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Amp meter jumps when transmitting

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rv7a.builder(at)yahoo.com
Guest

Posted: Sun Apr 27, 2014 4:39 am Post subject: Amp meter jumps when transmitting

Hello Group,

     I have a Vans amp meter installed in my RV-7A. When I activate the PTT on the Garmin GNC300XL the amp meter jumps to full scale. I disconnect the antenna coax from back of the radio and hit the PTT and the amp meter needle stays still. I turn off the radio and bring my handheld into the cockpit and hit the transmit button from 2 feet away and a very slight movement in the amp meter is detected. Bringing the handheld closer to the amp meter will make the needle jump more when the PTT is activated. I think I  have determined this to be a RF inference problem. My questions are 1) Will the amp meter eventually be damaged by these extreme movements? 2) Is there a fix? 3) Am I alone here or have others experience this phenomena?

 

Thanks. John. RV-7A Just about ready to fly 



 





 [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Apr 27, 2014 5:42 am Post subject: Amp meter jumps when transmitting

At 07:35 AM 4/27/2014, you wrote:

Hello Group,

      I have a Vans amp meter installed in my RV-7A. When I activate 

the PTT on the Garmin GNC300XL the amp meter jumps to full scale. I 

disconnect the antenna coax from back of the radio and hit the PTT 

and the amp meter needle stays still. I turn off the radio and bring 

my handheld into the cockpit and hit the transmit button from 2 feet 

away and a very slight movement in the amp meter is detected. 

Bringing the handheld closer to the amp meter will make the needle 

jump more when the PTT is activated. I think I have determined this 

to be a RF inference problem.



    I bought a Van's ammeter some years ago to

    explore it's vulnerabilities to strong RF.



    See pictures here:



http://tinyurl.com/mpx8hze



    I discovered that no only was the instrument

    devoid of any firewall for RF interference,

    it was even directionally sensitive!!! See

    pictures



http://tinyurl.com/m4xlj2u



http://tinyurl.com/kvo4vwk



    Just waving the hand-held from side to side

    would produce behaviors in the pointer error

    that mimicked the motion of the antenna.

My questions are 1) Will the amp meter eventually be damaged by these 

extreme movements?



    No



  2) Is there a fix?



    Probably, but labor intensive and clumsy on

    a finished instrument. It would have been FAR

    better that the manufacturer demonstrated

    a knowledge of DO-160 in the first place.



  3) Am I alone here or have others experience this phenomena?

    No doubt there are many others. Since it's

    a transient event that affects the display

    only while talking, it's a cosmetic behavior.

    You might consider just 'living' with it.



    With one caveat . . . make sure that your coax

    connectors are good at both ends of the feedline . . .

    it wouldn't hurt to do an SWR check.  The

    phenomenon you're observing MIGHT be the

    result of a very RF-Hot cockpit due to loss

    of shield ground on either end of the coax.



    But it your antenna system is golden, then

    there are no risks for just ignoring it.



    I wrote to Van's about this condition . . . never

    heard back from them. It no doubt affects

    their entire line of instruments with

    electronic signal conditioning.



   Bob . . .

rv7a.builder(at)yahoo.com
Guest

Posted: Sun Apr 27, 2014 6:10 am Post subject: Amp meter jumps when transmitting

Thanks Bob for that great analysis. John.

     On Sunday, April 27, 2014 6:57 AM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

  

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



At 07:35 AM 4/27/2014, you  wrote:

Hello Group,

      I have a Vans amp meter installed in my RV-7A. When I activate 

the PTT on the Garmin GNC300XL the amp meter jumps to full scale. I 

disconnect the antenna coax from back of the radio and hit the PTT 

and the amp meter needle stays still. I turn off the radio and bring 

my handheld into the cockpit and hit the transmit button from 2 feet 

away and a very slight movement in the amp meter is detected. 

Bringing the handheld closer to the amp meter will make the needle 

jump more when the PTT is activated. I think I have determined this 

to be a RF inference problem.



    I bought a Van's ammeter some years ago to

    explore it's vulnerabilities to strong RF.



    See pictures here:



http://tinyurl.com/mpx8hze



    I discovered that no only was the  instrument

    devoid of any firewall for RF interference,

    it was even directionally sensitive!!! See

    pictures



http://tinyurl.com/m4xlj2u



http://tinyurl.com/kvo4vwk



    Just waving the hand-held from side to side

    would produce behaviors in the pointer error

    that mimicked the motion of the antenna.

My questions are 1) Will the amp meter eventually be damaged by these 

extreme movements?



    No



  2) Is there a fix?



    Probably, but labor intensive and clumsy on

    a finished instrument. It would have been FAR

    better that the manufacturer demonstrated

    a knowledge of DO-160 in the first place.



  3) Am I alone here or  have others experience this phenomena?

    No doubt there are many others. Since it's

    a transient event that affects the display

    only while talking, it's a cosmetic behavior.

    You might consider just 'living' with it.



    With one caveat . . . make sure that your coax

    connectors are good at both ends of the feedline . . .

    it wouldn't hurt to do an SWR check.  The

    phenomenon you're observing MIGHT be the

    result of a very RF-Hot cockpit due to loss

    of shield ground on either end of the coax.



    But it your antenna system is golden, then

    there are no risks for just ignoring it.



    I wrote to Van's about this condition . . . never

    heard back from them. It no doubt affects

    their entire line of  instruments with

    electronic signal conditioning.



http://www.matronics=   -->

deej(at)deej.net
Guest

Posted: Sun Apr 27, 2014 6:51 am Post subject: Amp meter jumps when transmitting

On 4/27/2014 8:35 AM, rv7a.builder wrote:

 	  Quote: 	
		   I disconnect the antenna coax from back of the radio and hit the PTT 

 and the amp meter needle stays still.


	


Just as an aside, it is generally a bad idea to activate a transmitter 

with no antenna attached.  There is a good chance of damaging the 

transmitter by doing this.



fyi



-Dj



-- 

Dj Merrill - N1JOV - VP EAA Chapter 87

Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/

Glastar Flyer N866RH - http://deej.net/glastar/

rv7a.builder(at)yahoo.com
Guest

Posted: Sun Apr 27, 2014 7:21 am Post subject: Amp meter jumps when transmitting

Thanks for telling me that. I won't try that again. What actually happens that could damage the transmitter? Thanks. John

     On Sunday, April 27, 2014 8:10 AM, Dj Merrill <deej(at)deej.net> wrote:

  

  --> AeroElectric-List message posted by: Dj Merrill <deej(at)deej.net (deej(at)deej.net)>



On 4/27/2014 8:35 AM, rv7a.builder wrote:

 	  Quote: 	
		   I  disconnect the antenna coax from back of the radio and hit the PTT 

 and the amp meter needle stays still.


	


Just as an aside, it is generally a bad idea to activate a transmitter 

with no antenna attached.  There is a good chance of damaging the 

transmitter by doing this.



fyi



-Dj



-- 

Dj Merrill - N1JOV - VP EAA Chapter 87

Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/

Glastar Flyer N866RH - http://deej.net/gNavigator?AeroElectric-List" target="_blank">http://www.matronics.com/Navsp;  -->

kdb.rv10(at)gmail.com
Guest

Posted: Sun Apr 27, 2014 9:07 am Post subject: Amp meter jumps when transmitting

I saw this problem years ago also. Their electronic manifold pressure gauge has same issue. I replaced the MP with a non-electric version. The rest of my instruments are from an EFIS. No problems with this configuration.



K. Belue

RV-10



Sent from my iPhone



On Apr 27, 2014, at 8:41 AM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:



 	  Quote: 	
		   

 

 At 07:35 AM 4/27/2014, you wrote:

 Hello Group,

     I have a Vans amp meter installed in my RV-7A. When I activate the PTT on the Garmin GNC300XL the amp meter jumps to full scale. I disconnect the antenna coax from back of the radio and hit the PTT and the amp meter needle stays still. I turn off the radio and bring my handheld into the cockpit and hit the transmit button from 2 feet away and a very slight movement in the amp meter is detected. Bringing the handheld closer to the amp meter will make the needle jump more when the PTT is activated. I think I have determined this to be a RF inference problem.

 

   I bought a Van's ammeter some years ago to

   explore it's vulnerabilities to strong RF.

 

   See pictures here:

 

 http://tinyurl.com/mpx8hze

 

   I discovered that no only was the instrument

   devoid of any firewall for RF interference,

   it was even directionally sensitive!!! See

   pictures

 

 http://tinyurl.com/m4xlj2u

 

 http://tinyurl.com/kvo4vwk

 

   Just waving the hand-held from side to side

   would produce behaviors in the pointer error

   that mimicked the motion of the antenna.

 

 

 My questions are 1) Will the amp meter eventually be damaged by these extreme movements?

 

   No

 

 2) Is there a fix?

 

   Probably, but labor intensive and clumsy on

   a finished instrument. It would have been FAR

   better that the manufacturer demonstrated

   a knowledge of DO-160 in the first place.

 

 3) Am I alone here or have others experience this phenomena?

 

 

   No doubt there are many others. Since it's

   a transient event that affects the display

   only while talking, it's a cosmetic behavior.

   You might consider just 'living' with it.

 

   With one caveat . . . make sure that your coax

   connectors are good at both ends of the feedline . . .

   it wouldn't hurt to do an SWR check.  The

   phenomenon you're observing MIGHT be the

   result of a very RF-Hot cockpit due to loss

   of shield ground on either end of the coax.

 

   But it your antenna system is golden, then

   there are no risks for just ignoring it.

 

   I wrote to Van's about this condition . . . never

   heard back from them. It no doubt affects

   their entire line of instruments with

   electronic signal conditioning.

 

 

 

 

 

  Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Apr 27, 2014 9:55 am Post subject: Amp meter jumps when transmitting

At 09:50 AM 4/27/2014, you wrote:

 	  Quote: 	
		  



On 4/27/2014 8:35 AM, rv7a.builder wrote:

>I disconnect the antenna coax from back of the radio and hit the 

>PTT and the amp meter needle stays still.



Just as an aside, it is generally a bad idea to activate a 

transmitter with no antenna attached.  There is a good chance of 

damaging the transmitter by doing this.


	




    Back in the days of germanium output transistors

    (yes Martha, there WERE germanium devices capable

    of several watts at VHF) it was considered poor

    form if not instant death to one's output transistors

    to key a transmitter into an open circuit.



    Modern output devices are much more rugged. Further,

    transmitters at-risk for high SWR damage are fitted

    with automatic shut-down circuits for protection.





   Bob . . .

deej(at)deej.net
Guest

Posted: Sun Apr 27, 2014 2:53 pm Post subject: Amp meter jumps when transmitting

On 4/27/2014 11:21 AM, rv7a.builder wrote:

 	  Quote: 	
		   Thanks for telling me that. I won't try that again. What actually 

 happens that could damage the transmitter? Thanks. John


	


Hi John,

     I am sure someone else on here can explain the technical details 

better than I, but the simple version is that if the transmitter does 

not have circuitry built in to protect against it, it can blow some of 

the parts in the final amplifier stage of the transmitter. Hopefully 

someone else can chime in with more details of exactly how and why.



     There is probably a good chance that a modern solid state radio has 

this protection built in, but unless one knows for sure, there is no 

reason to take the expensive chance that it doesn't.  I'd be more 

concerned with the older radios, but in general it is just good practice 

to make sure that you have an antenna or a dummy load attached to the 

antenna port before keying up the transmitter.  My personal choice is to 

make sure there is an antenna attached before even powering a radio on, 

regardless of whether I am going to key the transmitter part.



-Dj



-- 

Dj Merrill - N1JOV - VP EAA Chapter 87

Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/

Glastar Flyer N866RH - http://deej.net/glastar/

henador_titzoff(at)yahoo.
Guest

Posted: Sun Apr 27, 2014 4:24 pm Post subject: Amp meter jumps when transmitting

Dj, John,



Here's what happens when a transmitter hurls RF energy down a transmission line.  First, the transmission line has a characteristic  impedance.  Impedance is almost like a resistance except it's comprised of a mixture of capacitor reactance, inductive reactance and resistance.  Reactances have currents and voltages that are 90 degrees out of phase.  This means they don't "burn" up any of the energy, whereas resistance has voltage and current in phase and does burn up energy.  Check out the attached picture from Wiki, which shows how the capacitance, inductance and resistances are modeled as lumped components. Ideally, the series and parallel resistances are zero.  In practice they're not but designers try to minimize them to decrease attenuation.

When this energy traveling down the transmission line reaches the end, what happens?  If there's a resistor there that is equal to the transmission line's characteristic impedance, then ideally all of the energy is dissipated in that resistor as heat, since the voltage and current waves are in phase.  If an antenna that is matched to the line is there, the power is magically transferred to the atmosphere, because the antenna's job is to match the impedance of the cable to free space impedance, which is 376 Ohms.  It isn't really magic, at least mathematically, but one has to understand  Maxwell's and Gaussian's laws to know how this happens and why free space impedance is 376 Ohms.

So let's say the end of the transmission line is open or doesn't match the impedance.  In the open case, the energy has nowhere to go except to be transmitted right back to where it came from.  Let's say the transmitter's transistors  are generating voltage waves that are 10V peak to peak.  This means that the designer has to choose components that can handle this voltage plus some, say another 10V, in order to provide longevity and reliability.  When the reflected energy arrives at the transmitter output, the two waves (one going and one coming) can add up to a  worst case number of 20V peak to peak if the phasing is correct. This comes very close to exceeding the design limitation of the transmitter transistors.  If the designer specs the transistors to less than 20V, then the two added waves' peak voltage could very well destroy the transistors and/or other components.  The designer could add transorbers or some other devices designed to limit the voltage build up at the transmitter to keep it from malfunctioning, but it's up to the designer and his design specs.



Also, the transmitter has an impedance of its own, and for maximum power transfer it should equal the line's impedance.  When the reflected wave comes back, if there is a slight mismatch between the transmitter and line impedances, there will be some power dissipation at the transmitter but some of the power (wave) will reflect back to the end of the line.  This means there are several waves on the line, but each reflection decreases in amplitude because of losses along the line and at the ends.  All of these waves have to be added or subtracted to find the real voltages at the ends.



So the bottom line is can the transmitter handle the reflected waves such that when they add up, the end voltage doesn't damage the transmitter components, which of course have maximum voltage and power limits.  I add power in there because power causes heat and components can only handle so much maximum temperature.



Hope this helps.

 

Henador Titzoff



 	  Quote: 	
		          From: Dj Merrill <deej(at)deej.net> To: aeroelectric-list(at)matronics.com  Sent:  Sunday, April 27, 2014 6:52 PM Subject: Re: Amp meter jumps when transmitting  

 --> AeroElectric-List message posted by: Dj Merrill <deej(at)deej.net (deej(at)deej.net)>On 4/27/2014 11:21 AM, rv7a.builder wrote:> Thanks for telling me that. I won't try that again. What actually > happens that could damage the transmitter? Thanks. JohnHi John,     I am sure someone else on here can explain the technical details better than I, but the simple  version is that if the transmitter does not have circuitry built in to protect against it, it can blow some of the parts in the final amplifier stage of the transmitter. Hopefully someone else can chime in with more details of exactly how and why.     There is probably a good chance that a modern solid state radio has this protection built in, but unless one knows for sure, there is no reason to take the expensive chance that it doesn't.  I'd be more concerned with the older radios, but in general it is just good practice to make sure  that you have an antenna or a dummy load attached to the antenna port before keying up the transmitter.  My personal choice is to make sure there is an antenna attached before even powering a radio on, regardless of whether I am going to key the transmitter part.-Dj-- Dj Merrill - N1JOV - VP EAA Chapter 87Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/Glastar Flyer N866RH - http://www.matronics.com/Navigator?AeroElectric-Listhttp://www.matronics.com/contribution</==================

2014_04_27_Transmission_Line_Circuit.jpg

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Apr 27, 2014 4:45 pm Post subject: Amp meter jumps when transmitting

 	  Quote: 	
		  So the bottom line is can the transmitter handle the reflected waves 

such that when they add up, the end voltage doesn't damage the 

transmitter components, which of course have maximum voltage and 

power limits.  I add power in there because power causes heat and 

components can only handle so much maximum temperature.


	


    I'm aware of no supplier to aviation that does not

    consider the rare but possible failure of a coax

    connection . . . it's common practice to build

    in protection, robustness or a combination of the

    two.



   Bob . . .

henador_titzoff(at)yahoo.
Guest

Posted: Sun Apr 27, 2014 5:49 pm Post subject: Amp meter jumps when transmitting

This is very true, Bob, but I would also like to add that the possibility of an open in the connectors and coax is more common than "rare."  Most of these failures occur during build, which are accidental, corrosion or failure to tighten down connectors correctly.

While aviation suppliers will consider the rare but possible failure you mention below, there are several scenarios where this is not true.  One scenario is the supplier receiving counterfeit parts that do not meet specs.  Another scenario is a shady buyer ordering the wrong parts and a faulty lot  is manufactured and shipped.  Manufactured lots vary from lot to lot, and some lots may sneak through that do not meet specifications but work well until "something happens."  In particular, this business of counterfeit parts has been plaguing manufacturing for at least two decades now.



 

Henador Titzoff

 	  Quote: 	
		          From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

 To:  aeroelectric-list(at)matronics.com 

 Sent: Sunday, April 27, 2014 8:44 PM

 Subject: Re: Amp meter jumps when transmitting

  

 

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

 	  Quote: 	
		  So the bottom line is can the transmitter handle the reflected waves 

such that when they add up, the end voltage doesn't damage the 

transmitter components, which of course have maximum voltage and 

power limits.  I add power in there because power causes heat and 

components can only handle so much maximum temperature.


	


    I'm aware of no supplier to aviation that does not

    consider  the rare but possible failure of a coax

    connection . . . it's common practice to build

    in protection, robustness or a combination of the

    two.



   Bob . . =   --> http://www.matronics.com/Navigator?AeroElectric-Le great content also available via p;                 -Matt Dralle, Li==========

 

 

 	


   

 [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Apr 27, 2014 6:51 pm Post subject: Amp meter jumps when transmitting

 	  Quote: 	
		   >Manufactured lots vary from lot to lot, and some lots may sneak 

 through that do not meet specifications but work well until 

 "something happens."  In >particular, this business of counterfeit 

 parts has been plaguing manufacturing for at least two decades now.


	


    Forgive me my friend but we're reaching WAAaaayyyy down into

    the worry bucket with this line of reasoning. Once

    you open that door . . . where do the caveats end?

    Cracked magneto rotors? Contaminated fuel? Bogus rivets?

    The world is indeed fraught with risks. Nonetheless,

    the vast majority of misadventures in every

    venue have nothing to do with parts that fail

    to meet published requirements. Adding such

    worries to the knowledge base is potential misdirection

    of valuable attention from much greater risks.

   Bob . . .

henador_titzoff(at)yahoo.
Guest

Posted: Mon Apr 28, 2014 12:26 pm Post subject: Amp meter jumps when transmitting

You're right that I'm going down a road fraught with all sorts of relatively low risk items.  Just trying to explain why an open transmission line might kill a transmitter that's otherwise designed to survive it.  I hope my explanation of why the voltage could theoretically double at the transmitter helped explain to some how this phenomenon happens.

Henador Titzoff

[quote]        From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Sunday, April 27, 2014 10:50 PM

 Subject: Re: Amp meter jumps when transmitting

  

 

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

 	  Quote: 	
		   >Manufactured lots  vary from lot to lot, and some lots may sneak 

 through that do not meet specifications but work well until 

 "something happens."  In >particular, this business of counterfeit 

 parts has been plaguing manufacturing for at least two decades now.


	


    Forgive me my friend but we're reaching WAAaaayyyy down into

    the worry bucket with this line of reasoning. Once

    you open that door . . . where do the caveats end?

    Cracked magneto rotors? Contaminated fuel? Bogus rivets?

    The world is indeed fraught with risks. Nonetheless,

    the vast majority of misadventures in every

    venue have nothing to do with parts that fail

    to meet published requirements. Adding such

    worries to the knowledge base is potential misdirection

    of valuable attention from much greater ronics.com/Navigator?AeroElectric-List" target="_blank">http://www.matronm/" =   --> 

   

 [quote][b]

deej(at)deej.net
Guest

Posted: Mon Apr 28, 2014 12:34 pm Post subject: Amp meter jumps when transmitting

On 04/28/2014 04:22 PM, Henador Titzoff wrote:

 	  Quote: 	
		   You're right that I'm going down a road fraught with all sorts of

 relatively low risk items.  Just trying to explain why an open

 transmission line might kill a transmitter that's otherwise designed to

 survive it.  I hope my explanation of why the voltage could

 theoretically double at the transmitter helped explain to some how this

 phenomenon happens.

 

 Henador Titzoff


	




Your explanation helped me, and matched my limited understanding of how

it works, as well as allowing me to learn more.



Thank you!  



-Dj



-- 

Dj Merrill - N1JOV - VP EAA Chapter 87

Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/

Glastar Flyer N866RH - http://deej.net/glastar/

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