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RF Problem

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jeff(at)rmmm.net
Guest

Posted: Sun Feb 12, 2006 4:45 pm Post subject: RF Problem

HI All,

I remember this was discussed before, but to know resolution as I 

recall. I Have been fighting an RF problem with my I-Com radio. The RF 

is obviously getting into the ground as even the trim LED's are 

effected. I have a Stratomaster engine monitor from MGL that seams to 

work great until I hit the push to talk button. It then goes black and 

the trim and Navaid LED's go crazy as well. I have a Bob Archer antenna 

in the tail and the radio sounds clear and transmits well. When tested 

with any other antenna the same thing occurs. The power to the antenna 

is about 7 watts and there was only about a half a watt or less coming 

back on the shield when tested.  I made sure some time ago that the com 

RG cable to the antenna was isolated from any other cables. We have 

checked, and all grounds are good on the radio. I have been told to 

install some ferrite RF suppressors on the ground and output of the 

transmitter and to place them on the ground and power going into the 

engine monitor. Before I order these have others run into this and have 

you determined the cause and solution? Any Ideas are very welcome as I 

have been scratching my head for a week!



Thanks in advance,

Jeff Roberts

A258 - N128LJ

Waiting inspection 1st week in March.

paul.mcallister

Joined: 09 Jan 2006
Posts: 177
Location: Waukesha, WI USA

Posted: Sun Feb 12, 2006 5:20 pm Post subject: RF Problem

Jeff,



I have a Bob Archer antenna in the tail of my Europa.  My trim control &

Navaids go nuts when I transmit and I haven't ever solved the problem.  My

SWR is spot on, and the I never have a problem being heard, so the

transmitter is working well.



I am about to go down the ferrite bead route as well, I would be interested

to know how you get on.



Paul



--

SPurpura(at)aol.com
Guest

Posted: Sun Feb 12, 2006 5:57 pm Post subject: RF Problem

DOES YOUR RADIO SHARE A COMMON GROUND OR HAVE ITS OWN.

flyinggpa(at)comcast.net
Guest

Posted: Sun Feb 12, 2006 6:21 pm Post subject: RF Problem

 	  Quote: 	
		  DOES YOUR RADIO SHARE A COMMON GROUND OR HAVE ITS OWN.


	


I was thinking the same thing. The Navaid is having a voltage problem. Make sure the radio has "lots" of wire on the power side.  My BENDIX/KING called for two # 18 wires on both the + and  -  side.  I think "your problem" is what they were trying to avoid. It never hurts to have to much wire size.  (make it bigger)

n3eu(at)COMCAST.NET
Guest

Posted: Sun Feb 12, 2006 8:03 pm Post subject: RF Problem

 	  Quote: 	
		   I was thinking the same thing.  Make sure the radio has

"lots" of wire
	


 	  Quote: 	
		   on the power side.  My BENDIX/KING called for two # 18

wires
	


 	  Quote: 	
		   on both the + and  -  side.  I think "your problem" is

what they were
	


 	  Quote: 	
		   trying to avoid. It never hurts to have to much wire size.

(make it bigger)
	


 	  Quote: 	
		  


	


Two wires for +14V IN and GND are for redundancy.  Rather

common in avionics boxes.  I'm afraid lack thereof will not

solve the orig complaint.  In plastic airplanes, the

radiated field is a strong, vigorous one, easily affecting

other electrical items.  In aluminum planes, those affected

items are significantly shielded by the airframe.  I know

this from me little handy field strength meter, while

xmitting, with the meter inside my aluminum plane, vs.

sticking it out the window in better line-of-sight from the

xmitting antenna.  It's needle can peg with a resounding

click!



I'd first try the ferrite suppressors to trap the EMI

radiated to wiring of affected devices. Those things abound

everywhere these days from wall-brick "switching power

supplies" to charge the battery in consumer devices, through

those now found on the RF cable feeding digital, high-def TV

sets or digital cable boxes.



Reg,

Fred F.

jeff(at)rmmm.net
Guest

Posted: Sun Feb 12, 2006 8:45 pm Post subject: RF Problem

Paul,

I'm going to remove the panel and have the local avionics shop that 

wired it install the ferrite beads where I mentioned. As soon as I 

reinstall it I'll let you know. I guess I can live with it to but I'd 

rather fix it now if possible.

Thank you all for your comments.

Regards,

Jeff

A258 - N128LJ

Waiting inspection 1st week in March



On Feb 12, 2006, at 7:15 PM, Paul McAllister wrote:



[quote] 

 <paul.mcallister(at)qia.net>



 Jeff,



 I have a Bob Archer antenna in the tail of my Europa.  My trim control 

 &

 Navaids go nuts when I transmit and I haven't ever solved the problem. 

  My

 SWR is spot on, and the I never have a problem being heard, so the

 transmitter is working well.



 I am about to go down the ferrite bead route as well, I would be 

 interested

 to know how you get on.



 Paul



 --

n9zes(at)verizon.net
Guest

Posted: Mon Feb 13, 2006 5:52 am Post subject: RF Problem

Jeff,



I have a Bob Archer antenna in the tail of my Europa.  My trim control &

Navaids go nuts when I transmit and I haven't ever solved the problem.  My

SWR is spot on, and the I never have a problem being heard, so the

transmitter is working well.



I am about to go down the ferrite bead route as well, I would be interested

to know how you get on.



Paul



---> I've had a bit of experience with RF problems, being a ham operator for the past decade or so, both with a 5 watt 144MHz handheld and also a 150 watt SSB HF radio.  The wierd part is the 5 watt radio caused more issues than the big rig.  I could wipe out every TV in our house with it.



The problem is not with the transmitter, or the SWR of the antenna.  The problem is with other wiring, like the trim servo leads, picking up the radiated power and bringing it back to whatever is there.  The solid state components in the 'box' act like a diode rectifier (a.k.a. crystal radio) and that power just overloads the circuitry.  Most solid state electronics today is pretty well wide open to RF interferrence.  Telephones are usually really bad, TV's, alarm systems, touch lamps, etc. are great at getting RF into them.



Part of the problem is the Europa itself. Since it's glass, the fuselage offers no internal shielding of other equipment from the radio transmissions like a Spam Can would.



The other problem is that any leads to servos, lighting, etc. will pick up the transmitted power, and be especially bad if the lead lengths are a multiple of the frequency (in 1/4 wavelengths).



A few solutions to try:



1) Make sure the radio chassis is grounded well to the airframe ground bus.

2) Make sure you are using good coax for the antenna lead (double shielded if necessary - foil and braid)

3) Get a ferrite bead assortment (Amidon is one brand).  The ferrites do NOT go on the radio, but on everything else that is affected.  This would mean that signal and power leads to trim systems, engine monitors, etc. all need to have beads or torroids applied.

4) In worst case situations, you need to actually shield the affected equipment itself, which means building a grounded box around the device from copper sheet, etc.



Chris

topglock(at)cox.net
Guest

Posted: Mon Feb 13, 2006 10:26 am Post subject: RF Problem

Jeff,



I'm using the same setup Icom/Archer.  My coax runs through a 1" x 2" 

channel in the left of the fuse, along with the transponder coax, left 

wing wiring and a couple of other power wires.  You've ridden in the 

bird and, as you probably know, there is no interference, at all.  The 

only time I had a probelm, was with the mic going to open and affecting 

the trim, tripping the breaker.  That turned out to be a short in 

intercom wiring.  Once it was fixed, the problem went away.  I'd check 

all other connections, including grounds, just to be sure they are all 

good.  Other than that, I'm stumpped, but that's not hard to do... 



I know you're close to first flight.  Keep us apprised.  Hope to see you 

at Sun-N-Fun...



Jeff - N55XS

141 hours



JEFF ROBERTS wrote:



 	  Quote: 	
		   

 

 HI All,

 I remember this was discussed before, but to know resolution as I 

 recall. I Have been fighting an RF problem with my I-Com radio. The RF 

 is obviously getting into the ground as even the trim LED's are 

 effected. I have a Stratomaster engine monitor from MGL that seams to 

 work great until I hit the push to talk button. It then goes black and 

 the trim and Navaid LED's go crazy as well. I have a Bob Archer antenna 

 in the tail and the radio sounds clear and transmits well. When tested 

 with any other antenna the same thing occurs. The power to the antenna 

 is about 7 watts and there was only about a half a watt or less coming 

 back on the shield when tested.  I made sure some time ago that the com 

 RG cable to the antenna was isolated from any other cables. We have 

 checked, and all grounds are good on the radio. I have been told to 

 install some ferrite RF suppressors on the ground and output of the 

 transmitter and to place them on the ground and power going into the 

 engine monitor. Before I order these have others run into this and have 

 you determined the cause and solution? Any Ideas are very welcome as I 

 have been scratching my head for a week!

 

 Thanks in advance,

 Jeff Roberts

 A258 - N128LJ

 Waiting inspection 1st week in March.

 

 

 

 

 

 

 

  

  

  

 

 

 

 

 


	




--

jeff(at)rmmm.net
Guest

Posted: Mon Feb 13, 2006 1:38 pm Post subject: RF Problem

Hi Jeff, hows it going? Yes I agree the ground is the most likely place 

it's getting in but I'v run a second ground to the radio rack the 

engine monitor the trim and still can't get rid of it. I'll try the 

ferrite beads next. I too ran all my coax down the opposite side 

keeping them away from the others wires. I'll be taking the panel to 

Ron Dupler at the local avionics shop and letting him have a stab at it 

as myself and two other local plastic plane builders are all stumped. 

Looks like Paul McCallister is having the same problem.

I probably wont have the hours flown off by Sun & Fun but I still may 

be there. I have a friend that lives not far from Lakeland thats 

expecting me. I'll let you know or call your cell then.

Thanks, and we'll let you know of the first flight.

Jeff

A258

On Feb 13, 2006, at 12:06 PM, Jeff B wrote:

 	  Quote: 	

 Jeff,

 I'm using the same setup Icom/Archer.  My coax runs through a 1" x 2"

 channel in the left of the fuse, along with the transponder coax, left

 wing wiring and a couple of other power wires.  You've ridden in the

 bird and, as you probably know, there is no interference, at all.  The

 only time I had a probelm, was with the mic going to open and affecting

 the trim, tripping the breaker.  That turned out to be a short in

 intercom wiring.  Once it was fixed, the problem went away.  I'd check

 all other connections, including grounds, just to be sure they are all

 good.  Other than that, I'm stumpped, but that's not hard to do... 

 I know you're close to first flight.  Keep us apprised.  Hope to see 

 you

 at Sun-N-Fun...

 Jeff - N55XS

 141 hours

 JEFF ROBERTS wrote:

> 

>

> HI All,

> I remember this was discussed before, but to know resolution as I

> recall. I Have been fighting an RF problem with my I-Com radio. The RF

> is obviously getting into the ground as even the trim LED's are

> effected. I have a Stratomaster engine monitor from MGL that seams to

> work great until I hit the push to talk button. It then goes black and

> the trim and Navaid LED's go crazy as well. I have a Bob Archer 

> antenna

> in the tail and the radio sounds clear and transmits well. When tested

> with any other antenna the same thing occurs. The power to the antenna

> is about 7 watts and there was only about a half a watt or less coming

> back on the shield when tested.  I made sure some time ago that the 

> com

> RG cable to the antenna was isolated from any other cables. We have

> checked, and all grounds are good on the radio. I have been told to

> install some ferrite RF suppressors on the ground and output of the

> transmitter and to place them on the ground and power going into the

> engine monitor. Before I order these have others run into this and 

> have

> you determined the cause and solution? Any Ideas are very welcome as I

> have been scratching my head for a week!

>

> Thanks in advance,

> Jeff Roberts

> A258 - N128LJ

> Waiting inspection 1st week in March.

>

 --

n3eu(at)comcast.net
Guest

Posted: Mon Feb 13, 2006 2:58 pm Post subject: RF Problem

Chris Beck wrote:



 	  Quote: 	
		   The weird part is the 5 watt radio caused more issues than

 the big rig.  I could wipe out every TV in our house with

it.
	


 	  Quote: 	
		  

Chris, ain't that fun.  My 2.3W-carrier VHF handheld, at 20
	


feet from small (cheap) TVs, will briefly make the screen

black and kill audio.  But just inches anywhere from a new,

big Sony flat-screen digital -- absolutely nothing.  It may

be as much circuit design as shielding of the "victim"

device, as interference I guess is intolerable for the big

bucks you have to pay!



 	  Quote: 	
		   2) Make sure you are using good coax for the antenna

 lead (double shielded if necessary - foil and braid)


	


I would consider "bettering" the coax a last resort.  If I

take said handheld and xmit in the vicinity of a RG-58 patch

cable (unterminated) at the input of my 200mHz oscilloscope,

coax about antenna length, I might see like only 10mV a few

feet from this cable.



Since receive is the reciprocal of xmit in these matters,

the corollary is shielding the input wires to the victim

device, single or multi-conductor as convenient.  The shield

would not be a ground path, just grounded at the instrument

end, I would say.



 	  Quote: 	
		   3) Get a ferrite bead assortment (Amidon is one brand).


	


Ferrite beads or small toriod donuts have a frequency spec

and may be less than what we need if small.  A larger donut

allows spiral winding (twice at least) around the core.



If instead of RG-58 in above test, I then use plain, solid

wire.  Again about 1/4-wavelength.  Scope sensitivity will

have to be readjusted...a lot!  If I lengthen the wire to

random length (nonresonant), way down. If I then take a 1"

ferrite cylinder with even 3/8" ID, pass the wire through it

and near the BNC input, scope trace is way down.  Make one

spiral turn around the ferrite, way down again.  So,

ideally, the wire should be spiral-wound around a donut a

couple times.  For instrumentation as the victim device, I'd

try input wires first, like sensor wires.  Ten of millivolts

on the 14V or ground wire shouldn't matter much.



Google: ferrite core suppressor, for ideas, sources, and

white papers on the science.  Rather than undo wiring, I'd

first try the plastic encased clamp-on suppressors.  One may

be able to liberate one off a consumer device wall charger,

and affix it around the wire bundle to the instrument.  To

see if we're going in the right direction.



Reg,

Fred F.

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