radio power vs transmission distance?

Discussion in 'Instruments / Avionics / Electrical System' started by rubber314chicken, Jun 20, 2008.

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  1. Jun 20, 2008 #1

    rubber314chicken

    rubber314chicken

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    looking at radios, I see many different values for the output power; some hand helds have 1.5W CW (morse code?) and 5.0W PEP (max power possible?) while the Bendix-Kings have 16W minimum. Is it possible to increase that 5.0W to something bigger (amplifier inline with the antenna, or larger antenna?), and what kind of range would that give you?

    speaking of which, I'm looking at this handheld: http://www.aircraftspruce.com/catalog/avpages/icom_a24.php and how good does it look? I'm liking the built in NAV radio, so I don't have to use a GPS as well.

    edit- what about having a connector to an antenna mounted on the plane somewhere, would that help with the transmission distance? and what about the fact that it is like two radios in one, is the antenna on it just for the COM frequencies, or does it do both sets of frequency?
     
    Last edited: Jun 20, 2008
  2. Jun 21, 2008 #2

    Rhino

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    That generally refers to the power of the carrier. It has nothing to do with Morse Code, though Morse Code is one way to modulate a carrier. Handhelds will generally have less power out than a panel radio. Part of that is due to the antenna system (the handheld antenna is less efficient due to the size), and part is because using higher power on a handheld will run the battery down much faster, making it less usable.

    That's peak emitted power, the max power possible.

    That's possible, but it may not be legal. It also increases the chance of interfering with other equipment.

    Define "larger antenna". Antennas are designed to be 'resonant' at a specific wavelength, or multiple/divisible thereof, and getting a longer antenna would mean it would no longer be resonant on the aviation bands, and thus unusable. Generally, the closer an antenna is to the actual wavelength of the intended frequencies, the better it will transmit and receive. I.e., all else being equal, a half wave antenna is generally better than a quarter wave antenna. There are variations on that rule though, such as loading, location and polarization. What you need is the best gain and SWR.

    Depends on the radio, the cables connecting it, the frequency used, the ground plane, antenna location and the gain of the antenna itself.

    Nice radio. I have the A6, which is the same radio without the nav functions.

    The nav function of the A24 is a VOR, not a GPS, so having the A24 makes no difference if you have a GPS or not.

    Yes, and I recommend that if you plan to use a handheld regularly.

    The antenna is for both.

    If you plan to use a handheld radio on a regular basis, it would be good to have an antenna installed on the aircraft because that gives you the most gain and power out. Keep the cable as short as feasible, and make absolutely sure you have good ground connections. I also recommend a cable that allows the radio to operate through your comm panel or directly through your headset. It's very hard to hear otherwise. If you use a handheld radio with the 'rubber duck' antenna that comes with it, try to keep the radio as close to vertical as possible when you transmit (don't hold it sideways). The antenna is vertically polarized, and the further you move it away from vertical orientation, the less efficient it is.
     
    Last edited: Jun 21, 2008
  3. Jun 21, 2008 #3

    rubber314chicken

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    thanks for the info, and I do know its VOR, not GPS, which IMHO is the only way to navigate.

    edit- what antenna would I want to use because I do not see anything that on aircraft spruce for 108 to 137 MgHz, every thing is just either for the COM band, or the NAV band. also, do you have any good links on antenna location and gain? I know what gain is, but I'd like to read up on it some more, along with positioning of the antenna.
     
    Last edited: Jun 21, 2008
  4. Jun 21, 2008 #4

    Jman

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    Just curious about your preference for navigating with a VOR. Why would you prefer it over GPS? The only experience I have with VOR is what it took to get my instrument ticket in Army Flight school. I use GPS exclusively now because our aircraft is not equipped with a VOR.
     
  5. Jun 21, 2008 #5

    rubber314chicken

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    because it came first, and not as many people know how to use it in comparison to a GPS. And I'd rather carry one device instead of two.
     
  6. Jun 22, 2008 #6

    Rhino

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    I would join the Matronics forum for AeroElectric and ask that question there. The guy form AeroElectric (Bob) is a wizard at this kind of stuff.

    http://forums.matronics.com/viewforum.php?f=3

    There is also the AeroElectric site.

    http://www.aeroelectric.com/
     
  7. Jun 22, 2008 #7

    rubber314chicken

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    thanks for the links
     
  8. Jun 22, 2008 #8

    djschwartz

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    With regards to the original questions:

    CW means Continuous Wave and generally refers to the power output when the carrier is not modulated. That is, when you are not speaking into the microphone.

    PEP mean Peak ENVELOPE power and refers to the maximum momentary power that is output when there is modulation. In an AM (amplitude modulated) radio such as an aircraft COM radio, the PEP will be 4 times the CW power when the AM depth of modulation modulation is 100%. Radios are typically not operated at 100% DDM as they usually distort badly so in the PEP is usually less than 4 times the CW Power. Note that for an FM radio, such as a marine VHF, the PEP is the same as the CW power.

    In free space the range varies as the square root of the transmit power, which is to say it takes 4 times the power to get twice the range. Figuring out the exact range for a radio link requires knowing the transmitter's power, the receiver's sensitivity, and the gain of both antennas.

    In order to put a power amplifier in between the radio and the antenna you would also need a means of switching it out when you are receiving. And, of course, you would need to find a power amplifier designed for the aircraft band. You might find something intended for the 2 meter ham band that can be modified; however, that would be a violation of FCC (not FAA) rules. Any transmitter operating in the aircraft band is required to be FCC certified whether it is installed in an aircraft or not.
     
  9. Jun 22, 2008 #9

    rubber314chicken

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    thanks for that info. So CW would be when important for receiving? which isn't too important for towered airports, because they have super high power transmitters, right? but important more for aircraft to aircraft? or am I just talking about nothing here?

    and I saw on an armature (ham) radio website that a 5w transmitter got about 15 miles, which would be less with obstructions.

    http://www.aircraftspruce.com/catalog/avpages/antennasystems.php running one of those bad boys, positioned right, would increase that in one direction, but decrease in another, right?

    and last time I checked, I'm not going to be flying into class bravo, and its not likely that I'll fly into class charlie, infarct I'd probably be in class delta and un towered most of the time, which doesn't require more that 10 miles (I see a 5 mile radius for my local class delta), so that radio would be adequate for me, right? although I do happen to live JUST outside class bravo airspace (the ring that intercepts the ground) and I'm under the second ring that goes to 1900 ft, so if that means anything as far as radio requirements (although I don't plan on entering the class bravo) please let me know.

    edit- also, I plan on a mode C transponder in the panel, and a handheld radio and a gps (which as much as I dissed them, I realize they are important for avoiding the airspace when flying). Would that be enough to enter an airspace?
     
    Last edited: Jun 22, 2008
  10. Jun 22, 2008 #10

    Waiter

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    An external antenna on the handheld will improve performance, significantly.

    Remember, for best performance, COMM antennas need to be oriented Vertically, and NAV antennas need to be Horizontally.

    GPS needs to have a unobstructed view of the the sky (10 degrees above the horizon)

    Transponder (oriented vertically) needs an unobstructed view of the ground (10 degrees below the horizon)

    If you have a rag or composite plane. these antennas can easily be mounted inside or embedded in the skin.

    Example:all the antennas on my LongEZ, COMM, NAV, Marker, GPS, and even the old Loran C antenna, are embedded into the skin of the rudders, canard, fuselage, and even the landing gear legs.

    This is a photo of a COMM antenna that uis embedded in my rudders:

    http://www.iflyez.com/images/LongEZ_Wing_190.jpg


    Here is a short HOW-TO on embedding a NAV antenna into the skin of the canard:

    http://www.iflyez.com/LongEZ_Construction_Photos_Canard.shtml


    (The ELT antenna is folder over and inside the pilots headrest)

    Waiter
     
    Last edited: Jun 22, 2008
  11. Jun 22, 2008 #11

    djschwartz

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    When comparing transmitters what you really need to know are its power and the cleanliness of its modulation. With an FM radio these two are independent of each other (or "orthogonal" to use the fancy engineering term). With an AM radio they are inter related. This, combined with there being multiple different ways to spec the performance such radios can make an apples to apples comparison difficult. I would compare power based on "CW" or "carrier" power, which mean the same thing. If the radio only specifies PEP, then you need to try to calculate what the carrier power would be for that PEP. As is said, if they are specifying PEP at 100% DDM, then the carrier power will be 1/4 of the given PEP value. If they specify PEP at 40% DDM the carrier power will be 1/2 of the given value. Icom and Bendix/King both specify transmit power as carrier power. Neither offers any specification for modulation cleanliness; however, both are known to be excellent quality radios.

    In general, any decent quality radio with an typical external antenna will give you more than enough range for normal aircraft operations. If you intend to operate in remote areas and need maximum range, then buy a high quality radio with a high carrier output power specification and make sure you have a good antenna installation.
     
  12. Jun 22, 2008 #12

    djschwartz

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    A vertically polarized antenna such as the one you reference is still omni directional in the horizontal plane. So, in level flight it will be fine. However as you bank in a turn the high gain antenna's pattern will be pointed at the sky towards the wing that is high and to the ground towards the wing that is low. This could cause problems with communication at long range in some cases.
     
  13. Jun 24, 2008 #13

    Dana

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    I have the Icom A24. It works quite well for what I've been using it for, i.e. talking to other aircraft on the local Unicom frequencies. I have yet to use the VOR functions, but they're more intended as a backup, not a primary navigation tool.

    The rubber duck antenna included with the radio is a compromise, intended for convenient portability. I remoted my antenna since the A24 will not work with a headset with the antenna directly attached to the radio, due to RF feedback in the headset cord. I could probably get better performance with a 1/4 wave antenna instead of the rubber duck as many other pilots do, but I haven't tried it yet.

    -Dana

    Aviation has made the world a lot smaller, but it's still hard to miss it if you fall.
     
  14. Jun 25, 2008 #14

    jgnunn

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    With a suitably placed antenna in the fuselage, what comms range could be expected from something like a hand held Icom while transmitting directly ahead? Could one expect 10 miles at minimum?
     
  15. Jun 25, 2008 #15

    Waiter

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    This depends greatly on your altitude and the serounding terrain.

    Assuming flat terraine, and your parked on the ramp, 10 miles may be pushing it.

    However, once your airborne, should be no problem. I would anticipate a 1.5 watt handheld could easily reach the following distances, if your tallking to a ground station (i.e. Tower or ATC that has a high quality antenna). These distances would be much farther if your talking to anither aircraft. Once your above the trees and other obstructions, your going to be limited by the curvature of the earth:

    50 ft AGL > 10 miles
    1000 ft AGL > 20 Miles
    5000 ft AGL > 50 Miles
    10000 ft AGL > 75 miles
    20000 ft AGL > 125 miles
    40000 ft AGL > 300 miles

    Waiter
     
  16. Jun 25, 2008 #16

    jgnunn

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    Thanks for the info. I was as you probably guessed, refering to being inbound and calling ahead to somewhere.
     

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