Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited's mid week edition for Tuesday-Wednesday 2 -3 November 2010
By Arnie Coro
radio amateur CO2KK

Hi amigos radioaficionados... I am welcoming you all with our traditional salute... Hi amigos radioaficionados ! This is the mid week edition of your favorite radio hobby program, the one and only always attempting to provide you with information about all the possible ways that you and I can enjoy this wonderful hobby... from experimenting on frequencies below 9 kiloHertz that apparently do not require licensing as yet, to helping a young person
to assemble her or his first radio receiver... from watching the Sun with a special telescope to detect the presence of sunspots to ending up pretty tired after participating in a 48 hours long ham radio contest... Yes amigos, oui mes amis, Si my friends, there are more than 86 ways of enjoying the wonderful and always challenging radio hobby...
Here is a good example in today's Dxers Unlimited item one: Big worldwide contest during the weekend... short wave propagation conditions were not all that great... nevertheless , I heard several DX stations running very low power, and still making nice two way contest contacts !!! I tried for just an hour or so to work on the 10 meters band with 5 Watts, and made several contacts with stations as far away as four thousand nautical miles from Havana, while using a very simple G5RV wire antenna system... With solar flux below 90 units, this was a good example
of how the big worldwide ham radio contests do make possible nice contacts under marginal band conditions !!!

Item two: A long time Dxers Unlimited listener sent an e-mail asking about a topic that was dealt with here some time ago. Amigo Jonathan wanted to know more about the project of a low cost amateur radio station that could be built using standard and not hard to find electronic components... Well amigo Jonathan , the receiver of that project was completed at the begining of this year, and so far has proven to be not only quite sensitive, but also
very reliable. It is a solid state direct conversion radio receiver , based on the use of common NPN silicon transistors... As a matter of fact, I even tried to make one of the prototypes using the same transistor type for all the receiver circuits, just like it was done by K8IQY, Jim Kortge
a US radio amateur that designed a series of ham radio equipment that used only 2N2222 type general purpose transistors. In my prototype, I used a locally available clone of the 2N2222 with excellent success. So amigo Jonathan, as I always done, this answer on the air to your
question has already also been sent via e-mail, directly to you , with the complete details and circuit diagrams of the Super Islander Version 5.1 receiver... By the end of 2010, I am almost sure that the prototype transmitter to match this radio will be completed... At this moment the big stumbling block is the lack of the proper NPN silicon output transistors capable of delivering around 25 Watts, a power output level that according to my long time experience with short wave propagation on the 40 meters band, is the minimum power that will provide
reliable communications links under poor propagation conditions.

Standby for a few seconds.. a station ID is coming up, and aftewards , the mid week edition of Dxers Unlimited will continue... I am Arnie Coro, radio amateur CO2KK in Havana...

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This is Radio Havana Cuba, the name of the show is Dxers Unlimited, and this is a program totally devoted to the promotion and development of the radio hobby … Here is now item two of this mid week edition...
When I told a local friend that has a very nice backyard
that he could try an underground antenna to try to reduce the level of radio noise he was having to deal with... amigo Aurelio thought that I was joking... No Aurelio, this is not a joke... you can dig a trench of about 2 feet depth, that is about 60 centimeters, and place inside it a PVC pipe....The length of the trench should be at least 10 meters long, but results with longer lengths of the buried antennas are better... I told Aurelio that his underground antenna
will work nicely on the 40, 30 , 20 and 17 meters bands...And that his noise level will go down dramatically once he finished installing his new stealth antenna system. A few days later I received a phone call from Aurelio, inviting me to have lunch with him and his family
and then finishing to install the underground antenna. We had a nice Saturday lunch, with nice vegetables that Aurelio buys from the nearby organic farming plot, and then, after a short break, we proceeded to place the wire dipole inside the buried PVC one inch diameter
pipe. The antenna was configured as a dipole, with each leg having a total length of 8 meters or about 26 feet. The antenna was fed with 50 ohms coaxial cable, and we went immediately to his ham radio station, connected the coaxial cable to his antenna tuner and started to listen to the 40 meters band... Aurelio was surprised, when he realized how quiet the reception was... The noise level was moving the S meter of his transceiver barely to S1 !!! At the flip
of an antenna switch, we compared the noise level with his 40 meters inverted V … and found out that the noise level had gone down 8 S units... almost 50 decibels !!!
Now Aurelio is compiling the observations he is making every day using the underground dipole antenna and his classic fan dipole that is hanging on his concrete rooftop.... During a phone call he told me that using the underground antenna he was able to log several new stations because of the much better signal to noise ratio that is possible with the buried antenna. I must emphasize that this underground antenna is used at Aurelio's location as a receive only system, and that so far no attempt has been made to use it for transmitting on the amateur bands. A much simpler low profile antenna that achieves quite similar results is the so called SNAKE ANTENNA, that is made by just laying a length of coaxial cable on the ground with the outer braid connected to the inner conductor of the coaxial feedline, and the inner conductor of the antenna connected to the outer braid of the feedline... At the end of the SNAKE ANTENNA , a 50 or 75 ohms terminating resistor is connected... This antenna can be laid over the grass of the yard or over the roofs, and will pick up much less noise than wire antennas installed between tall masts.

Aurelio is going to make a 20 meters long version of the SNAKE ANTENNA and add it to the ongoing experiment … comparing his results with the three antenna systems , the buried wire enclosed inside an underground PVC pipe, the coaxial snake antenna and his wide band fan dipole installed between two masts.
Si amigos, yes my friends , oui mes amis... buried and on the ground antennas have proven to improve the signal to noise ratio at urban locations where short wave reception has become extremely difficult due to the presence of so many different types of noise generating equipment, like computers, TV sets, especially the extremely noisy PLASMA SCREEN television sets, and some less well known urban noise generators like automatic furnaces, tropical fish tanks air pumps, burglar alarms, and even the now more and more common so called intelligent electricity meters !!!
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And now amigos , as always at the end of the program, here is one of the favorite sections of Dxers Unlimited.... Arnie Coro's HF plus low band VHF propagation update...Solar activity has moved down a lot during the past 24 hours... a single active sunspot region is on sight, and it will soon be turning away , so we may see a few days of a spotless SUN, with all its negative consequences for short wave propagation, especially on frequencies above 15 megaHertz... The solar flux figure that you should use to make your own propagation forecasts is 75, seven five, that will give you a very good picture of how the HF bands will behave during the rest of the week...

Don't forget to send your signal reports, comments about Dxers Unlimited and other Radio Havana Cuba programs to inforhc at enet dot cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba,
Havana, Cuba