote:
| Quote: | Bob and/or other electronics gurus--
I'm using revision 11 and looking at chapter 11 (switches) and also the FAQ's...I have attached an excerpt from the FAQ's that I think applies to my question as well...it's a gentleman inquiring about using either a "3PDT" switch (I think numerically this is a "3-3 switch"?) to change between two comm radios.
If I have a panel mount comm radio (with it's own antenna) and a portable comm radio (an SP-200 with it's own antenna) and a simple two-place intercom system (i.e. PM 3000), I believe I need the above referenced three-pole double-throw (3-3) switch to swap between the two radios: a pole for the wire going to the headset earphones, a pole for the wire coming from the headset microphone, and a pole to swap the PTT line. By doing this, I can swap radios without having to go through the intercom system which is in-line with your philosophy (which I agree with) of minimizing knob-twisting distractions. I don't see any examples of triple pole switches in the book and I can't find any in the Spruce catalog, but if I'm thinking correctly, do you have a suggested resource for obtaining one? Otherwise is there another switching logic I should consider? Once again, everyone please feel free to shoot holes in my ideas. Thanks.
Lincoln Keill
Sacramento, CA
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jetboy
Joined: 22 Jul 2006
Posts: 233
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| Posted: Thu Dec 20, 2007 1:38 pm Post subject: Re: swapping two radios using 3P/DT switch? |
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wouldnt you want to leave both audios available? This can be done by joining the audio lines or through series resistors of around 100 ohms if you dont use an audio panel. Just turn the volume down on the radio not being used.
Most GA aircraft use a DPDT toggle switch (C150) or DP rotary switch (C152/C172-182) to select the transmitter for the mic / PTT.
Ralph
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Ralph - CH701 / 2200a |
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JOHN TIPTON
Joined: 17 Sep 2006
Posts: 239
Location: Torquay - England
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| Posted: Thu Dec 20, 2007 3:34 pm Post subject: swapping two radios using 3P/DT switch? |
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Steinair have a selection, which they say are used for audio switching etc
[quote] ---
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nuckolls.bob(at)cox.net
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| Posted: Fri Dec 21, 2007 7:43 am Post subject: swapping two radios using 3P/DT switch? |
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At 12:09 PM 12/20/2007 -0800, you wrote:
| Quote: | Bob and/or other electronics gurus--
I'm using revision 11 and looking at chapter 11 (switches) and also the
FAQ's...I have attached an excerpt from the FAQ's that I think applies to
my question as well...it's a gentleman inquiring about using either a
"3PDT" switch (I think numerically this is a "3-3 switch"?) to change
between two comm radios.
If I have a panel mount comm radio (with it's own antenna) and a portable
comm radio (an SP-200 with it's own antenna) and a simple two-place
intercom system (i.e. PM 3000), I believe I need the above referenced
three-pole double-throw (3-3) switch to swap between the two radios: a
pole for the wire going to the headset earphones, a pole for the wire
coming from the headset microphone, and a pole to swap the PTT line. By
doing this, I can swap radios without having to go through the intercom
system which is in-line with your philosophy (which I agree with) of
minimizing knob-twisting distractions. I don't see any examples of triple
pole switches in the book and I can't find any in the Spruce catalog, but
if I'm thinking correctly, do you have a suggested resource for obtaining
one? Otherwise is there another switching logic I should consider? Once
again, everyone please feel free to shoot holes in my ideas. Thanks.
Lincoln Keill
Sacramento, CA
|
Check out the C&K 7301P3YZQE switch at:
http://tinyurl.com/ypqomr
and
http://www.aeroelectric.com/Pictures/Switches/7301P3YZQE.jpg
Bob . . .
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BUCSDDS(at)aol.com
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| Posted: Fri Dec 21, 2007 9:07 am Post subject: swapping two radios using 3P/DT switch? |
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Bob or anyone else with the correct answer to my question,
I have an issue with my Headset/PTT/Microphone wiring. I have a Garmin SL-30, SL-40 and the PMA 4000 by PS Engineering intercom. I hear a squeal when I press the PTT switch. If the intercom is turned off the squeal doesn't occur while pressing the PTT switch. I'm wondering if a 3P/DT switch would be a good option. If so, what schematic should I use??
Thanks in advance for any help!
Marwin Goff
Des Moines, IA
Marwin Goff
DSM
Varieze O-200
515-360-0778
bucsdds(at)aol.com
See AOL's top rated recipes and easy ways to stay in shape for winter.
[quote][b]
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