please, short listen in the HAM bands

[mc-20]

Suppose you were out to sea,  a long way from any noise, would any of those tiny  hand held sets still work like the 6m, 2m, 70cm or do they need to use repeaters on land to go very far.

Mike
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[Ron D'Eau Claire-2]

Mike asked:
Suppose you were out to sea,  a long way from any noise, would any of those
tiny  hand held sets still work like the 6m, 2m, 70cm or do they need to use
repeaters on land to go very far.

----------------------

It depends greatly on propagation conditions, Mike. It's unlikely that
you'll work anyone beyond line-of-sight using a hand-held on 144 MHz and
above. Still, more powerful stations work long distances on those bands
using everything from atmospheric effects such as "tropospheric ducting"
that tends to guide signals through layers of the atmosphere to bouncing
signals off of the moon itself. 6 meters - 50 MHz - is considered to be on
the border between VHF and HF. When sunspots are at their most active,
sometimes the sort of propagation you see on HF appears on 6 meters as well
- typical ionospheric skip.

The biggest enemy of skip propagation such as you see on HF is atmospheric
absorption. Absorption increases as the frequency goes down. This absorption
is caused by ions in the atmosphere created by solar radiation. They are why
you don't see "daytime DX" on 160, 80 and normally even 40. After dark the
absorption drops rapidly as the ions dissipate and the skip lengthens as the
ionosphere grows weaker yielding longer skips and better signal strengths
over skip distances on the lower frequencies.

On about 14 MHz and up, the absorption caused by ions in the atmosphere is
weak enough to hear skip most of the time. That's why those bands provide
"daylight" DX, although again the skip is usually shorter during the day
since the ionosphere is more dense when facing the sun. As you move up in
frequency, signals have even less absorption and the skip is longer as they
penetrate deeper in to the ionosphere. That's why 10 meters will produce
longer daylight DX, typically, than say 20 meters, when 10 is open. The
lower absorption at those frequencies is exactly why little rigs like the
QRP version of the K2, the K1 and KX1 can work around the world with a
simple antenna when conditions are right. But it takes just the right amount
of solar energy to produce skip but not too much absorption. And when
there's too much absorption, even a kilowatt can't push a signal through.  

If there's not enough solar energy reaching the ionosphere, signals above a
certain frequency won't be returned to the earth so there is no skip at all.
The bands above that frequency are then useful only for local ground-wave
contacts, much like the VHF bands for most users. That frequency above which
skip propagation no longer works is called the "Maximum Usable Frequency".
It varies from as low as 4 or 5 MHz at periods of low solar activity and in
the late night hours to well above 30 MHz during high solar activity.

During periods of highest sunspot activity, the Maximum Usable Frequency may
move high enough for the 6 meter band to provide skip. When that happens,
the signals tend to be very good because of the exceedingly low absorption
in the ionosphere.

Back in the "great granddaddy" of all the Solar cycles since radio was
launched - in the late 1950's - I was on duty in the Army checking out a
"walkie talkie" that shared the same frequencies as the 6 meter Ham band. I
was in southern California when I heard a Ham calling CQ on the frequency I
happened to have tuned in. The walkie talkie ran perhaps 100 milliwatts of
AM phone - about equal to 10 or 20 milliwatts of SSB perhaps. It had a 1/4
wave whip sticking out of the top of the unit for an antenna. Since I had a
Ham license, I called him using my Ham call. He came back. He was in Denver,
Colorado, more than 1,000 miles away from me. We had a chat for a few
minutes before I had to return to military duties.

So it can happen. At that time there were also a great many reports of TV
DX. Television was still fairly new, and  many areas of the country had only
one or two stations on the air. People reported picking up TV stations on
the frequencies around the 6 meter band up to almost the 2 meter band over
distances of hundreds or thousands of miles.  

Ron AC7AC


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[Geoffrey Mackenzie-Kennedy-2]

Hello Mike, you wrote:

Suppose you were out to sea,  a long way from any noise, would any of those
tiny  hand held sets still work like the 6m, 2m, 70cm or do they need to use
repeaters on land to go very far.

--------------------------------------------------------

It would be very difficult to add anything to what Ron, AC7AC,  has said,
but I would like to make comment on one form of propagation that allows long
distance contacts to be made using very low power, particularly on 6m.  It
is called 'Sporadic E',  and although it appears most frequently during May,
June, July and December, throughout a solar cycle, it can appear during any
month and at any time of the day or night. What happens, it is believed, is
that parts of the E layer in the ionosphere become ionized sufficiently to
reflect the VHF RF signal back to earth, and if these parts or patches
become small, the skip is very selective - people just miles apart do not
hear the same thing. Sometimes a number of patches will be in the right
places to allow the signal to skip along over several hops, or even more
interesting a signal seems to become stuck up there, only coming back to
earth at some great distance. When this happens, signals say one hop away
are not heard.

What actually happens is still a bit of a mystery. It has been reported, and
I have only heard this happen twice, a Sporadic E opening will occur on 2m
and hours later on 6m, but this is very rare and does not "obey the rules".
What causes 'Sporadic E' is as yet not understood, although many good ideas
have been put forward.

The important thing is that with very low power, it is possible to have a
lot of fun during a 'Sporadic E' opening on 6m. I understand that there is a
G who never runs more than 250mW on 6m.

Back in 1958, somebody on Guam caused near panic on the West Coast. He had
wound up some military AM QRP rig on 6m to see whether it worked. It did.
Ron's experience reminded me of this episode, although Guam - W6 would have
been by F2 in 1958, and all of us on the East Coast prayed no doubt.

73, Geoff
GM4ESD



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