Radio Habana Cuba
Dxers Unlimited

Dxers Unlimited's weekend edition for Saturday-Sunday 2-3 April 2005

By Arnie Coro
radio amateur CO2KK

Hi amigos radioaficionados ! This is the weekend edition of your
favorite radio hobby program, Dxers Unlimited, with yours truly, Arnie
Coro, at the microphone...It's my great pleasure to share with you about
eighteen minutes providing our extremely popular HF plus low band VHF
propagation update and forecast, so that you can plan your listening or
operating time ... ASK ARNIE , with answers to your radio hobby related
questions, technical topics, and more !!! Let's start with A VERY
INTERESTING PROPAGATION ITEM: SPORADIC E SKIP SEASON SEEMS TO BE HAVING
A VERY EARLY START !!! Si amigos, that's the headline, for the past
several days during this week, reports of excellent sporadic E openings
keep coming in, something that one should expect to be happening by mid
May, and of course during the whole month of June, but not at the end of
March and begining of April !!! My perception is that several elements
have combined to produce this unusually early sporadic E layer skip
openings... First of all, the very low sunspot count, as there seems to
be a correlation between the number of sunspots and the presence and
duration of sporadic E openings, and in second place, it is highly
probable that the Earth has passed trough an area of cosmic dust,
something I must yet confirm with several of my astronomer friends...
So, here is my advice, if you enjoy TV and FM band Dxing, or are a radio
amateur with a rig that will operate on the six meters band, keep
monitoring for more possible openings ... if they do happen during the
next two weeks, then we may well be able to enjoy an excellent summer
time sporadic E season !!! Item two: down to the AM broadcast band...
the very low solar activity has produced enhanced propagation conditions
that shows up shortly before local sunset and provides excellent
reception of DX stations up to just after local sunrise... so , if you
are an avid AM broadcast band Dxer, enjoy the last part of the
equinoctial DX season before summer time static and ionospheric noise
levels set up... Item three: This one for owners of vacuum tube
receivers... and YES, there are many of those radios still around,and
many of them, well kept by their owners provide excellent reception even
after 40, 50 , 60 or even more years after they were built... Here is
today's tip... if you want to reduce the frequency drift of your old
vacuum tube radio, keep listening for today's Dxers Unlimited technical
topics section , when I will provide detailed information on how to
improve those old vacuum tube radios frequency stability...
I'll also tell you about more antenna experiments, answer a question
about antenna experiments and at the end of the show, have your tape
recorder or notepad ready for copying Dxers Unlimited's HF plus low band
VHF propagation update and forecast... I am Arnie Coro, in Havana, back
with you in a few seconds...
......
Si amigos, very low sunspot count, an almost spotless Sun, good times to
homebrew more antennas for your radios... Here is more information about
recent antenna experiments... the 2 meters FM sub-band antenna described
during Dxers Unlimited's weekend edition brought a lot of attention from
listeners in nine different countries, from Canada to Jamaica, from
Mexico to Australia and five European countries !!! Let me add that
experiments with this simple omnidirectional low cost wire antenna were
continued here, and they showed that the bandwidth obtained when using
number 12 PVC insulated wire for the antenna elements was quite good if
one considers that these are rather thin, and thus high Q radiators... I
carefully checked the resonant frequency of each of the two dipoles, and
was able to build a second version of the antenna with a lower resonant
frequency ,as required by our two meter band assignment here in Cuba
that at present spans from 144 to 146 megaHertz. Placing the antenna in
a length of thick wall PVC pipe also changed the resonant frequency
downward, something that was to be expected. For those of you interested
in homebrewing this very low cost, simple to build , omnidirectional two
phased vertical elements antenna array, I have prepared a graphic file
that shows how to build this antenna , the list of materials and
closeups of the details... send for the 2 meters vertical
omnidirectional antenna files ... send mail to arnie@rhc.cu, again,
arnie@rhc.cu....
.........
And now antenna topics part two... a combo option between ASK ARNIE and
Antenna Topics... answering listener Herbert from Montana , USA... Sure
amigo Herb, one could add a third half wave radiating element to the 2
meter band antenna described during the weekend edition, but that will
require adding a second phasing coil... plus the third almost one meter
long wire radiator... This will increase the gain of the antenna by
about one decibel, and lower the take off angle a little, while also
increasing the length of the whole antenna to such an extent that if you
want to use if at a permanent installation enclosed inside a length of
PVC pipe, then it would require the use of no less than three insulated
supporting ropes to keep the PVC pipe vertical... Here, once again, we
see the famous rule of diminishing returns... With a single radiating
element, the antenna is just another J pole, by adding the phasing coil
and the second vertical element , we have a version of the SUPER J
antenna, that uses a phasing coil instead of a quarter wave transmission
line phasing system... Now, adding the second coil and third radiator,
will make the antenna , longer, heavier and more difficult to adjust
amigo Herb, so, now I am almost sure that you understand my answer...
But, if still in doubt, don't hesitate to write me again to arnie@rhc.cu...
......
A news item... Caribbean Relay station in Antigua, operated by the BBC
and Deutsche Welle is now permanently off the air... confirmed, March 31
during the BBC's English language Caribbean morning service on 15190
kHz... Nothing heard here on that frequency, so my guess is that this
one was not re-allocated to another relay site like Sackville in Canada,
or Kouru in French Guiana... Possible reason for mothbolling the two 250
kiloWatt transmitters and antennas.... again not confirmed , may be just
another cost cutting measure, in favor of more TV satellite time by both
stations...
Now the technical topics section... with a small item about how to
improve the frequency stability of vacuum tube receivers... This is a
simple , totally reversible modification that can be done in a few
hours , and will definetely make the radio much more stable... It's
built in a small piece of glass epoxy PC board, and is nothing more than
a three ampere 50 volts peak inverse voltage diode, a ten thousand
microfarads electrolytic capacitor, a 3 or 5 ampere current handling
capacity integrated circuit voltage regulator and a pair of one
microfarad tantalum capacitors, plus a 470 ohms 2 watt carbon
resistor... This small circuit board can be fitted inside the old vacuum
radio chassis , where usually there is lot of space available ... The
board is connected to one side of the 6.3 volts AC filament supply and
to chassis ground... Then its output is connected via shielded wire to
the filament of the receiver's first local oscillator or mixer vacuum
tube... In more elaborate vacuum tube radios a separate local oscillator
tube is used, while simpler radios combine the functions of local
oscillator and mixer in a single stage, that is known as a converter...
Feeding the filaments of the separate local oscillator tube or the
converter tube with the regulated DC voltage, typically 6.3 volts DC
used in the great majority of vacuum tube vintage radios , enhances the
frequency stability of the receiver and also,if you feed DC to the
filaments of the audio pre-amplifier stage , the audio distortion will
go down because of the reduction of the so called intermodulation
distortion index, that is among other factors the result of mixing
products between the actual audio and 120 Hertz HUM ... In an upcoming
edition of Dxers Unlimited, I'll tell you about the addition of a
voltage regulating zener diode to supply the local oscillator plate and
screen electrodes,another simple and totally reversible modification
that will also improve the reception because applying regulated voltage
to the plate and screen in case the oscillator is a tetrode or pentode,
enhances the frequency stability considerably.
Si amigos, keeping those old so called boat anchor radios working is
certainly a challenge, but, well worth the efforts involved as they
usually provide excellent audio quality, especially if you use a large
size loudspeaker in a well built acoustic cabinet.
.....
This is Dxers Unlimited's weekend edition amigos, and let me tell you
that our station, Radio Havana Cuba, about to celebrate its 44th
anniversary May Day of 2005, is a one hundred percent QSL station, yes
, since the first day when we went on the air, we have verified
reception reports with QSL cards and verification letters.
Send your QSL requests with a detailed reception report of our programs
to arnie@rhc.cu, again arnie@rhc.cu, or VIA AIR MAIL , send a postcard
and to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
And now amigos, as always at the end of the show, here is Dxers
Unlimited's HF plus low band VHF propagation update and forecast...
Solar activity continues at very low level , but expect disturbed
geomagnetic conditions caused by higher than normal solar wind
speed...Expect higher than normal probabilities of sporadic E events
during the next few days, so be on the lookout for DX signals on the
frequency range from 40 to 110 megaHertz, that includes low band VHF
point to point and mobile communications systems, low band TV channels,
the six meters amateur band and when the sporadic E clouds have a very
high free electron density,reception of FM broadcast stations from
between 500 and 1200 miles away or more are quite possible... See you at
the mid week edition of the program next Tuesday and Wednesday UTC days
amigos !!!