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8826Re: [UV-3R] Aircraft band

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  • Les Niles
    Nov 13, 2013
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      Yes, slope detection might give a usable signal from an AM receiver listening to an FM transmitter.  (BTW, slope detection occurs in the receiver.  It’s *not* due to the FM transmitter modulating the amplitude as someone else suggested — the filtering in a transmitter after the modulator is much too wide for that to happen.)

      But even if that does work, it will be a one-way communication channel — the FM receiver will not demodulate an AM signal.  FM receivers go to quite a bit of effort to reject AM; that’s why we use them.  There are a few emergency scenarios in which such one-way communication might be of some value, but it would be much, much better to have bidirectional communication.  And as you point out, Bill, even if the UV-3R can be tuned to 121.5MHz, it’s probably not going to generate much of a radiated signal.  If the antenna is inside a metal airplane, it would probably be unusably weak if the modulation method were correct.

      Your approach is much better: use the UV-3R to communicate with stations on frequencies/services that it is designed for, relaying to air traffic control or other services as necessary.

        -Les W6VN



      On 13 Nov 2013, at 13:23, Bill Maxwell <wrmaxwell@...> wrote:

      oops, that FM was a typo on my part. 

      I think you are asking a lot of the slope detection capability of a receiving Airband  station that in virtually every instance, is going to be tuned fairly precisely to 121.5 MHz. 

      A FM signal has a constant amplitude, so there is no variation for an AM detector to detect. Slope detection of FM on an AM receiver normally relies on being able to tune slightly off frequency so that the slope of the incoming signal offers some amplitude variation. Few airband radios have true free tuning VFOs, as they would introduce a potential incompatibility with the highly standardised ICAO requiremernts.

      I can't answer your question regarding CHIRP as I haven't tried it. Another question though is whether your UV-3RR will produce any useful output on 121.5MHz. As has been pointed out frequently on this and other Baofeng groups, overcoming the frequency limits set in the firmware is one thing, overcoming the hardware limitations of the radio is another. I guess the only way to find out is to try it.

      I also carry a Baofeng in addition to the airband ht and the aircraft radio. In my case though, I have programed in all my local amateur frequencies, some UHF CB frequencies I know are likely to be monitored and the marine distress frequency. I wouldn't hesitate to use any of them in an emergency

      Bill

      On 14/11/2013 12:33 AM, dovidjensen@... wrote:

      What I really wanted was advice getting CHIRP freq limits bypassed so I can program down at air band, nothing I can see in the .conf files.

      There is no way for me to edit a post once it is sent on Yahoo groups as they go out via email immediately, but anyone who knows would see and understand the obvious typo so I didn't pollute the group with an extra post.  

      I carry the UV-3R in my pocket daily so why not have a few programmed channels to backup my larger air band HT which I mostly leave in my bag.  The HT is itself a backup to the aircraft NAV/COM radios.

      BTW Bill, you should know that air band radios are AM only so 121.5 is also AM not FM, in an unlikely emergency though a slightly distorted voice is far better than none especially at no additional price.



      ---In uv-3r@yahoogroups.com, <wrmaxwell@...> wrote:

      Not ideal? Well, even assuming running FM on an AM frequency allocation is going to work, buzzy or otherwise, there wouldn't be much point tuning in 122.5 MHz., as the rest of the world, sensibly using FM radios, will be monitoring the real  international distress frequency of 121.5 MHz. I suggest you get yourself an Airband handheld, using AM, and get far more reliable communications, especially when it may count.
      On 13/11/2013 8:22 PM, dovidjensen@... wrote:


      While it is not ideal running FM on the AM aircraft band the distortion is not bad, it just sounds a bit buzzy like talking through a blown headset.  
      I tried to program my UV-3R MkII using CHIRP on Ubuntu Linux but it will not allow me to program that far down in frequency.
      I want between 118–138Mhz or even just 122.5Mhz distress freq so I can use it for emergency calling. 




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