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MaxNr(at)aol.com
Guest

Posted: Sun Jan 27, 2008 12:54 pm Post subject: Dumb questions

I have been sitting in the back row on this list, hoping to learn something. I was born without any electronic genes. I am building an all metal light sport plane.(Zenith) Right or wrong, I developed the habit (over five decades of personal, military and commercial flying) of listening to broadcast radio on the ADF. I'm thinking that I need to install an of the shelf automobile radio in my project. No second hand Ebay ADF's. My two questions are: Will I fry the radio if I use only a headset and no speakers? About the antenna. I know that I should mount it vertically, but it must withstand airspeed excursions to Vne (156kts/180mph) without going L shaped. I've come up with somehow jamming it inside the canopy, or insulating it and mounting against the landing gear, or inside some kind of tubular mast on the belly. I did come across a NOS Volkswagen telescoping antenna in my shop. It would be great if that Lyc carburetor turns up again the same way. Somebody stop me if I'm on the wrong track. This isn't the most pressing problem out there, but all suggestions are appreciated.

 Bob Dingley 

**************

Start the year off right.  Easy ways to stay in shape.

     http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489  [quote][b]

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jon(at)finleyweb.net
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Posted: Sun Jan 27, 2008 2:06 pm Post subject: Dumb questions

Hi Bob,

  

 Might I suggest you take a look at satellite radio - like XM (http://www.xmradio.com) or Sirius?  I've been flying with an XM setup (Roady XL) and love it.  I can move it from car to airplane to house or listen on my computer/Internet, in-flight station reception doesn't fade out every 15 minutes (as I fly away from a station), and the antenna is a little tiny thing that is mounted inside my airplane (zero drag).  It does require a subscription so is not free.  In my plane, I just connect the radio output to my intercom music input.

  

 Jon

--

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jindoguy(at)gmail.com
Guest

Posted: Sun Jan 27, 2008 2:25 pm Post subject: Dumb questions

Bob, I'm no expert, but I did learn this from one. Some automotive audio systems use completely separate grounds for each channel. For that you'd have to rewire your headphones and run three jacks instead of two. This info may be old, it was a few years ago and things move on, but it never hurts to ask the sales guy or look at the wiring layout of any system you're thinking of buying.

 

Rick



On Jan 27, 2008 2:49 PM,  <MaxNr(at)aol.com (MaxNr(at)aol.com)> wrote:

[quote] I have been sitting in the back row on this list, hoping to learn something. I was born without any electronic genes. I am building an all metal light sport plane.(Zenith) Right or wrong, I developed the habit (over five decades of personal, military and commercial flying) of listening to broadcast radio on the ADF. I'm thinking that I need to install an of the shelf automobile radio in my project. No second hand Ebay ADF's. My two questions are: Will I fry the radio if I use only a headset and no speakers? About the antenna. I know that I should mount it vertically, but it must withstand airspeed excursions to Vne (156kts/180mph) without going L shaped. I've come up with somehow jamming it inside the canopy, or insulating it and mounting against the landing gear, or inside some kind of tubular mast on the belly. I did come across a NOS Volkswagen telescoping antenna in my shop. It would be great if that Lyc carburetor turns up again the same way. Somebody stop me if I'm on the wrong track. This isn't the most pressing problem out there, but all suggestions are appreciated.

  Bob Dingley 

**************

Start the year off right.  Easy ways to stay in shape.

     http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489   	  Quote: 	
		  



ist" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List

tp://forums.matronics.com

_blank">http://www.matronics.com/contribution



	
[b]

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nuckolls.bob(at)cox.net
Guest

Posted: Mon Jan 28, 2008 5:25 am Post subject: Dumb questions

At 04:21 PM 1/27/2008 -0600, you wrote:



 	  Quote: 	
		  Bob, I'm no expert, but I did learn this from one. Some automotive audio 

systems use completely separate grounds for each channel. For that you'd 

have to rewire your headphones and run three jacks instead of two. This 

info may be old, it was a few years ago and things move on, but it never 

hurts to ask the sales guy or look at the wiring layout of any system 

you're thinking of buying.



Rick



On Jan 27, 2008 2:49 PM, <<mailto:MaxNr(at)aol.com>MaxNr(at)aol.com> wrote:

>I have been sitting in the back row on this list, hoping to learn 

>something. I was born without any electronic genes. I am building an all 

>metal light sport plane.(Zenith) Right or wrong, I developed the habit 

>(over five decades of personal, military and commercial flying) of 

>listening to broadcast radio on the ADF. I'm thinking that I need to 

>install an of the shelf automobile radio in my project. No second hand 

>Ebay ADF's. My two questions are: Will I fry the radio if I use only a 

>headset and no speakers? About the antenna. I know that I should mount it 

>vertically, but it must withstand airspeed excursions to Vne 

>(156kts/180mph) without going L shaped. I've come up with somehow jamming 

>it inside the canopy, or insulating it and mounting against the landing 

>gear, or inside some kind of tubular mast on the belly. I did come across 

>a NOS Volkswagen telescoping antenna in my shop. It would be great if 

>that Lyc carburetor turns up again the same way. Somebody stop me if I'm 

>on the wrong track. This isn't the most pressing problem out there, but 

>all suggestions are appreciated.


	


    What Rick is referring to is the differential balanced PAIR

    of wires that goes to each speaker. This is a technique that

    allows TWO amplifiers to drive both wires of a speaker out

    of phase with each other. This effectively doubles the potential

    peak-to-peak voltage to drive each speaker . . . 4x the watts

    without having to resort to power supply boosters or very low

    impedance speakers. It also eliminated the need for an output

    coupling capacitor . . . a fat passive rascal that was a

    necessary inconvenience. See:



http://www.aeroelectric.com/Pictures/Schematics/LM4752.pdf



    Here's a "single ended" stereo amplifier. Note the

    1000 uF capacitors in series with the speakers. Note

    also that the speakers are grounded on one side. See:



http://www.aeroelectric.com/Pictures/Schematics/LM4950.pdf



    Here we see two amplifiers wired to each side of the

    speaker. No 1000 uF capacitor needed.



    Most car radios use a similar scheme with one pair

    of dif-amps for the front speakers and another pair

    for the rear speakers, a total of eight, ungrounded

    wires.



    There are perhaps a half-dozen ways to adapt the

    speaker outputs of a radio to the headphone inputs

    of the intercom. However, many automotive radios have

    line output features for taking stereo audio to external

    amplifiers. These are already in the ballpark for

    connection directly to the stereo inputs of an intercom

    system. They're already single-ended and shielded against

    case ground for the radio.  I'll suggest you seek a radio

    with the AUX OUTPUT feature and start from there. If this

    proves unsatisfactory, I can show you how to craft an

    interface network to go between your radio's speaker

    outputs and the stereo inputs of your intercom.



    The antenna is another deal entirely. Vertically

    polarized, medium wave signals run along the

    ground and work really fine with short antennas on

    ground based vehicles. Once you leave the ground,

    performance for a short whip antenna degrades.



    The antenna input to an automotive AM receiver is

    a unique beast. It's a very high impedance port

    that is performance degraded by CAPACITY. If you

    cut the feedline open on a car radio antenna, you

    may find that the center conductor is a very small

    single strand of wire supported down the center of

    the coaxial cable by a hollow plastic tube. This

    high-impedance coax was supplied to us in large spools

    at Cessna way back when . . . it was necessary for

    the purpose of extending the sense antenna feeder from

    radio on the panel to a feed-through insulator on

    the cabin roof.



    I suspect that this input philosophy is still used.

    Off-the-shelf car antennas come with a run of this

    specialized "coax" that is already terminated to mate

    with jacks on radio and base of antenna.



    The 'ideal' AM receiver antenna for airborne applications

    would be the "ferrite loopstick" described in the

    'Connection's section on antennas. This is an H-field

    antenna that is not unlike that which your ADF uses

    to find bearing of an incoming signal. Unfortunately,

    the loopstick IS directional. Unless you can rotate the

    antenna, you would need 2 or three of the things along

    with an ability to switch between them as well as tune

    them to the station's frequency for best reception.



    This calls for some experimentation. Ideally, your

    radio's antenna input would be characterized for

    performance with a longer piece of coax (higher

    capacity) and a relatively long wire antenna not

    unlike that used for sense antennas of the earliest

    ADFs. In this respect, the ADF receivers and AM radio

    receivers have a great deal in common with respect

    to crafting a high performance antenna with an

    exceedingly small size compared to the wavelength

    of energy being tapped.



    Crafting a "high speed" whip antenna has it's

    challenges. My first thought is that actual orientation

    of the antenna would have little effect on performance.

    I think I'd experiment with a "trailing wire" . . .

    a 5' of wire that attaches to a suitable fitting

    just before you taxi out. Or, consider crafting a

    j-bend antenna, not unlike that used for marker

    beacons. Use the standard AM radio antenna that's

    a solid rod. Heat it with a torch so that you can

    put a 90-degree bend in it about 6" from the base.

    Then allow it to fair rearward and support the tip

    on an insulated mast of some variety.



    Check with the automotive radio/audio shops for

    an antenna with longer than usual coax cable.

    This might be for a truck, van or RV. The antenna

    can't be a telescoping variety . . . solid stainless

    rod is called for. But then, depending on your

    particular installation, perhaps a standard automotive

    antenna for a sedan will have enough coax. See what

    it takes to install it on the belly modified and

    supported as described above.



    Let us know how it works out!



    Bob . . .

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