DXERS UNLIMITED
MID-WEEK EDITION
10-11 February 2004
Hi amigos radioaficionados ! Excellent propagation conditions on the HF bands
were observed here in Havana since early Monday UTC day, exactly as our
exclusive and not copyrighted weekend propagation forecast had
predicted !!! Early morning Tuesday, the amateur 20 meters band was in excellent
shape for long haul DX, and several international shortwave broadcast stations
on the adjacent 19 meters of 15 megaHertz band could be
heard on my ultrasimple crystal radio... YES,you heard it right... signals on 19
meters were so strong, that I took my ultrasimple crystal radio, connected it to
the extended double zepp or EDZ antenna's downlead and WOW
!!! No less than four stations could be heard , with two of them coming in
pretty loud on the high impedance magnetic headphones... NOW, you must realize
that this crystal set has absolutely no power supply ... the
signal coming in from the antenna is simply detected and the resultant audio is
coupled to the high impedance headphones !!! My ULTRASIMPLE short wave bands
crystal set is extremely easy to homebrew, and you may want to build one just
for fun... If you happen to have a nice and long wire antenna, chances are good
that your ULTRASIMPLE will bring in at least some stations on the 49 megaHertz
or 6 megaHertz international short wave broadcast band during your local evening
hours.... Reception on the higher frequency bands is not as easy... but, as I
said at the begining of the show, propagation conditions since Sunday evening my
local time are so good that signals have reached very high field intensity level,
so high in fact, as to allow the ULTRASIMPLE receiver to pick up several
stations on the 19 meters or 15 megaHertz band...Item two: QUESTION... sent in
by a listener in Puerto Rico... Arnie, how long will it take for solar cycle 23
to reach its minimum... ANSWER.. amigo Jose, solar scientists are predicting the
end of cycle 23 sometime between the years 2006 and 2007... but let me add that
solar cycles don't come to an abrupt screeching tires halt... what happens is
that the cycle that is ending and the one that is starting will co-exist for a
while... and observers can see sunspots from the old cycle and sunspots from the
new one at the same time...Now amigo Jose, let me add that the period between
now and the year 2009 will provide us with rather low solar activity, making
reception of the bands above 20 megaHertz less and less frequent... So , if
possible, try to install an external antenna for improving reception between 5
and 15 megaHertz so that you may continue to enjoy short wave listening during
the solar minimum years...
Item three: It's going to be our technical topics section..Item four QSL on the
air, and at the end of the show , as always... our exclusive and not copyrighted
Dxers Unlimited's twice weekly propagation update and forecast... Stay tuned,
I'll be back after a short break...
.....
Si amigos , this is Radio Havana Cuba, the name of the show is Dxers Unlimited
... I am Arnie Coro in Havana, and the show continues with our popular technical
topics section...Si amigos, yes my friends, oui mes amis... radio is certainly a
technical hobby , and that's one of its most attractive aspects for technically
minded persons...learning the technical aspects of radio and experimenting is a
lot of fun ... for example, experimenting with antennas can prove to be
addictive... homebrewing antennas and comparing results forms part of this hobby,
and many radio clubs around the world encourage their members to bring their
antennas to yearly field events , where sets of professional measuring
instruments and antenna experts provide club members with actual objective
measurements of their homebrew antennas compared to standard reference ones. Of
course
that the only antennas that can be readily transported are the ones used at VHF,
UHF and Microwave frequencies... and that's why the antenna measuring
competitions take place on those frequencies... I have had the opportunity of
participating in several antenna gain measuring contests , and all I can say is
that it was a lot of fun !!! The competitions have to be held in an open field ,
out in the clear, level land... with at least several hundreds of wavelengths at
the lowest operating frequency completely clear of any obstacles... The standard
procedure is to install two operating tables... one for transmitters and the
other one for the measuring equipment... The antenna experts will tell you that
they will always do comparative and not absolute measurements... and that's done
using at least one reference or standard antenna, very carefully built following
a design that provides a predictable gain... The other approach is to use a half
wave dipole at the frequency were antenna gain is to be measured, and then
reference all measurements to the dipole... something you will see in antenna
literature as dBd, meaning decibels of gain or loss compared to a standard half
wave reference dipole. Transmitter power needs to be measured with a high degree
of precision, and the use of a very well calibrated step attenuator is
essential... Once the antenna measuring range is up and running, you will have a
lot of fun watching the faces of those submitting their antennas to the tests...
sometimes huge Yagis with many elements will show less actual gain than a
smaller , but better designed one... you will learn why your friend Arnie Coro
advises not to use the 2 meters band hand held FM radios rubber duck antennas...
as measurements will typically show that they are at least - 6 dB below a
reference dipole , and some of those helically wound rubber encapsulated
antennas sometimes have -9 and even -10 dB loss , turning a lot of the handie
talkie's power into heat , and also making reception much more difficult...
Antenna measuring competitions are outdoor activities that will provide radio
club members with a nice opportunity of learning more about the hobby, having
fun, and going back home with a full set of antenna data that can never be
obtained without the use of sophisticated equipment and the know-how of antenna
experts...By the way, the last time I was present at an antenna measuring
competition, someone came with a
simple half square antenna for the 2 meters band made of number 10 copper wire
and PVC pipe sections... the antenna was measured and it provided a bit over 4
dbd, or 4 decibels above the reference dipole, and showed a very nice and clean
radiation pattern shaped like a number 8, making it an ideal antenna for a home
or portable station that can be built at very low cost, and that needs almost no
adjustment when fed with 50 ohm coaxial cable...
After seeing that HALF SQUARE coming out so well at the field tests, that's one
I am recommending to users of the two meter amateur band... If you already own a
two meter band handie talkie, I can provide you with the
easy to understand instructions that will help you build the WIRE AND PVC HALF
SQUARE for the two meter band , send an e-mail to arnie@rhc.cu, and you will be
receiving the HALF SQUARE INFO PACKAGE real soon... And when you write, don't
forget to add a signal report and comments about the program to your e-mail !!!
.....
This is Dxers Unlimited coming to you from Havana, and here we are enjoying
beautiful weather... at 10 AM local time Tuesday when I was preparing the HF
propagation update and forecast, the sky was completely blue, ceiling unlimited...
and the temperature was a nice and comfortable 25 degrees Celsius , with the
relative humidity hovering around 60 percent... Gorgeous weather, so nice indeed
that I took a little break to go out to the garden and take a look at the bird
feeder antenna... Yes, that's right, my backyard garden has a bird feeder that
also doubles as an antenna for the six and two meter bands...The pole that
supports the feeder is a vertical antenna for 6 meters, that I keep connected to
a converter and receiver for monitoring possible openings.. Atop the bird feeder
is a two meter band antenna,and both are fed with the same coaxial cable that
reaches the bird feeder by way of buried PVC pipe...I took a fifteen minute
break enjoying Cuba's winter weather... and came back to writing the script at
10 AM local time, 15 hours UTC... A quick scan of my desktop digital receiver
told me that the 10 meter band was closed,totally closed, as I couldn't hear any
of the familiar automatic beacons that tell you that signals are propagating,
15m meters was open with several two way
QSO's in progress using the 21070 kiloHertz spot frequency for the PSK31 digital
keyboard to keyboard mode... on the 17 meter amateur band at five minutes past
15 UTC a Belgian radio amateur , using single side band voice was in contact
with a fellow ham in Ohio, with several other QSO's in progress on the 18
megaHertz or 17 meters band...The I tuned in to 20 meters and found it in pretty
good shape for skip distances between about
700 and 1500 miles, and 40 meters , as usual during the daytime was in use by
several Cuban radio amateurs using that band's unique near vertical incidence
skywave or NVIS propagation mode...I would had liked to work some DX on 17
meters , but the script of the show was waiting to be finished !!! Anyway, the
short monitoring break removed by eyes from the computer screen, gave me a
chance to walk to the garden and take a short break... Now at 10.20 AM local
time, fifteen hours 20 UTC , I am back writing again... As promised now here is
item four QSL on the air...QSL on the air to amigo George in Colorado, W0HIO is
George's ham radio callsign... he wrote a nice note to me about the passive grid
radio frequency power amplifiers...a topic I have dealt with here and at several
amateur radio technical topics discussion lists... here is what George tells me
in his e-mail:
Hi Arnie
I find your short treatise on the passive grid linear amplifier quite
interesting......so much so that I looked up the articles by G2DAF and others
about this system......In the original article by G2DAF, ie the R.S.G.B.
bulletin April, 1963, he talks about this linear amplifier being used in SSB
service........my question to you is do you know if this circuit would work as
an Amplitude Modulated linear amplifier? Are the units you constucted used in
the SSB mode, or AM, or both?Thank you so much for your time. I always enjoy
reading your comments on the Glowbug website. Cheers........
73 George Dittmar W0HIO
Well amigo George, thanks for your nice comments, and let me tell you that I
never attempted to use the passive grid amplifier as a linear to boost an A3A or
amplitude modulated phone signal.. I think it would be quite interesting to set
up a passive grid G2DAF amplifier so that it would amplify an AM signal ! May
initial guess is that it would reproduce the AM envelope waveform and that its
overall efficiency will be higher than the
33 percent expect from a classic class B linear amplifier when running AM... If
you have time to run the test, please do it,and tell us about your results !!!
And now amigos , as always at the end of the show, here is Arnie Coro's HF
propagation update and forecast...HF conditions are expected to degrade by
Thursday when the effects of the high speed solar wind coming from a coronal
hole will be starting. Solar flux was hovering around 120 units, and will
probably start to move down by the end of the week. Expect openings short
opening on 28 and 24 megaHertz , and longer band openings on the 21,18 ana 14
megaHertz amateur bands. Best daytime reception on the internatinal short wave
broadcast bands is going to be on 16 and 19 meters and around sunset, 25 and 31
meters will provide good reception. See you all hopefully at the weekend edition
of the program, in the meantime enjoy the nice HF propagation and don't forget
to send your signal reports and comments about this show as well as any radio
hobby related questions you may want to ask ... Send mail to arnie@rhc.cu, or
via AIR MAIL to Arnie Coro, Radio Havana
Cuba,Havana, Cuba.