> Posted By WB2WIK
> What local deserts are you going to where no repeaters are available? On
6m, repeaters on Santiago Peak, Palomar Mountain, and Frazier Peak alone can
cover about 90% of southern California (including thousands of square miles
of nothingness) if you have a well-equipped mobile.
Our usual haunts are Anza Borrego and the Mojave, with occasional forays
We have good topo maps, etc, with which to see which repeaters should be
visible on our various
trips. The problem is that you can be very effectively screened from a
repeater just by driving into
a canyon with high walls. If you were a few hundred feet vertically higher
up, no problem - but as it is,
> I think your questions and comments, while sounding reasonable, are made
before actually getting on 6m and seeing what the band's like. 1/4-wave
vertical whips for mobile-to-mobile coverage will likely provide better
coverage than anything else you could use.
Actually, no, we have been out on a number of trips since getting the rigs
and my questions are a
result of observing the results that we've had and thinking about how we
might be able to achieve
better communications in the type of terrain that we inhabit.
In fact, we usually have better communications using 2m than 6m, even though
we have twice the
power o/p on 6m than we do on 2m. I suspect this is partly because there
are more 2m repeaters
so the average distance to a repeater is lower; and also because the 2m
antennas are siginficantly
more efficient (5/8 lambda, and the roof is a better ground plane for 2m
than for 6m).
> Horizontal polarization "to minimize QRM" really doesn't make a lot of
sense, since 6m is so underutilized that I'd defy one to find QRM! During
the largest band openings of the decade, November 17-18 when 6m was open to
the entire world, there wasn't QRM. Under normal conditions, it's hard to
find anyone to talk to, let alone finding QRM.
> A high takeoff angle is exactly what you _don't_ want, for extended
mobile-to-mobile coverage. NVIS doesn't exist on 6m, at least not 99% of
the time. NVIS is an F-layer mode, and the m.u.f. is well below 6 meters
about 330 days a year, so the likelihood of being able to use this mode on
six is pretty slim.
Since we are only looking for an effective radius of say 10 miles from the
transmitter, I was thinking that
even a highly inefficient backscatter mechanism would be usable, if one were
transmitting/receiving in the
right direction. I guess if the MUF is at 15MHz then what's coming back at
50MHz is probably too many
orders of magnitude down to be usable.
> Groundwave is an LF-MF phenomenon which does not occur on six meters, at
all. Hams use this term improperly, quite often, so it's easy to understand
where this comes from; however, ground wave above about 3 MHz just ain't.
Local propagation on VHF is either "direct wave" (line of sight) or via one
of the tropospheric scatter modes.
> If you're looking for extended m-to-m coverage over wide distances,
without repeaters, I'd recommend you simply switch from FM to SSB. The mode
change, alone, without doing anything else, will improve weak signal
readibility about 20 dB, and extend the range of mobile communications quite
substantially. I note my m-to-m range on 6m FM is ~20 miles when both
stations are running 1/4-wave whips and 25W rigs. It extends to about 60-80
miles by simply flipping the switch to SSB. That might do it!
Interesting. We have done some experiments with line-of-sight comms at
distances up to about 40-50
miles (topo maps to the rescue again). We didn't find a significant
difference between FM simplex and
SSB, even reducing the power signifcantly from the 50W we started at. Over
what sort of terrain have
you had 80 mile mobile-to-mobile communications?
Once you get out of line-of-sight switching mode didn't help us at all. I
wonder if this is related to the
local noise level (audio and/or electrical).
Anyone have recent experience with squalos? I have one built but since it's
horizontally polarized I
seem to need a pair in order to conduct comparitive tests.
Thanks for the interesting feedback,
--ian K3IMW/6 somewhere up a canyon