On Thu, 2007-07-12 at 20:12 -0500, Stuart Rohre wrote:
> Kim,
> On the plains, you should be able to do 50 miles simplex with a mobile FM
> ham transceiver, or commercial equivalent, especially if you use a mast to
> elevate the 2 m antenna on the vehicles. That way, static from lightning
> is not an issue as FM will reject it.
Yes, but in rejecting the noise the sensitivity threshold for the FM
receiver is raised to the peak level of the noise so while it may not
put out audio noise, it won't hear either.
>
> As a matter of fact, NVIS with low to ground antennas such as the 80m dipole
> only 9 feet off the ground, lowered summer static to the point that it was
> NOT an issue, doing NVIS and skip contacts off the low dipole at Field Day.
> The improvement in Signal to Noise ratio by lowering a dipole is remarkable,
> and can only be appreciated by setting up and doing it!
But an 80m dipole isn't exactly agile on a 12' wide road.
>
> In past Field Days, 80 m SSB had been a lost cause due to the usual "Summer
> Static" of distant thunderstorms. With a low horizontal dipole antenna, the
> angle of incoming thunderstorm static is rejected, or the antenna is less
> sensitive to those angles of signal arrival.
>
> Now, if you were operating in a box partly on the TX Caprock and partly
> below, you might have some trouble with simplex VHF, but if you are out on
> the plains, you will likely be OK at 30 to 50 watts VHF FM simplex.
Only if the FM is wider than used these days, say with 15 kHz deviation
instead of 2.5 KHz... Way back when we did use that wider deviation
before repeaters, 30 miles mobile to mobile simplex was common, but it
isn't easy with the narrower deviation. The commercial frequencies went
narrow, not for better hearing and range, but only to supply more
channels, knowing it would reduce the range.
Going narrower to SSB gets the best return on range but the thunderstorm
static is significant, I don't have many observations at UHF and higher
on SSB during a storm.
But another mode might work and that's FM (say 5 KHz deviation)
microwave bounced off the thunderhead. In the last year or two that has
resulted in contacts from NW Iowa to Winnipeg on 10 GHz. It does take
some operator skill to pick the path and keep the antenna aimed, but it
might not be so critical for paths of only 70 miles (the diagonal of a
50 x 50).
>
> Stuart
> K5KVH
>
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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