Radio range

Discussion in 'Avionics and Upgrades' started by FORANE, Jun 12, 2018.

  1. FORANE

    FORANE Pattern Altitude

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    Flew IFR yesterday on a couple hour cross country trip. Radios worked fine until about the 4th handoff. Switched from center to the class c approach I was passing, called them and no answer. Tried both radios, no answer. Tried pulling out squelch, no answer. Back to the previous center frequency and was advised the class C could hear me but I didn't receive them.

    A little further in the trip and was handed off from 1 center frequency to another same center different frequency. Again, no reply. Back to previous center frequency and they offered a 3rd frequency to try, again no reply until I had traveled about 20 nm.

    Nearing destination handed off to the nearby class C approach. Could barely hear them and for a while could only hear them with squelch pulled open.

    Current radios are GTR 200 and 430W.
    Have had poor reception range and clarity issues (but seemingly not on all frequencies) since install (years).

    When I installed the Avidyne IFD 440 in place of the 430W its radio seemed to work very well but I only had it in the plane for 2 flights.

    Long ago when I had a Collins VHF 251 (using the same antenna as the 430) it worked fantastically well in clarity and range.

    I have changed the RG 400 cables a few years ago so doubt those are a factor.

    What causes poor radio range?
    What is the best radio you have used?
     
  2. eman1200

    eman1200 Touchdown! Greaser!

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    any chance this was in the vicinity of charleston wv? heading up that way, I am always prepared for atc to ask me to try to reach another plane and occasionally they can't hear me as well.
     
  3. FORANE

    FORANE Pattern Altitude

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    About 150 nm Southeast of there.
     
  4. wilkersk

    wilkersk Cleared for Takeoff

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    I wouldn't assume the problem was yours. Your radio is line-of-sight. If they can hear you, and you can hear everyone else, your radio is working. But, the guys on the ground may be having trouble with their set up. Their audio/txmt controls are a bit more complex than the audio panel in your aircraft.
     
  5. denverpilot

    denverpilot Taxi to Parking

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    Without knowing what was going on at the transmitting end, you can’t tell if you have a problem.

    All you can do is wait and see if the radio seems continually “deaf” and if a pattern emerges, have the system tested for sensitivity and selectivity with proper test gear.

    If it passes those hooked to the coax, sweep the antenna and see if it’s developed an internal problem.

    And of course on-board interference can trump all ground tests. Make sure you unplug the chargers for any on board gadgets and turn off the gadgets completely to make sure they’re not just massive broadband RF noise generators.
     
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  6. FORANE

    FORANE Pattern Altitude

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    Who / where can I find folks with the knowledge / equipment to do these tests? I know a couple avionics guys but don't think they go much beyond make harness, install or remove, test transponders and send for service.

    I have seen a couple chargers that cause problems in the past. I think my current ones are ok.
     
    Last edited: Jun 13, 2018
  7. Unit74

    Unit74 En-Route

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    There is a hole in south Arkansas where I have actually been told to switch to another frequency and in 20 miles, contact us. You can slowly hear center fade in.......
     
  8. Clark1961

    Clark1961 Touchdown! Greaser!

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    There’s a similar problem in SE Colorado, SW Kansas, Panhandle Oklahoma where Kansas City, Denver, and Albuquerque sorta meet. It’s a no-man’s land. The Kansas City guy said “the frequency they [Denver] has you on” and didn’t change me to a better freq for another 20 miles. Maybe most of the experienced guys who understand the coverages and know what to do have retired? Maybe the letter agreements on handoffs are screwed up? Maybe maintenance sucks? At least the standing eastern Colorado radar coverage was fixed on my last trip east even if I couldn’t hear center on the published freq...
     
  9. wilkersk

    wilkersk Cleared for Takeoff

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    Anyone doing installs on certified aircraft should know how to use an inline VSWR to verify your coax/antenna.


    That being said, the simple fact that YOU being heard by ATC means that your antenna an coax are doing their job.

    It’s more likely the problem is not yours. But someone else’s.

    I’ve had problems recently with squelch staying open on the handheld rig in my little airplane. I traced it back to a noisy USB brick I was using to power my iPad. I had my headset plug adapter for the handheld laying right next to it. As soon as I moved things around, the problem went away. But that doesn’t sound anything like what you are describing.
     
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  10. FORANE

    FORANE Pattern Altitude

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    I have a SWR meter for the frequency range of aircraft coms. In the past I have discovered failing cable with it. When I had failing cable I could hear transmission of others but my transmitted range dropped drastically. it may be others transmission range but I have had other radios with better range and clarity.
     
  11. denverpilot

    denverpilot Taxi to Parking

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    Well... they should have test gear but...


    He’s right. If you’re getting to them the problem is likely the other direction. Or locally created interference like he had with the USB stuff.
     
  12. denverpilot

    denverpilot Taxi to Parking

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    It’s always been bad down there as long as I can remember. I don’t think they have very good transmitter sites. I don’t think it’s a talent thing, more of a “we can’t find anywhere to put a transmitter up high that has microwave or land line service”. But who knows.

    Just always been bad there. Also bad going south out of CO in the valley that extends south of Alamosa going southwest.

    I know one of the Denver based guys who usually works on the radars and he gets lovely trips to lovely La Quinta hotels all over the WY, CO, and surrounding area. Hahahaha.

    He sometimes posts that he’s working on the other boxes at the sites that aren’t radars and he’s pretty sharp, so I think if it gets reported and they can do anything about it, he’s on the road... enjoying the lovely rural hotels of backwoods CO, WY, and I think someone covers eastern UT from the other side because I never see him there.

    Weirdest thing how I met him. He’s a rabid Broncos fan and my mom (like all non-aviation people) thinks all pilots know all FAA people so she introduced us after meeting him on some Broncos forum. Haha.
     
  13. weirdjim

    weirdjim En-Route

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    It is pretty simple. Over dead-flat territory (Iowa comes handily to mind) radio range is given as: range (in miles) = 2 times the square root of your altitude (in feet). This is for a ground station on the flat level earth.

    For example, 5000' AGL over Iowa City, I would expect to JUST be able to hear an ATIS station that is about 140 miles away. So be reasonable. Pick a LOT of ATIS stations that are in your area and map their distances. Can you hear them 20 miles out? 50 miles out? A hundred miles out? And so on. If so, then your entire receiver operation is just fine and the ATC ground station has a bit of a problem. You can't do a damned thing about it. But if you can only hear the ATIS 20 miles out then YOU'VE got the problem.

    Jim
     
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  14. ejensen

    ejensen Pattern Altitude

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    ATC lost me IFR at 14500 south west of Monarch pass. They knew about it and almost exactly where I'd get them again (Badger Mtn). Another big gap is along I-25 a bit north and south of the state line.
     
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  15. FORANE

    FORANE Pattern Altitude

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    Most certainly I have had trouble hearing atis beyond 40 miles at better than 5000. I figure the problem has been mine. On my flight last night I turned off the 430 and restarted it into the setup menu. I found the com setup page and increased the squelch numbers of s833. It seemed to improve the reception of the 430. Perhaps increasing the s833 decreased interference from frequencies not being used (as we are on 25.0 khz)?

    Strangely, the 430w install manual page 5-15 states for sq250 may be set 0-63 with the higher the number the less signal required to break squelch. My s250 numbers were already high.
    For sq833 may be set 0-63 with the higher the number the more signal is required to break squelch. My s833 numbers were low.
    There is a note that software 2.00 or earlier the s250 squelch operation was reversed. So, if one had early software then updated the software, it may change how often the squelch breaks.
     
    Last edited: Jun 16, 2018
  16. denverpilot

    denverpilot Taxi to Parking

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    Badger lost backhaul telecom a few years ago in winter and was down for quite a while for multiple agencies including FAA. State has a snow cat for the winter but it can be a pain to fix some of the sites and Badger is “above average PITA”. Not the worst, but not the easiest to get to.

    One of the downsides of nice high mountain sites that have great RF line of site. They’re also harder to repair in winter.

    Remember squelch is simply where the “muting” takes place on a signal.

    Changing squelch settings doesn’t fix sensitivity (how well you hear a signal) or selectivity (how well the radio rejects other strong signals that reduce sensitivity at the desired frequency) problems, or do anything about local interference covering up an otherwise strong received signal.

    If the radio is working correctly, it’ll meet the sensitivity and selectivity numbers in the service manual when directly connected to an RF test set / signal source.

    Once that’s known, the problem then is known to be external to the radio. Bad antenna, bad coax, local interference, weak transmitter at the other end...

    It’s a logical troubleshooting thing. Know the radio works to spec before chasing other things. A field test of sensitivity and selectivity is SUPPOSED to be the simplest place to start.

    But many shops chase other things first without a logical step by step troubleshooting plan.

    Why? I don’t know.

    Taking a battery operated RF service monitor to the airplane and plugging a known-good coax directly into the connector on the back of the radio and doing a quick SINAD test (measured in dB) and seeing if the rig is working properly internally is only about a ten minute job.

    Anyway. Don’t get too hung up on squelch. Squelch would only be adjusting where the radio “turns on audio” on a signal, and if you’re having to adjust it from a value where it worked fine previously, it indicates the receiver has a more basic problem or the antenna system does... or something is creating a lot of local broadband RF interference.

    Here’s an interesting check. Take a handheld along. If the handheld also can’t hear well in the same locations the panel radio can’t, that tells you the problem isn’t the aircraft radio. Within reason. The HT antenna won’t be as good as the aircraft’s antenna but at altitude it should be only slightly worse. Could even hook the HT directly to the aircraft antenna and do a comparison of that as well.

    Most aircraft that have two Comms, the simple test is to swap antennas between the radios. If the problem follows the antenna you know where the problem is. If it stays with the original problem radio, it’s the receiver. But if only one antenna and radio on board, understandably that’s not an option.
     
  17. FORANE

    FORANE Pattern Altitude

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    Where can I find a guy with a RF test set / signal source / service monitor? Or can I just buy one and perform this test myself? Are the test sets expensive?


    My 430w hasn't degraded in performance; it never seemed to receive very well. Distant transmissions would become hard to hear or not received at all unless I opened squelch and then had to try and hear them over the carrier noise.

    We have 2 comms. Both seem to perform similarly. The only time I had a real good radio was when I had the Collins VHF251. It worked very well on the same antenna the 430w uses now. When I put in the Avidyne IFD440 its radio seemed to work well on the same tray / cable / antenna as the 430w (but I only had it in for 2 flights).

    One time I did see a very significant drop in my radio transmission range. I checked and found high SWR. I removed the RG400 to find it internally broken due to lack of properly securing the cable, leading to repetitive stress damage from bouncing at the connection to the antenna.

    Another time I went to an avionics guy / A&P who suggested we reroute the RG400 antenna cables as far from power cable as possible. We rerouted the RG400 under longerons on either side of the cabin well away from power line. That didn't seem to help much or at all.
     
  18. denverpilot

    denverpilot Taxi to Parking

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    Most any avionics shop would have one.

    If the two comms are performing similarly and don’t share a VHF antenna, the likelihood the problem is in those two radios themselves, is pretty low.

    The next point where things would be “in common” would be power or audio path. Is this maybe an intercom/audio panel problem? (Hard to tell what you’re hearing from here...)

    Have you tried using Comm 1 in whatever “failsafe” mode the audio panel provides when it’s off, where it bypasses itself and switches the input and output of Comm 1 directly to the radio?

    Not an aviation radio, but I have had switching audio transistors go bad in a ham rig and that trashed the audio output... made it weak and noises.

    So I’m just mentioning it as a possibility... following the audio path from radio to headset, instead of looking at the RF path, might yield something, if the radio works properly on a test set. Just doing a “process of elimination” type of troubleshooting, remotely.

    Got an audio recorder that can be plugged into the headset path? (Or a Lightspeed headset with the Bluetooth recording feature?) Recording what it sounds like when it’s bad might help someone figure it out.

    Just tossing out ideas here.
     
  19. Ben2k9

    Ben2k9 Pre-takeoff checklist

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    I’ve had the same issue when using VFR flight following. Was making contact with next station as directed but got no response. So I would wait a bit and try again. Finally they came in and said they could hear me all along but I apparently couldn’t hear their response.
     
  20. FORANE

    FORANE Pattern Altitude

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    Yup, you can try a couple things like pulling your squelch out to see if you then hear them, or trying a second radio. Beyond that? Back to prior frequency or wait like you did.

    I have figured out that going into some familiar fields I will typically be handed off in location A but typically cannot hear the next facility until location B... very predictable.
    Something else I have done going into my home field when I am handed off on the home fields controlling approach but don't hear them is to switch to an alternate frequency for the home fields controlling approach that I always hear better.
     
  21. A1Topgun

    A1Topgun Pre-takeoff checklist

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    I had a similar problem and traced it to a USB adapter and or cable to iPad. Another local pilot had a new stack installed in his Baron. He was furious after his return flight after the install and was ready to call the install shop about the quality of their work when someone told him to remove the USB and try the radios. All worked well. It seems the USB adapters can cause reduced reception sensitivity.
     
  22. FORANE

    FORANE Pattern Altitude

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    Oh yes, they sure can. I have had a few power supplies for tablets, etc throw all sorts of noise into the radios. I don't think I am currently experiencing that problem though. When I did have that issue, I had comms break squelch very easily all the time. This led to turning down the squelch setting and not hearing transmissions I should have heard. This in turn led to blaming the radio...