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0. 12:15 AM - Just 3 Days Left - Please Make Your List Contribution Today! (Matt Dralle)
1. 08:33 AM - Re: comm tx causing avionics fluctuations (Tom Goddard)
2. 10:44 AM - Re: comm tx causing avionics fluctuations (Noel Loveys)
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| Subject: | comm tx causing avionics fluctuations |
Hi Noel,
We have worked most of this out. I know it has been a few months. We are
going to externally mount the antennas. We did a trial test with a dummy
load and then with the antenna hooked to a long coax and tried different
external mounts and all the RFI went away. We are fairly certain then
that
all our trouble is radiated emission. I have some questions:
1. How far apart should the external antennas be=85 what=92s the
minimum
distance
2. Can they share the same ground plane as long as they both make
ground with it
3. Can the TXP antenna share the same ground plane
4. Do you have an antenna recommendation?
5. Should one be top mounted and one bottom mounted on the
fuselage
tail cone?
Tom
_____
From: owner-avionics-list-server@matronics.com
[mailto:owner-avionics-list-server@matronics.com] On Behalf Of Noel
Loveys
Sent: Tuesday, October 09, 2007 10:53 AM
Subject: RE: Avionics-List: comm tx causing avionics fluctuations
Tom:
Just a few Ideas.
Just as the radiating element of your antenna should be 1/4 wave length
the
ground plane should also be at least that size. If it isn't don't worry
you
can stick a ground plane inside your fuselage with contact cement using
aluminium foil for the ground plane itself. Make sure it is connected
to
the braid side of the coax at the antenna end. The ground plane should
also
be as close as reasonably possible to perpendicular to the radiating
element.
The advice you got to check out your antenna system sounds good to me.
Transmitters aren't too bright and when you feed their output to a
miss-matched antenna system the fool transmitter works harder to get the
signal out. This means it draws a lot more current and of course heats
up.
The end result can be a burned out final amplifier (expensive) or a
popped
circuit breaker. (Cheap if you don't reset it)
Most of the other things you mentioned can be easily attributed to the
same
antenna problem. High current draw by the transmitter will cause the
voltage regulator to cut in possibly to the point before an over voltage
indication.... BTW you generally get that OV indication after the
alternator has been shut down to protect it.
It just crossed my mind that I have seen high draw on a transmitter. It
occurred when there was a crack in the centre conductor inside the coax
to
the antenna. Do a continuity test on the centre conductor of the coax.
When you do that continuity test try wiggling the connectors while
hooked up
to the VOM. Your problem can also be caused by a cold solder joint or a
bad
crimp in a connector.
Finally my pet peeve is bad grounds. Aircraft electrical systems need
to
have as close to perfect ground as possible. You would be surprised the
effect of a bit of black corrosion under the grounding strap that
connects
your engine to the frame across the engine mount will have on your whole
system. Make sure any grounding straps are clean under the nuts/bolts
that
connect them to the various parts of the frame. Make sure there is good
continuity from the grounding posts behind your instrument panel to the
engine block. Also make sure the voltage regulator is mounted on a
clean
surface. Many newer solid state regulators require the case have a good
ground.
You may want to borrow another transmitter and temporarily connect it to
your antenna system and the AC power. If you get the same effect on
transmit then you will know for sure it is your installation and not the
transmitter itself.
The advice to get your antenna system checked out is capitol. Avionics
techs have equipment that can do amazing things. Ten minutes on a
Cushman
could end up saving many $$ chasing a problem.
To recap:
*Put your antenna system under the microscope. That's probably where
your
problem is located.
*Check the continuity of all grounding straps. a good idea to check on
an
annual basis.
*If possible try another transmitter (not a hand held) in your plane You
only need to connect the antenna and aircraft power and see if you get
the
same problem.
If this doesn't fix the problem then you are going to have to get some
local
expertise... Preferably with equipment. Good places to look for help
are
Telco, Amateur radio, Television stations. Only certified avionics
shops
should open avionics cases or make modifications to avionics systems.
You
should keep that in mind if you have a certified plane.
Where do you keep your plane?? if at YHZ you may want to contact Uli
Huber
at Atlantic AV in Springfield he has technicians who should be able to
get
you going in short order...... Bring money ;-)
Hope this helps.
Noel Loveys, RPP, AME intern
Campbellton, Newfoundland,
Canada
Tel: 709-261-2705
HYPERLINK "mailto:noelloveys@yahoo.ca"noelloveys@yahoo.ca
-----Original Message-----
From: owner-avionics-list-server@matronics.com
[mailto:owner-avionics-list-server@matronics.com] On Behalf Of Tom
Goddard
Sent: Monday, October 08, 2007 10:09 PM
Subject: Avionics-List: comm tx causing avionics fluctuations
Does any one have experience with comm tx causing transient changes in
their engine analyzers egt/cht and voltages in glasairs or other
fiberglass
airframes? As we continue to debug our panel this problem is now up for
a
solution. I have heard that it may be "antenna standing wave
reflections"?
Our vert servo on the TruTrak is affected during Tx as well. We assumed
that
the other systems being affected were due to the close proximity of the
comm
antenna coax and the aircraft charging system as they all run through
the
center console of our Glasair III for a short distance in close
proximity.
Maybe I am wrong and it is more to do with the Standing Wave Reflection?
Our other bugs caused by the comm. Tx are:
1. transient voltage rise on both buses from 14.1 to 14.6 (this is
a
real voltage change measured by and external meter)
2. egt and cht values decrease by 300 and 100 degrees F
respectively
(these are obviously not real temp changes)
3. Ray Allan trim and flap indicators flicker (the trim and flaps
don't actually move)
The following is something Tim Hedding of B&C alternators sent me:
1. Check the transmitting antenna systems for SWR. Check that the
antenna,
transmission line and transmitter output are of the same impedance and
that
the connections and ground planes are good. Use an SWR bridge or antenna
analyzer to check the antenna system matching / efficiency.
There must be some other glass airplanes out there that have seen some
of
these quirks.
Tom
Tom Goddard
100 Miner Lane
Grand Pre, N.S.
B0P 1M0
9026702511 Cell
9025427315 Fax
08/10/2007 9:04 AM
href="http://www.matronics.com/Navigator?Avionics-List">http://www.matr
onics
.com/Navigator?Avionics-List
href="http://forums.matronics.com">http://forums.matronics.com
09/10/2007
8:44 AM
Checked by AVG.
11/28/2008
8:17 AM
Message 2
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| Subject: | comm tx causing avionics fluctuations |
I believe the recommended distance antennae should be is greater than three
feet. (for COM.Nav antennae) Some planes have two phased antennae for com.
The installation instructions will specify the distance between the
antennae. That is done on some installations to give a directional quality
to the com radio. VOR antennae are usually horizontal and therefore are
usually mounted on the tail of the plane.
XPNDR antenna are usually placed on the bottom of the airplane because their
primary purpose is to communicate with ground stations. They should also be
limited to about 200 mi in range so that they don't cause distance
interference.
The ground plane is actually a form of reflector so the short answer is yes
several antennae, even on several different frequencies, can share a ground
plane. In fact on metal planes the whole of the skin is considered to be
ground plane. Tube an rag planes the whole frame is considered to be ground
plane.
Transponders use different frequencies than con/nav antennae. Therefore
their antennae are shorter. Use the antenna recommended with your
transponder.
Com radios are usually vertically polarized antennae mounted on the top of
the plane where they can reach other planes and distant ground based towers.
So the long and short of it is Com on top.. XPNDR on the bottom and VOR
on the tail. GPS if you have it will have the antenna on top where it can
see the sky, RADALT will be on the belly of the plane. ADF goniometer
(loop) antenna can be either on top or bottom of the plane the same is true
of the ADF sense (long wire) antenna.
Without the aid of an avionics shop I wouldn't try to install an HF rig in a
plane... but if you do 80 meters is a blast at even 1000'.
Hope this helps
Noel
From: owner-avionics-list-server@matronics.com
[mailto:owner-avionics-list-server@matronics.com] On Behalf Of Tom Goddard
Sent: Friday, November 28, 2008 1:01 PM
Subject: RE: Avionics-List: comm tx causing avionics fluctuations
Hi Noel,
We have worked most of this out. I know it has been a few months. We are
going to externally mount the antennas. We did a trial test with a dummy
load and then with the antenna hooked to a long coax and tried different
external mounts and all the RFI went away. We are fairly certain then that
all our trouble is radiated emission. I have some questions:
1. How far apart should the external antennas be. what's the minimum
distance
2. Can they share the same ground plane as long as they both make ground
with it
3. Can the TXP antenna share the same ground plane
4. Do you have an antenna recommendation?
5. Should one be top mounted and one bottom mounted on the fuselage tail
cone?
Tom
_____
From: owner-avionics-list-server@matronics.com
[mailto:owner-avionics-list-server@matronics.com] On Behalf Of Noel Loveys
Sent: Tuesday, October 09, 2007 10:53 AM
Subject: RE: Avionics-List: comm tx causing avionics fluctuations
Tom:
Just a few Ideas.
Just as the radiating element of your antenna should be 1/4 wave length the
ground plane should also be at least that size. If it isn't don't worry you
can stick a ground plane inside your fuselage with contact cement using
aluminium foil for the ground plane itself. Make sure it is connected to
the braid side of the coax at the antenna end. The ground plane should also
be as close as reasonably possible to perpendicular to the radiating
element.
The advice you got to check out your antenna system sounds good to me.
Transmitters aren't too bright and when you feed their output to a
miss-matched antenna system the fool transmitter works harder to get the
signal out. This means it draws a lot more current and of course heats up.
The end result can be a burned out final amplifier (expensive) or a popped
circuit breaker. (Cheap if you don't reset it)
Most of the other things you mentioned can be easily attributed to the same
antenna problem. High current draw by the transmitter will cause the
voltage regulator to cut in possibly to the point before an over voltage
indication.... BTW you generally get that OV indication after the
alternator has been shut down to protect it.
It just crossed my mind that I have seen high draw on a transmitter. It
occurred when there was a crack in the centre conductor inside the coax to
the antenna. Do a continuity test on the centre conductor of the coax.
When you do that continuity test try wiggling the connectors while hooked up
to the VOM. Your problem can also be caused by a cold solder joint or a bad
crimp in a connector.
Finally my pet peeve is bad grounds. Aircraft electrical systems need to
have as close to perfect ground as possible. You would be surprised the
effect of a bit of black corrosion under the grounding strap that connects
your engine to the frame across the engine mount will have on your whole
system. Make sure any grounding straps are clean under the nuts/bolts that
connect them to the various parts of the frame. Make sure there is good
continuity from the grounding posts behind your instrument panel to the
engine block. Also make sure the voltage regulator is mounted on a clean
surface. Many newer solid state regulators require the case have a good
ground.
You may want to borrow another transmitter and temporarily connect it to
your antenna system and the AC power. If you get the same effect on
transmit then you will know for sure it is your installation and not the
transmitter itself.
The advice to get your antenna system checked out is capitol. Avionics
techs have equipment that can do amazing things. Ten minutes on a Cushman
could end up saving many $$ chasing a problem.
To recap:
*Put your antenna system under the microscope. That's probably where your
problem is located.
*Check the continuity of all grounding straps. a good idea to check on an
annual basis.
*If possible try another transmitter (not a hand held) in your plane You
only need to connect the antenna and aircraft power and see if you get the
same problem.
If this doesn't fix the problem then you are going to have to get some local
expertise... Preferably with equipment. Good places to look for help are
Telco, Amateur radio, Television stations. Only certified avionics shops
should open avionics cases or make modifications to avionics systems. You
should keep that in mind if you have a certified plane.
Where do you keep your plane?? if at YHZ you may want to contact Uli Huber
at Atlantic AV in Springfield he has technicians who should be able to get
you going in short order...... Bring money ;-)
Hope this helps.
Noel Loveys, RPP, AME intern
Campbellton, Newfoundland,
Canada
Tel: 709-261-2705
<mailto:noelloveys@yahoo.ca> noelloveys@yahoo.ca
-----Original Message-----
From: owner-avionics-list-server@matronics.com
[mailto:owner-avionics-list-server@matronics.com] On Behalf Of Tom Goddard
Sent: Monday, October 08, 2007 10:09 PM
Subject: Avionics-List: comm tx causing avionics fluctuations
Does any one have experience with comm tx causing transient changes in
their engine analyzers egt/cht and voltages in glasairs or other fiberglass
airframes? As we continue to debug our panel this problem is now up for a
solution. I have heard that it may be "antenna standing wave reflections"?
Our vert servo on the TruTrak is affected during Tx as well. We assumed that
the other systems being affected were due to the close proximity of the comm
antenna coax and the aircraft charging system as they all run through the
center console of our Glasair III for a short distance in close proximity.
Maybe I am wrong and it is more to do with the Standing Wave Reflection?
Our other bugs caused by the comm. Tx are:
1. transient voltage rise on both buses from 14.1 to 14.6 (this is a
real voltage change measured by and external meter)
2. egt and cht values decrease by 300 and 100 degrees F respectively
(these are obviously not real temp changes)
3. Ray Allan trim and flap indicators flicker (the trim and flaps
don't actually move)
The following is something Tim Hedding of B&C alternators sent me:
1. Check the transmitting antenna systems for SWR. Check that the antenna,
transmission line and transmitter output are of the same impedance and that
the connections and ground planes are good. Use an SWR bridge or antenna
analyzer to check the antenna system matching / efficiency.
There must be some other glass airplanes out there that have seen some of
these quirks.
Tom
Tom Goddard
100 Miner Lane
Grand Pre, N.S.
B0P 1M0
9026702511 Cell
9025427315 Fax
08/10/2007 9:04 AM
href="http://www.matronics.com/Navigator?Avionics-List">http://www.matronics
.com/Navigator?Avionics-List
href="http://forums.matronics.com">http://forums.matronics.com
09/10/2007 8:44 AM
Checked by AVG.
11/28/2008 8:17 AM
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