Antenna problems

I am having (I think) antenna problems in my Helio Courier. The radio is a
Garmin 530. The antenna is a forward swept :"V" type mounted high on the
vertical stabilizer. There is a splitter that spilts the output from this
one antenna into two VOR signals and a single GS signal. The NAV flag on
the HSI drops into view and then retracts many times on ILS and LOC
frequencies. The GS seems fine and the HSI D-bar doesn't scallop. This
same 530 works fine in the MU-2 and there are no flag issues in the Helio in
GPS mode, so I don't think it is the radio.

A few questions spring to mind:

Some of the coax is RG-58U, would the newer RG 400U improve things?

The splitter will supply two VOR recievers. Am I losing something even
though I have only one reciever plugged in? Would a splitter with only one
GS and one VOR output help any? (I doubt it)?

I haven't been up on a ladder to look at the antenna but is the problem
likely to be grounding and/or corrosion? I also have not followed the coax
all the way from the antenna to the radio so there could be connectors along
the way, how much do you lose for each connector?

Mike
MU-2
Helio Courier

Some of the coax is RG-58U, would the newer RG 400U improve things?

If the existing cables are in good condition (no kinks or cuts) it should
work, although I would guess that since the RG400U is the approved type, it
probably just has slightly better shielding qualities.


The splitter will supply two VOR recievers. Am I losing something even
though I have only one reciever plugged in? Would a splitter with only
one
GS and one VOR output help any? (I doubt it)?


If the unused outputs of the splitter are not terminated, it could cause a
problem. If the unused outputs are empty, you can try making your own
terminators with the appropriate connector (BNC, PL-259? whatever) and a 1/4
watt 47 ohm resistor, as a test.

I haven't been up on a ladder to look at the antenna but is the problem
likely to be grounding and/or corrosion? I also have not followed the
coax
all the way from the antenna to the radio so there could be connectors
along
the way, how much do you lose for each connector?


Insertion loss for connections is about 1dB, in good condition, but
corrosion may form over time, causing loss of signal. Check them out.

Mike
MU-2
Helio Courier

Thanks Mike! I will try terminating the unused port and check the
connectors. Do the symptoms sound like they could be ground plane related?

Mike
MU_2
Helio Courier


"Mike W." wrote in message
...

Some of the coax is RG-58U, would the newer RG 400U improve things?

If the existing cables are in good condition (no kinks or cuts) it should
work, although I would guess that since the RG400U is the approved type,
it
probably just has slightly better shielding qualities.


The splitter will supply two VOR recievers. Am I losing something even
though I have only one reciever plugged in? Would a splitter with only
one
GS and one VOR output help any? (I doubt it)?


If the unused outputs of the splitter are not terminated, it could cause a
problem. If the unused outputs are empty, you can try making your own
terminators with the appropriate connector (BNC, PL-259? whatever) and a
1/4
watt 47 ohm resistor, as a test.

I haven't been up on a ladder to look at the antenna but is the problem
likely to be grounding and/or corrosion? I also have not followed the
coax
all the way from the antenna to the radio so there could be connectors
along
the way, how much do you lose for each connector?


Insertion loss for connections is about 1dB, in good condition, but
corrosion may form over time, causing loss of signal. Check them out.

Mike
MU-2
Helio Courier

You may have water in the coax line. If so it will have a lot of
loss. Find a ham radio operator with a MFJ antenna analyzer and
water will show up as excessive VSWR. This meter has a built in low
power tuneable osc to check the swr so it will not harm any thing.

The flag flipping is most likely due to a beat frequency between the
engine RPM and the glide slope modulation frequency. Change the prop
pitch a little to change the engine speed a hundred RPM and this
should go away. You do not want the prop blades rate to be a sub
multiple of 90 or 150 Hz. This will make the indicator pointers dance
and the flags flip a lot.
John


On Wed, 02 Feb 2005 02:29:34 GMT, "Mike Rapoport"
wrote:

I am having (I think) antenna problems in my Helio Courier. The radio is a
Garmin 530. The antenna is a forward swept :"V" type mounted high on the
vertical stabilizer. There is a splitter that spilts the output from this
one antenna into two VOR signals and a single GS signal. The NAV flag on
the HSI drops into view and then retracts many times on ILS and LOC
frequencies. The GS seems fine and the HSI D-bar doesn't scallop. This
same 530 works fine in the MU-2 and there are no flag issues in the Helio in
GPS mode, so I don't think it is the radio.

A few questions spring to mind:

Some of the coax is RG-58U, would the newer RG 400U improve things?

The splitter will supply two VOR recievers. Am I losing something even
though I have only one reciever plugged in? Would a splitter with only one
GS and one VOR output help any? (I doubt it)?

I haven't been up on a ladder to look at the antenna but is the problem
likely to be grounding and/or corrosion? I also have not followed the coax
all the way from the antenna to the radio so there could be connectors along
the way, how much do you lose for each connector?

Mike
MU-2
Helio Courier

Having an un-terminated connector on the splitter will not cause the
problem you are describing. Definately trace out the coax from the splitter
back to the antenna and look for splices (connectors). A poorly made
connector could add a lot more than 1db of loss. Look at the antenna
connections and balun... it could be the orginal (how old is your airplane?)

Don't overlook the possibility that the radio is not seated all the
way in the tray.

Thanks John, I will try to find someone with the antanna analyzer. The GS
doesn't use the NAV flag (the GS pointers just move out of view) so I don't
think that is the problem. I will try changing the RPM anyway.

Mike
MU-2
Helio Courier

"John_F" wrote in message
...
You may have water in the coax line. If so it will have a lot of
loss. Find a ham radio operator with a MFJ antenna analyzer and
water will show up as excessive VSWR. This meter has a built in low
power tuneable osc to check the swr so it will not harm any thing.

The flag flipping is most likely due to a beat frequency between the
engine RPM and the glide slope modulation frequency. Change the prop
pitch a little to change the engine speed a hundred RPM and this
should go away. You do not want the prop blades rate to be a sub
multiple of 90 or 150 Hz. This will make the indicator pointers dance
and the flags flip a lot.
John


On Wed, 02 Feb 2005 02:29:34 GMT, "Mike Rapoport"
wrote:

I am having (I think) antenna problems in my Helio Courier. The radio is
a
Garmin 530. The antenna is a forward swept :"V" type mounted high on the
vertical stabilizer. There is a splitter that spilts the output from this
one antenna into two VOR signals and a single GS signal. The NAV flag on
the HSI drops into view and then retracts many times on ILS and LOC
frequencies. The GS seems fine and the HSI D-bar doesn't scallop. This
same 530 works fine in the MU-2 and there are no flag issues in the Helio
in
GPS mode, so I don't think it is the radio.

A few questions spring to mind:

Some of the coax is RG-58U, would the newer RG 400U improve things?

The splitter will supply two VOR recievers. Am I losing something even
though I have only one reciever plugged in? Would a splitter with only
one
GS and one VOR output help any? (I doubt it)?

I haven't been up on a ladder to look at the antenna but is the problem
likely to be grounding and/or corrosion? I also have not followed the
coax
all the way from the antenna to the radio so there could be connectors
along
the way, how much do you lose for each connector?

Mike
MU-2
Helio Courier

Mike
MU-2
Helio Courier


After spending at least $9000 for a 530 and then installation, I can't
imagine not ripping out all the crappy old antenna and wiring and replace
with new. How old IS that junk?

I wouldn't even use a technician who didn't automatically do that.

Karl
I practice what I preach.

"kage" wrote in message
...


Mike
MU-2
Helio Courier


After spending at least $9000 for a 530 and then installation, I can't
imagine not ripping out all the crappy old antenna and wiring and replace
with new. How old IS that junk?

I wouldn't even use a technician who didn't automatically do that.

Karl
I practice what I preach.


Two years old. Kind of a foolish polity IMHO. The cost of replacing
everything along with the possibility of damaging the interior, cross
threading nutplates, scratching the paint ect outweighs the remote chance
that the coax is bad. Similiarly the antenna is just two pieces of
stainless steel wire and a balun. Now if you had the airplane completely
apart, I would agree that changing any low cost parts that look suspect and
will be difficult to access when the airplane is together makes sense.

Mike
MU-2

Mike,

The symptoms you describe suggest an intermittent connection somewhere in
the nav receive RF chain. If the GS and VOR/LOC use the same antenna, and
the GS works OK, this suggests that the problem is most likely in the
splitter or the cabling/connectors between the splitter and the radio. The
"open" VOR output on the splitter MIGHT be a source of the problem, but it's
not very likely. (However, terminations are cheap and simple to install --
I'd put one on just for general principles.)

See if you can duplicate the problem on the ground in an area where a VOR,
VOT, or LOC signal can generally be received. Watch the NAV flag while
wiggling the various cables, connectors, etc. On the other hand, any
avionics shop should have the equipment needed to quickly and accurately
check out the entire antenna/splitter/cabling system.

--
-Elliott Drucker

The problem turned out to be a broken coax. It was broken at the connector
at the antenna end. The coax was not long enough to reach the antenna
anymore so I theorize that it was broken by someone pulling it tight inside
the fusilage. It also had no strain relief. Seems to be working now (on
the ground)

Mike
MU-2
Helio Courier