Wednesday, November 16, 2016

DXers Unlimited: November 13

Radio Havana Cuba
Dxers Unlimited weekend edition for Sunday 13 November 2016
By Arnie Coro
radio amateur CO2KK
Hola amigos radioaficionados all around the world and orbiting planet Earth... I am Arnaldo, Arnie, Coro radio amateur CO2KK, your host here at the weekend edition of Dxers Unlimited. Yes, this is your favorite radio hobby program and here is item one.... A snapshot of solar activity that shows very clearly how cycle 24 continues its track towards the upcoming solar minimum... So far this year 2016, we have experienced 23 days of zero sunspots ... and this data was taken on Thursday 10 November... when I started to write the script for this weekend show... Solar activity continues to be very low, so it may happen that when the this program goes ont  air we may have observed at least one more day of a blank Sun... Last year our nearest star was at a much more active state, so every single day of 2015 saw at least one sunspot group registered by solar optical astronomers....
Item two: I am very happy to see how much interest is generated among Dxers Unlimited's listeners every time a home building of radios topic is presented... Interaction with listeners that have built and tested some project published here has provided excellent feedback to improve some designs...

Aiming at making possible to build at home radio receivers and transmitters, I decided to lay out a set of rules... with the number one of them all stating that the circuits designs should only use electronic parts that are presently available in most countries around the world. That  limitation led to looking at recycling as the main source of parts, something that has proven to be quite effective... Just to give you an example... there is an ever increasing amount of what may be described as electronic junk that should be taken apart to enrich your parts bins... My most recent adquisitions were two computer UPS units that could not be repaired because of the fact that they used some rare integrated circuits that could not be found... Nevertheless the two units provided two excellent rugged well built power transformers, high current silicon rectifiers, several high power MOSFET devices and many other small parts, plus the line cords, fuse boxes and the metal cabinet.... One of the two units was easily converted into an excellent battery charger to keep a pair of high ampere hour rating lead acid batteries at maximum charge by means of a float charging circuit... The other UPS had its power transformer and all other parts inside removed and the well built metal cabinet will soon be hosting a nice 2 vacuum tubes linear power amplifier for an amateur radio station... Just take a look around and see if at home or at work you may find old electronic equipment that may be stripped of many parts before sending them to a recycler...

Now item three:  ASK ARNIE... la numero uno, the number one most popular section of this show is now on the air answering listener Mario from Mexico City who is very concerned about the extremely high background noise level at his apartment building... Mario says in his e'mail that it is next to impossible to tune in but the most powerful AM Mexico City stations... and reception from 2 megaHertz all the way to the top end of the amateur ten meters band is also blocked by very high noise levels when he uses his rooftop two sets of nests of dipoles antennas for the 80, 40, 30, 20, 17, 15 , 12 and 10 meters bands. Antenna one has the 80, 40 , 30 and 20 meters dipoles in parallel , fed by means of a one to one balun, while Antenna two has parallel dipoles for the 17, 15, 12 and 10 meters bands...also fed via a very well built one to one balun ferrite core transformer.   Mario adds that he is using on the higher frequency bands nest of dipoles a special double shield coaxial cable that when installed proved to be picking up less noise than the typical RG213 50 ohms coaxial cable previously used... He says that his low frequency bands nest of dipoles rooftop antenna is practically useless because it picks up a tremendous amount of noise... Mario ends his very well documented e'mail by asking me to recommend an antenna that could help him deal with the very high noise level present at his location...  In a few seconds I will be answering the question, jus after a short break for a station ID

This is Radio Havana Cuba, the name of the show is Dxers Unlimited, and here is the reply to listener Mario's question about what antenna types could help him deal with his very high noise level... Amigo Mario there are two antennas that have proven to be quite effective at locations that have very high radio frequency broadband noise levels... One , you have heard about it here at Dxers Unlimited countless number of times... I am talking about a well built Tilted Terminated Folded Dipole that for the frequency range from 6 to 30 megaHertz will need to be about 16 meters overall length... In order to be really effective the best way to install it is a sloping antenna, with a tilt angle of between 30 and 45 degrees... So the TTFD will need less space than its 16 meters overall length to work properly... All I can say is that although the TTFD does introduce a certain amount of power loss when transmitting, a side by side comparison with a half wave dipole cut for a specific operating frequency always shows that the TTFD is a much quieter antenna... Looking at the baseline of a spectrum analyzer and switching between the two antennas, one can actually measure the difference in noise level ...
The other antenna that will certainly help you deal with the high ambient radio frequency broadband noise level at your downtown Mexico City colonia or neighborhood is the time proven tuneable magnetic loop... that is much more challenging to use, because it requires constant retuning due to the very high Q factor or sharpness of resonance... And when located at the rooftop, it must be operated by means of a high precision remote control system. By the way professional magnetic loop antennas are very, yes, very expensive while well built home made ones can provide excellent performance at much lower cost...
Now our next radio hobby related topic... coming from the weekend edition of Dxers Unlimited information about the Brazilian Time Standard Station that operates on 10 megaHertz
The transmitter is running one kilowatt into a one half wave dipole antenna , and it has the callsign or call letter PPE. It uses standard A3H modulation
The transmission content consists of sending the Brazilian Legal Time that is UTC minus three, using a female voice that says Observatorio Nacional fallowed by the current time in hours minuts and seconds.. and sending a short beep tone of one thousand Herz every second and later on three two hundred milliseconds long beeps at the 58, 59 and 60 seconds of each minute making the station easy to distinguish from other time stations. My understanding is that the station does not claim to be a frequency standard transmission although it should be for all practical purposes close enough to ten megaHertz.  Now a short form solar activity report... The Sun continues in a very quiet state, with the sunspot number at 12 on Wedenesday November 9 and back toZERO sunspots on Thursday 10 November when I had to finish writing the script for an unusually early recording session that took place late Thursday UTC day .... Hope to
See you all at the middle of the week program , Tuesday and Wednesday UTC days....and do not forget to send me your radio hobby related questions because on many ocassions the answers have proven to be quite useful to many other listeners around the world... Send mail to inforhc at enet dot cu, again inforhc at enet dot cu , and of course that your signal reports and comments will also be most appreciated amigos.
(Arnie Coro)