Wednesday, June 20, 2018

Arnie Coro’s DXers Unlimited program – June 19 edition

Radio Havana Cuba

Dxers Unlimited middle of the week program for Tuesday 19 June 2018
By Arnie Coro, radio amateur CO2KK

Hola amigos radioaficionados.... Yes, this is the middle of the week program of Dxers Unlimited, your favorite radio hobby program, reaching you when we went through a geomagnetic disturbance that sent the planetary disturbance indice are known as the A index above the 30 units mark.

Way back during the year 2015 we were keeping a close watch at an increase in solar activity , as we fallowed the development of solar cycle number 24, the one with the most unusual behavior in more than a century.

Let me warn you all...Be aware that some of those ways of playing with your radios may involve a lot of work on your part, studying complex technical problems and perhaps also requiring a significant investment ... like for example, if you ever decide to try amateur radio Earth Moon Earth communications ....even when using the new and really amazing digital communications programs like JT 65, JT9 and FT8., you will still need a nice and the bigger the better antenna system !

Fortunately, there are other ways of enjoying our radio hobbies that can provide low cost and easy to put in practice modes, like FM broadcast band DXing using just a radio receiver for the frequency range where those stations transmit connected to an external antenna.

I am a long-time fan of FM broadcast band DXing because it is quite different from the classic AM broadcast band hunt for long distance stations, this is due to the fact that the propagation of the FM band signals is dominated by both weather related events and not very frequently by highly ionized part of the ionosphere at the height of the E layer. By the way we are right now at the yearly peak of the Sporadic E season, that makes possible nice loggings on the FM broadcast band.

Let me add that another low cost way of enjoying the radio hobby has a connection with the preservation of our Planet Earth, because it is based on building radios and accessories using recycled electronic components that are desoldered from equipment that is no longer possible to repair.

Here at DXers Unlimited our regular listeners have already sent me several examples of radio sets built using recycled components that I then have attempted to duplicate with a high degree of success Si amigos, yes my friends, oui my Canadian francophone listeners, this past weekend I took some time to try to organize my big garage workshop, a quite challenging job, that led me to find the long time lost notebook where the hand written notes and diagrams of several of DXers Unlimited listeners circuit ideas where kept. Of course, that I tried to finish at least the organizing effort required by workbench number one, but the finding of the notebook cut short the rest of the planned job as an immediate start up to locate the parts to build one of the radios began.

To make a long story short, after spending a few hours on a breadboard version of the CFL radio, the audio module was finished and it was quite amazing to see how the NPN switched mode medium power transistors used by the Compact Florescent Lightbulbs amplified the low level audio tone fed to it from my workbench test.

This is Radio Havana Cuba, the name of the show is Dxers Unlimited, our middle of the week program is now on the air, and now the story about the CFL radio receiver circuit diagram continues. 

The original design came from radio amateur AA1TJ Michael Rainey, who built the receiver using mostly parts from broken compact florescent lightbulbs.

In the original circuit Michael used an audio amplifier following the direct conversion product detector. It was made using two stages of the BUL128A transistors that provided enough gain for producing enough audio output into a pair of headphones coupled by means of an impedance matching transformer. I decided to add a third NPN high gain transistor that was connected between the product detector and the two-stage original audio amplifier to increase the audio output.

This proved to be a very worthwhile modification because the audio output increased significantly. The prototype receiver used a very simply one transistor VFO, but again this was improved by building a replica of Wes Hayward W7ZOI three transistors Colpitts oscillator that was set to tune from three thousand five hundred to three thousand six hundred kilohertz so that it will cover the 40 meters band from seven thousand zero zero zero to seven thousand two hundred, where most of the amateur radio activity in our part of the world takes place. The Polyakov harmonic-mixer type of product detector requires a local oscillator injection frequency at half of the frequency to be received. 

By mid-afternoon Sunday the receiver was working quite well, picking up several Cuban single side band stations on the national calling frequency of seven thousand one hundred and ten kilohertz, and later during the early evening I was able to pick up South and Central American stations also, plus a station from Echo Alpha eight land, the Canary Islands.

The amazingly simple receiver uses a very small number of parts, that were mostly recycled from different sources, mainly from several defunct Compact Fluorescent Lightbulbs. The radio does not provide loudspeaker output, but the audio level on the headphones is quite adequate.

A similar project following the same design criteria was designed for making use of recycled parts to build a three-stage crystal controlled CW radiotelegraphy low power transmitter, but I sound found out that with CFL lightbulbs transistors type BUL128A the rig could only work up to the 80 meters band... All attempts to make the BUL128A transistors oscillate on the 40 meters band failed...

Now item three here at the middle of the week edition of DXers Unlimited, that is on the air just after the half hour newscast of our English language program.

Ask Arnie - is our second most popular section of the program, second only to our HF propagation updates and forecasts presented whenever possible at the end of the show. 

Ask Arnie today will be answering a question sent by several listeners that want to know about the Ionospheric Forward Scatter propagation mode, a very interesting source of DX signals from some of the world’s high power short wave stations transmitter sites.

Although during the past several years the number of high power transmitter sites has gone down because of the closing of many relay stations, and even primary sites like was the case of Radio Canada’s Sackville, New Brunswick site... avid short wave listeners equipped with very good receivers and antennas very often are able to pick up the Ionospheric Forward Scatter signals when the high power short wave stations operate on the higher bands...with high gain antennas, something seen mainly when very high power transmitters are operated on the frequency bands between 15. 1 and 21.8 megahertz.... that translated into short wave bands means from 19 meters to 13 meters.

At this phase of the solar cycle very few stations are using the 21 megahertz or 13 meters band, and I have not heard a single international short wave broadcaster using the 11 meters or 26 megahertz band where Ionospheric Forward Scatter would be most noticeable when running high power and large antenna arrays.

If you are able to pick such signals they will be coming from transmitter sites located between 500 and 1500 miles from you.

And now at the end of the show.... our HF propagation update and forecast...

Solar flux hovering around 75 units and solar activity continues to be low. Expect many Sporadic E skip propagation events during the last 10 days of the month of June and first two weeks of July.

Send your signal reports and comments about the show plus your radio hobby related questions to and via air mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba

Listen for the weekend edition of DXers Unlimited coming up Sunday and also early Monday UTC days.
(Arnie Coro/R Havana Cuba)