Is 2m or 70cm better for specific circumstances?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KD7ICN, Sep 19, 2016.

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  1. KD7ICN

    KD7ICN Ham Member QRZ Page

    Long time lurker, first post.

    I need to build a device that will activate upon reception of a DTMF command. I am trying to decide if 2m or 70cm would be best.

    I am leaning toward 70cm, as the physical size of the antenna is a factor. So, first question: would 2m offer any advantage given my specific set of circumstances?

    My circumstances:
    I am a member of a research team out of Weber State University: http://harbor.weber.edu/
    We fly a wide variety of instrument packages on weather balloons to 100,000ft and more. We never get above the stratosphere, but occasionally get above the ozone layer.
    One device, the cutdown, would benefit from having at-will control.
    This is strictly line-of-sight! I am watching the balloon from the ground with my own eyes, and have seen several pop.
    We usually fly in good weather, as clouds are bad for the instruments, especially the cameras. But I may need to send the signal through a layer of clouds.
    All of our support vehicles have dual-band transceivers capable of 50W transmitting power. This is what I would use to send the signal.
    The payload could be up to 50 miles away, in a straight line.

    My second question is which part of the 70cm band should I use? This is not immediately obvious from the band plan. Obviously, nothing that is being used locally.

    Thanks,
    Jeff
    KD7ICN
     
  2. K9STH

    K9STH Ham Member QRZ Page

    True line of sight, either band will work fine.

    For a "clear" frequency, the 70 cm band is much more suited. As for a frequency, below 432 MHz is going to be much less likely to have activity as those between 432 MHz and 450 MHz.

    Glen, K9STH
     
    N1XDS likes this.
  3. N1XDS

    N1XDS QRZ MODERATOR Volunteer Moderator QRZ Page

    Like what Glen has already said...For the best clear the 440 band is used for everyday and night conversations between ham users or clubs for their daily meetings on their repeater systems. Around my area the 2 meter/145-147 band is used but some repeater owners uses 440 band/70cm which where I talk on when I get a free chance to. This thread below should help.

    http://forums.qrz.com/index.php?threads/total-newbie-question-2m-70cm.238879/

    - Jamie
     
  4. KC4YLV

    KC4YLV Ham Member QRZ Page

    Colorado Front Range is an excellent exhibit of two bands working together. There are wide area repeaters covering the whole Denver area on both bands, and many of them are linked, both in same-band networks and 2m <-> 70cm networks.

    The 2m repeaters don't really work downtown due to the buildings, whereas the 70cm ones fare much better. I often hear people pop back and forth on their commute, starting on 2m when they're farther out, switch to 440 when they're closer in. In addition, there are a lot of geological formations especially on the west side of town that can give pretty strong coverage shadows; a lot of the 70cm machines fill those in (and we have a LOT. I think my last count was ~50 2m repeaters and about 75 70cm repeaters within "5 watt HT" distance of my QTH)

    Regardless of what band you use, don't just 'pick a frequency' - please look up your state/region's band plan as well as the plan of any states it may overfly/cover. There are usually subbands dedicated to experimental use that would be good candidates.
     
    N1XDS likes this.
  5. ND5Y

    ND5Y Ham Member QRZ Page

    I'm surprised nobody has pointed out that it's not legal for a university to use amater radio for business purposes.
     
  6. K8MHZ

    K8MHZ Ham Member QRZ Page

    There is an exception for schools and teachers.

    And don't be surprised if someone points out the proper way to spell amateur.

    Don't worry, I won't report you to the spelling po-leece.
     
    KC4YLV likes this.
  7. K7JEM

    K7JEM Ham Member QRZ Page

    Did you know that the word "business" is not even used in part 97? Which specific rule do you think is being violated?
     
    KC4YLV likes this.
  8. NC5P

    NC5P Ham Member QRZ Page

    If you want a quiet band that's not used much consider 222-225.
     
  9. N8EKT

    N8EKT Ham Member QRZ Page

    at 100,000 ft, you will likely be hearing WAY too much from way too far away on either band and the receiver would be totally deafened by the barrage of RF from hundreds of miles away

    And you should NEVER need 50 watts for line of sight transmissions of that nature

    1 watt would be far more power than needed

    the interference from repeaters and stations HUNDREDS of miles away will be a given

    For such experiments, much higher and less used frequencies would be a wise choice

    Consider 1296mhz or above
     
  10. WA9WVX

    WA9WVX Ham Member QRZ Page

    Jeff,

    Since you have Dual Band Mobiles, I would recommend using a Circular Polarized Antenna on those Mobiles as the RF Signal will cut through the Atmosphere like a Screw when pointed up at the Balloon's receiver assuming that receiver has the DTMF Decoder. You weren't very clear where the DTMF Decoder is being used.

    K9STH Glen is correct on the UHF Band although if you select a frequency down in that section of the UHF Band 420 through 430 MHz, our neighbors to the north, Canada is legally using some of those frequencies for their Public Safety personnel.

    Beam me up Scotty!:D

    Dan
    WA9WVX
     

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