Doesn't 440Mhz penetrate objects in the environment better than the 2-meter band?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KC0BUS, Jul 27, 2017.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Just look at the "safety" regions vs. operating frequency to see the difference in signals "passing right through" dielectrics (like human bodies) and being absorbed by them.

    To get away from the influences of windows and reflections just try each while standing in the middle of a wooden barn having no windows. Every time I've done that, 2m was absolutely better than 70cm for equivalent power and distance.
     
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    We had a round barn and I went crazy when I could not find a corner to pi$$ in. :mad:

    440 goes thru small windows great but multi path can cause issues.
     
    N0NB likes this.
  3. WA4SIX

    WA4SIX Ham Member QRZ Page

    Would this be due to the water content, or the fact that many branches might be close to resonance?

    Ed
     
  4. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    SWP:

    It is the foliage, not the branches, that have the effect. The "water content", in the foliage, affects the resonance and, as such, the answer to your question is yes!

    Usually, the attenuation is higher during the warmer months when the moisture, in the foliage, is the highest.

    Glen, K9STH
     
    K3XR likes this.
  5. WA9SVD

    WA9SVD Ham Member QRZ Page

    Just out of curiosity, but aren't both types of "evergreen?" (My allergies sure know cypress when they smell it!:()
     
  6. AG7FY

    AG7FY Ham Member QRZ Page

    In my limited experience playing with yagis on vhf/uhf, 2 meters gets much better reflections off nearby hills. With all the hills in my area 440 is pretty limited to line of sight. Even with the 1/2 wave antenna on my truck I seem to be able to make better contact on simplex as I drive around small hills and buildings.

    Maybe that's part of the difference? 440 works better when it needs to penetrate a structure, 2m is more likely to reflect the signal to somewhere else outside?
     
  7. KM4DYX

    KM4DYX XML Subscriber QRZ Page

    Here is a link to a USMIL study regarding VHF and HF attenuation of Ground Wave signals in a jungle environment. You may wish to skip to page 30, figure 1 "Radio Wave Attenuation Through Jungle and Woods."

    Appendix A of this pub is a reprint of a study from 1944 that summarizes the earliest U.S. testing of what we would later call "NVIS."

    http://www.dtic.mil/dtic/tr/fulltext/u2/445943.pdf

    73,
    Al
     
    KX4O likes this.
  8. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    DYX:

    Unfortunately, that document only covers frequencies below 100 MHz and is dated 1963.

    Motorola did not really "discover" foliage problems for 450 MHz systems until 1966.

    Glen, K9STH
     
  9. KM4DYX

    KM4DYX XML Subscriber QRZ Page

    Sure, you're right. But it's not hard to extrapolate where that curve is heading...

    73,
    Al
     
  10. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    DYX:

    Not necessarily! There are factors like resonance that enter into the equation. The trend is for the higher the frequency the more the attenuation. However, the type of foliage also plays a role with trees such as pine and cypress having considerably more attenuation than trees like maple and oak on the 70 cm band and higher frequencies.

    Glen, K9STH
     

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