Re: [HCDX] Dxers Unlimited script for 6-7 February 2007

["Prof. Arnaldo Coro Antich" <inforhc@xxxxxxx>]

Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited’s mid week edition for February 6-7 2007
By Arnie Coro
CO2KK

Hi amigos radioaficionados, with our traditional salute to those of you 
that are listening to this radio hobby program around the world, it’s my 
pleasure to share with you about seventeen minutes of air time, and also 
we are now regularly on the the world wide web with streaming audio from 
our website www.radiohc.cu, from 05 to 07 hours UTC…
Now here is item one, our number one most popular section of the show… 
ASK ARNIE, that today is answering a letter
that came via e-mail from Atlanta, Georgia, USA. Here is the letter…
Dear Arnie:
I heard your show on Saturday February 3, 2007 and found it very 
interesting.  Reception in Atlanta was excellent.  In particular the 
segment about front end filters and amplifiers.  Could you please email 
to me a copy of the materials describing your filters and amplifiers.

Thank you.
Signed
Joseph
Now here is part one of my answer to amigo Joseph…
Dear amigo:
Thanks for the reception report.It would be nice to know on what 
frequency you had such an excellent reception...as we are using several 
frequencies to your part of the world, and also the show is on the air 
at different times of the day.
As regards to your request, I will send you detailed information about 
the "boxes" that I have designed and built to improve short wave 
receivers front ends,including the schematic diagrams.
I also use them on my homebrew receivers with excellent results.
First of all you and all short wave listeners must realize that there 
are huge signals now present all along the short wave spectrum, that 
come from very powerful transmitters running up to 500 and even 1000 
kiloWatts that are then connected to antenna systems that concentrate 
the power into a very limited target area, so the so called effective 
radiated power may be in some cases up to 100 megaWatts, or one hundred 
million Watts !!!
So, radio receivers have to deal with those huge signals at their input 
a problem that becomes especially difficult when the radio is connected 
to a large size external antenna.
Signals present at the antenna input terminals of the receiver are
really significant, and they may generate many problems, like something 
  known as cross modulation , that makes reception of the desired 
station practically impossible because the very powerful signal from 
another station mixes with the desired station making listening 
extremely difficult.
That's why even a very simple antenna input attenuator connected between 
the external antenna and the radio receiver helps so much in providing 
better reception. Even a good quality carbon potentiometer of between 
500 and 2000 ohms will help a lot to improve reception, especially in
the case of low cost receivers that don't have very good front end 
selectivity.
A better option is a resistive STEP ATTENUATOR, that may even be 
calibrated in DECIBELS OF ATTENUATION , something that may prove to be 
quite helpful in assesing the signal strength of different stations.
The STEP ATTENUATOR that I use here is calibrated in the following steps 
0 dB attenuation, that is antenna connected directly to the receiver's 
antenna input 3 dB attenuation, that meaning that half of the signal 
power is attenuated
10 dB attenuation, that meaning that the signal reaching the receiver is 
one tenth of the signal available at the input
20 dB attenuation , that meaning that the signal reaching the receiver 
is one hundred times less than the signal at the input of the attenuator 
and finally 30 dB , which is rarely used, but still useful when doing 
some tests, and , of course 30 dB means that the power available at the 
receiver's
antenna terminals is one thousand times less than at the input of the 
attenuator.
It is really amazing to operate a low cost portable short wave receiver 
using a properly connected external antenna via an input  resistive 
attenuator.
In another e-mail and also here, on the air , for the benefit of other 
Dxers Unlimited’s listeners, I will describe  the tuneable bandpass 
input filters that will complete my "number one box".... a piece of 
equipment that for some odd reasons no commercial manufacturer of radio 
accesories is offering to the worldwide radio hobby community, making it 
necessary for individuals to homebrew them...

Now standby for a few seconds , a station ID follows…
I am Arnie Coro , radio amateur CO2KK in Havana, stay right on this 
frequency or keep connected to www.radiohc.cu
Amigos !!!

………………
This is Radio Havana Cuba, the name of the show is Dxers Unlimited, and 
yes amigos, we do QSL, we do verify reception reports with a beautiful 
QSL card that is sent VIA AIR MAIL and absolutely free of charge, as we 
believe that every international short wave station must QSL to its 
listeners as a nice thank you gesture for listening !!! Now here is item 
two of this mid week edition of the program…The also very popular 
antenna topics section… Monday afternoon I had a nice two way contact 
with CO3LE , Eduardo, who is an amateur radio operator that lives about 
50 miles away from my home. I had perfect copy from his low power two 
meters band amateur station, and when I asked him what he had done to 
improve his signal into the Cuban capital so much, he replied that he 
had just finished building and installing a nine elements Yagi antenna 
that I designed several years ago for my son Arnie Junior CM2KW amateur 
radio station. Eduardo CO2LE reduced the power output of his FM two 
meters band transceiver to just one Watt and I was still able to copy 
him with my zero dB gain omnidirectional antenna.
This nine element Yagi antenna does need a rotor , because its radiation 
pattern is very sharp, requiring that it be aimed very precisely to the 
station you want to contact. Eduardo , who is a very good mechanic also, 
has designed and built a homebrew rotor using a large truck’s windshield 
wiper motor, to which he added a control box and power supply, as well 
as stop limit switches… The 24 volts DC motor has a gear train with a 
very large ratio of revolutions delivered by the motor to the 
revolutions delivered by the gear train , so the antenna takes about one 
and half minutes to sweep around the 360 degrees of the compass, that is 
a very speed for turning around a directional antenna system… faster 
speeds make aiming the antenna difficult, and slower ones will take a 
very long time to complete one revolution…Given the high cost of antenna 
rotors , Eduardo’s project may prove to be a very attractive option for 
radio hobby enthusiasts that also enjoy doing mechanical work… He has 
promised to bring to Havana on his next trip the complete diagrams of 
how he has built the antenna rotor using a big truck windshield wiper 
motor, an item that can be found in many scrap yards at very low cost or 
just by asking for it…
These direct current motors and their gear trains are very rugged and 
well built, and only second to the superb aircraft windshields wiper 
motors and gear trains, that are, as expected , designed and built to 
much higher standards…
……..
Now here at Dxers Unlimited’s mid week edition is our next item…. The 
technical topics section, that today will deal about a very useful radio 
hobby shack accessory… a variable voltage direct current power supply, 
capable of delivering well filtered and regulated DC between 1.5 volts 
and 24 volts… a range that will provide the possibility of testing and 
operating a large number of electronic devices.
The prototype of this supply is capable of delivering up to 5 amperes of 
current, and its construction is rather simple, because it uses an 
integrated circuit voltage regulator that is installed on a large size 
heat sink. I have included two analog meters, one to measure the voltage 
using two scales,
One from zero to five volts, and the other from zero to twenty five 
volts, although recently a friend that visited my workshop suggested the 
use of yet another expanded scale so that the voltmeter will read from 9 
to 25 volts, so that more precise adjustments could be made in that very 
useful voltage range.
The current meter is calibrated in five scales, ranging from
500 milliamperes to 5 amperes, so that one may have a good idea of the 
current drawn by the equipment connected to this variable voltage 
workbench power supply, something very useful when one is attempting to 
do repair work, or when a nice piece of equipment is undergoing its 
first rounds of testing.
…….
Si amigos, yes my friends, digital communications systems are offering 
amateur radio operators the possibility of communicating under the very 
poor propagation conditions that are typical of the lowest activity 
phase of a solar cycle, like the conditions that we are having to deal 
with at this moment, and with the much lower night time maximum useable 
frequencies available, we are now seeing many more stations operating on 
40 meters using the very popular and rather easy to put to work PSK 31 
keyboard to keyboard digital communications mode…
Stations using PSK31 on 40 meters are gathering around 7070 kiloHertz as 
a center frequency,and the classic waterfall display is seeing many 
carriers of PSK31 stations on that frequency just after sunset local time…
And now amigos, as always at the end of the show, here is our exclusive 
and not copyrighted HF plus low VHF band propagation update and 
forecast. Let me start my telling you that February is the month of the 
year with the lowest probability of Sporadic E events…, so although 
sporadic E events may happen they are very rare at this time of the 
year.  REDICTIONS FOR 06 Feb 2007  10CM FLUX: 082 / AP: 007
PREDICTIONS FOR 07 Feb 2007  10CM FLUX: 081 / AP: 010
PREDICTIONS FOR 08 Feb 2007  10CM FLUX: 081 / AP: 010
COMMENT: Solar activity was very low during the last 24 hours. No flares 
above C level are expected for the next 72 hours.
Geomagnetic activity was very low during the last 24 hours. Quiet 
conditions are expected for the next 78 hours. The solar wind speed 
measured by the ACE spacecraft slightly increased to 400 km/s.
Optical sunspot number was at 16 on Monday,
Hope to have you all listening to Dxers Unlimited’s weekend edition 
amigos,and don’t forget to set aside a little time to send me Yours 
truly, signal reports and comments about today’s program to 
arnie@xxxxxx, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, 
Cuba.


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