Dxers Unlimited weekend editions
by Prof. Arnaldo Coro Antich
radio amateur CO2KK
Radio Habana Cuba
Radio Havana Cuba
Dxers Unlimited midweek edition for 8-9 June 2010
By Arnie Coro
radio amateur CO2KK
Hi amigos radioaficionados …sure, your are most welcome to the weekend edition of your favorite radio hobby program .
I am Arnaldo, Arnie, Coro, your friend in sunny Havana, where , once again, we are observing due to the rather low solar flux , but things have taken a turn for the better this Tuesday, following the sightings of three new sunspot groups have suddenly appeared on the solar disc... they are not large size sunspot regions, but at least one of them is growing at a fast rate... So, we may see the solar flux moving up from the almost baseline levels of the past few days.
Item two: I received several e-mail messages from listeners saying thank you Arnie for the tips regarding the three Tropical Broadcast Bands... known as 120, 90 and 60 meters, because they were named in the old days when meter wavelengths were used to define the short wave bands instead of making reference to the frequencies...
But again, I must emphasize that stations that can be heard at one specific location may not be heard at all at a different geographical location. So be aware when you hear on some radio Dxing hobby programs those endless lists of stations with their operating frequencies and time tables, that all that information may be absolutely worthless at your particular location amigos !!!
Item three: Minimum parts count homebrew short wave receivers can provide amazing performance when connected to a good antenna system. For example, tests done at CO2KK, my ham radio station using a receiver that has a total parts count below the 50 components mark, show that on the 40 meters band, during daytime propagation conditions, the little radio proves to be very effective and capable of providing excellent reception of even low power stations . Running comparisons with an excellent , home station receiver showed that the ultra simple direct conversion Polyakov harmonic detector radio is a nice option for emergency work, especially if you take into consideration that it runs under battery power and requires very little current to provide good audio output to a loudspeaker.
The use of a dual tuned bandpass input filter and a user friendly signal attenuator makes possible to use the Polyakov harmonic detector receiver for emergency communications activities, as a useful backup radio.
Stay tuned for more radio hobby related information amigos, it's coming to you from Havana, with solar flux now moving up past the 72 units mark and still climbing... I'll back with you in a few seconds after a short break for station ID.
This is Radio Havana Cuba, the name of the show is Dxers Unlimited, and you are now continuing to listen to the mid week edition of the program. I am Arnie Coro your host , and here is item four:
So far the Atlantic , Caribbean and Gulf of Mexico tropical hurricane season has proven to be very quiet... eight days after it began, there are no signs of areas that may develop into active storm regions...but due to the high sea surface temperatures weather experts are keeping a close watch... while radio amateurs continue to prepare for what has been described as a really active hurricane season.
Cuban radio amateurs will soon be participating in the second phase of the Meteoro 2010 emergency drill, where they will be testing several new recently installed two meters band repeaters provided with extra rugged antenna systems and backup emergency power.
In the Dominican Republic members of the International Amateur Radio Union national affiliate, the Radio Club Dominicano are also getting ready to provide much needed EMCOMS, or Emergency Communications when they are required.
During the past several hurricane seasons national radio societies of Mexico, Cuba, the Dominican Republic , Turk and Caicos Islands, and Jamaica have developed a highly succesful cooperation that has included relays required when propagation conditions on the 40 meters band made communications with nearby stations impossible.
The vulnerability of 2 meter band repeaters located on top of high rise buildings or at mountain top TV and FM stations transmitters sites, has made it necessary to activate 40 and 80 meters bands stations that are capable of providing emergency links without the use of the repeater systems. When propagation conditions make it difficult to establish short distance links, then radio amateurs make effective use of long distance relays that may be located hundreds or even up to two thousand miles away. During hurricane Wilma's devastating path over the Yucatan Peninsula, Cuban radio amateurs all over the island kept Mexican stations in constant touch with the capital city , by means of relays originating from different locations here in Cuba....
Some time later the effective IARU Region II Area C cooperation
worked “ in reverse” when Mexican amateurs provided links for Cuban
stations handling emergency traffic during a following
Item six: It's ASK ARNIE... la numero uno, the most popular section of Dxers Unlimited, that has helped listeners around the world not only to learn more about our wonderful hobby, but also to fix quite a few radios too... Today's question came from Australia, listener Barry wants to know if it is true or not that one can make a shielded balanced transmission line just by placing to coaxial cable lengths together and connecting the shields or braids of the cable at both ends... He also wants to know what will be the resultant impedance of that balanced shielded transmission line. Well amigo Barry, the answer is YES... and connecting the shields together at both ends of the two coaxial cables works very well indeed. The impedance will be twice the value of a single unbalanced coaxial line.
For example, my 150 ohms shielded balanced transmission line that is feeding a broadband fan dipole antenna here , is made by paralleling two 75 ohms type RG11U cables... The advantage of using this shielded parallel line compared to an unshielded one, is that it can be routed to the antenna tuner without the need of installing line support posts and special insulated gates to bring into the building the open wire line.
Losses with the dual balanced coaxial cable feedline are much higher than what you will be expecting from open wire lines, but if the cable runs are not too long, this system works very well and effectively blocks noise pickup due to the shielded nature of line.
And now amigos at the request of many listeners, htere is again the report about the Polyakov harmonic detector ham bands receiver so.. QSL on the air to the many listeners that have shown their interest in learning more about the low parts count, single band ham radio receiver that uses the amazing Polyakov harmonic detector circuit for detecting the signals coming from the antenna and turning them directly into audio.
I am in the very interesting process of testing the performance of different types of diodes... from antique germanium point contact glass encapsulated diodes, to the most up to date third generation hot carrier diodes...
As expected, and that was no surprise, the expensive high tech hot carrier diodes provided the best performance, but , the difference observed between a pair of common silicon computer switching diodes, type 1N4148 and the hot carrier devices was really hard to detect, becoming significant only when receiving very weak signals.
I even went further and used a pair of not very well matched diodes, again finding out that the difference in performance was very , very small, but of course that I recommend that you carefully match the two high speed silicon switched diodes before installing them to the receiver's printed circuit board.
This little gem has become a basic building block that will form part of a low cost , yet highly useful, single band ham radio transceiver, that follows the so called low parts count philosophy.
Again, as stated during previous programs, we do have at hand the dot
pdf files of several versions of the low parts count Polyakov harmonic
detector low parts count receivers... that can be built using mostly
recycled electronic components, many of them having been desoldered from
broken compact fluorescent light bulbs circuit boards.. Assembling your
own direct conversion receiver using the marvelous Polyakov product
detector circuit is a lot of fun, and once you have it working, it will
become one of your favorite receivers without any doubts. The very low
parts count , straightforward circuit offers an amazing performance, and
I simply can not find an answer to a question sent by several listeners
regarding why there are no commercially built or kit radios using this
type of detector...
You are listening to the weekend edition of Dxers Unlimited, coming
to you from Havana, via short wave and also from our streaming audio
service located at www.radiohc.cu...
Si amigos, again a reminder that the summer solstice is just around the corner, and with it, we will be seeing a very interesting phenomenon that I have been closely monitoring during the past week... the maximum useable frequency curve is showing show its peak after local sunset, something that is caused by the thermal expansion of the ionosphere during the daytime and the corresponding contraction as soon as the Sun sets over a part of the world...
And before I forget, let me remind you that my newly designed KK-5 Mark Two Hula Hoop Magnetic Loop Antenna, is very easy to homebrew, and works very well as a receive only antenna system within the frequency range from 10 to 30 megaHertz. By winding more or less turns using the PVC plastic loop tubing as a coil form, it is possible to make this antenna resonate down to even the 40 meters band, and it will work OK there for receiving, but the efficiency will be very low indeed when transmitting. The fact is, that due to its characteristics my KK-5 Mark Two Hula Hoop Magnetic Loop has a very high Q and thus is a very narrow banded antenna.
As a matter of fact it can be put to very good use at locations where high ambient man made radio frequency noise makes operation of a ham radio station difficult. You can learn more about Arnie Coro's KK-5 Mark Two Hula Hoop Magnetic Loop by sending an e-mail to inforhc at enet dot cu, again inforhc at enet dot cu... or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
And now amigos as always at the end of Dxers Unlimited, here is Arnie Coro's HF plus low band VHF propagation update and forecast. Solar activity moving up, three new small sunspot regions now easily seen with simple telescopes equipped with image projection devices... Expect more sporadic E openings from 9 Am to 12 noon local time, and another peak starting from 4 pm to 8 pm local time...
Don't forget to send me your signal reports and comments about the program amigos... Send e-mail to inforhc at enet dot cu … and VIA AIR MAIL your letters and postcards will be received at the following address Arnie Coro, Radio Havana Cuba, Havana Cuba...