MILITARY
COLLECTOR GROUP POST, July 29/98
Index:
SOME NVIS
DISCUSSION; From Sean T. Kelly, and Dennis Starks
MEMBERS WRITE;
Special Event Reports, & War Time
Photos/Films.
BC-611, AND
INVERTER POWER SUPPLY SWITCHING PROBLEMS;
From Ed Guzick, and Dennis Starks
HUMOR;
***********************************************
SOME NVIS
DISCUSSION;
NVIS; Some more
web sites and even more questions:
There's a drawing of the PRC-70 in the
Army's on line FM 24-18. Does anybody
know anything about their use with the Atomic Demolitions Units
(Engineers).
Here's the
URL:www.atsc-army.org/cgi-bin/atdl.dll/fm/24-18/24180100.gif
There's a new
book out on military history that has a few paragraphs on use of
the PRC-74
by Rangers in Veit Nam. There wasn't
much there but they gave the
impression that it wasn't a sure bet to be able to communicate
every
sked.
Two more gifs of interest are FM 24-18
Figure M-14 and
M-15:www.atsc-army.org/cgi-bin/atdl.dll/fm/24-18/24180164.gif
and 24180165.gif The first one is titled Communications
success with the AN/PRC-74 as a
function of time of day and antenna type over a 12-mile path in
low
mountains, spring(sic) and summer(sic) 1963.
The thing claims that from
8 am to 1 pm you could just walk around with the rig on your back
and
talk over said 12 mile path. I'd love to
know what kind of antenna they
were using on the other end of the path.
Figure M-15 is titled Communications success
as a function of range for the AN/PRC-74
in mountainous and varied terrain-including jungle in
Thailand. It depicts the same frequency used for the
first graph, but with a 30% plus
20% or minus 10% success rate. I'm
guessing that the first graph is
showing the results from a limited test, and the second from a
more
complete test.
There are some more drawings and charts
which you can get to by going first to
the FM 24-18 appendex
M:www.atsc-army.org/cgi-bin/atdl.dll/fm/24-18/FM24-_22.htm
There's one of the Shirley
folded dipole for NVIS. It looks like my
UHF bowtie antenna flat on it's back
and cut for HF. That gave me the idea to
put foil on the screen of the
TV antenna, which dramatically improved reception (which had been
driving me nuts for two years-damn rich people and their
old-fashioned
wind-powered sailboats). There's also a
table showing effective
radiated power for several different antennas used for NVIS.
(Let's see now, if I can boost the power of
my PRC-47 to a kilowatt using built-in
whip antenna, it'll work as well as my 1 watt HW-7 into a dipole,
or as
well as 100 watts into a dipole lying on the ground. Better
get a
motorcycle helmet to shield from the
RF...).
http://prairie.lakes.com/~jstanley/NVISPAT/fig8.gif
is a graph
showing relitive gain of various antenna types at all angles from
the zeinith
to the horizon. When Dennis said he
had some expirience with
NVIS it really peaked my curiousity. I
enjoy listening to the emergency
communications net on 75 meters here in the evening. They
check by
city, so I can make a map showing locations of signals recieved as
the
net progresses. This using the built in
whip antenna of my shortwave from
Radio Shack. So Dennis, what's the scoop
on NVIS?
Anybody else into
shooting bolts at the sky?
ps: FM 7-93 has an appendix on NVIS. It's online
at the same site above. Worth reading.
Sean T.
Kelly email is
sean_k@hotmail.com
------------------------------------------------------------------------------
"Communications success with the
AN/PRC-74 as a function of time of day and antenna type over a
12-mile path in
low mountains, spring(sic) and summer(sic) 1963."
The date of this
material in conjunction with the PRC-74 would indicate that these
were
experiments being conducted, and the radio in question was most
likely not the
PRC-74, but it's commercial ancestor the Huges HC-161. Is it
possible that
these may have been the result of field trials of the radio
itself? Interesting!
A low mounted (in terms of wave length)
standard dipole will produce near vertical radiation. The antenna
you note that
looks like a folded dipole is most likely terminated between it's
ends with a
non-inductive resistor and is much shorter(in terms of wave
length), and has an
extremely wide bandwidth as compared to a standard folded dipole.
This minute,
I can't recall the proper name for this antenna but a version of
it has been
available from Barker & Williamson for many years and is said
to be in
service by various military organizations world wide.
The radios standard whip antenna will
also
work well for NVIS propagation, but not if kept vertical where
it's radiation
pattern will be at a low angle, it must be laid over producing a
high angle of
radiation. In it's vertical position it's best suited for ground
wave
communications through dense foliage up to 5 miles where there are
no
geographic obstructions. Or long range ground to air, or for long
(Skywave)
propogation at distances over 150 miles(and not under). One
advantage of NVIS
becomes apparent in adverse terrain where an NVIS signal can be
bounced off the
atmosphere sending a signal from one side of a mountain to the
other.
A simple case in point, a couple years
ago
while returning home from a friends house 90 miles distant(George
WD0ALN) in
hilly southern Missouri, I had a GRC-9 mounted between the front
seats in my
1965 International Scout. We thought it would be neat to see how
far I could
get before communications were lost on 75 meters in the afternoon.
The antenna
used was an old Webster Band Spanner slightly modified with some
mast
extensions underneath the antenna proper, thus elevating the load
surface
producing a center loaded antenna. I was only able to talk to
George for about
five miles before losing contact. I then pulled the Scout over to
the side of
the highway, pulled the antenna down to a near horizontal position
and tied it
off. Our communications were then extended to near 20 miles. The
antenna in the
upright position produced a low angle of radiation which was good
for ground
wave only(in this application). Pulling it over to the horizontal
plain
produced a very high angle of radiation(due to it's proximity to
ground) well
suited for NVIS propagation. George and I repeated this experiment
some months
later when we were headed off into the wilds of eastern Kansas on
a Search
& Collect mission. This time the same antenna was used, but
the radio was a
PRC-47. Constant calls on 75 meters to our destination(about 150
miles) began
when we left home that morning. At about 100miles contact was
made, and
Jim(W0RRL) was able to then talk us in, right to his door step. I
might add
that the PRC-47 was always on low power(20 watts).
Even at a kilowatt your PRC-47 will not
produce short range communications(other than ground wave) with
it's vertical
whip antenna, your 1 watt HW-7 on a low mounted dipole, will. For
reliable
communications at ranges up to 150 miles on say 75 meters, reverse
wave
propagation is used, I/E typical military frequency-to-time-of-day
usage for
long range communications would be 2-6mc for nighttime, and 8-12mc
in the
daytime. The opposite of this is used for NVIS propagation, so a
75meter net
will operate very will during daylight hours. Remember, the object
of NVIS
propagation is to produce "reliable short to medium range
communications"when other means are not suitable". Your emergency
75
meter net operates on this band under the premise that in an
actual emergency
VHF or UHF repeaters might not be left in operation.
The reasoning for Navy's testing of NVIS
propagation on the other hand is not same as that of the other
services. Here
the object was to provide secure inter-task force communications
between ships
being deployed, say an Aircraft Carrier, or Battleship task force,
the maximum
distance between ships being around 100 miles. It should be
stressed, that
properly orchestrated NVIS propagation bounces off the atmosphere
only once.
The advantage of such a practice was the
inability of and adversary to use conventional Direction Finding
techniques and
equipment mounted in aircraft to locate said task force. Where it
was possible
for these same aircraft to easily locate a VHF or UHF signal out
to 500 miles
or more. To this end, in the late 1970's experiments were
conducted which used
a URT-23(1kw) transmitter modified with an attenuator pad mounted
between the
exciter and the power amplifier that resulted in a total output
power of around
one watt or less(ironic isn't it!). We called it LNFR(Limited Near
Field
Radiation), or something like that, memory is fading me in my old
age. Low
mounted horizontal wire antennas and reverse wave-propagation were
used with
limited RF output. The expected result was a signal that would
radiate nearly
strait up, bounce back to earth only once then dissipate. Thus
providing the
desired minimal area of coverage with nothing left over for the
bad guy's to
sniff out.
While I cannot comment directly on the
success of these experiments as I was a simple Radioman at the
time tasked with
the operation of those modified URT-23's. I can however relate a
story which
could very well be related. In 1977(or thereabouts) a task force
centered
around the Aircraft Carrier USS John F. Kennedy headed off in the
Atlantic
bound for the Mediterranean. Such movements are always kept very
hush-hush for
some reason(though everybody knows all about it anyway). Complete
radio
silence(EMCOM) was normally the practice on the trans-Atlantic leg
of these
trips, but on this occasion the low power URT-23's were left in
operation. It
was common practice for the Russians to send out a Bear Bomber
modified as
described above for direction finding and surveillance to locate
these task
forces bound for the Med. At about 3/4 way across the Atlantic,
this Bear was
thought to be way over due so the Captain(Jerry O Tuttle, a real
dip shit)
ordered six Tomcats into the air to go out and look for it, then
escort it in
so's to prevent it from otherwise just wondering into the
Carrier's air space
thus avoiding possible incident. Three days later all
non-essential personnel
were ordered onto the flight deck to provide a single finger
salute for the
Bear. Having been found by the Tomcats it was being escorted in so
it could
take it's pictures. Had our NVIS experiment worked?
On a unrelated note, just prior to my
arrival aboard "Big John" in late 1976, she had had her 10kw
amplifiers removed due to the generally accepted idea that this
much power was
over-kill and unnecessary for long range communications.
Dennis Starks;
MILITARY RADIO COLLECTOR/HISTORIAN
military-radio-guy@juno.com
***********************************************
MEMBERS WRITE;
Special Event
Reports, & War Time Photos/Films, and the
SCR-511(Pogo-Stick) which would tend to show Marine Corps use in
early WW-II.
History CH had one of the WWII
documentaries going and managed to get a
kwik glimpse of a
"Horsey Talky" stuck in the sand during a Marine landing
on some Island.
The only thing about some of those shows is that they have
been edited from
a pile of footage and whats on the screen doesn't always
match the
story. A friend said there were several
shots of GIs carrying
the radios in the
documentary on the Italian campaign but I have not seen
that one.
Pretty darn good narrative Dennis! Have
had
similar things happen hauling
boats, hardwood,
trucks, and even radios. Going thru deepest LA in a dying
VW Camper FULL of
Mil BoatAnchor and realizing the Randall .45 got left
home is a real
workout for the adrenal gland. Couldn't stop for gas
anywhere without
a long down hill to pop start the thing. Poor old
Westfalia was
loaded shoulder deep back to front with TCS stuff including
AC supply bunch
of GRC-9 with pwr supplies, RBSs etc . Sure didn't want to
have to walk away
from the load in places where English was a second
language.
Ed Zeranski This is a private opinion or statement.
home email: ezeran@cris.com
ed) the subject
of the dubious origins of printed photos and films, as they were
combined with
captions, and subject matter, came up during our series "Mystery
Radio,
the SCR-511". They can still be valuable provided they are closely
inspected by multiple authorities expert in varied fields. I/E
closer
inspection of the other equipment in the seen might prove far more
valuable
that the caption. In the case of the BC-745(Pogo-Stick) we had an
Airborne
trooper that was supposedly in the Mediterranean, but the presents
of an M1A1
carbine showed that this was late war. The identification of such
things as
uniforms, knives, and other ancillary equipment also help
correctly determine
dates, places, and services.
A photo in my library of Signal Corps
origin has the caption that reads "Army Signalman disembarks ship
for
marine assault with Walkie Talkie on his back". The photo is
actually of a
Marine, and the "Walkie Talkie" is a TBY! So record those History
Channel shows, and use you VCR to closer inspect the goings on in
each clip.
***********************************************
BC-611, AND
INVERTER POWER SUPPLY SWITCHING PROBLEMS;
Dennis,
As you know, one
problem encountered when building an alternate power supply is how
to
turn it on/off. Mark's BC-611 idea (which I never saw) using an IC
that operates by rapidly shaking it three times comes the closest
as I
would assume it required no hard wired connections to the
transceiver.
My guess would be he used a counter and a mercury switch?
I've thought
about using various switches, relays or transistor circuits but I
can't get around the hard wired connection and that's the rub!. I
heard
of a uA sensing IC switch but never came across one. However, it
would
probably need to be wired in. On a BC-611 there
is little room for anything. I've used a small relay wired to
operate
off the filament voltage and my present method uses the existing
antenna switch but requires 3 wires tacked onto the chassis. It
works
but there must be a better way. All my schemes revolve around
using the filament voltage, however, I've yet to come up with a
brilliant idea.
How to switch the
converter without using hard wiring between the receiver and the
supply? So far I do not have a solution. Any ideas?
Ed Guzick
ed) Mark Gluch is currently off line due to AOL
troubles, and a dead monitor, so he can't respond just now in
regard to his
BC-611 on/off switching method. But it
did use a mercury switch and an IC counter.
Unlike most military radios that use a
single switch contact, & ground leg switching of all their
batteries to
turn them on and off simultaneously, the BC-611 uses two tandem
switch contacts
to connect the heater & B+ batteries to their respective loads
via the
positive side of the batteries separately. When operation from an
inverter and
rechargeable battery is desired, this presents the peculiar
problem of turning
on two distinctive power supplies with a single switch yet still
keeping them
isolated. To compound this problem, a primary power source must be
connected,
& switched that provides both heater, and inverter power
supplies, yet this
same switch must pass both the voltage of the primary power
source, and one of
the secondary ones while also keeping them isolated. Of course,
this is
imposible, so we must contrive a method buy which one switch will
control a
second switch that will in turn serve our purpose.
I don't know what your using as a primary
power supply or it's voltage. If it is a design similar to, or the
same as that
I presented you are probably using four "D" cells in series for
around 5 volts which makes an output of around 90 from the
inverter.
Try something along this line, I know you
have a selection of tiny relays, some even 1.5 volt, use one of
these with it's
coil(and maybe a resistor) in series with the heater supply, place
a small 6
volt light bulb in parallel with the seriesed relay-coil/resistor.
The
resultant current drain when the radio is switched on will close
the relay
turning on the inverter. The resistor will compensate for relay
coil resistance,
and the combination relay coil/resistor will provide a voltage
drop for the
heaters to operate from.
The light bulb acts like a ballast tube
to
protect the tube heaters, and when full-on contributes to the
voltage drop
needed. When the radio is first turned on, the light bulb will
glow brilliantly
because of the low heater resistance, but as the radios heaters
warm up, this
glow will fade to near nothing as heater resistance goes up. Some
experimentation will of coarse be required due to the various
relay/light bulb
combinations/availability, so it would be a good idea to calculate
the radio's full-on heater resistance so that a
substitute load can be used preventing radio damage.
Another approach would be to use a two
transistor "flip-flop" circuit or even the current sensing methods
you mention, but either system would still require the use of a
small
relay(dependant on current drain, and transistor size), and a
ballast type
heater voltage control circuit. So in the interest of minimum
parts count(the
relay coil is an integral part of the heater voltage control
circuit thus
serves a dual purpose), and simplicity the above might be the best
way. Once
you've hit upon the right relay-coil type, resistor, and light
bulb
combination, you might let us know about it. A possible commercial
source for
miniature low voltage relays might be those little DIP relays once
available
from (eeek) "Radio Shack", in 5, 6 and 12vdc versions.
One final note, while the relay coil,
dependant on it's resistance and current requirement, may be
placed in parallel
with a large wattage voltage dropping resistor(typically 5 watts
or more),
their sum resistance will be higher than that needed for the
operation of the
radio's heaters. It's the variable resistance of the light bulb
placed in
parallel with these that brings the total circuit resistance
within the
operational range of the radio's heaters. A light bulb must be
selected as a
companion to the power-resistor/relay-coil, that draws sufficient
current when
cold to allow the radio's heaters to slowly light up. If you are
lucky enough
to have a supply of 1.5 volt relays, the coil itself need not be a
part of the
heater/ballast circuit, it can simply be connected between the
output of the
circuit and ground, in this case only the power resistor, and
light bulb form
the ballast regulator circuit for the radio's heaters.
All your ideas and input are eagerly
sought
on this subject.
Dennis Starks;
MILITARY RADIO COLLECTOR/HISTORIAN
military-radio-guy@juno.com
***********************************************
HUMOR
Seeing as how
Powerball in the USA is over $200 million this week, I
thought today's
joke was appropriate...
A guy named Joe
finds himself in dire trouble. His business has gone
bust and he's in
serious financial trouble. He's so desperate he decides
to ask God for
help. He begins to pray... "God, please
help me. I've lost my business and if I
don't get some
money, I'm going
to lose my house as well. Please let me
win the
lotto." Lotto night comes
and somebody else wins it. Joe again
prays... "God, please
let me win the lotto! I've lost my business, my house and
I'm going to lose
my car as well". Lotto night comes
and Joe still has no luck. Once again, he
prays... "My God, why
have you forsaken me?? I've lost my business, my house, and
my car. My wife
and children are starving. I don't often ask you for
help and I have
always been a good servant to you. PLEASE just let me
win the lotto
this one time so I can get my life back in order." Suddenly there
is
a blinding flash of light as the heavens open and Joe
is confronted by
the voice of God Himself: "Joe, meet
Me halfway on this. Buy a ticket."
----------------------------------------------------------------------------------
A man who lived
in a block of apartments thought it was raining and put his
head out the
window to check. As he did so a glass
eye fell into his hand.
He looked up to
see where it came from in time to see a young woman looking
down. "Is this yours?" he asked. She said, "Yes, could
you bring it
up?"
and the man
agreed. On arrival she was profuse in
her thanks and offered the man
a drink. As she was very attractive he agreed. Shortly
afterwards she said,
"I'm about
to have dinner. There's plenty; would
you
like to join
me?" He readily accepted her offer
and both enjoyed a lovely
meal. As the evening was drawing to a close the
lady said, "I've had a
marvelous
evening. Would you like to stay the
night?" The man hesitated
then said,
"Do you act like this with every man you meet?" "No," she
replied,
"only those
who catch my eye."
----------------------------------------------------------------------------------
An old Jewish woman
took it upon herself to travel to Nepal to meet with this famous
guru. Her friends tried to dissuade her,
saying that
the trip was long and
arduous, and with her varicose veins it could mean real trouble.
They
could not talk her out of it, however. So, she made her
preparations and set out. It began with
a 36-hour flight on Air
India with four stopovers, followed by 2 hours on a rickety
propeller plane
from WWI. Then a ride on a cog
railway. Then a 2-day trek in a camel caravan
over icy mountain paths. She was half
dead when she reached the
guru's village. There she learned that
it would be perhaps ten days
before she could have an audience with the guru because so
many seekers
had come to see him. She was also told that when she entered
the
guru's tent, she would only be allowed to speak five words,
since the guru
was so busy. So, she rested and prepared, all the while trying to
choose
her five words carefully. Finally, the day
came. Into the tent she went and seated
herself on the hard stool
facing the guru. And then she leaned
over and spoke: "Enough
already, Sheldon, come home."
--------------------------------------------------------------------
The ambassador of
a small African nation chanced to visit
Russia, and was
entertained by his opposite number, the
Russian
ambassador. For three days, the African
ambassador was wined,
dined, and
generally treated to the best hospitality that Russia had to
offer.
On the final day
of his visit, the Russian ambassador said
"As your
stay is coming to an end, it is time for you to
play our
traditional game, Russian roulette. One
of the
six chambers of
this gun is loaded - you spin the cylinder,
point the gun at
your head, and pull the trigger." This phased the
African slightly, but he was a proud man
of a warrior
people, and to show fear would be unthinkable.
Both men took
their guns, spun, and pulled the triggers.
<click>
<click>
Both chambers
were empty, and both ambassadors
breathed a sigh
of relief. The African
ambassador was much impressed with the
courageous game,
and thought hard about the subject
before the
Russian Ambassador was due to visit his
country the next
year. When the visit
came, the African ambassador treated the
Russian with all
hospitality, until the final day of his
stay. Leading him to a
private room in the palace, the African
ambassador spoke
"Now it is time for you to
sample our game,
African roulette". So saying, he led
the Russian into the room, the only
occupants of
which were six beautiful, naked women.
The African
ambassador said "These women are the
most beautiful
members of one of our tribes. Any one
of them will
provide you with oral sex - take your pick".
The Russian was
not entirely averse to this idea, but
he couldn't see
the connection with Russian Roulette. He said
"Well, ok, great, but where's the roulette part?
Where's the
danger?"
With a big grin
on his face, the African ambassador
Answered,
"One of them is a cannibal"
***********************************************
(The preceding
was a product of the"Military Collector Group Post", an
international
email magazine dedicated to the preservation of history and the
equipment that
made it. Unlimited circulation of this material is authorized so
long as the
proper credits to the original authors, and publisher or this
group are
included. For more information conserning this group contact
Dennis Starks at,
military-radio-guy@juno.com)
***********************************************