Today's Message Index:
----------------------
1. 06:20 AM - Transponder ()
2. 07:11 AM - Re: Transponder (Brian Lloyd)
3. 07:16 AM - Re: Transponder (Hopperdhh@aol.com)
4. 07:22 AM - Re: Transponder (Hopperdhh@aol.com)
5. 07:42 AM - Re: Transponder (Fred Fillinger)
6. 07:50 AM - Re: Transponder (Brian Lloyd)
7. 08:07 AM - Re: Transponder (James E. Clark)
Message 1
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--> Avionics-List message posted by: <rfg842@cox.net>
I have a similar question. As far as I'm concerned, the first place to start in
checking out avionics in an aircraft is the antenna; after making sure the unit
has power.
Not knowing much about avionics, how do you check to make sure you have a good
connection with the antenna; what equipment do you use and what readings should
you expect?
Would appreciate any assistance.
Bob, Wichita
>
>
Message 2
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--> Avionics-List message posted by: Brian Lloyd <brianl@lloyd.com>
On Sep 10, 2004, at 9:20 AM, <rfg842@cox.net> wrote:
> --> Avionics-List message posted by: <rfg842@cox.net>
>
> I have a similar question. As far as I'm concerned, the first place
> to start in checking out avionics in an aircraft is the antenna; after
> making sure the unit has power.
>
> Not knowing much about avionics, how do you check to make sure you
> have a good connection with the antenna; what equipment do you use and
> what readings should you expect?
Troubleshooting an antenna or feedline problem for a transponder is
pretty difficult since it requires specialized equipment. Fortunately
it is so simple that if you do it right, it will work.
1. Visually inspect the cable and then check the it with an ohmmeter.
You should have zero ohms from center-pin to center-pin, zero ohms from
outer-shell to outer-shell, and infinite ohms from center-pin to
outer-shell. Make sure you flex the cable while doing this to check
for any bad connection.
2. Make sure antenna is projecting downward and is attached to a flat
metal plate at least 6" in diameter.
3. Check to make sure that the center-pin to outer-shell on the
antenna show infinite ohms.
If you really want to be sure you need to go to an avionics shop that
has a transponder test set. They can verify the output of the
transponder right at the antenna connector and they can verify that the
antenna is radiating a proper signal. To just test it and not
calibrate it shouldn't cost more than a couple of dollars and if the
shop isn't busy they may just do the test for free, especially if they
think you will pay them to troubleshoot any problems found.
Something else to consider: transponder signals are of sufficiently
high frequency that they are subject to shading. Think of the antenna
as a light bulb and any piece of metal as a wall that casts a shadow.
If the shadow falls on the ATC radar antenna, your signal to them will
probably go away.
For example, my RV-4 had the transponder antenna mounted between the
gear legs. I could make my ATC reply disappear just by turning my
airplane so that one of the gear legs was interposed between the
transponder antenna and the ATC RADAR antenna.
If you have the antenna in the baggage compartment anything you put in
there is potentially going to shade the antenna. For this reason I
strongly recommend that you mount your transponder antenna on the belly
of the airplane. I know you are trying to reduce drag to the absolute
minimum but the belly of the airplane, especially downwind from the
engine cooling air outlet, is already a turbulent area and any antennas
there are unlikely to have any effect in the effective flat-plate drag
of the airplane.
Brian Lloyd 6501 Red Hook Plaza
brianl@lloyd.com Suite 201
+1.340.998.9447 St. Thomas, VI 00802
Message 3
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--> Avionics-List message posted by: Hopperdhh@aol.com
In a message dated 9/10/04 8:21:09 AM US Eastern Standard Time,
rfg842@cox.net writes:
> --> Avionics-List message posted by: <rfg842@cox.net>
>
> I have a similar question. As far as I'm concerned, the first place to
> start in checking out avionics in an aircraft is the antenna; after making sure
> the unit has power.
>
> Not knowing much about avionics, how do you check to make sure you have a
> good connection with the antenna; what equipment do you use and what readings
> should you expect?
>
> Would appreciate any assistance.
>
> Bob, Wichita
Bob,
The transponder is a simple 1/4 wave vertical. What this means is that there
is nothing in the base of the antenna except the insulator. Check it by
making sure the inner conductor of the coax shows continuity to the antenna, and
that it is not shorted to the mounting flange. Also, the shield of the coax
must contact ground at the mounting flange of the antenna. There's not much to
go wrong. The problems would be in the mechanical connections.
Hope this helps.
Dan Hopper
RV-7A (Flying 41 hours)
Message 4
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--> Avionics-List message posted by: Hopperdhh@aol.com
Brian,
Much better answer than mine! I think I better just listen -- er read!
Dan H
In a message dated 9/10/04 9:12:20 AM US Eastern Standard Time, br
ianl@lloyd.com writes:
> Troubleshooting an antenna or feedline problem for a transponder is
> pretty difficult since it requires specialized equipment. Fortunately
> it is so simple that if you do it right, it will work.
>
> 1. Visually inspect the cable and then check the it with an ohmmeter.
> You should have zero ohms from center-pin to center-pin, zero ohms from
> outer-shell to outer-shell, and infinite ohms from center-pin to
> outer-shell. Make sure you flex the cable while doing this to check
> for any bad connection.
>
> 2. Make sure antenna is projecting downward and is attached to a flat
> metal plate at least 6" in diameter.
>
> 3. Check to make sure that the center-pin to outer-shell on the
> antenna show infinite ohms.
>
> If you really want to be sure you need to go to an avionics shop that
> has a transponder test set. They can verify the output of the
> transponder right at the antenna connector and they can verify that the
> antenna is radiating a proper signal. To just test it and not
> calibrate it shouldn't cost more than a couple of dollars and if the
> shop isn't busy they may just do the test for free, especially if they
> think you will pay them to troubleshoot any problems found.
>
> Something else to consider: transponder signals are of sufficiently
> high frequency that they are subject to shading. Think of the antenna
> as a light bulb and any piece of metal as a wall that casts a shadow.
> If the shadow falls on the ATC radar antenna, your signal to them will
> probably go away.
>
> For example, my RV-4 had the transponder antenna mounted between the
> gear legs. I could make my ATC reply disappear just by turning my
> airplane so that one of the gear legs was interposed between the
> transponder antenna and the ATC RADAR antenna.
>
> If you have the antenna in the baggage compartment anything you put in
> there is potentially going to shade the antenna. For this reason I
> strongly recommend that you mount your transponder antenna on the belly
> of the airplane. I know you are trying to reduce drag to the absolute
> minimum but the belly of the airplane, especially downwind from the
> engine cooling air outlet, is already a turbulent area and any antennas
> there are unlikely to have any effect in the effective flat-plate drag
> of the airplane.
>
> Brian Lloyd 6501 Red Hook Plaza
> brianl@lloyd.com Suite 201
> +1.340.998.9447 St. Thomas, VI 00802
>
Bob,
The transponder is a simple 1/4 wave vertical.=A0 What this means is that there
is nothing in the base of the antenna except the insulator.=A0 Check it by
making sure the inner conductor of the coax shows continuity to the antenna,
and
that it is not shorted to the mounting flange.=A0 Also, the shield of the coax
must contact ground at the mounting flange of the antenna.=A0 There's not much
to
go wrong.=A0 The problems would be in the mechanical connections.
Hope this helps.
Dan Hopper
RV-7A (Flying 41 hours)
Message 5
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--> Avionics-List message posted by: "Fred Fillinger" <n3eu@comcast.net>
> ...
> Not knowing much about avionics, how do you check to make sure you
have a good connection with the antenna; what equipment do you use and
what readings should you expect?
>
> Bob, Wichita
> >
The only common box I know of is the good old MFJ-259B antenna
analyzer that many hams have and like to show off. It will test for
coax loss, even fairly accurately measure its length. However, it
will not test the antenna at xpondr frequency. A metal stub antenna
is conducive to physical inspection and test of continuity/ground
isolation with an ohmmeter. Patch in a length of newish RG-58 and go
fly. If the xponder now works with lossy RG-58 at 1 gHz, replacing
the cable with correct stuff should solve any problem. The proper way
to test in the air is about 50nm from an ATC site at 5-6000 feet AGL,
maybe closer in if using an RG-58 patch. Fly a very lazy 360 (sweeps
can be as much as like 20 seconds apart) and ask ATC to watch for
"dropouts."
Reg,
Fred F.
Message 6
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--> Avionics-List message posted by: Brian Lloyd <brianl@lloyd.com>
On Sep 10, 2004, at 10:22 AM, Hopperdhh@aol.com wrote:
> --> Avionics-List message posted by: Hopperdhh@aol.com
>
> Brian,
>
> Much better answer than mine! I think I better just listen -- er read!
Thanks. I am a ham and I worked my way through college working in an
avionics shop. Now I build wireless ISPs. I have a little experience
with things radiolike. :
)
Brian Lloyd 6501 Red Hook Plaza
brianl@lloyd.com Suite 201
+1.340.998.9447 St. Thomas, VI 00802
Message 7
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--> Avionics-List message posted by: "James E. Clark" <james@nextupventures.com>
One other point to check is to connect the antenna connector to ANOTHER
piece of coax and check as described below.
A friend of mine had a problem and I **think** the problem in the end was
that all checked out fine to the test below but when the coax was pushed
onto the antenna the pin slid back just a bit or was not protruding enough
to make a good contact.
James
> -----Original Message-----
> From: owner-avionics-list-server@matronics.com
> [mailto:owner-avionics-list-server@matronics.com]On Behalf Of
> Hopperdhh@aol.com
> Sent: Friday, September 10, 2004 10:22 AM
> To: avionics-list@matronics.com
> Subject: Re: Avionics-List: Transponder
>
>
> --> Avionics-List message posted by: Hopperdhh@aol.com
>
> Brian,
>
> Much better answer than mine! I think I better just listen -- er read!
>
> Dan H
>
>
> In a message dated 9/10/04 9:12:20 AM US Eastern Standard Time, br
> ianl@lloyd.com writes:
>
> > Troubleshooting an antenna or feedline problem for a transponder is
> > pretty difficult since it requires specialized equipment. Fortunately
> > it is so simple that if you do it right, it will work.
> >
> > 1. Visually inspect the cable and then check the it with an ohmmeter.
> > You should have zero ohms from center-pin to center-pin, zero ohms from
> > outer-shell to outer-shell, and infinite ohms from center-pin to
> > outer-shell. Make sure you flex the cable while doing this to check
> > for any bad connection.
> >
> > 2. Make sure antenna is projecting downward and is attached to a flat
> > metal plate at least 6" in diameter.
> >
> > 3. Check to make sure that the center-pin to outer-shell on the
> > antenna show infinite ohms.
> >
> > If you really want to be sure you need to go to an avionics shop that
> > has a transponder test set. They can verify the output of the
> > transponder right at the antenna connector and they can verify that the
> > antenna is radiating a proper signal. To just test it and not
> > calibrate it shouldn't cost more than a couple of dollars and if the
> > shop isn't busy they may just do the test for free, especially if they
> > think you will pay them to troubleshoot any problems found.
> >
> > Something else to consider: transponder signals are of sufficiently
> > high frequency that they are subject to shading. Think of the antenna
> > as a light bulb and any piece of metal as a wall that casts a shadow.
> > If the shadow falls on the ATC radar antenna, your signal to them will
> > probably go away.
> >
> > For example, my RV-4 had the transponder antenna mounted between the
> > gear legs. I could make my ATC reply disappear just by turning my
> > airplane so that one of the gear legs was interposed between the
> > transponder antenna and the ATC RADAR antenna.
> >
> > If you have the antenna in the baggage compartment anything you put in
> > there is potentially going to shade the antenna. For this reason I
> > strongly recommend that you mount your transponder antenna on the belly
> > of the airplane. I know you are trying to reduce drag to the absolute
> > minimum but the belly of the airplane, especially downwind from the
> > engine cooling air outlet, is already a turbulent area and any antennas
> > there are unlikely to have any effect in the effective flat-plate drag
> > of the airplane.
> >
> > Brian Lloyd 6501 Red Hook Plaza
> > brianl@lloyd.com Suite 201
> > +1.340.998.9447 St. Thomas, VI 00802
> >
>
> Bob,
>
> The transponder is a simple 1/4 wave vertical.=A0 What this means
> is that there
>
> is nothing in the base of the antenna except the insulator.=A0 Check it by
> making sure the inner conductor of the coax shows continuity to
> the antenna,
> and
> that it is not shorted to the mounting flange.=A0 Also, the
> shield of the coax
> must contact ground at the mounting flange of the antenna.=A0
> There's not much
> to
> go wrong.=A0 The problems would be in the mechanical connections.
>
> Hope this helps.
>
> Dan Hopper
> RV-7A (Flying 41 hours)
>
>
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