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ELT antenna placement

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paul.r.kuntz(at)gmail.com
Guest

Posted: Fri Jul 15, 2011 9:33 pm Post subject: ELT antenna placement

I'm installing a 121.5/406 MHz ELT in my homebuilt project.  The installation instructions tell me to put the ELT whip antenna at least 3 feet from my VHF radio antenna.  Is this really necessary?  There is the possibility of manually activating the ELT in the air in the event of an emergency, while continuing to communicate with the VHF radio, but I'm thinking that the more likely scenarios will be to operate one or the other, but not both.  That is, the ELT becomes a factor only in the case of a true emergency, in which case I would first squawk emergency and communicate the situation by VHF voice (flying the airplane first, of course).  Then, activate the ELT (one button press) if a forced landing appears inevitable, but I'm probably done talking on the radio at that point.

 

Is the concern simply the presence of another vertically oriented conductor in relatively close proximity to the antenna in use, thus influencing its performance?  Even if both the ELT and the VHF radio are active at the same time, is 3 ft of separation important?

 

At any rate, it would be more convenient from an installation perspective to put them closer together.  Any advice?



Thanks,

Paul Kuntz

  [quote][b]

email(at)jaredyates.com
Guest

Posted: Sat Jul 16, 2011 12:42 am Post subject: ELT antenna placement

In one prior case, we had an airplane that was transmitting ground control voice (121.9) over 121.5. We attributed it to resonance on the elt antenna, which was in a non standard location for that type, closer than normal to the vhf com.  After moving the elt antenna back a couple of feet the bleed over stopped.  This type of problem might be something to consider in your decision. 





On Jul 16, 2011, at 1:28, Paul Kuntz <paul.r.kuntz(at)gmail.com (paul.r.kuntz(at)gmail.com)> wrote:



[quote]I'm installing a 121.5/406 MHz ELT in my homebuilt project.  The installation instructions tell me to put the ELT whip antenna at least 3 feet from my VHF radio antenna.  Is this really necessary?  There is the possibility of manually activating the ELT in the air in the event of an emergency, while continuing to communicate with the VHF radio, but I'm thinking that the more likely scenarios will be to operate one or the other, but not both.  That is, the ELT becomes a factor only in the case of a true emergency, in which case I would first squawk emergency and communicate the situation by VHF voice (flying the airplane first, of course).  Then, activate the ELT (one button press) if a forced landing appears inevitable, but I'm probably done talking on the radio at that point.

 

Is the concern simply the presence of another vertically oriented conductor in relatively close proximity to the antenna in use, thus influencing its performance?  Even if both the ELT and the VHF radio are active at the same time, is 3 ft of separation important?

 

At any rate, it would be more convenient from an installation perspective to put them closer together.  Any advice?



Thanks,

Paul Kuntz

   	  Quote: 	
		  



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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Sat Jul 16, 2011 3:10 am Post subject: ELT antenna placement

7/16/2011



Hello Paul, You wrote: "Is this really necessary?"



After 6 years plus of construction and many hours of preparation for the 

first flight in my KIS TR-1 experimental amateur built aircraft I was unable 

to taxi out of the apron area because every time I keyed my number one VHF 

com radio to request taxi clearance from ground control the ELT transmitter 

was activated -- very frustrating.



The problem was caused by proximity and orientation of the antennas of the 

two devices. I eventually relocated the ELT antenna -- problem solved.



OC



PS for Bruce: Knowledge of 14 CFR 91.207 (f) (4) permitted me to disable the 

ELT and complete the first flight as plannned.



=================================================================



Time: 10:33:48 PM PST US

Subject: ELT antenna placement

From: Paul Kuntz <paul.r.kuntz(at)gmail.com>



I'm installing a 121.5/406 MHz ELT in my homebuilt project.  The

installation instructions tell me to put the ELT whip antenna at least 3

feet from my VHF radio antenna.  Is this really necessary?  There is the

possibility of manually activating the ELT in the air in the event of an

emergency, while continuing to communicate with the VHF radio, but I'm

thinking that the more likely scenarios will be to operate one or the other,

but not both.  That is, the ELT becomes a factor only in the case of a true

emergency, in which case I would first squawk emergency and communicate the

situation by VHF voice (flying the airplane first, of course).  Then,

activate the ELT (one button press) if a forced landing appears inevitable,

but I'm probably done talking on the radio at that point.



Is the concern simply the presence of another vertically oriented conductor

in relatively close proximity to the antenna in use, thus influencing its

performance?  Even if both the ELT and the VHF radio are active at the same

time, is 3 ft of separation important?



At any rate, it would be more convenient from an installation perspective to

put them closer together.  Any advice?



Thanks,

Paul Kuntz

dave.saylor.aircrafters(a
Guest

Posted: Sat Jul 16, 2011 4:13 am Post subject: ELT antenna placement

I agree, I've seen comm radios set of a nearby ELT on several

occasions.  It's not uncommon at all.



I'd keep those antennas away from each other.



Dave Saylor

AirCrafters

140 Aviation Way

Watsonville, CA 95076

831-722-9141 Shop

831-750-0284 Cell



On Sat, Jul 16, 2011 at 4:06 AM,  <bakerocb(at)cox.net> wrote:

 	  Quote: 	
		   



 7/16/2011



 Hello Paul, You wrote: "Is this really necessary?"



 After 6 years plus of construction and many hours of preparation for the

 first flight in my KIS TR-1 experimental amateur built aircraft I was unable

 to taxi out of the apron area because every time I keyed my number one VHF

 com radio to request taxi clearance from ground control the ELT transmitter

 was activated -- very frustrating.



 The problem was caused by proximity and orientation of the antennas of the

 two devices. I eventually relocated the ELT antenna -- problem solved.



 OC



 PS for Bruce: Knowledge of 14 CFR 91.207 (f) (4) permitted me to disable the

 ELT and complete the first flight as plannned.



 =================================================================



 Time: 10:33:48 PM PST US

 Subject: ELT antenna placement

 From: Paul Kuntz <paul.r.kuntz(at)gmail.com>



 I'm installing a 121.5/406 MHz ELT in my homebuilt project. Â The

 installation instructions tell me to put the ELT whip antenna at least 3

 feet from my VHF radio antenna. Â Is this really necessary? Â There is the

 possibility of manually activating the ELT in the air in the event of an

 emergency, while continuing to communicate with the VHF radio, but I'm

 thinking that the more likely scenarios will be to operate one or the other,

 but not both. Â That is, the ELT becomes a factor only in the case of a true

 emergency, in which case I would first squawk emergency and communicate the

 situation by VHF voice (flying the airplane first, of course). Â Then,

 activate the ELT (one button press) if a forced landing appears inevitable,

 but I'm probably done talking on the radio at that point.



 Is the concern simply the presence of another vertically oriented conductor

 in relatively close proximity to the antenna in use, thus influencing its

 performance? Â Even if both the ELT and the VHF radio are active at the same

 time, is 3 ft of separation important?



 At any rate, it would be more convenient from an installation perspective to

 put them closer together. Â Any advice?



 Thanks,

 Paul Kuntz

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Sat Jul 16, 2011 6:30 am Post subject: ELT antenna placement

Another risk is that many ELT transmitters are poorly shielded from 

strong adjacent RF. Flying near a TV or FM transmitter antenna can cause 

the oscillator of the ELT transmitter to radiate harmonics, which then 

are picked up by your com radio, breaking squelch and causing poor 

reception. My plane used to suffer from this syndrome until I moved one 

of the VHF antennas to the belly.

On 7/16/2011 5:10 AM, Dave Saylor wrote:

 	  Quote: 	
		   



 I agree, I've seen comm radios set of a nearby ELT on several

 occasions.  It's not uncommon at all.



 I'd keep those antennas away from each other.



 Dave Saylor

 AirCrafters

 140 Aviation Way

 Watsonville, CA 95076

 831-722-9141 Shop

 831-750-0284 Cell



 On Sat, Jul 16, 2011 at 4:06 AM,<bakerocb(at)cox.net>  wrote:

> 

>

> 7/16/2011

>

> Hello Paul, You wrote: "Is this really necessary?"

>

> After 6 years plus of construction and many hours of preparation for the

> first flight in my KIS TR-1 experimental amateur built aircraft I was unable

> to taxi out of the apron area because every time I keyed my number one VHF

> com radio to request taxi clearance from ground control the ELT transmitter

> was activated -- very frustrating.

>

> The problem was caused by proximity and orientation of the antennas of the

> two devices. I eventually relocated the ELT antenna -- problem solved.

>

> OC

>

> PS for Bruce: Knowledge of 14 CFR 91.207 (f) (4) permitted me to disable the

> ELT and complete the first flight as plannned.

>

> =================================================================

>

> Time: 10:33:48 PM PST US

> Subject: ELT antenna placement

> From: Paul Kuntz<paul.r.kuntz(at)gmail.com>

>

> I'm installing a 121.5/406 MHz ELT in my homebuilt project.  The

> installation instructions tell me to put the ELT whip antenna at least 3

> feet from my VHF radio antenna.  Is this really necessary?  There is the

> possibility of manually activating the ELT in the air in the event of an

> emergency, while continuing to communicate with the VHF radio, but I'm

> thinking that the more likely scenarios will be to operate one or the other,

> but not both.  That is, the ELT becomes a factor only in the case of a true

> emergency, in which case I would first squawk emergency and communicate the

> situation by VHF voice (flying the airplane first, of course).  Then,

> activate the ELT (one button press) if a forced landing appears inevitable,

> but I'm probably done talking on the radio at that point.

>

> Is the concern simply the presence of another vertically oriented conductor

> in relatively close proximity to the antenna in use, thus influencing its

> performance?  Even if both the ELT and the VHF radio are active at the same

> time, is 3 ft of separation important?

>

> At any rate, it would be more convenient from an installation perspective to

> put them closer together.  Any advice?

>

> Thanks,

> Paul Kuntz

>

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jul 16, 2011 6:54 am Post subject: ELT antenna placement

At 07:10 AM 7/16/2011, you wrote:


Saylor <dave.saylor.aircrafters(at)gmail.com>



I agree, I've seen comm radios set of a nearby ELT on several

occasions.  It's not uncommon at all.



I'd keep those antennas away from each other.



    It would appear to be the only option. It

    may be very $difficult$ to fix what appears

    to be a design bug internal to the ELT.



    The earliest ELT's used a spring-loaded

    mass to close an activation switch in response

    to g-forces of a crash. No doubt modern ELTs

    use the solid-state acceleration sensors

    for this task . . . which produce VERY tiny

    signals requiring a lot of circuit gain.



    This type of circuitry offers a high risk

    of vulnerability to RF interference. This

    may be an area where qualification of the

    device to standard DO-160 (good for part

    23) stresses was insufficient to stand off

    the extra-ordinary vulnerabilities of these

    kinds of circuits.  A lot of hardware we

    did for the military and for Part-25 and up

    applications was exposed to really nasty

    RF radiation . . . 200 volts/meter or more

    . . . during qualification. No doubt this

    extra step in qualification would have exposed

    vulnerabilities that are now plaguing customers.



 > Paul wrote:



 > I'm installing a 121.5/406 MHz ELT in my homebuilt project. Â The

 > installation instructions tell me to put the ELT whip antenna at least 3

 > feet from my VHF radio antenna. Â Is this really necessary? Â There is the

 > possibility of manually activating the ELT in the air in the event of an

 > emergency, while continuing to communicate with the VHF radio, but I'm

 > thinking that the more likely scenarios will be to operate one or the other,

 > but not both. Â That is, the ELT becomes a factor only in the case of a true

 > emergency, in which case I would first squawk emergency and communicate the

 > situation by VHF voice (flying the airplane first, of course). Â Then,

 > activate the ELT (one button press) if a forced landing appears inevitable,

 > but I'm probably done talking on the radio at that point.

 >

 > Is the concern simply the presence of another vertically oriented conductor

 > in relatively close proximity to the antenna in use, thus influencing its

 > performance? Â Even if both the ELT and the VHF radio are active at the same

 > time, is 3 ft of separation important?

 >

 > At any rate, it would be more convenient from an installation perspective to

 > put them closer together. Â Any advice?



    Give it a try . . . but with a Plan-B for moving

    one or both of the antennas to achieve demonstrably

    necessary separation. I suspect that not all ELT

    products are victim to the hypothesized vulnerability

    I cited above. There are no grave performance issues

    that would arise from antenna proximity issues so if

    you "get away Scott free" with your desired configuration,

    you're good to go.



   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jul 16, 2011 7:19 am Post subject: ELT antenna placement

At 09:27 AM 7/16/2011, you wrote:

 	  Quote: 	
		  



Another risk is that many ELT transmitters are poorly shielded from 

strong adjacent RF. Flying near a TV or FM transmitter antenna can 

cause the oscillator of the ELT transmitter to radiate harmonics, 

which then are picked up by your com radio, breaking squelch and 

causing poor reception. My plane used to suffer from this syndrome 

until I moved one of the VHF antennas to the belly.


	


    Interesting! I hadn't thought of that scenario. Unlike

    transceivers where the antenna is connected to a receiver

    input circuit 99.9% of the time, the ELT antenna is

    permanently connected to the output circuitry of a

    transmitter's power output stage.



    A strong analog TV station impressed on the ELT

    antenna could be conducted into the non-linear,

    transistor junctions where the TV signal could

    produce inter-modulation products that spread over

    a very wide spectrum. Now that we're all-digital

    in the off-air TV world, I suspect probability

    is reduced. I'm aware of no other "trash rich"

    high power signals that would produce this

    effect today.



    This is a phenomenon that was never explored

    by DO-160 although I've read some military

    qualification test protocols that do look for

    inter-modulation mixing and re-radiation of

    foreign energies coming down the antenna feedline.

   Bob . . .

BobsV35B(at)aol.com
Guest

Posted: Sat Jul 16, 2011 7:49 am Post subject: ELT antenna placement

Good Morning Paul and Jared,

  

 Way out of my area of expertise, but it is my understanding that having  another vertical metal element close to the transmitting or receiving antenna  makes the combination very directional.  Rarely a problem when close to the  station but could reduce the range capability at some angles from the  aircraft.

  

 Happy Skies,

  

 Old Bob

 Do Not Archive

  

  

  In a message dated 7/16/2011 3:42:58 A.M. Central Daylight Time,  email(at)jaredyates.com writes:

  	  Quote: 	
		     In one prior case, we had an airplane that was transmitting ground    control voice (121.9) over 121.5. We attributed it to resonance on the elt    antenna, which was in a non standard location for that type, closer than    normal to the vhf com.  After moving the elt antenna back a couple of    feet the bleed over stopped.  This type of problem might be something to    consider in your decision. 

   

   

On Jul 16, 2011, at 1:28, Paul Kuntz <paul.r.kuntz(at)gmail.com (paul.r.kuntz(at)gmail.com)>    wrote:

   

    	  Quote: 	
		       I'm installing a 121.5/406 MHz ELT in my homebuilt project.  The      installation instructions tell me to put the ELT whip antenna at least 3      feet from my VHF radio antenna.  Is this really necessary?  There      is the possibility of manually activating the ELT in the air in the event of      an emergency, while continuing to communicate with the VHF radio, but I'm      thinking that the more likely scenarios will be to operate one or the other,      but not both.  That is, the ELT becomes a factor only in the case of a      true emergency, in which case I would first squawk emergency and communicate      the situation by VHF voice (flying the airplane first, of course).       Then, activate the ELT (one button press) if a forced landing appears      inevitable, but I'm probably done talking on the radio at that      point.



Is the concern simply the presence of another vertically      oriented conductor in relatively close proximity to the antenna in use, thus      influencing its performance?  Even if both the ELT and the VHF radio      are active at the same time, is 3 ft of separation important?



At any      rate, it would be more convenient from an installation perspective to put      them closer together.  Any advice?



Thanks,

Paul Kuntz

 	  Quote:

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Sat Jul 16, 2011 4:06 pm Post subject: ELT antenna placement

It was particularly obnoxious in Phoenix, where the VFR transition over 

Sky Harbor has you aimed right at an antenna farm that has 80 percent of 

all broadcast stations for the area, distance less than 7 nm. Probably a 

few million watts being radiated between the FM and TV stations 

transmitters there. As soon as I disconnected the ELT coax from the ELT, 

I could fly right up within a mile of those towers with no problem, but 

with it connected, as soon as I got within 10 nm constant squelch break 

and weak reception both on KX155 and on KX170(McCoy conversion). Had it 

happen elsewhere, but not where it caused problems when I had to be in 

communication with approach inside Class B airspace. Fixed as soon as I 

removed one of Comant 121 antennas from top of fuselage and replaced 

with Comant 122 on belly. I've heard of many other ELT installs having 

same problem. As you say, I don't think there were a lot of requirements 

for RF interference back in 1973 when the TSO was originally written.

On 7/16/2011 8:16 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		  

    Interesting! I hadn't thought of that scenario. Unlike

    transceivers where the antenna is connected to a receiver

    input circuit 99.9% of the time, the ELT antenna is

    permanently connected to the output circuitry of a

    transmitter's power output stage.



    A strong analog TV station impressed on the ELT

    antenna could be conducted into the non-linear,

    transistor junctions where the TV signal could

    produce inter-modulation products that spread over

    a very wide spectrum. Now that we're all-digital

    in the off-air TV world, I suspect probability

    is reduced. I'm aware of no other "trash rich"

    high power signals that would produce this

    effect today.



    This is a phenomenon that was never explored

    by DO-160 although I've read some military

    qualification test protocols that do look for

    inter-modulation mixing and re-radiation of

    foreign energies coming down the antenna feedline.

   Bob . . .

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

paul.r.kuntz(at)gmail.com
Guest

Posted: Sat Jul 16, 2011 5:51 pm Post subject: ELT antenna placement

Thanks for all the feedback.  Seems like the prudent approach will be to accept the ELT installation instructions and mount the ELT at the specified 3+ feet of separation from the VHF antenna.  I'd rather do that now than face the potential for troubleshooting and installation rework later.

 

Paul Kuntz



On Sat, Jul 16, 2011 at 7:51 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 [quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> 

 

 At 07:10 AM 7/16/2011, you wrote:

 --> AeroElectric-List message posted by: Dave Saylor <dave.saylor.aircrafters(at)gmail.com (dave.saylor.aircrafters(at)gmail.com)>

 

 I agree, I've seen comm radios set of a nearby ELT on several

 occasions.  It's not uncommon at all.

 

 I'd keep those antennas away from each other.

 



    It would appear to be the only option. It

    may be very $difficult$ to fix what appears

    to be a design bug internal to the ELT.

 

    The earliest ELT's used a spring-loaded

    mass to close an activation switch in response

    to g-forces of a crash. No doubt modern ELTs

    use the solid-state acceleration sensors

    for this task . . . which produce VERY tiny

    signals requiring a lot of circuit gain.

 

    This type of circuitry offers a high risk

    of vulnerability to RF interference. This

    may be an area where qualification of the

    device to standard DO-160 (good for part

    23) stresses was insufficient to stand off

    the extra-ordinary vulnerabilities of these

    kinds of circuits.  A lot of hardware we

    did for the military and for Part-25 and up

    applications was exposed to really nasty

    RF radiation . . . 200 volts/meter or more

    . . . during qualification. No doubt this

    extra step in qualification would have exposed

    vulnerabilities that are now plaguing customers.

 

 > Paul wrote:

 

 > I'm installing a 121.5/406 MHz ELT in my homebuilt project. Â The

 > installation instructions tell me to put the ELT whip antenna at least 3



 > feet from my VHF radio antenna. Â Is this really necessary? Â There is the

 > possibility of manually activating the ELT in the air in the event of an

 > emergency, while continuing to communicate with the VHF radio, but I'm

 > thinking that the more likely scenarios will be to operate one or the other,



 > but not both. Â That is, the ELT becomes a factor only in the case of a true

 > emergency, in which case I would first squawk emergency and communicate the



 > situation by VHF voice (flying the airplane first, of course). Â Then,

 > activate the ELT (one button press) if a forced landing appears inevitable,

 > but I'm probably done talking on the radio at that point.

 >

 > Is the concern simply the presence of another vertically oriented conductor

 > in relatively close proximity to the antenna in use, thus influencing its



 > performance? Â Even if both the ELT and the VHF radio are active at the same

 > time, is 3 ft of separation important?

 >

 > At any rate, it would be more convenient from an installation perspective to



 > put them closer together. Â Any advice?

 

    Give it a try . . . but with a Plan-B for moving

    one or both of the antennas to achieve demonstrably

    necessary separation. I suspect that not all ELT

    products are victim to the hypothesized vulnerability

    I cited above. There are no grave performance issues

    that would arise from antenna proximity issues so if

    you "get away Scott free" with your desired configuration,

    you're good to go.

 

 

 

   Bob . . . 



 

 

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