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Thread: Radio Transmission Issue

  1. #1
    Wag2+2's Avatar
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    Radio Transmission Issue

    I have a KY 97 14 volt com with a whip antenna. I can pick up transmissions loud and clear from 50 miles away. However, when I transmit it doesn’t seem to push out a strong signal. Within 5 miles it is good but 10 miles and beyond it appears to fade fast with interference that makes it difficult for ATC to pick up and understand. Any ideas on what the issue might be? Thanks in advance.
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    wireweinie's Avatar
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    Are you sure the antenna is for VHF frequencies? Do you have a model number of the antenna or a pic? It sounds like the wrong antenna or improper installation. If the antenna is rated for VHF com freq's, pull it off and make sure you have good metal to metal contact with the panel it's mounted on (no paint) and if it's on a fabric plane make sure you have some type of ground plane under the antenna mounting location.

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    Radio Transmission Issue

    Not sure but battery or alternator power? Might want to see if it is charged up.
    Last edited by PA-12 on Baumanns; 11-14-2018 at 10:13 PM.
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    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by PA-12 on Baumanns View Post
    Not sure but battery or alternator power? Might want to see if it is charged up.
    on that thought...

    maybe its not able to draw the current to transmit without lag voltage drop/noise due to bad connection in rack..

    maybe pull it out of rack and re rack it....

    also try cleaning ground and power wire connection and breaker connections...

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    BC12D-4-85's Avatar
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    Is there a radio shop or installer that you can have inspect the installation? It takes experience to deal with this. Hearing is one thing and most do ok even during iffy installations unless the local radio frequency noise is high, but signal output is the elephant in the room that may need attention. Local noise (both audio like loud sounds and electrical static), microphone and its voice modulation setup, wiring both power for the radio and to the antenna, and antenna working conditions like mounting can affect output. These aircraft radios are limited on power and fabric aircraft might need a tuneup.

    Gary
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    wireweinie's Avatar
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    Can you give us some history of this issue? New installation or new rebuild? Ongoing problem or new problem with old installation?

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    Wag2+2's Avatar
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    It is a rag and tube fuselage. Will sent a pic of the antenna in a couple of days when I get back to town. I noticed over the past few years since I bought the aircraft when I try to contact someone 20 miles or more away ( air to air) I don’t get a response. Seems to be ok in closer. Only recently I was advised the quality was not great but it’s probably been an issue for a while. Battery and alt seem ok as there is no problem starting the O-360 and the ammeter acts normal. I will follow-up on the suggestions and will advise.

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    Wag2+2's Avatar
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    Attached is a pic of the antenna. Reseated the unit in the tray and went for a test flight. Response was 5 by 2 at 15 miles. Will be checking all the connection points next.
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  9. #9
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Wag2+2 View Post
    Attached is a pic of the antenna. Reseated the unit in the tray and went for a test flight. Response was 5 by 2 at 15 miles. Will be checking all the connection points next.
    pull antenna and clean where it mounts to fairing & the ring from coax outer sheath/braid... make sure that's still connected, or i should say grounded well from the coax... sometimes it's separate screw into fairing from coax sheath

    not much of a ground plain back there for it to use either... did it work well at one time?

  10. #10
    wireweinie's Avatar
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    It's a good antenna (oldy but goody). But Mike's right, most likely crappy connection to ground plane. Most of those are mounted much farther forward on that faring strip, too.

    If the coax is the old black RG 58 and you're having this trouble, you might want to consider replacing the coax cable with new RG 400 and crimp on BNC connector. To attach the coax to that antenna, crimp a ring terminal onto the center conductor and fasten to the antenna stub. Attach a pigtail lead to the braided coax shield and solder the other end to the tabbed, star washer that SHOULD be between the lower insulator half and the fairing strip. If the star washer is not available, crimp a ring terminal to the pigtail and fasten it to a clean, paint free spot on the fairing, close to the antenna base.

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    Just from the photo it looks like the antenna is perched in the middle of the fuselage. Not sure - that would be a difficult mount, and if for some reason the stringer was not making good contact with fuselage steel (powder coat?) then you would have a unidimensional ground plane.

    On the other hand, I have seen antennae with no ground plane work fine - we have a rubber ducky on the windshield of a Chief, driven by a handheld, that works in the San Diego and Santa Monica environments. I did not think it would work at all.
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    Quote Originally Posted by bob turner View Post
    Just from the photo it looks like the antenna is perched in the middle of the fuselage. Not sure - that would be a difficult mount, and if for some reason the stringer was not making good contact with fuselage steel (powder coat?) then you would have a unidimensional ground plane.

    On the other hand, I have seen antennae with no ground plane work fine - we have a rubber ducky on the windshield of a Chief, driven by a handheld, that works in the San Diego and Santa Monica environments. I did not think it would work at all.
    Bob,

    It looks like it’s mounted to the right wing root fairing. Angle of the photo is a bit deceptive, methinks.

    MTV

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    Wag2+2's Avatar
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    Thanks for the feedback. Will try to work on the rest of it this weekend.

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