Quote:
Originally Posted by HTNut
In summary, because VHF signals have longer wavelengths, they're a bit tougher to receive in comparison to UHF signals, which have shorter lengths.
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One big misnomer stated. VHF is actually easier to receive than UHF. But with a lot of qualification. First I am not talking about
DTV or analog modulation. Plain VHF is easier to receive than UHF (modulation type not withstanding).
You also have to have antennas to scale, and here comes the problem with handheld VHF TV. Also the impulse noise issue.
If you have two antennas to scale (not small compact versions) and you transmit X amount of power on both VHF and UHF , the VHF receiver will see more power (remember I am NOT talking about
DTV, just RF).
Hence this is why in
DTV the UHF stations have to run a lot more power.
This would seem good that VHF has better range and takes less power.
But the fact that impulse noise is inversely related the frequency, means on VHF the noise is stronger, a lot stronger and really bad on ch 2-6.
Now combine that with the fact that a hand held device to have a full sized VHF antenna would need a whip (ch 7-13) of about 30 inches (end fed dipole) you now have something that is not so hand held anymore.
If you shrink the antenna and put VHF antenna inside the handheld you loose a lot of gain. If we reduce the size of the VHF antenna to 15 inches (still too big for a handheld) we are now at -3dbd (3db below the dipole standard).
We take that down more 7 1/2 inches and we have -6dbd of antenna gain.
Probably a realistic internal VHF in a hand held would be 3 inches which would be about -10 dbd gain antenna. Terrible! If you hold it in your hand even worse with your hand shielding it.
Many VHF stations are just trying to go up 3 to 4
db to over come the noise. Now you try and pick them up with an antenna that intentionally looses 10
db to be small and you don't have much reception.
It would work within say 5 miles of a tower, but after that, the impulse noise and lack of signal would render VHF mobile a problem.
I just wanted to point out the whole picture, not that VHF is bad unto itself.
VHF Reception to ruin the mobile DTV experience?
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