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#1
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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 |
#2
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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 |
#3
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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 |
#4
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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. |
#5
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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 |
#6
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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 |
#7
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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. |
#8
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"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 |
#9
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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 |
#10
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And I wouldn't have you for a customer for all the tea in China. What a
numbnuts. Jim "kage" wrote in message ... 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. |
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