Re: [HCDX] Dxers Unlimited´s mid week edition for 10-11 June 2008

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

Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited´s mid week edition for 10-11 June 2008
By Arnie Coro
Radio amateur CO2KK

Hi amigos radioaficionados around the world and in space… I am Arnie 
Coro,radio amateur CO2KK, your host here at RHC´s twice weekly radio 
hobby program. Now here is item one: Extremely low solar activity 
continues, with the effective sunspot number reaching just 2 units 
during the Monday morning hours local time in Havana, that is from 11 to 
15 hours UTC. All the world´s ionospheric vertical incidence sounders 
are registering a very weak ionosphere, due to the very low free 
electrons count per cubic centimeter, that is the yardstick used by 
scientists to measure ionization. Maximum useable frequencies at the 
peak times are not exceeding more than 25 megaHertz, and then this is 
happening for very short periods of time. So, if you happen to pick up 
DX signals on frequencies above 25 megaHertz, you can be sure that they 
are reaching you via the Sporadic E clouds that are typical of this time 
of the year and that have nothing to do with solar activity. Item two: 
From time to time the world receives news about a sensational new 
antenna system … it happens over and over, only to end up to be yet 
another scam to funnel money into the pockets of bandits, or in the best 
case, the claims for the ultra miniature antennas with the efficiency of 
a huge rhombic or curtain array may come from someone that , although 
honest may be absolutely ignorant of electromagnetic wave theory… This 
seems to be the case with a Swiss invention, quote , unquote on the word 
invention, that goes under the name of the ROOMCAP antenna, whose 
inventor claims that the 1.5 meters long piece of metal and a coil is 
capable of replacing a full size half wave dipole antenna on the lower 
frequency amateur bands. The inventor, again quote, unquote on the word 
inventor, refuses to provide information about his antenna, and is 
requesting one hundred dollars to be paid to him for a compact disc with 
the instructions on how to build his ROOMCAP magic antenna… Recently he 
posted yet another message on one of the popular antenna e-mail lists , 
asking list members to visit a web site where he is showing the latest 
test of his antenna , something I did at once, only to find that the 
antenna test is a comparison between a two wavelengths horizontal loop 
and the very short
1.5 meters long ROOMCAP placed on the roof of a small car…
And amigos, that is like comparing apples and oranges, because the Swiss 
inventor is ignoring the standard procedure to field
Test HF antennas that calls for installing not one but two reference 
antenna systems, a quarter wave vertical monopole over a ground screen 
of 120 quarter wave radials, and a vertical half wave dipole, with the 
lower branch of the dipole at a quarter wavelength above the ground, and 
fed with a transmission line that must leave the center of the elevated 
vertical dipole at a 90 degrees angle …
So amigos, be aware that false claims about small HF antenna´s 
performance are constantly appearing , especially now that it is so easy 
to create a website and fill it with what best could be described as 
rubbish…
More radio hobby related items coming up in a few seconds when the mid 
week edition of Dxers Unlimited continues in just a few seconds… I am 
Arnie Coro in Havana…
………………..

Si amigos, you are listening to Radio Havana Cuba´s Dxers Unlimited 
radio hobby program and now here is item three of
today´s program, our technical topics section that will be dealing a bit 
more about simple homebrew radios, the ones that you can show with pride 
to family and friends while bringing in loud and clear several of the 
world´s international broadcast stations.
I remember a few years ago , when a friend visited my shack and left 
with a small plastic bag full of electronic components and two circuit 
diagrams that I had drawn for him. Two days later he calls me on the 
phone and says… Coro, listen to this, and sure, I was able to hear our 
own Spanish language program over the phone line… Amigo Carlos then said 
that what I was hearing was coming out of the radio he had just 
completed to build following the first of the two circuit diagrams he 
had taken home . That radio receiver was picking up our 12000 kiloHertz 
transmission from the Bauta transmitting center with just a one meter 
long wire antenna attached to it. Carlos then told me that the 
regeneration control was working very smoothly and that he was able to 
pick a popular amateur radio morning round table on 40 meters by 
advancing the regeneration control until the single side band signals 
were received clearly. Now listen to this: the circuit diagram of that 
radio uses just four active devices, draws very little current from the 
power supply and can be built into a very small box. The three 
transistors used are common NPN type signal devices that Carlos recycled 
from a TV set, and the integrated circuit audio amplifier was the LM380 
IC I gave him.
Carlos told me that he had wound several coils, and that so far he was 
able to pick up stations from the low end of the AM broadcast band up to 
the 19 meters or 15 megaHertz international short wave broadcast band. 
He then asked about the possibility of switching the coils , so I 
started to look into my parts bins to see if I could find a dual pole 
three, four or five positions wafer switch, and fortunately my search 
was rewarded with the finding of a very nice looking ceramic wafer 
switch, two poles and five positions that Carlos has already put to good 
use in a second radio he has built…He has left the first experimental 
receiver that was mounted on a small piece of half inch plywood, as a 
demonstration project to be taken to our next radio club meeting, as 
there are many other club members interested in home brewing simple 
receivers… Carlos and I talked about the tools that he had used to build 
the two radios, and he said all he needed to homebrew the radios where a 
30 Watts soldering iron, a set of long nose pliers, a side cutter plier 
and a small screwdrivers set, plus his digital multi meter . Carlos 
knows how to identify the different electronic components very well, and 
he also is good at following a circuit diagram, two very important 
elements that are essential requirements if you want to start 
homebrewing radios.
Si amigos, yes my friends, oui mes amis, developing your skills to 
homebrew radio equipment is one of the 84 ways of enjoying this 
wonderful hobby , yours and mine: RADIO…
…..
QSL on the air, YES, QSL on the air to Dxers Unlimited´s listeners that 
have requested the Polyakov simple short wave
Receiver circuit diagram… I now have ready here a small text file with 
more information about that very simple circuit , that uses just two 
signal diodes , a transistor injection oscillator and a two transistors 
audio amplifier … Of course amigo Kevin that you can add an integrated 
circuit audio amplifier following the two transistors of the receiver´s 
audio stage, and that will bring up the set´s volume to room filling 
levels… But, you will need more current from the power supply, so the 
batteries will last much less than when they are feeding just the three 
transistors of the original receiver design. Answering amigo Edward from 
the UK, I must emphasize that the Polyakov detector is not your best 
option for listening to AM stations , because you must keep the 
frequency of the injection oscillator within just a few cycles per 
second from the AM station´s carrier frequency or otherwise your audio 
will show a sort of growling sound that is very annoying. Do remember 
that the Polyakov detector requires that the local injection oscillator 
operates at half the receiver´s frequency , something that is very 
useful as it is easier to make oscillators more stable when they operate 
on lower frequencies. As a matter of factI have used the Polyakov 
antiparallel diodes mixer,that by the way is the correct name of the 
circuit, to down convert a 2 point two GigaHertz signal to a 144 
megaHertz IF, and it worked very well also in this particular 
application. When used as a product detector you actually have two main 
frequencies at the output, and one of them is, of course, the audio from 
the station you want to hear !!!. As compared with a four diode double 
balanced product detector, the Polyakov twin antiparallel diodes product 
detector has several advantages, and one of them is the fact that the 
injection oscillator frequency is operated at half of the signal 
frequency…For those of you that have not yet sent a request for the dot 
pdf file of the ultra simple 40 meters amateur band Polyakov detector 
receiver, let me remind that the e-mail address to send your request to 
is inforhc@xxxxxxx, again slowly and using the phonetic alphabet… 
inforhc@xxxxxxxxxx It is a very small size computer file that is sent as 
an e-mail attachment, as a matter of fact it is only 32 kilobytes of 
data so it will be downloaded just after pushing the download key of 
your computer.
…………….
Just to complete the information about the easy to homebrew Polyakov 
detector receiver for the amateur bands, let me add that a 30 meters 
band version requires the use of a five megaHertz variable frequency 
oscillator, that at the same time provides an excellent calibration 
mark, because you only need to zero beat the five megaHertz injection 
oscillator to any time and frequency standard station that uses this 
frequency or also 10, 15 and 20 megaHertz. The amateur 30 meters band 
starts at 10.1 megaHertz and it is a digital modes only ham band, in 
other words you won´t hear any phone stations from 10.1 to 10.150 
megaHertz, or at least you should not hear any voice signals there, 
although from time to time illegal stations do use that range of 
frequencies for their outlaw activities… The ultra simple receiver uses 
a one transistor variable frequency injection oscillator, but a more 
sophisticated , and of course more complicated version uses a classic 
three transistors VFO or variable frequency oscillator, that is made of 
a Colpìtts oscillator stage, followed by a two transistors buffer for 
optimum isolation. Using a field effect transistor for the oscillator 
stage increases both long term stability and makes the circuit less 
sensitive to small voltage and temperature variations, because the FET 
or field effect transistors are high impedance devices that provide much 
better performance than bipolar transistors when used in oscillator 
circuits.
…………

ASK ARNIE , si ASK ARNIE, yes ASK ARNIE is the most popular section of 
this program, and Dxers Unlimited listeners from all around the world 
send their questions that when answered here have made possible for many 
other listeners to learn more about radio and solve some practical 
problems too. Today´s question sent by Jonathan from Lagos in Nigeria is 
typical of type of request I get here every day, Jonathan wants to know 
what would be the best amateur band or bands to set up at his soon to be 
on the air ham radio station, and he adds, Arnie , of course that I am 
looking for your answer regarding the relation between the present phase 
of the solar cycles and what may be or may not be worthwhile . Well 
amigo Jonathan, the two solar cycles are now in what is the beginning of 
an overlap period that may extend for a period even as long as a year, 
and solar activity is going to remain within effective sunspot numbers 
that won´t go higher than 20 units… Under such circumstances, my advice 
is that whatever resources you are going to invest on your ham radio 
station, should go to antenna systems from 160 meters to 20 meters, with 
perhaps a very simple wire antenna added for operation on the bands from 
17 meters to 10 meters. You will find that most of the time , at this 
phase of the solar cycles, frequencies above 18 megaHertz will simply 
won´t propagate trough the ionosphere… But, from time to time, as for 
example during the summer months you may hear some activity on 12 and 10 
meters via sporadic E skip…. Amigo Jonathan , if your budget is limited 
try installing a 40 meters band half wave dipole as high and as in the 
clear as possible, and add to it a pair of twenty meters band elements, 
so that you will end up with an effective three bands antenna… The 40 
meters band dipole, the 20 meters band dipole that are both half 
wavelength resonant antennas and then your 40 meters band antenna will 
also perform quite nicely as a three half waves center fed system on the 
15 meters band. If you are planning to use , as you explain in your 
e-mail a modern high tech solid state transceiver with a built in 
automatic antenna tuner, feeding the above mentioned antenna with 50 
ohms coaxial cable via a one to one balun will allow you to enjoy 
amateur radio during the next two years or so, and allow enough time for 
the future installation of a rotatable multiband Yagi antenna that will 
provide optimum performance during the peak years of the new solar cycle.
And now as always at the end of the show here is Arnie Coro´s Dxers 
Unlimited´s HF plus low band VHF propagation update and forecast… Very 
low solar activity, just one sunspot active region in sight, a lot of 
sporadic E skip all over the northern hemisphere, including great 
double, triple and even four hops propagation events… See you next 
Saturday and Sunday UTC days at the weekend edition of the program 
amigos… !!!


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