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jpx(at)Qenesis.com
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 Posted: Fri Aug 07, 2009 7:52 am Post subject: Radio noises |
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Advice please.
A friend of mine has a Pitts he recently purchased and has been
fighting to fix ugly noises in the radio since he bought it.
The electrical system is quite simple - no lights, VFR panel, single
radio, transponder, basic intercom, battery, alternator and starter.
The radio is a King KX145, which has reportedly passed a bench test.
The noise sounds to me like engine induced noise. It is not clean
white noise, but continuous static with lots of scratches and pops in
it.
Before I got involved, the radio was bench tested. The original
antenna on the turtledeck was taken off the and grounds cleaned up.
The avionics shop talked him into a new antenna, which was installed
on the bottom of the aircraft instead, and a new cable which connects
to about a 1 foot long pigtail coming out of the back of the radio
rack. Now he has spent over $1000 and the problem persists.
So yesterday, I got in the plane with him and we played around on the
ground. The static exists whenever the radio's squelch is
unsquelched, or when receiving a less than very strong signal. That
is, the tower and ATIS are cleanly heard, but an aircraft calling from
12 miles is easily understood among a background of static. This is
with the engine not running and just the radio powered on.
With the engine running the static is pretty much the same, except you
need to turn the volume up a bit due to the external engine and wind
noise. The static does not change when the alternator is switched on
and off. It does not change at all with engine rpm or when switching
mags on and off. So even though it sounds very much like engine
interference, it must not be, since it can be heard with the engine
stopped.
Curiously, the static is much louder as the plane is oriented toward
the south-east. So listening to the ATIS broadcast, the audio is
clean for about 270 degrees of the circle, but the voice stays the
same, but the background static dramatically increases to almost as
loud as the voice, when facing the southeast quadrant. This
directional characteristic is the same whether behind the hangars, or
out on the main ramp a half mile away.
To be sure the VOR antenna and the COM antenna cables were not mixed
up, I unplugged them one at a time and got no difference. In the end,
we had all the antenna cables unplugged and the receive audio was the
same ???? Both handhelds available receive no audible signal without
their antenna connected. So how can we be picking up the ATIS without
an antenna ? Could the signal be picked up via the intercom wires ?
The intercom requires pushing a switch to talk to the other person.
Yesterday, I pulled the jacks off the panels. They are wired with
proper shielded cable and I installed insulated washers at the jacks,
just in case there was some grounding problem. No change.
Generally tranmit is quite good. I have picked up this aircraft, very
clearly, when flying my own 20 miles apart. Generally the tower
reports our transmissions as 5x5, however, when on the ramp facing
southeast, they report the transmission is slightly garbled. The
owner reports sometimes having to change direction in flight in order
to call up the tower.
Ideas what should be done next ? I have suggested another bench test
of the radio, which probably won't tell us anything that wasn't
revealed the first time. I don't have access to a VSWR meter. The
wiring is pretty shabby, so perhaps just re-wiring it all from scratch
is a good idea.
I intend to make a patch cable that will allow testing the entire
cable and antenna installation with a handheld radio.
Jeff Page
Dream Aircraft Tundra #10
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nuckolls.bob(at)aeroelect
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| Posted: Fri Aug 07, 2009 11:50 am Post subject: Radio noises |
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At 10:51 AM 8/7/2009, you wrote:
Advice please.
<snip>
Now he has spent over $1000 and the problem persists.
So yesterday, I got in the plane with him and we played around on the
ground. The static exists whenever the radio's squelch is
unsquelched, or when receiving a less than very strong signal. That
is, the tower and ATIS are cleanly heard, but an aircraft calling from
12 miles is easily understood among a background of static. This is
with the engine not running and just the radio powered on.
What, if any other accessories are operating on the
airplane during this test. Try pulling all other breakers/
fuses except radio/audio system to search out possible
cause/effect on board the aircraft. In particular, make
sure the alternator's regulator is not powered up.
With the engine running the static is pretty much the same, except you
need to turn the volume up a bit due to the external engine and wind
noise. The static does not change when the alternator is switched on
and off.
Oops, Okay . . . scratch the alternator.
It does not change at all with engine rpm or when switching
mags on and off. So even though it sounds very much like engine
interference, it must not be, since it can be heard with the engine
stopped.
agreed.
Curiously, the static is much louder as the plane is oriented toward
the south-east. So listening to the ATIS broadcast, the audio is
clean for about 270 degrees of the circle, but the voice stays the
same, but the background static dramatically increases to almost as
loud as the voice, when facing the southeast quadrant. This
directional characteristic is the same whether behind the hangars, or
out on the main ramp a half mile away.
Does the noise go away when you disconnect the antenna?
Have you checked for presence of this noise while away
from the field? The directional effects suggest possible
local source on the ground.
To be sure the VOR antenna and the COM antenna cables were not mixed
up, I unplugged them one at a time and got no difference. In the end,
we had all the antenna cables unplugged and the receive audio was the
same ????
Okay, that answers that question.
Both handhelds available receive no audible signal without
their antenna connected. So how can we be picking up the ATIS without
an antenna ? Could the signal be picked up via the intercom wires ?
Good question. Back in the good ol' days the radios for light
aircraft were not subjected to many sources of outside stimulus
and testing for vulnerabilities on other than power and antenna
lines was limited. Nowadays, we look at ALL wires which enter
or exit the box along with shielding integrity of the box itself.
This is one of Ed King's earliest crystal synthesized radios
that came out about 1975 as I recall. Have you checked to see
if this radio still qualifies under tightened frequency
accuracy and receiver bandwidth requirements were levied for
8.33 Khz channel spacing?
The intercom requires pushing a switch to talk to the other person.
Yesterday, I pulled the jacks off the panels. They are wired with
proper shielded cable and I installed insulated washers at the jacks,
just in case there was some grounding problem. No change.
Generally tranmit is quite good. I have picked up this aircraft, very
clearly, when flying my own 20 miles apart. Generally the tower
reports our transmissions as 5x5, however, when on the ramp facing
southeast, they report the transmission is slightly garbled. The
owner reports sometimes having to change direction in flight in order
to call up the tower.
Hmmmm happens in flight too and is getting into the
the transmitter?
Ideas what should be done next ? I have suggested another bench test
of the radio, which probably won't tell us anything that wasn't
revealed the first time. I don't have access to a VSWR meter. The
wiring is pretty shabby, so perhaps just re-wiring it all from scratch
is a good idea.
I intend to make a patch cable that will allow testing the entire
cable and antenna installation with a handheld radio.
Good lick too. I was considering that suggestion. Also, check
performance at the top end of the comm frequency rage with a
remotely located hand held for weak signal. See if the problem
is frequency sensitive.
Bob . . .
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rdunhamtn(at)hotmail.com
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| Posted: Sat Aug 08, 2009 4:18 am Post subject: Radio noises |
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Jeff C
Just my $0.02 worth but...
I think your friend suffers from what I consider to be the most common cause of dissatisfaction with VHF COMM performance in OBAM aircraft... unrealistic expectations!
With all due respect C gentlemen...
If the AM background noise is the same during flight as it is on the ground with the engine off C that's as good as it gets.
If C while on the ground with the belly mounted antenna inches from the ground and upward radiation blocked by the aircraft itself C you can clearly understand ATC C ATIS and another plane 12 miles away C that's as good as it gets.
The directionality of the "static" and the transmit is not curious at all. All antennae C except "ideal" antennae of urban legend C produce a signal strength pattern that is lobular. That is C the radio "reaches out" more (or less) in certain directions than others. With the antenna on the belly C there are numerous metallic objects nearby C like gear legs C that serve to produce sometimes dramatic and unpredictable signal strength lobes. So C once again C that's as good as it gets.
Not sure on this one but... The fact that you can hear ATIS without an antenna just serves to underscore how good your radio is(!) and how close you are to the ATIS antenna. Bob has mentioned on this forum that we should not obsess over dimensions of marker beacon antennae because the MB signal is so strong and we're flying just dozens of yards over the thing that we'll get the info anyway. This is a similar situation I suspect.
Again C if you guys can communicate "very clearly" from 20 miles apart C that's as good as it gets.
"Ideas what should be done next?" Bolt it down C adjust the squelch and start punching holes in the sky!
Enjoy.
Rodney in Tennessee
Unabashed Nuckollhead
Standard Disclaimer: I'm no avionics engineer. But C I plan on staying in a Holiday Inn Express next month at the American Sonex Association Fly-in in Crossville C TN.
Express your personality in color! Preview and select themes for Hotmail®. Try it now. [quote][b]
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rv9jim(at)juno.com
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z747pilot(at)verizon.net
Guest
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| Posted: Sat Aug 08, 2009 7:21 am Post subject: Radio noises |
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Hey Flyers,
A small formula here that may help you out: take the Square root of the antennea hight (aircraft hight) and multiply it by 2.23 and this should give you a rough idea of your VHF range.
Regards,
z747pilot
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Rodney Dunham
Sent: Saturday, August 08, 2009 8:12 AM
To: aeroelectric-list(at)matronics.com
Subject: RE: Radio noises
Jeff,
Just my $0.02 worth but...
I think your friend suffers from what I consider to be the most common cause of dissatisfaction with VHF COMM performance in OBAM aircraft... unrealistic expectations!
With all due respect, gentlemen...
If the AM background noise is the same during flight as it is on the ground with the engine off, that's as good as it gets.
If, while on the ground with the belly mounted antenna inches from the ground and upward radiation blocked by the aircraft itself, you can clearly understand ATC, ATIS and another plane 12 miles away, that's as good as it gets.
The directionality of the "static" and the transmit is not curious at all. All antennae, except "ideal" antennae of urban legend, produce a signal strength pattern that is lobular. That is, the radio "reaches out" more (or less) in certain directions than others. With the antenna on the belly, there are numerous metallic objects nearby, like gear legs, that serve to produce sometimes dramatic and unpredictable signal strength lobes. So, once again, that's as good as it gets.
Not sure on this one but... The fact that you can hear ATIS without an antenna just serves to underscore how good your radio is(!) and how close you are to the ATIS antenna. Bob has mentioned on this forum that we should not obsess over dimensions of marker beacon antennae because the MB signal is so strong and we're flying just dozens of yards over the thing that we'll get the info anyway. This is a similar situation I suspect.
Again, if you guys can communicate "very clearly" from 20 miles apart, that's as good as it gets.
"Ideas what should be done next?" Bolt it down, adjust the squelch and start punching holes in the sky!
Enjoy.
Rodney in Tennessee
Unabashed Nuckollhead
Standard Disclaimer: I'm no avionics engineer. But, I plan on staying in a Holiday Inn Express next month at the American Sonex Association Fly-in in Crossville, TN.
Express your personality in color! Preview and select themes for Hotmail®. Try it now. [quote]
href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List
href="http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
[b]
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jbr79r(at)yahoo.com
Guest
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| Posted: Sat Aug 08, 2009 4:05 pm Post subject: Radio noises |
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I'm a little confused with the formula you proposed for simplicity lets say the antenna height is at 9 feet above ground sq root of 9=3x2.23 =6.69? ( feet , meters inches miles???)
James Robinson
Glasair lll N79R
Spanish Fork UT U77
From: z747pilot <z747pilot(at)verizon.net>
To: aeroelectric-list(at)matronics.com
Sent: Saturday, August 8, 2009 8:19:11 AM
Subject: RE: Radio noises
.hmmessage P { PADDING-BOTTOM:0px;MARGIN:0px;PADDING-LEFT:0px;PADDING-RIGHT:0px;PADDING-TOP:0px;} BODY.hmmessage { FONT-FAMILY:Verdana;FONT-SIZE:10pt;} Hey Flyers,
A small formula here that may help you out: take the Square root of the antennea hight (aircraft hight) and multiply it by 2.23 and this should give you a rough idea of your VHF range.
Regards,
z747pilot
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Rodney Dunham
Sent: Saturday, August 08, 2009 8:12 AM
To: aeroelectric-list(at)matronics.com
Subject: RE: Radio noises
Jeff,
Just my $0.02 worth but..
I think your friend suffers from what I consider to be the most common cause of dissatisfaction with VHF COMM performance in OBAM aircraft... unrealistic expectations!
With all due respect, gentlemen..
If the AM background noise is the same during flight as it is on the ground with the engine off, that's as good as it gets.
If, while on the ground with the belly mounted antenna inches from the ground and upward radiation blocked by the aircraft itself, you can clearly understand ATC, ATIS and another plane 12 miles away, that's as good as it gets.
The directionality of the "static" and the transmit is not curious at all. All antennae, except "ideal" antennae of urban legend, produce a signal strength pattern that is lobular. That is, the radio "reaches out" more (or less) in certain directions than others. With the antenna on the belly, there are numerous metallic objects nearby, like gear legs, that serve to produce sometimes dramatic and unpredictable signal strength lobes. So, once again, that's as good as it gets.
Not sure on this one but... The fact that you can hear ATIS without an antenna just serves to underscore how good your radio is(!) and how close you are to the ATIS antenna. Bob has mentioned on this forum that we should not obsess over dimensions of marker beacon antennae because the MB signal is so strong and we're flying just dozens of yards over the thing that we'll get the info anyway. This is a similar situation I suspect.
Again, if you guys can communicate "very clearly" from 20 miles apart, that's as good as it gets.
"Ideas what should be done next?" Bolt it down, adjust the squelch and start punching holes in the sky!
Enjoy.
Rodney in Tennessee
Unabashed Nuckollhead
Standard Disclaimer: I'm no avionics engineer. But, I plan on staying in a Holiday Inn Express next month at the American Sonex Association Fly-in in Crossville, TN.
Express your personality in color! Preview and select themes for Hotmail®. Try it now. [quote]
href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-Listhref="http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
http://www.matronics.c==================
[b]
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wooody04(at)bellsouth.net
Guest
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| Posted: Wed Aug 19, 2009 7:24 am Post subject: Radio noises |
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is that answer in miles?
z747pilot wrote: [quote] .hmmessage P { PADDING-BOTTOM: 0px; MARGIN: 0px; PADDING-LEFT: 0px; PADDING-RIGHT: 0px; PADDING-TOP: 0px } BODY.hmmessage { FONT-FAMILY: Verdana; FONT-SIZE: 10pt } Hey Flyers,
A small formula here that may help you out: take the Square root of the antennea hight (aircraft hight) and multiply it by 2.23 and this should give you a rough idea of your VHF range.
Regards,
z747pilot
From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com) [mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of Rodney Dunham
Sent: Saturday, August 08, 2009 8:12 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: RE: Radio noises
Jeff,
Just my $0.02 worth but...
I think your friend suffers from what I consider to be the most common cause of dissatisfaction with VHF COMM performance in OBAM aircraft... unrealistic expectations!
With all due respect, gentlemen...
If the AM background noise is the same during flight as it is on the ground with the engine off, that's as good as it gets.
If, while on the ground with the belly mounted antenna inches from the ground and upward radiation blocked by the aircraft itself, you can clearly understand ATC, ATIS and another plane 12 miles away, that's as good as it gets.
The directionality of the "static" and the transmit is not curious at all. All antennae, except "ideal" antennae of urban legend, produce a signal strength pattern that is lobular. That is, the radio "reaches out" more (or less) in certain directions than others. With the antenna on the belly, there are numerous metallic objects nearby, like gear legs, that serve to produce sometimes dramatic and unpredictable signal strength lobes. So, once again, that's as good as it gets.
Not sure on this one but... The fact that you can hear ATIS without an antenna just serves to underscore how good your radio is(!) and how close you are to the ATIS antenna. Bob has mentioned on this forum that we should not obsess over dimensions of marker beacon antennae because the MB signal is so strong and we're flying just dozens of yards over the thing that we'll get the info anyway. This is a similar situation I suspect.
Again, if you guys can communicate "very clearly" from 20 miles apart, that's as good as it gets.
"Ideas what should be done next?" Bolt it down, adjust the squelch and start punching holes in the sky!
Enjoy.
Rodney in Tennessee
Unabashed Nuckollhead
Standard Disclaimer: I'm no avionics engineer. But, I plan on staying in a Holiday Inn Express next month at the American Sonex Association Fly-in in Crossville, TN.
Express your personality in color! Preview and select themes for Hotmail®. Try it now. [b]
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sarg314(at)gmail.com
Guest
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| Posted: Wed Aug 19, 2009 7:46 am Post subject: Radio noises |
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Jim:
In what units do you measure the antenna? Inches?
What if you have bent whip antenna? Is it the total length of the antenna or the perpendicular distance from the fuselage?
On Wed, Aug 19, 2009 at 8:18 AM, Jim Streit <wooody04(at)bellsouth.net (wooody04(at)bellsouth.net)> wrote:
| Quote: | is that answer in miles?
z747pilot wrote: | Quote: | Hey Flyers,
Â
A small formula here that may help you out: take the Square root of the antennea hight (aircraft hight) and multiply it by 2.23 and this should give you a rough idea of your VHF range.
Â
Regards,
Â
z747pilot
|
|
--
Tom Sargent
[quote][b]
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mrspudandcompany(at)veriz
Guest
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| Posted: Wed Aug 19, 2009 8:42 am Post subject: Radio noises |
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Tom,
I believe what Jim is saying has NOTHING to do with antenna length. It is the ALTITUDE of the aircraft! So, the range is the square root of the altitude times 2.23.
Maybe Tom can clarify this and give us units of measure.
Roger
Jim:
In what units do you measure the antenna? Inches?
What if you have bent whip antenna? Is it the total length of the antenna or the perpendicular distance from the fuselage?
On Wed, Aug 19, 2009 at 8:18 AM, Jim Streit <wooody04(at)bellsouth.net (wooody04(at)bellsouth.net)> wrote:
is that answer in miles?
z747pilot wrote:
Hey Flyers,
A small formula here that may help you out: take the Square root of the antennea hight (aircraft hight) and multiply it by 2.23 and this should give you a rough idea of your VHF range.
Regards,
z747pilot
--
Tom Sargent [quote] [b]
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sarg314(at)gmail.com
Guest
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| Posted: Wed Aug 19, 2009 10:24 am Post subject: Radio noises |
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Yes, of course! You should never read the RV-list while at work - it's too distracting. Just stop work and focus on the list.
On Wed, Aug 19, 2009 at 9:29 AM, ROGER & JEAN CURTIS <mrspudandcompany(at)verizon.net (mrspudandcompany(at)verizon.net)> wrote:
| Quote: |
Tom,
Â
I believe what Jim is saying has NOTHING to do with antenna length. It is the ALTITUDE of the aircraft! So, the range is the square root of the altitude times 2.23.
Â
Roger
|
--
Tom Sargent
[quote][b]
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tonybabb(at)alejandra.net
Guest
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| Posted: Wed Aug 19, 2009 10:38 am Post subject: Radio noises |
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Altitude is in feet, range is in miles. - I think.
Tony
Velocity SEFG 62% done, 78% to go
www.alejandra.net/velocity
[quote]
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