Dxers Unlimited weekend editions
by Prof. Arnaldo Coro Antich
radio amateur CO2KK
Radio Habana Cuba
Radio Havana Cuba
Hi amigos radioaficionados, welcome to the weekend edition of your favorite radio hobby show, with complete coverage of all the more than 85 ways that you and I enjoy when playing with our radios...
More than 85 different and some certainly fascinating ones, like using radio receivers that obtain the electricity to operate using a lemon as the active electrochemical cell ... The lemon radio works best when using high gain germanium transistors that are able to operate with very low voltages...
Yes, there are many ways of learning about electronics by experimenting with your radios... for example, I now have a nice stockpile of electronic components that were desoldered from the circuit boards contained inside compact fluorescent light bulbs or CFL 's as they are also known... transistors , resistors, capacitors, diodes, choke coils that instead of going to a landfill and polluting Mother Earth, are now available to assemble such nice circuits as a direct conversion amateur bands receiver that is very easy to assemble and provides what could best be described as amazing performance...
Sure amigos, radio provides an almost endless list of possibilities if you are experimentally minded... and whenever you want to spend some time meeting people from half way around the world without having to be looking at a computer screen and connected to the Internet, just obtain your amateur radio license and start calling CQ DX on the higher frequency ham bands.
Now here is our good news of the day: Solar activity continues... after a short break, the Sun is once again active, and two sunspot regions are now under close scrutiny by the world's solar observatories. Solar flux has stayed above 80 units and the ionosphere is supporting propagation on the 21 megaHertz or 15 meters amateur band for many hours every day.
Stay tuned right on this frequency, or keep your world
wide web connection to www dot radiohc dot cu, as the weekend edition of
Dxers Unlimited will continue in just a few seconds.
You are listening to Radio Havana Cuba , the name of the show is Dxers Unlimited and here is now item three of todayīs program...
Our very popular technical topics section with a
description of RECYCLUS...
You must be careful when removing the glass bulb from the circuit board, and then proceed to properly dispose of it,... once this is done it is an easy task to place the circuit board on a support and begin desoldering the parts .
Once you have finished the desoldering session, the next task is to test the parts removed from the circuit boards...
Resistors are easily tested with a digital multimeter, while transistors can also be separated betwee good and bad by using , again, your digital multimeter... you wonīt know the actual gain of the transistor, but a bad one will show up immediately with the digital multimeter test. Capacitors are tested for leakage using a power supply and , once again, the extremely useful test instrument... the digital multimeter.
If you happen to have an resistance, inductance , capacitor bridge, then you can even determine the actual value of those components.
Once this is done, then take some time to study the circuit diagram of the RECYCLUS PLUS receiver ... and then start picking up the parts required to build the radio and put them into a small box...
Here is now a bit of advice from your amigo Arnie
Coro, never, and I mean it, never begin to assembly an electronics
project before ALL, yes ALL the required parts are available and tested
A separate text file will provide you with additional information about this direct conversion receiver that has proven to be extremely sensitive when built to tune in the 40 meters amateur band. I have yet to change the bandpass dual tuned input filterīs coils and capacitors and the VFO to be able to test the receiver on the 30 meters or 10 megaHertz amateur band, one of the most interesting frequency assignments to the amateur radio service on the HF spectrum.
The RECYCLUS PLUS direct conversion receiver uses a very efficient product detector circuit known as the Polyakov harmonic mixer, that has several important advantages over the classic diodes broadband mixer circuits.
The Polyakov harmonic mixer uses a half frequency injection , that meaning that your variable frequency oscillator must operate at half the frequency that you want to receive, making possible to build a more stable oscillator, because it will be operating at half the frequency that you are receiving.
It is a fact of life that lower frequency oscillators operating between 1 and 10 megaHertz are much more easy to home brew than identical circuits operating between 5 and 20 megaHertz. In the case of the RECYCLUS PLUS receiver prototype, the local oscillator operates from 3.5 to 3.6 megaHertz, in order to cover the segment of the 40 meters band , 7.0 to 7.2 megaHertz that is now allowcated to the amateur radio service on a worldwide basis.
A short description of the RECYCLUS PLUS receiver's design will follow in a few seconds after a short break for station ID... stay tuned, I am your friend Arnie Coro, broadcasting from sunny Havana , Cuba
Si amigos, yes my friends, oui mes amis, you are
listening to the weekend edition of Dxers Unlimited, coming to you from
Radio Havana Cuba, and now here is part two of today's Technical
Here is now the full description of the circuit.
The antenna is connected to the input of the receiver by way of a very simple, yet effective signal attenuator... it is just a 500 ohms or 1000 ohms carbon track potentiometer... The signal is then routed to a dual tuned bandpass input filter, that provides the all important front end selectivity.
The two coil forms used were made using plastic pill bottles of about 25 millimeters or one inch diameter, but you can also use small cuts of PVC or Polyethylene pipe or tubing of diameters between 19 and 25 millimeters, that is from ū of an inch to one inch diameter.
Winding the coils is very easy, as you will find out. Using small diameter copper enamel insulated wire , also recycled from the compact fluorescent lightbulbs small inductances was a logical choice... and all I can say is that the bandpass input filter works very well indeed.
You can experiment by using variable capacitors for tuning the filter circuits, instead of relying on the fixed capacitors that are shown on the pictorial circuit diagram. The bandpass dual tuned input filter is connected to the Polyakov anti-parallel diodes product detector input port.
The local oscillatorīs output is connected to the other port of the detector. At the output of the Polyakov detector you will obtain audio ... that is then fed to the two stage audio frequency amplifier that is built using the compact fluorescent lamp big switch mode transistors.
Of course amigos, that you can use smaller and better transistors for the RECYCLUS receiverīs audio stages...
BUT... what was wanted by the designer was to make use of the transistors desoldered from the CFLīs circuit boards ...
The other active component of the receiver circuit is the variable frequency injection oscillator, and in this case, I found out that although a CFL transistor could be used, it was possible to obtain much better results, more precisely an oscillator with higher frequency stability by using a small signal high gain NPN silicon transistor, that by the way, also came from a recycling effort , as it was desoldered from a TV set 's circuit board's intermediate frequency amplifier stage ...
In an upcoming edition of Dxers Unlimited , I will be telling you more about the RECYCLUS PLUS direct conversion HF bands receiver prototype, that is now installed right next to my Kenwood TS-820-S transceiver, so that I can switch back and forth between the two receivers and dynamically compare results...
So far, the RECYCLUS PLUS has proven to be a very sensitive radio , but its lack of selectivity shows up when the 40 meters band opens up for DX during the local late afternoon hours.
During the daytime, when 40 meters is only occupied by local and semi-local stations, switching between the TS- 820 ' s receiver and the RECYCLUS PLUS is a very interesting experience.... as both radio deliver very nice audio output.
The Kenwood TS-820-S transceiver has an excellent totally analog receiver, that makes it a great choice as a second set for an experienced radio amateur, or as a first radio for a beginner, if the new radio amateur can find a second hand unit in good shape...
There are no RECYCLUS PLUS second hand receivers of course... you must make your own, but again, as I have said here many times before , there is nothing like listening to a station using a radio that you have built all by yourself...
Yes, stay in touch, because in the next edition of Dxers Unlimited, I will be telling to you more about the RECYCLUS PLUS direct conversion amateur band transceiver, that can be built for the 160, 80, 40, and 20 meter bands, that so far are the ones tested here .