RADIO HABANA CUBA
DXERS UNLIMITED
MID-WEEK EDITION
TUESDAY, NOVEMBER 12, 2001
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hi, amigos radioaficionados! welcome to the mid week edition of your favorite radio hobby program, Dxers Unlimited, coming to you from Radio Havana Cuba on the air and on our Dxers Unlimited website! I am Arnie Coro, radio amateur CO2KK, your friend in Havana and host of this twice-weekly show devoted to our wonderful hobby yours and mine... RADIO!
Here is item one: More than 420 Cuban radio amateurs participated actively on the Hurricane Michelle communications emergency nets... and yes, we all learned a lot in case another similar event happens in the future...more about the use of NVIS antennas on 40 and 80 meters to handle the emergency traffic in an upcoming edition of Dxers Unlimited.
Item two: The ionosphere is now at its lower height above the Earth in the Northern Hemisphere, the low height of the F2 layer is increasing the free electron per cubic centimeter to such a level that very high daytime maximum useable frequencies are now very frequent....The 12, 10 and 6 meter amateur bands are opening up for long haul DX on a daily basis, a situation that will continue during the next two to three weeks...
Item three: homebrewing your radios is yet another one of the more than sixty two ways of enjoying our wonderful hobby, I invite you to stay tune and listen to the description of my new SUPER-REGENERODYNE the latest of my homebrew receivers now almost ready to move from the workbench to the operating table.
I'll be back with you after this musical interval... Margarita Delgado is my sound engineer at RHC studio 7... I am Arnie Coro in Havana...
You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited and here is Item three in detail, a full description of Arnie Coro?s SUPER-REGENERODYNE a homebrew receiver especially designed for the experimenter and those radio enthusiasts that really want to operate their receivers!!! Ready to copy? OK! Here we go:
The SUPER REGENERODYNE is a hybrid radio receiver, this means that purists, glow bug purists who advocate the exclusive use of vacuum tubes won't like it very much, at least until they build one!!! Then I am sure they will change their minds. So the SUPER REGENERODYNE is a hybrid, because its separately built power supply is an all solid state one....
SO, now that you know that this is a hybrid receiver, using both solid state devices and vacuum tubes, let's start describing the unique power supply... The radio has really three power supplies built on a separate chassis, that is, connected to the receiver chassis via a shielded multi-conductor cable that is about 2 meters or 6 feet long.... The first power supply is used to power the filaments of the vacuum tubes, and it is a very well-filtered and regulated supply that operates at 12.6 volts DC, with enough current to handle the filaments of all the vacuum tubes used in the SUPER REGENERODYNE...
You may ask why 12.6 volts, and here is the answer, it is a lot easier to filter and regulate direct current at the 12.6 volts level than at a lower level, and once you have the well filtered and regulated 12.6 volts, it is very, very easy to add integrated circuit regulators right next to the 6.3 volts vacuum tubes if you do use them in your receiver as I do... So, I send 12.6 volts DC regulated to the receiver's main chassis, and place several integrated circuit three terminal low cost regulators that handle up to around 900 milliamps or a bit more right next to the 6.3 volts filament vacuum tubes... Those vacuum tubes that do use 12.6 volts for their filaments receive that voltage from the main 12.6 volts main bus bar.
Using the well-filtered and well-regulated DC on all the vacuum tubes helps to make the SUPER REGENERODYNE noise floor at a very low level indeed....no hum at all whatsoever! The second power supply is the high voltage unit for the vacuum tube's anodes or plates and screens... It operates at a relatively low voltage, following the design philosophy of several famous radio receiver manufacturers, like Collins Radio, Drake and the Russian family of R-250 communications receivers...
The high voltage unit operates at 150 volts DC, and at this moment is not electronically regulated, something I will probably add in the upcoming second prototype of the SUPER REGENERODYNE.... But, I did include a pair of gaseous discharge voltage regulator vacuum tubes that operate at 105 or 108 volts, depending on the type available... By the way, starting the discharge in those tubes required that their input voltage be high enough, something that gave me a headache, before I decided that a separate supply was needed for that purpose. By the way, I do use avalanche type silicon rectifiers, and a simple but very effective step starting system, so that the two high voltage power supplies start slowly to avoid inrush peak currents. The DC filtering is done using three beautiful collector's item oil capacitors of 10 microfarads at 600 volts DC, and two huge 10 henry at 200 milliamps filter chokes for the anode and screen supply, and three 8 microfarad at 600 volts capacitors and two 10 henry at 110 milliamps filter chokes for the plus 105 volts supply... an overkill for the 60 or 70 milliamps needed, but those were the recycled parts I had here!
The supply's power transformer was especially designed and built by yours truly, with a very wide margin safety factor, providing the capability of operating under the most strict commercial continuos service parameters!!! This is a once-in-a-lifetime power supply, amigos!!!! And YES, you can use if for many radio and electronics-related experiments, if you provide a way of accessing to the different voltages via a safety terminal trip connector.... BE CAREFUL: 150 volts and 105 VOLTS DC are HIGH VOLTAGES!!! Once again, this is not a one-weekend project, but once you finish this power supply, I am sure thay you are going to be a very happy person!!! By the way, the 12.6 volts well-filtered and regulated power supply was designed to provide a current of 10 amperes, so it, all by itself will also serve to power up a ham radio HF or VHF transceiver in the 50 watt class too!!!
More about the SUPER-REGENERODYNE after this brief musical interval... Amigos, you are tuned to Radio Havana Cuba, the name of the show is Dxers Unlimited and our e-mail address is arnie@radiohc.org
Now let's continue with the description of the SUPER REGENERODYNE's front end.... Yes, I have received a lot of e-mail messages requesting the ZL2JJ regenerodyne receiver information package, as more and more Dxers Unlimited's listeners are learning to enjoy the unique properties of regenerative receivers... The front end of Arnie Coro's SUPER-REGENERODYNE has many interesting features, among them full protection against static discharges, an input attenuator, and a tuned bandpass input circuit that uses high Q coils wound on ceramic coil forms.
As I said here in a previous edition of Dxers Unlimited, all work needed to build the well-designed front end is worth every minute of it... As a matter of fact, a friend from Las Tunas province that recently visited here CO8KY, Josue, an electronics professional engineer himself, commented that just building the front end of the SUPER-REGENERODYNE to add it ahead of a conventional receiver will be a very worthwhile project.... After many experiments, I settled for one of the three RF amplifiers tested, the one that uses the cascode circuit using a dual triode that was especially designed for front end TV tuner use, testing the ECC85, ECC88, ECC189 and the Russian 6H23P, finding that all four of them performed very nicely indeed... The pentode front end, using the very common 6BA6 or Russian 6K4P came in a close second, because it was not as good when using the receiver in the frequency range from 40 to 52 megaHertz.
The mixer circuit used in the SUPER-REGENERODYNE front end is the little known PULLEN MIXER, using two triodes and providing excellent performance. I have built several crystal controlled oscillators for this front end, and two VFO type oscillators... The final design uses a very common triode-pentode vacuum tube, with the pentode oscillating and the triode acting as a cathode follower. The front end's output range is from 2 to 3 or from 2 to 4 megaHertz, and using it ahead of an old vacuum tube receiver built in the nineteen fifties by Hallicrafters, the S40B, has provided so far many hours of wonderful short wave reception with this dual conversion system... so a spin off of the whole project is that if you already own a short wave receiver with limited capabilities, spending time in building just the front end of the SUPER-REGENERODYNE may prove to be a very worthwhile project...
To further test this concept, I connected the last version of the front end to a portable digital receiver, a Sony ICF 7600, finding that reception in the range from 5 to 29 megaHertz was much better, after a variable attenuator was installed between the output of the front end and the Sony's antenna input circuit... In an upcoming edition of Dxers Unlimited, I will provide PART TWO of the SUPER-REGENERODYNE that includes the 2 to 4 megaHertz RF amplifier stage used mostly for isolation purposes, the regenerative detector stage, the BFO, and the audio chain that includes easy to implement audio filtering networks...
As I have said here many times, homebrewing your dream receiver can take a lot of time, but modular construction allows you to build and test it on a step-by-step basis... My number two front end, a prototype, has ended up ahead of the old Hallicrafters S40B, whose main dial now is kept tuning from 2 to 4 megaHertz while the band changing is done at the front end by switching crystals!!!
Any questions, want to know more about the ZL2JJ regenerative or the SUPER-REGENERODYNE? Just drop me a postcard to Arnie Coro, Radio Havana Cuba Havana, Cuba... or via e-mail to arnie@radiohc.org
And now, amigos, just before going QRT here is Arnie Coro's HF plus 6 meters propagation update and forecast: Solar flux for November 12 was very near 225 units, and the A index, the geomagnetic planetary disturbance indicator, was at a very low level of just 2, indicating a very quiet field. Solar activity was moderate, and it may move to high during the next 24 to 72 hours.
Solar Activity Forecast: Solar activity is expected to be at moderate to high levels. Region 9690 remains capable of producing a major flare during the period. Region 9692 retains a slight chance of producing a major flare. Region 9692 will rotate off the visible disk in the next day. Old Region 9672 (S18, L=268) is due to return on 13 November. This region produced several M and X-class events during its last rotation.
We are going to witness very high daytime maximum useable frequencies reaching the 6 meter or 50 megaHertz amateur band and providing transcontinental F2 DX for several hours. Nighttime reception will show an enhancement that will make possible Dx signals to be heard on the 13, 16 and 19 meters international short wave bands, and the 15, 17 and 20 meter amateur bands... See you next Saturday and Sunday UTC.
Arnie Coro CO2KK
Havana, Cuba
November 13, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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