Let's do the math for all to see.
Assuming a 9dB increase in signal for every halving in distance and
using your number of 1800'. Then there would be a 9dB increase in
interference @ 900', 18dB @ 450', 27dB @ 225', 36dB @ 112', 45dB @ 56',
54dB @28' etc. In the near field the noise increases even faster. This
does NOT pass the reasonableness test in my opinion. Perhaps you were
hearing something else or that maybe there was something wrong with the
vehicle but this is no where close to what I have seen.
I have made over 70,000 mobile contacts and have driven by many hybrid
cars on deserted roads in the western US activating counties and have
heard noise occasionally from hybrid cars but never at the level you
indicate. By far the worst noise offenders on the roads are the noisy
AC inverters that a lot of truckers use but I have never heard one of
those at distances like 1800'. So I guess we have a difference of opinion!
Larry, W0QE
FYI:
The near field is generally considered to be ~0.62*sqrt((d^3)/lambda)
where "d" is the largest dimension of the antenna or about 15' for a
car, "d^3" is "d" cubed, and lambda is the wavelength of the frequency
in the same units as "d".
On 4/10/2012 9:42 PM, KD7JYK DM09 wrote:
> : This is rubbish. Measurements I have made at HF show an 8-10dB increase
> : in signal every time the distance is halved for ground wave. Do the
> : math! I have a neighbor with a 2010 Prius and I have followed him
> : within a couple of car lengths around town with my mobile setup and hear
> : NO noise that I can attribute to his Prius. There might be some noise
> : within the vehicle but no way is anyone hearing it a quarter mile away.
>
> Well, whoopity-doo for you. In the meantime, I've heard them at great
> distances over several years and can tell when they are coming, even when I
> can't see them, for example on another road, behind buildings, mixed within
> other traffic, et cetera. Maybe not ALL of them, but all that I've heard
> can be seen coming down the road with increasing signal strength, total
> elimination of my HF reception within a couple of hundred feet or so, then
> decreasing signal strength as they head down the road away from me. It's
> pretty obvious out here in the rural areas when a Prius is the ONLY car
> visible within a valley and passing me on the only road within many tens of
> square miles.
>
> As you suggested, I did the math. Based on where I was and where the last
> Prius I heard was when I first heard it, it came out to closer to 1,800',
> MORE than a quarter mile. I'm guessing it WASN'T you neighbour... In the
> meantime I turn down the volume when I hear them coming.
>
> Kurt
>
>
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