Radio Havana Cuba

Dxers Unlimited

Dxers Unlimited's mid week edition

By Arnie Coro

radio amateur CO2KK

Hi amigos radioaficionados ! You are listening to the mid week edition
of your favorite radio hobby program. I am Arnie Coro, and here is the
most up to date information about solar conditions... For the 11th of
October UTC day, solar flux is expected to be at the baseline level of
70 units, and the Ap index forecast is set at 6 units...A comment from
the Belgium based center SIDC states that, and I quote: Solar and
geomagnetic activity is quiet and expected to remain so for the next 48
hours - the all quiet alert remains valid. The only two sunspot groups
present are rotating of disk soon. X-ray background radiation is below
the A-level. At the end of the week (Saturday-Sunday) there is a
possibility for geomagnetic distrubances due to the passage of a coronal
hole. Last rotation it produced a minor storm. October 10th ESTIMATED
ISN : 015, BASED ON 08 STATIONS. So be prepared to deal with very low
maximum useable frequencies during the next several days....

Item two: YES , two series connected 9 volts batteries and also two
series connected 1.5 volts D cells provide power to the single 3 volts
filament vacuum tube in a fun project... An experimental regenerative
receiver that using a 3S4 tube is able to pick up lots of short wave
staions, including ham radio signals on the 40 meters band with a
specially wound bandspread coil. This is yet another example of low
parts count projects, but finding the parts for building a replica of
this late nineteen forties radio is not that easy... That's why at the
amateur radio training program that we run for our local Radio Club, the
receiver project that I promote among the participants used readily
available parts that can be found locally by recycling electronic equipment.

No need to use sophisticated ferrite or iron powder toroid cores or
other rather rare stuff, as standard half inch or three quarters inch
PVC pipe ( for those of us using the Metric system that means 12.7 and
19 millimeters diameter pipes ) will supply all the coil forms that you
may want for as many radios as you may ever want to homebrew.

We also use a 12 volts DC regulated power supply built around a locally
plentiful transformer recycled from solid state TV sets, and this supply
is also used later for powering other ham radio related projects..

Si amigos, yes my friends... the sound of a homebrew radio, one that you
have built yourself is always quite different... You can verify that all
by yourself by building even the simplest radio receiver !!!

More radio hobby related information coming up in few seconds when
Dxers Unlimited's mid week edition continues...

Stay tuned...

......

This is Radio Havana Cuba, the name of the show is Dxers Unlimited and
here is item three of today's program... The popular antenna topics
section that will be devoted to answering a question sent by a listener
in Norway... Amigo Olaf, who listens very early in the morning his local
time to our 6060 kiloHertz frequency wants to know why many beginners
radio books discourage the use of vertical antennas for receiving... and
he wants to know if that is right or wrong. Well amigo Olaf, I fully
agree with that recommendation... Vertical antennas are to be avoided
for receive only applications, especially in urban or semi-urban areas
for one solid reason: man made electromagnetic disturbances are
essentially vertically polarized, so a vertical antenna will pick up
much more local noise than a horizontal antenna. At remote locations,
like when I go to the beautiful seaside resort of Varadero Beach, a
vertical installed right next to the ocean is a fantastic antenna for
working DX, because of its low take off angle... and of course, that
right next to the ocean, and away from buildings and industrial
installations the noise level is very low... So amigo Olaf, my advice is
that if you want to install a single antenna for listening to short wave
signals between 6 and 30 megaHertz as you tell me in your e-mail, try
first a TTFD or Tilted Terminated Folded Dipole... and don't forget to
use a higher value terminating resistor that the one usually recommended
in the textbooks. My tests here show that a terminating resistor value
of between 750 and 900 ohms is ideal , and that a 12 to 1 balanced to
unbalanced broadband transformer will do a great job with this antenna ,
that for your particular application should be about 15 meters long or
maybe a little longer if you want to pick up stations starting around 5
megaHertz. Use well shielded 75 ohms coaxial cable to connect the
broadband balun to the receiver, and my personal experience is that a
simple PI network antenna tuner between the antenna and the radio will
improve reception .

My latest prototype TTFD uses eight 60 centimeters long fiberglass
spreaders , a non inductive 820 ohms resistor assembled by connecting in
pararell ten 8200 ohms 2 Watt carbon resistors, and a homebrew 12 to 1
balanced to unbalanced broadband transformer.

This antenna is exactly 15 meters long and is installed sloping gently
at a 30 degree angle from my tallest tower. It works very well as an all
around receiving antenna for the frequency range between 5 and 50
megaHertz, and I use it ocassionally for transmitting on the 40, 30, 20,
17, 15, 12 and 10 meter bands, by connecting the 75 ohm downlead to my
ham station's antenna tuner. And before I forget , during a 6 meter
band opening this summer , I made a mistake in selecting the proper
coaxial cable, and was actually using the TTFD instead of my MOXON
rectangle 6 meter band beam antenna... That I found out , and this is
the funny and amazing part of the story, after working more than 50 DX
stations on 6 meters, and I must add that I was carefully watching the
standing wave ratio meter set to the reflected power position... AND the
SWR was never higher than 1.5 to one !!!

Si amigos, sometimes even a mistake will teach you something new about
antennas... in this case the lesson learned was that the 15 meters long
and 50 centimeters wide TTFD with a 820 ohms terminating resistor
somehow seems to work quite well at the lower segment of the 6 meters or
50 megaHertz amateur band where most of the DX activity concentrates...

......

QSL , QSL , QSL on the air, YES, the new Radio Havana Cuba antennas are
making possible much better reception by our listeners around the world.
The most recent example, several spanish speaking listeners living
around the Great Lakes region of North America are reporting excellent
reception of our new 13750 kiloHertz morning frequency beaming to that
part of the continent.

Reports tell me that the signal is very stable, with little fading, and
that this channel is coming in very well around Chicago ... This antenna
is the high band segment of the 340 degrees azimuth high gain curtain
array... During the evenings we use the low band segment of the antenna
on 9820 kiloHertz ,starting at 00 UTC in Spanish until 0100 UTC, and
then switching to English from 01 to 05 UTC...

Now here is item five: Frequency drift on a battery powered short wave
receiver... is that possible amigo Arnie ? That was the question asked
by a listener Alan from Toronto. He owns an ETON S350 receiver, and
tells me that the radio drifts badly on the short wave bands, especially
when he is using the SW3 band that starts around 16.8 megaHertz... Alan
also adds that the ETON S350 he own also drifts quite fast off the
selected frequency on the SW2 band, that on his particular radio starts
on 7.76 megaHertz... And then he ASKS ARNIE...

What can be done to fix this ?

Well amigo Alan, your radio seems to have a really bad problem, that is
making it practically useless for short wave listening, as no one will
be tuning and retuning the radio following the station you want to
listen to, because the radio drifts of frequency... My advice is to look
for the circuit diagram of the receiver and try also to find the
workshop repair manual from Grundig ETON... I suspect that there is a
bad soldered connection at the local oscillator section...or there may
be a bad component , probable a capacitor that changes value as it heats
up...

BUT , please listen carefully, my advice is not to attempt to repair
this problem, unless you are a very experienced electronics technician,
as this solid state radio has the parts soldered to a printed circuit
board quite close to each other, requiring the use of a special
soldering iron with a very fine tip and temperature regulation, in order
to avoid damaging other parts...

AND you are absolutely right amigo Alan, that ETON S350 radio should had
never passed the quality control station at the factory or assembly
plant with that huge frequency drift problem !!!

Some time ago, I had to deal with a similar problem , but with an older
receiver... and it took quite some time to find that a ceramic capacitor
was the cause of the frequency drift problem. Following the advice of
friend that fixes radios for a living, I placed the tip of the soldering
iron close to each component of the local oscillator circuit one at a
time... until a very sudden drift happened right after the tip of the
soldering iron was near the capacitor that formed part of a capacitive
divider in the Colpitts oscillator circuit...

Amigo Alan, keep in touch, and tell me when you fix the radio what was
the cause of the problem , so that it can be passed along to other
listeners that own that same Grundig ETON S350 receiver.

.....

And now amigos, as always at the end of the show, here is the second
most popular section of Dxers Unlimited, Arnie Coro's HF and low band
VHF propagation update and forecast... Let's start with the VHF low band
forecast, because the autumn equinoctial Trans Equatorial Propagation
season is soon to be coming to an end by the end of this month... HF
propagation conditions are in really poor shape, because for many days
the solar flux has been at baseline levels, so the ionosphere doesn't
support propagation on frequencies above 20 megaHertz for a large
percentage of the daytime hours. Expect very low solar activity and very
low maximum useable frequencies until at least Saturday, but you can
always have a change of picking up some DX if you devote some time
starting at just a half hour before your local sunset...

Hope to see you all here on this frequency or world wide web connection
next Saturday and Sunday UTC days amigos, and don't forget to send your
signal reports, QSL request, radio hobby questions and comments about
the program directly to my e-mail address arnie@rhc.cu, or VIA AIR MAIL
drop me a postcard to Arnie Coro, Radio Havana Cuba, Havana, Cuba