There is a considerable amount of path loss, so, in theory, all the "good
things" you would want for long-haul troposcatter (or sporadic-E) are
useful for ionoscatter. High ERP, low angle take-off and low environmental
noise. Research says scattering occurs around 80-90 KM up, so more-or-less
the same ionospheric height as some sporadic-E. Because there is
refraction in the ionosphere, there will be a minimum distance for
Ionoscatter of approx 800-1000 KM ("skip zone"), with a maximum distance
based on your ability to get a signal into that 80-90 KM high sweet spot
(just like Es). Distances shorter then 800-1000 KM can be covered
(somewhat unreliably) with troposcatter. Studies show there is a diurnal
(daily) variation in ionoscatter signal strength of around 10 dB, with
minimum attenuation (maximum signal strength) occurring at mid-path noon.
Note that path attenuation increases rapidly as frequency increases. The
optimum traffic frequency (FOT) for ionoscatter was calculated many years
ago as 50-60 MHz, taking into account path loss vs typical band noise
levels. At low and mid-band frequencies, path loss increases about 5 dB
for every 10 MHz upward change of frequency. This is why ionoscatter at
144 MHz is much more difficult.
Jay W9RM
DM58 CO
Keith J Morehouse
Managing Partner
Calmesa Partners G.P.
Olathe, CO
On Mon, Oct 24, 2016 at 11:32 AM, Mark Spencer <mark@alignedsolutions.com>
wrote:
> Hi this is interesting. From a practical perspective I'd be curious in
> knowing if there is much difference in what needed to be successful using
> long haul tropo scatter versus iono scatter on 50 MHz ?
>
> Presumably bigger antennas, higher power levels and a clear view of the
> horizon will all be useful ?
>
> The comments about the K index and time of day for iono scatter are of
> particular interest to me.
>
> 73
> Mark S
> VE7AFZ
>
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting
|