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VHF antennae splitter

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Bill Allen

Joined: 24 Aug 2009
Posts: 42
Location: UK

Posted: Fri Feb 09, 2018 9:30 am Post subject: VHF antennae splitter

Is there a device (a “splitter”) which can enable two VHF comms to share one antennae (not transmitting at the same time)



Bill Allen



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ceengland7(at)gmail.com
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Posted: Fri Feb 09, 2018 12:25 pm Post subject: VHF antennae splitter

On 2/9/2018 11:29 AM, Bill Allen wrote:

 	  Quote: 	
		   



 Is there a device (a “splitter”) which can enable two VHF comms to share one antennae (not transmitting at the same time)



 Bill Allen


	


If you use any kind of 'splitter', the transmitting radio will be 

radiating into the other radio's receiver input. Not a good plan. There 

are automated switches that allow connecting two comms to the same 

antenna, but the automated switches are typically pretty pricey; likely 

more expensive than an extra antenna and installation bits/pieces. And, 

with a single antenna/feed line, you lose redundancy in the most likely 

failure area of a radio 'system'.



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Bill Allen

Joined: 24 Aug 2009
Posts: 42
Location: UK

Posted: Fri Feb 09, 2018 1:37 pm Post subject: VHF antennae splitter

Thanks Charlie,

Good points. This installation is on a composite airframe (a LongEz) and the copper dipole antennas are under the skin and thus not possible to replace without major surgery, and having external antennae is an added-drag which we do our best to avoid on these airframes. One has gone faulty, hence my curiosity to see if there was another way do it.

Bill 

Sent from my iPad

 	  Quote: 	
		   On 9 Feb 2018, at 21:30, Charlie England <ceengland7(at)gmail.com> wrote:

> On 2/9/2018 11:29 AM, Bill Allen wrote:

> 

> 

> Is there a device (a “splitter”) which can enable two VHF comms to share one antennae (not transmitting at the same time)

> 

> Bill Allen

 If you use any kind of 'splitter', the transmitting radio will be radiating into the other radio's receiver input. Not a good plan. There are automated switches that allow connecting two comms to the same antenna, but the automated switches are typically pretty pricey; likely more expensive than an extra antenna and installation bits/pieces. And, with a single antenna/feed line, you lose redundancy in the most likely failure area of a radio 'system'.

 ---

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Eric Page

Joined: 15 Feb 2017
Posts: 245

Posted: Fri Feb 09, 2018 2:15 pm Post subject: Re: VHF antennae splitter

Bill,



Just a few questions to help clarify what you're looking for and how it might be solved...



Do you want both radios to share the antenna for simultaneous receiving, but only one to be able to transmit?  Or, would you be happy with only one radio "seeing" the antenna at a time (for RX and TX) and the other radio disconnected (no RX or TX)?



Must the switching be automatic (i.e. when a transmitter is keyed), or is a manual switch OK?



Are your PTT switches wired through an audio panel such that only one radio's transmitter can be keyed at a time?  Or, is it possible for the pilot to key #1 while the GIB simultaneously keys #2?



Eric

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ceengland7(at)gmail.com
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Posted: Fri Feb 09, 2018 2:21 pm Post subject: VHF antennae splitter

Disclaimer: I'm no RF engineer; I've just played with a few radios.

If you're not obsessed with test range perfection levels, you can do a lot of really sloppy stuff that will still work very well. I've seen copper tape VOR antennas wrapped around the rear of the canopy on Thorps and Mustang IIs. '1/4 wave' comm antennas (without ground plane) curved up and along the canopy of low wing a/c. Etc, etc. Shucks, try some copper tape down one main gear leg. Might be enough metal in/around the engine area to provide a bit of a ground plane, though it would be wildly asymmetrical. With modern radios, you're not going to damage the transmitter; just reduce its performance a bit when you get it wrong. 

Charlie

But speaking of test range, unless you're doing some very accurate testing I doubt you'd notice the addition of one swept comm antenna, especially if mounted on the belly toward the rear of the plane. 

On Fri, Feb 9, 2018 at 3:29 PM, Bill Allen <billallensworld(at)gmail.com (billallensworld(at)gmail.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: Bill Allen <billallensworld(at)gmail.com (billallensworld(at)gmail.com)>

 Thanks Charlie,

 Good points. This installation is on a composite airframe (a LongEz) and the copper dipole antennas are under the skin and thus not possible to replace without major surgery, and having external antennae is an added-drag which we do our best to avoid on these airframes. One has gone faulty, hence my curiosity to see if there was another way do it.

 Bill

 Sent from my iPad

 > On 9 Feb 2018, at 21:30, Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:

 >

 > --> AeroElectric-List message posted by: Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)>

 >

 >> On 2/9/2018 11:29 AM, Bill Allen wrote:

 >> --> AeroElectric-List message posted by: Bill Allen <billallensworld(at)gmail.com (billallensworld(at)gmail.com)>

 >>

 >> Is there a device (a “splitter”) which can enable two VHF comms to share one antennae (not transmitting at the same time)

 >>

 >> Bill Allen

 >

 > If you use any kind of 'splitter', the transmitting radio will be radiating into the other radio's receiver input. Not a good plan. There are automated switches that allow connecting two comms to the same antenna, but the automated switches are typically pretty pricey; likely more expensive than an extra antenna and installation bits/pieces. And, with a single antenna/feed line, you lose redundancy in the most likely failure area of a radio 'system'.

 >

 > ---

 > This email has been checked for viruses by Avast antivirus software.

 > https://www.avast.com/antivirus

 >

 >

 >

 >

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