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Author Topic: Aeronautical mobile antenna installation  (Read 1282 times)
N3JQD
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Posts: 21




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« on: September 05, 2007, 07:15:06 PM »

Anyone with experience in using an HF rig in a small plane, I need some assistance.  I wish to simplfy that statement a bit.  I will be using only the first freq. on 60M, w/ an IC 706M2G. (i.e CH. 1) For several reasons. One is that I won't be using a tuner. Two; 60M is restricted in power so I won't be drawing too much from a cig. lighter on the instrument panel. Third reason is that I have people whom that I speak with daily which are willing to listen for me during this attempt. As there will be high ambient background noise from the large windmill up front.  My intent is to duplicate the flight conditions a few times and try to detect the following: "when does ground wave stop and become skip"? The receiving parties are suitably spaced & this little experiment should work.  So, what kind of antenna should I try?  Wire or something like a dedicated Hamstick.  If this is pure folly, then tell me so.  I have to do these flights whether or not I try this experiment w/ the radio. I just wanted to try my mobile radio in a plane anyway. P.S. This will not be a permanent install. Thanks. 73s N3JQD
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NA0AA
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Posts: 1042




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« Reply #1 on: September 05, 2007, 08:01:09 PM »

Your antenna choices are going to be limited by physical requirements - even at 100 mph the wind will snap off many common antenna, not to mention how durable is the sheet metal to which it's attached?

You might want to investigate the SGC autotuners, then you go out of the top of the cabin, back to the top of the vertical stablizer to an insulator, turn and go to a wingtip with the end of the wire - it's endfed at the cabin roof.

With this and an autotuner you can work most bands above 80 meters.

The other option would be a trailing wire antenna but you cannot do that single handed [ask me how I know], and they are a bit more trouble to rig since you need an insulated tube to the exterior where it will fly free behind the airplane.

Not to worry, I broke in my IC-735 in aeronautical mobile service over India.  Amazing how much abuse those finals could take while I tried to tune the trailing wire.

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W3LK
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Posts: 5639




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« Reply #2 on: September 06, 2007, 07:30:27 AM »

And ANY installation will need to be inspected and signed off on by a certified Avionics tech and maybe even an airframe and power plant tech. Unlike automobiles, you can't make changes to an aircraft, even private, without certified approval.

Remember any auto coupler designed for wire antennas must be installed within inches of the antenna.

73,

Lon - W3LK
Naugatuck, Connecticut
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W3LK
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Posts: 5639




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« Reply #3 on: September 06, 2007, 07:35:52 AM »

<< 60M is restricted in power so I won't be drawing too much from a cig. lighter on the instrument panel. >>

You do NOT want to power your radio this way!!! Even with the power reduced to 50w, your rig will draw more current than the socket can safely deliver. An HT, yes; an HF rig, no.

Additionally, I believe aircraft electrical systems are 24V, aren't they?

And why just 60m?

73,

Lon - W3LK
Naugatuck, Connecticut
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N3JQD
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Posts: 21




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« Reply #4 on: September 06, 2007, 07:36:04 AM »

OK, thanks for your input. I was thinking of an antenna inside the back passenger area.  ( 6 pax Saratoga ).  But, the signal would be greatly attenuated.  So, a wire trailing may be best. I could rig up a small MFJ tuner, ground it to the airframe, & let one "random" wire trail thru the rear door. See how it goes.  Basically, this is a similar arrangement to what I use at home. One random wire up into a tree. 73s N3JQD Bob
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KB1OCC
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Posts: 172




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« Reply #5 on: September 06, 2007, 07:44:12 AM »

Isn't there a remote danger of that "one random wire" getting hung up on some control surface?
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N3JQD
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Posts: 21




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« Reply #6 on: September 06, 2007, 07:45:44 AM »

W3LK.  Thanks for the comments.  This plane is 12V. I didn't think about the "approval" thing.  I'll check with an A&P that I know. As for 60M, it's just that its propagation lasts fairly evenly through my area. ( NE quadrant of the US.) The current draw that I see from my power supply is usually around 7A @ 25W. Or, 9A @ 40W when I'm talking now on 60M.  I have a portable stack that I use for toting around the assembly. It consists of the radio, a tuner & a gel-cell battery.  Just Velcro'd all together. I could use that arrangement perhaps.  73 N3JQD
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N3JQD
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Posts: 21




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« Reply #7 on: September 06, 2007, 08:32:39 AM »

KB1OCC.  Thanks. There shouldn't be any danger of entanglement the way I'll have it strung. I have it out a side vent & it will simply trail straight out towards the back.  The worse that will happen is static build-up. I have a thin tube that will be in the door jamb gasket where the wire will pass thru.
******************************************************
To everyone:  I appreciate the input & comments.  I will modify my antenna design and approach as the commentaries come in here to Eham.  Tnx. 73 Bob
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K0BG
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Posts: 9880


WWW

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« Reply #8 on: September 06, 2007, 12:10:37 PM »

Neither the AH-4, or any of the SGC units are rated for installation in an aircraft. As Lon alluded to, it takes special certification to do this.

I once worked for an amateur, who often flew the company plane. His take, "that are just times when amateur radio is inappropriate. This is one".

Alan, KØBG
www.k0bg.com
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W3LK
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Posts: 5639




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« Reply #9 on: September 06, 2007, 12:34:29 PM »

<<  I was thinking of an antenna inside the back passenger area. ( 6 pax Saratoga ). But, the signal would be greatly attenuated. >>

Forget the attenuation aspect. The potential for physical contact with the antenna, not to mention RF getting into your avionics is huge.

Either have an A&P and Avionics person do a proper HF installation or don't do it at all.

FWIW, one of my Navy MARS members used to fly C130s and would use a 100' trailing wire on HF. At 25,000' it's amazing what 100w will do. Smiley

73,

Lon - W3LK
Naugatuck, Connecticut
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W3LK
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Posts: 5639




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« Reply #10 on: September 06, 2007, 12:41:57 PM »

<< There shouldn't be any danger of entanglement the way I'll have it strung. I have it out a side vent & it will simply trail straight out towards the back. The worse that will happen is static build-up. >>

No, the worst thing is severe detuning as the wire parallels the body of the aircraft. And to make matters worse, movement of the wire in the slip stream will change the tuning as the position of the wire, relative to the body, varies. The only acceptable way to trail a wire antenna from an aircraft in flight is from the tail, so there's nothing around the wire but air.

This is one project, IMHO, that needs to be shelved.

73,

Lon - W3LK
Naugatuck, Connecticut
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WW5AA
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Posts: 2086




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« Reply #11 on: September 06, 2007, 12:56:20 PM »

This field day I put the Little Tarheel II in the Tomahawk. Base under the panel on the passenger side, and extended up between the passenger seat and the door. I used the short 37 inch whip, the tip just slightly curving around the rear Plexiglas. Still had wiggle room for the longer whip (80 meters maybe?). I used the VHF radio ground and power from the spare 30 amp breaker. No modifications, no STC required.  Worked about 50 calls, the longest was California on 15 meters (4000’ with 59+ reports). OK, let’s hear about how I am RFing my brain! I wish I had a huge plane like yours (:-)

73, de Lindy
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N3JQD
Member

Posts: 21




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« Reply #12 on: September 06, 2007, 01:48:26 PM »

W3LK.  Ok. I get the message.  I  happen to know an A&P that works for an avionics company, very nearby. This company specializes in UHF remote links for TV.  So they know all about RF / Amateur / and aviation.  The co. CEO is a pilot and an Engineer.  So it's one stop shopping.  I can just fire away w/ questions.
Check the latest response from a guy with a Tomahawk.

I thank everyone for their comments. 73 Bob
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NA0AA
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Posts: 1042




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« Reply #13 on: September 06, 2007, 03:58:19 PM »

A certificated [TSO'd] radio is ONLY required when that specific radio is used to meet the type certification of that aircraft for flight.  Auxillary radios such as Ham radios not used for navigation or communication with ATC nor part of the aircraft required equipment are exempt.

You may or may not be able to share an antenna though.

If you are going to go trailing wire, then you need to be able to either adjust the length or have a tuner, your choice.

You will make more effective use of the antenna if you put a small plastic funnel at the end of the trailing wire - it acts like a drogue chute plus keeps you from over retracting the wire.

Here's a thought:  Duct tape flexible plastic tubing to the exterior of the plane and thread the wire thru to the tail?

Sounds like fun either way.  I'd get another pilot to fly while I operated though.
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W3LK
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Posts: 5639




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« Reply #14 on: September 06, 2007, 04:54:39 PM »

Lindy, you are a braver man than I am.

73,

Lon - W3LK
Naugatuck, Connecticut
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