No rare, hard to find or UNOBTAINIUM components are used... and as a matter of fact many capacitors came from defunct compact fluorescent light bulbs.

Transcription

1 Radio Havana Cuba Dxers Unlimited's middle of the week program for Tuesday 15 September 2015 By Arnie Coro radio amateur CO2KK recorded Monday 14 Sept at 4 PM local time Hola amigos radioaficionados... I hope that you are enjoying the somewhat better propagation conditions that will accompany the expected increase in solar activity happening near the autumn equinox... This past weekend, with the help of a local young ham operator CL2ADA, Alexis, my home amateur radio station CO2KK has a new multi bands HF antenna. It followed a design by Len Cebik W4RNL, who optimized the classic G5RV dipole. All I can say is that despite having to fold back the ends of the dipole to accomadate the antenna into the available space... using a classic T type antenna tuner, this new skywire tunes very well to a minimum standing wave ratio on all ham bands from 80 to 10 meters... This new antenna will make possible to visit regularly my favorite QRP or low power stations sweet frequency on the 20 meters band... fourteen thousand zero sixty kilohertz, where you can find excellent CW Morse Code operators willing to dig your signal from the noise to complete a two way contact. Speaking about CW, the simplest possible form of radio communications, I want to share with you the following information about a work in progress here at my home electronics and mechanics workshop... After a lot of looking around for a minimalist CW station built using vacuum tubes with the possible exception of the high voltage rectifiers of the power supply I came out with the following set up idea: It is a 40 meters GENERAL PURPOSE CW station transmitter/receiver... Receiver: starts with a signal attenuator, bandpass dual tuned input filter, RF amplifier stage with 6BA6 or similar tube, followed by regenerative detector and

2 two stages of audio amplification provided by either a dual tube ECL82 or similar or by 6AU6 and 6AQ5 or similar combination, depending on availability. A very straightforward and classic design by all standards... Transmitter: 6AH6, 6AG7 or similar tube VFO tuned to 3.5 to 3.6 megahertz followed by another tube doubler, and then the final amplifier... with whatever tubes are at hand... Tested, among others 6L6G, 807, PL500, 6146 etc... CW keying by means of grid block keying. The power supply provides filament voltages... including ( in the luxury version regulated 6.0 volts DC for the filaments of the regenerative detector and the VFO ), 150 volts regulated using a VR150 or similar tube, and 250 volts for the rest of the tubes, except the final amplifier that can run from 300 to 600 volts DC. The bias supply is also used as the source for the grid block keying. Switching from receive to transmit is done by two relays... This rig is a rugged and reliable as you can imagine... AND, it does need some time for the VFO frequency to stabilize...takes about ten to fifteen minutes to settle down. Of course that it can be simplified by using crystal control, but quartz crystals here are simply not available, and besides that having VFO capability adds a lot of flexibility to the set. When asked by a local ham why use a regenerative detector instead of the already time proven direct conversion receiver of the Islander vacuum tubes rig, my answer was that with the regenerative detector, by careful tweaking you can achieve razor sharp CW selectivity, something impossible with the direct conversion radio. One additional advantage of this rugged CW transmitter/receiver set, is the use of a well designed front end with a signal attenuator and the dual tuned bandpass input filter...that limits the frequency response significantly to about 500 kilohertz centered on 7.0 megahertz.

3 No rare, hard to find or UNOBTAINIUM components are used... and as a matter of fact many capacitors came from defunct compact fluorescent light bulbs. No attempt is made to produce a miniature rig, and the power supply is on a separate metal chassis... so it can be used for other projects. With about 25 to 50 Watts of CW to a half wave 40 meters dipole, when band conditions are normal, you can really enjoy this rig... that produces a clean CW note. The only part that I consider critical or hard to find is the VFO tuning capacitor, that really needs to be a very good quality part...and of course that you will also need a high quality dial mechanism... The VFO must be well shielded, as well as the final RF amplifier stage... Yes amigos, sure my friend oui mes amis, all around the world there are millions of new old stock vacuum tubes without use...while some are certainly rare and hard to find, others are very common and for that reason can be obtained at low cost, or even free of charge from many different sources... The average life time of a well built receiving type vacuum tube has proven to exceed more than 70 years... and as a matter of fact, surplus World War II tubes that I have tested here under very strict operating parameters proved to be in like new conditions. You may have some difficulties in finding the tube sockets but in many instances they may be easily removed from old equipment. 8 pins OCTAL tube sockets were built to last, and they will tolerate the desoldering of all wires attached to them so they can be recycled. Somewhat less easy to recycle are the miniature 7 and 9 pins sockets, but the very well built ceramic ones will be easily recycled too.

4 The concept of a receiver and separate transmitter combo into the same cabinet is quite different from the classic modern days transceiver concept.. but essentially this rig will provide what you need, that is a receiver to pick up the signals and a transmitter to put you on the air... It is also a fact that you will need to acquire a skill that the old timers using separate receivers and transmitters had to learn, and that is how to zero beat the transmitter frequency to the frequency that your receiver is tuned to... But after some time you will do easily set your transmit frequency to zero beat or very near zero beat... By the way this set will tolerate huge line voltage excursions and power surges... something that can not be said of most of today's solid state transceivers. I am now working on version two of this rig, using whatever tubes I had at hand, and all looks well so far... The power supply is now completed and tested, and the parts for the regenerative receiver are all at hand, so that is going to be the next stage... I will keep Dxers Unlimited's listeners around the world updated on how this home brew project is going, with the high hope of having it finished by the end of the year... Stay tuned for more radio hobby related information coming to you from Havana. I am Arnie Coro, CO2KK, back in a few seconds----- musical short curtain Si amigos, this is Radio Havana Cuba and here is now our next radio hobby related item... Ask Arnie, answering a question sent in by listener Henry from Montego Bay in Jamaica... Henry wants to know if it is true that natural radio signals coming from Planet Jupiter can be picked up on a standard amateurs band receiver or transceiver that is able to tune to the 15 meters of 21 megahertz band.

5 Si, sure amigo Henry, with a simple half wave dipole and a wire reflector element below it, separated by about 3 meters from it, you can pick up Planet Jupiter's natural radio emissions that sound like waves landing on a beach. Use your receiver with the selectivity set to the widest available, and of course that you will need to know when Jupiter is up in the sky... One very interesting aspect of this ultra simple planetary radio astronomy set up is that you can actually detect the exact time when Jupiter appears and dissapears on your sky, by picking up the signals on the 21 megahertz band with the two elements Yagi antenna just described... Planetary radio astronomy is one of the more than 90 ways that you and I can enjoy this wonderful hobby amigos... Send your comments about this show, signal reports and raio hobby questions to arnie at rhc dot cu, or to inforhc at enet dot cu, and YES we do QSL, we do verify your reception reports with a very nice set of QSL cards!!!