To Jim Weir!

Discussion in 'Maintenance Bay' started by Hunt, May 18, 2020.

  1. Hunt

    Hunt Filing Flight Plan

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    I enjoy your column even though it goes over my head a lot the the time!

    In your your latest column you said a 5 watt hand held radio is lucky to put out 21/2 watts. There are a lot of inexpensive amplifiers out there that can boost the transmitting power but I don't know which one to choose! How many watt booster should I buy because I don't want to over do it and which is the correct on for an aircraft radio.Your advice would be appreciated and your advice might be suitable for your column.

    Andrew H. Bittinger
     
  2. SCCutler

    SCCutler Administrator Management Council Member PoA Supporter

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  3. weirdjim

    weirdjim En-Route

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    Before we go a lot further, I'd like to reference the article you are quoting. Please let me know the issue month this data was in.

    THanks,

    Jim
     
  4. Brad Z

    Brad Z Final Approach

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    His original post said "latest". Does that narrow it down at all?
     
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  5. wanttaja

    wanttaja En-Route

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    Not really. Jim writes a monthly column, which means the article in the most-recently-published magazine is something he worked on three or more months ago. He has written several articles since, which means the article the OP is asking about is nowhere near the forefront of Jim's memory.

    I don't have a column, but I have written a batch of articles for them. When someone comments on the "most recent" article, I don't which one they're talking about, either.

    Ron Wanttaja
     
  6. weirdjim

    weirdjim En-Route

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    What Ron Said :yeahthat: I turned in the October column last week.

    Jim
     
  7. weirdjim

    weirdjim En-Route

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    The reason I asked the question in the first place is that I don't ever remember using a 5 watt transmitter as an example. Figuring that the July issue has been sent to subscribers, here is what I actually said:

    "One of the greatest drawbacks to AM is the fact that it requires a carrier (which is the frequency you dialed up on your radio) and two “sidebands” that actually carry your voice. Each of those sidebands at best have one quarter of your radio’s power, and you can only hear at the receiver what is on one of the sidebands. Thus, your rock-crusher 10-watt radio you paid kilobucks to buy can only have the equivalent of 2.5 watts of “talk” power at the other end’s receiver. And vice versa."

    At 100% AM modulation, half of the power is contained in the carrier, and the other 50% is in the sidebands, split equally between the upper and lower sidebands. That's 2.5 watts of power in each sideband.

    Now, as to amplifiers, every aircraft band transmitter has to go through FCC part 87 type acceptance. (47CFR87) Type acceptance is a rather complex process involving getting your boots dirty tromping around in the cow pasture (there is a specification on how high the grass can be) with your transmitter mounted on a high platform and an equally high and well calibrated antenna a fixed distance away. You then make some very delicate measurements looking for spurious signals coming from the transmitter all the way from below the AM broadcast band up to the other side of the microwave oven/GPS frequencies. All the while with Bossy licking you on the neck.

    Then you go back into the lab where you freeze the transmitter, bake it, all the while looking for the same spurious signals, and you are looking for them all the way down to below one-ten-thousandth of the transmitter rated power.(-43 dBp). With and without modulation.

    Let's now talk amplifiers. I have NOT seen an amplifier that has gone through this type acceptance procedure, nor have I seen one that is usable for AM. Most of the "linears" I've seen are meant for CB use down at 27 MHz. and FM use in the amateur 2-meter (144 MHz.) band. FM, by its very nature, is designed to clip and limit the input signal to remove any residual AM. Nor is there any specification for spurious outputs other than the general "can't cause interference to another user" blanket rule.

    To top things off, the FCC takes a very dim view of bogus/unaaproved devices just wired up to an approved radio ... dim to the point of $10,000 and a year in the slammer for each time you key up the transmitter and spew garbage all over the band.

    I'm presuming this answered the question? :cheers:

    Jim
     
    Last edited: May 21, 2020
  8. PaulMillner

    PaulMillner Pre-takeoff checklist

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    does the FCC do more than a handful of enforcements a year? 100 maybe for 300 million people?

    Paul
     
  9. JOhnH

    JOhnH Touchdown! Greaser! PoA Supporter

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    I doubt seriously that 300 million people break that rule each year. So those hypothetical 100 busts might only apply to a few thousand people.
     
  10. PaulMillner

    PaulMillner Pre-takeoff checklist

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    I'm not just discussing THAT rule, but all FCC rules. They just don't do enforcement... look it up.
     
  11. weirdjim

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    I can only speak to my part of the world. And I can only speak to one instance that I was involved in. The FCC maintains a monitoring (i.e. listening) station in Livermore, just east of Oakland. I'm told by the officer that called me that there are half a dozen enforcement personnel at this station. They nailed one very prominent airshow performer at a Northern California airshow for using a rather sensitive frequency to coordinate his airshow, interrupting quite a few people licensed on that frequency. The fine was nominal (I believe it was $500 or so) and the jail time was suspended on the condition that he obtain a license for air-ground coordination of special events.

    Whether there is only ONE monitoring station for the whole country or whether there are dozens I'm not going to guess. Your crapshoot.

    Jim
     
    Last edited: May 23, 2020 at 4:39 PM
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  12. JOhnH

    JOhnH Touchdown! Greaser! PoA Supporter

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    I do believe that enforcement is rather random and sparse. Just like with the IRS, the mere threat of heavy fines and imprisonment keep most people (sorta) honest. But as Jim says, it does happy and I'm not going to risk it on purpose. I get into enough trouble by accident or through ignorance.
     
  13. weirdjim

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    And, to the original poster, Andrew, if you are going to post a question, it is polite to stick around and join the conversation. I know you are new and this is your first post, so welcome, and hope to hear more from you.

    Jim
     
  14. Brad Z

    Brad Z Final Approach

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    Mr. Bittinger probably forgot that he registered here and posted the message. He hasn't been back since the day after his post, lasting less than 24 hours total on POA. Maybe that's all he could handle, lol.
     
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  15. weirdjim

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    Well, anyway, we had a good conversation about putting linears on your aircraft radio and using it to melt the ice off the wings, good buddy, don'cha know? 10-4

    Jim
     
  16. wsuffa

    wsuffa Touchdown! Greaser!

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    Jim does a pretty good job on AM power and is spot on the other stuff.

    The challenge is defining what we mean by "power". Common definitions include "carrier power", "peak envelope power" and "average power". Most AM transceivers are "rated" at carrier power; the other two definitions are based on the amount of modulation that is produced: at 100% modulation, the "peak envelope power" is 4x the carrier power. "Average power" is based on the average modulation levels that the transmitter produces. If one listens to AM radio, one will notice that they typically used audio processing to raise the modulation level because it helps increase the average power and therefore helps overcome noise and increase the range. It's why AM broadcasts are harder to listen to for any length of time.

    Voice produces an inherently lower average modulation than music, so typical voice processing uses compression and clipping to generate a higher modulation level. Audio filtering (equalization) is often used to eliminate the audio frequencies that are not critical to transmit information, thereby allowing a compression/clipping circuit to produce higher modulation of the voice information. Sorta like the difference in talking to someone on the phone and using a VoIP communication.

    Jims right that each sideband has half the voltage and therefore 1/4 the power, but many receivers sum those two sideband a when they detect the signal. And they use the carrier as part of the detection process.

    Most handheld radios and some panel radios do a crappy job of processing voice for modulation purposes andhandhelds usually lack the battery power to achieve full peak envelope power. And those who speak softly tend not to modulate well, decreasing the average power and therefore the range. That's without even talking about antenna issues.

    And amplifiers, as Jim mentioned, are a problem. There are "linear" amplifiers made that cover aviation bands, but for a whole bunch of reasons you won't find them in airborne or portable equipment.

    The FCC's enforcement focus is on compliance and not causing harmful interference. If it's inadvertent, you're likely to get a warning. If it's willful, they'll be more aggressive. If you interfere with public safety stuff, they'll be all over it. And some of the public safety departments have their own enforcement equipment.

    Some of the enforcement actions I'm aware of involve truckers who used GPS jammers in their trucks near EWR, folks that got handheld radios and tried to divert planes by mimicking ATC, and equipment that interfered with ILS and VOR signals.

    There are a number, and most can be operated remotely. And the mobile equipment is pretty good (there's a video on YouTube of one of the field guys demonstrating it. It's well advanced from when I was one of the FCCs field engineers way back when (I went on to do bigger and better things). I still know a couple of the regional guys, as well as the former head of the field division who recently went to NTIA.
     
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  17. ktup-flyer

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    Isn’t it technically illegal to use a cellphone in an airplane?
     
  18. weirdjim

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    That is an FAA rule, not an FCC rule. The FCC is concerned with the technical specifications of the cellphone; the FAA is concerned with interference with airborne interference with flight systems.

    Jim
     
  19. jrcox19

    jrcox19 Pre-Flight

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    According to the FAA it is an FCC rule: https://www.faa.gov/about/initiatives/ped/
     
  20. weirdjim

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    Jim .........
     
    Last edited: May 24, 2020 at 2:19 PM
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  21. weirdjim

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  22. wsuffa

    wsuffa Touchdown! Greaser!

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    Jim, I never ran across the gentleman you mentioned. There were two groups in Laurel - one was the field monitoring station, the othe was the lab (that did the type acceptance/certification stuff). I worked in the NY office and dealt with the field guys & monitoring station in Laurel mostly, but not the certification guys (at least not very much).