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Re: [HCDX] Dxers Unlimited's mid week edition for 8-9 May 2007
Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited’s mid week edition for May 8-9 2007
By Arnie Coro
Radio amateur CO2KK
Hi amigos radioaficionados… welcome to the mid week edition of Dxers
Unlimited, that is reaching you when the Sun is taking yet another
break, as solar activity took a downward trend after sunspot active
region 953 just turned around and disappeared from Earth view… So expect
very low solar activity for the next several days, as the rather
extended tail end of solar cycle 23 continues.
By the way, some scientists are now saying that the actual end of this
cycle will not happen during 2007, and that the months of really minimum
solar activity will be from February to June of 2008… Really bad news
for amateur radio operators around the world amigos, as this means that
the HF propagation conditions won’t recover until well into 2008.
Item two: The ever popular and ever evolving TTFD, tilted terminated
folded dipole also known as squashed rhombic antenna keeps receiving
attention by Dxers Unlimited’s listeners around the world… And many of
our long time friends have a TTFD installed , with versions as small as
10 meters in length providing excellent results for receiving, while
even that very short 10 meters long version of the TTFD is capable of
providing good transmission for the amateur bands between 10 megaHertz
or 30 meters all the way up to 29.7 megaHertz, the upper limit of the 10
meters amateur band…
More about the TTFD in today’s ASK ARNIE section of Dxers Unlimited…
stay with us amigos, as the mid week edition of your favorite radio
hobby program continues after a short break for station ID..
……
Si amigos, this is Radio Havana Cuba, now 46 years on the air at your
service… Now Dxers Unlimited continues with ASK ARNIE, la numero uno,
the most popular section of this program… Today I am answering a nice
e-mail message from amigo Jim, who is also, as many Dxers Unlimited’s
listeners, an active radio amateur. Amigo Jim tells me about how he has
found a source of non inductive resistors for making the TTFD antenna,
and here is now my answer to his e-mail on this topic:
Dear amigo Jim:
Thanks for the nice note about locating a source of non inductive
resistors... Here is some information
that may help you with the TTFD project.
For my " receive and low power transmit" TTFD antennas, I have been
using for a long time a cluster
of 2 Watt dissipation high quality carbon resistors ( pure carbon ones,
not "carbon film ). connected in pararell.
For a typical TTFD capable of handling continuosly 10 Watts of RF
carrier output, I use 10 resistors of 2 Watts dissipation, connected in
pararell ... The values that seem to work very well are from 9100 ohms
to 6800 ohms...
The resulting "almost non inductive" resistor is placed inside a plastic
container, and the actual value may be between around 900 to 670 ohms (
taking into consideration the tolerance of the actual resistors values ).
The balun I have been using more consistently is a 9 to 1 , and feeding
the antenna with 75 ohm coaxial line...( the balun core is just a length
of ferrite rod, or you can use a 50 mm or 2 inch diameter ferrite toroid
ring )
I usually take the 75 ohms coax to my PI network antenna tuner for
transmitting QRP ( low power ) but for receiving, you don't need the
tuner ...
My latest version of the TTFD is just 15 meters long ( a bit less than
50 feet long ) which is shorter than a half wave dipole for the 40
meters band.
This 15 meter long TTFD has the upper wire separated from the lower wire
by 50 centimeters, but you can make it with a 30 centimeters separation
and I really can't see the difference...
The spreaders are made from fiberglass rods of about 12.7 mm diameter (
half inch ) for a permanent antenna ( very long lasting , especially if
you paint the fiberglass with good quality enamel paint )
For a lower cost antenna, you may use - as I do - lengths of PVC water
pipe , the one with thick wall cut to about 40 centimeters... make two
holes in them for the wires of the antenna... I tie them to the wire
with cable tie wraps for making a "fast" field day antenna, but for a
more permanent one I use copper wire...
The antenna is NOT LIGHT , so you must take this into consideration when
installing it, because the combination of the weight of the spreaders,
the plastic box with the resistors , the balun and the end insulators
does add up !!!
The antenna can be installed horizontally, but it is easier to install
it at an angle of between 20 and 45 degrees... and you save horizontal
space...
Amigo Jim, this is not a super efficient antenna... My comparisons
between this 15 meters long one tilted at 30 degrees , and a standard
half wave dipole for the 40 meters band, show that the TTFD signal on
7.1 megaHertz at distances between 100 and 1000 kilometers is anywhere
between - 2 dB to - 6dB ... that I think is quite reasonable, especially
if you realize that this antenna , the TTFD
will "work" from 6.5 all the way up to at least 25 mHz, although with
the tuner it even works on 10 meters ...
The half wave 40 meters dipole is longer - 20 meters long , and will
only work when fed with 50 ohms coaxial cable , on the 40 and 15 meters
amateur bands for transmitting, although it will receive OK from 6 to 30
mHz as tested here many times...
I hope that this update helps you ...
If you are short of space, a 10 meters long version of the TTFD works
from 10 megaHertz up to 30 megaHertz for transmitting, and you can
certainly use it as a receive antenna from 5 to 30 mHz too...
73 and DX
YOur amigo in sunny Havana
Arnie
Host of Dxers Unlimited
If you have any radio hobby related question or want to send a comment
about your antennas, rigs, experiences with HF propagation… you name it…
just send an e-mail to arnie@xxxxxx, again arnie@xxxxxxxxx
……
QSL on the air, QSL on the air to the many Dxers Unlimited listeners
that have sent Sporadic E skip propagation reports during the past week…
Sure, those reports do help to give a very good idea on how the current
sporadic E season is developing… According to a fast track analysis of
the reports, best times for monitoring the 10 and 6 meters bands and the
low band VHF TV band are from 7 AM to 11 AM local time, with a second
propagation window from about 3 PM to 8 PM local time, although I have
received several sporadic E reports telling me that TV stations
operating on channels 2, 3 and 5 in the deep South of the USA were
seeing in Ontario, Canada as late as 10 pm local time… And this of
course is a confirmation of the well known fact that sporadic E clouds
may appear at any time of the day, although they do have a rather
definite pattern of morning and local afternoon event been more frequent…
Si amigos, yes my friends, oui mes amis... The spring-summer sporadic E
season is now in full swing for our enjoyment, and I expect to have the
opportunity of saying HI ON THE AIR to many Dxers Unlimited listeners
that are also radio amateurs and enjoy the use of 10 meters and 6 meters
during the solar cycle independent Sporadic E season… AND for those of
you not familiar with this unique propagation mode, let me add that
after about half a century of enjoying sporadic E propagation, it
continues to fascinate me like the very first day I saw an American TV
station from Chicago, WBBM Channel 2 and a few minutes later another
station from Oklahoma on the same channel on my home RCA 17 inch black
and white TV set one day in early May of 1957…. From that very same day,
I have been a fan of TV Dxing second to none amigos !!!
…..
You are listening to the mid week edition of Dxers Unlimited, coming to
you via short wave and also from 05 to 07 UTC via our Internet streaming
audio that can be picked up from our website http://rhc.cu, YES, just
type rhc.cu on your browser input and you will be opening up our website
in Spanish, then click on the loudspeaker ICON, and start listening to
our streaming audio amigos !!! We will soon have it available full time
from 01 t0 07 UTC, as another audio channel is about to become available
here…
Now item five: Here is our technical topics section of Dxers Unlimited,
that today will be providing an update about the latest version of the
FAN Broadband dipole, that has evolved from computer modeling. This FAN
DIPOLE uses more wires on each leg of the antenna, a total of between
six to nine, and the actual shape of the geometry of the antenna is of a
dual cone… After working with one of the most up to date versions of
antenna computer modeling software, an engineer friend of mine that
teaches at Havana’s Technical University, came up with this version of
the FAN DIPOLE that is 6.7 meters long on each side, for a total of 13.4
meters or 44 feet overall length. The cone expands from zero at the
center insulator to a diameter of 3 meters. All the six or nine wires on
each side of the FAN DIPOLE end at a copper wire circle to which the
wires are soldered.
The antenna shows a very nice wideband frequency response from 6
megaHertz to 30 megaHertz , and when properly installed , at a height
above ground of no less than 10 meters, the antenna fed with 400 ohms
open wire balanced line is an excellent performer for both amateur radio
and short wave listening use. And let me add amigos,that it is certainly
a very nice looking antenna. This is not a one weekend project, and from
a mechanical point of view this BROADBAND FAN DIPOLE , does require a
very careful installation because of the weight and the number of wires
involved … BUT, again, it is an excellent antenna if you have enough
space for it, and can afford the supporting towers or masts that can
handle its weight.
A simpler and lighter three wires on each leg version of this antenna
works very well , but can not match the extremely nice standing wave
ratio curve of the 6 or 9 wires version.
And now amigos, as always at the end of the program, when I am here in
Havana, ready to copy, Arnie Coro’s Dxers Unlimited’s HF plus low band
VHF propagation update and forecast… Solar activity is now again at very
low levels, and if no new sunspots show up, we will have several days of
solar flux at baseline levels, and possible ZERO sunspot count… More ,
many more sporadic E skip events are coming up during the next several
weeks, and I expect this spring-summer sporadic E season to peak during
the second and third weeks of June… Hope to have you listening also to
our weekend edition of Dxers Unlimited next Saturday and Sunday UTC
days… Don’t forget to send me your comments about today’s program,
signal reports and any radio hobby related questions that you will want
to ask … Send mail to arnie@xxxxxx, or send a post card or AIR MAIL
letter to Arnie Coro, Radio Havana Cuba, Havana, Cuba
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