[MilCom] VHF LowBand?

Wed Apr 20 16:57:19 EDT 2005

Let me throw in a couple cents worth (adjusted for inflation,
of course  :-)   ) on the 30-50 MHz range.  A lot of this will
be from the Amateur perspective since I have been one for
31 years, but tying in with scanning and also being an
occasional user of the 45 - 50 end of it.

The Amateur 10 meter band runs from 28.0 to 29.7 Mhz, and
thus is not all that different, propagation-wise.  This is
a real "wierd" piece of spectrum, because it can behave
like our amateur HF bands in the sense of being subject to
the daily cycle of which layer of the ionosphere comes and
goes.  It is also subject to the 11-year solar cycle; when
the cycle is at peak and particularly in a "hot" cycle you
can quite literally work the world in the 10 meter band on
QRP (generally considered to be less that or equal to 5 watts).
I hold a "1000 Mile Per Watt" award on 10 Meter SSB for working
from Indiana to Lesotho (in southern Africa) at low power.

When we are in the low part of the cycle, as we are now, 10
meters only rarely opens up for any DX and when it does it
is NOT usually too spectacular.  Sometimes it will be nearly
totally "dead" for days on end, and I have seen it "dead" 
for nearly two weeks at a time without a break.

Often, this is when 10 meters starts acting like a VHF band,
in that you will get backscatter and e-layer contacts and I
dare say even some *possible* tropospheric ducting.  Really
*strange* things can happen on 10 meters.   :-)  I have heard
the band be open to the South Pacific (from Hawaii down to
Australia and New Zealand) and within a couple minutes you
stop hearing THEM and start hearing South America and a couple
minutes later the propagation shifts to some "short-skid" mode
and you're hearing stuff only a few hundred miles out that
you'd normally skip right over on 10 meters.

You say you want to "burn through" with a KW amp and huge
beam antenna up 100 feet or more?  Forget it.  When 10 drops 
dead you don't - the only thing you typically get from trying
that is your "ground wave" circle gets increased a bit.  :-)

Above 30 MHz it doesn't really change radically.  The radio
spectrum obviously doesn't care about the arbitrary designations
or descriptions that we give it.  :-)  So clear up to the top end
you get more or less the same thing.  I have done some work
in the cordless phone ranges, usually 46 and 49 as well as 
low power 2-way in the 49 Mhz range.  That far up I have 
seen decidedly fewer long distance signals, but you can get
"short skip" modes out a couple hundred miles, occasionally 
more.

That stuff is, of course, more like the Amateur 6 meter band.
6 is also a bit squirrelly  :-) like 10, but not quite as
completely schizoid.  My experience with 6 is that it's either
open or it's not, with less of the oddball shifting around.
Most hams, I think, will classify 6 meters as VHF, *period*.
A lot of them have a love/hate relationship with 6.  :-)

Translating that all over to scanning/monitoring and also to
issues with the military themselves, I think you have to look
at 30-50 as a "transition area" in the radio spectrum.  As such,
your performance can change from one end to the other and 
therefore, what works from 30 to 35 may be lousy at 45 to 50
and vice versa.  That means having an antenna that works over
the whole range is a compromise and therefore it would be 
smarter to have multiple antennas each with a narrower
bandwidth.  How many antennas you gonna stick onto an airplane,
anyway?  The radios are less of a problem in today's
technology; more than likely a 30 to 50 transceiver will work
about as well at one end as the other.

And in short, that is to say LOUSY.  There is a reason why the
FCC dumped cordless phones and baby monitors and low power
2 way into the 46 and 49 MHz range.  At the time that was done,
the technology for inexpensive consumer communications up above
400 was still a few years off......but being continuously 
reminded of the debacle of Citizen's Band they sure didn't want
to put this stuff where long-range propagation was not only
possible but LIKELY.  When the Class C Citizen's Band was created
and plopped into what used to be a ham band (11 meters) it had
to be one of the all-time FCC blunders.  11 meter propagation
is virtually identical to 10 meters, with incredible DX being
capable with low power.  Even with the FCC's rather tight
restrictions on CB (which was created as a personal, short range
communications service) it didn't take long for the users to
figure out that a 4 watt AM signal (and later, 12 watt SSB)
could "skip" a LOT further than the old 50 mile legal limit.  :-)
Some of you will doubtless recall what happened to CB about
1973 with the "Convoy" craze - it became a cesspool and utterly
unenforceable for a LONG time.  The root cause was a bad mismatch
between reality and "desired result".

Back to 30 to 50 MHz.  Those of you who have been at this scanning
thing long enough (in fact back to when "scanners" barely even
existed YET) will recall that 30 to 50 was far more populated
by very local users like cops, fire, ambulance etc. who were
also in the process of migrating up to the so-called VHF "HIGH"
band, which more or less started where the amateur 2 meter band
left off at 148 Mhz and ran clear up to the 170 MHz region.
Most early scanners stopped right there, which was a technology
issue.  While the less limited military budgets allowed for
contracting radios well up into the 400+ MHz range, that was
still outside of what most localities could afford.  Even as 
late as the late 70's and early 80's many localities were only
beginning to move up to the 400+ range.

The legacy - radios and associated equipment for the 30 to 50 MHz 
range are old and very well understood quantities and can be
manufactured cheaply and easily.  Hence, they can be acquired
in considerable quantity without breaking the bank.  My guess is
that this is a reason why some military units still use that
band AT ALL.  Like, why climb a mountain? "Because it's there."
VHF LOW works for short range, point-to-point communications
and at (relatively speaking) bargain basement prices.  If you
got 4 A-10's, or 4 helos or something flying at relatively low speeds
and not a real high altitude, the stuff that we often hear around 41
MHz +/- whatever is GREAT for A-2-A comms at short range, but
really LOUSY for those of us who want to hear it more than a
few miles away (most of the time).

For long range, this band sucks.  :-)

Duane
WB9OMC
Indiana

-----Original Message-----
From: milcom-bounces at mailman.qth.net [mailto:milcom-bounces at mailman.qth.net]
On Behalf Of MC
Sent: Wednesday, April 20, 2005 12:32 AM
To: milcom at mailman.qth.net
Subject: Re: [MilCom] Active Army/Army Reserve/Army National Guard Aero
LowBand?

X-SpamKiller-AcctId: 1
X-SpamKiller-MsgId: 1108433585.4167

Have to agree with Mac here, Green Comms suck.  As a former Army helo pilot
and TX ARNG pilot, we would only use the "Fox Mike" low band radios if all
else failed.  Very seldom would we ever get more than a couple of miles
range with them.  For air assaults and air mobiles, we used the VHF AM for
ATC, UHF AM for internal comms, and the FM low band radio as a backup or to
communicate with ground forces or range controls.

Mark
in Dallas

--- Mac McCormick III <kf4lmt at comcast.net> wrote:
> ----- Original Message -----
> From: "Ken" <rfinder1 at verizon.net>
> 
> > Wondering if anyone is monitoring activity on low
> band VHF, NFM -- you
> > don't need any special milcom receiver to monitor
> this activity.
> 
>     One problem that I have noted in trying to monitor "FOX MIKE"
>     traffic (and that's how low band is usually referred to by the
>     aircrews) is that it is line-of-sight and helicopters fly low.  As
>     a result, the helicopters get out of rather quickly below of their
>     low altitude.  Also, the "OPS" traffic is usually very brief and
>     hard to find when searching.
> 
>     Also, when searching for FM activity, don't forget to search
>     the 50-88 mhz range, not just 30-50 mhz.  Search the 6 meter
>     ham band, too.  It irritates many hams, but the Army in particular
>     shows up there from time to time.
> 
> Mac McCormick                      "Green Comms
> Suck"
> Savannah, GA
> http://mywebpages.comcast.net/kf4lmt/index.html
> 
> 
>
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