Re: [HCDX] Dxers Unlimited's mid week edition for 6-7 March 2007

["Prof. Arnaldo Coro Antich" <inforhc@xxxxxxx>]

A special edition for those who enjoy homebrewing the radios
they use to listen to DX


Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited's mid week edition for 6-7 March  2007
By Arnie Coro
radio amateur CO2KK

Hi amigos radioaficionados, with our now traditional salute, we are now 
starting up the mid week edition of your favorite radio hobby program, 
via short wave and also available from www radiohc dot cu from 05 to 07 
UTC... I am Arnie Coro, radio amateur CO2KK, that's my ham radio 
callsign, and yes I do enjoy a lot operate on CW, Single sideband and 
Digital Modes on the HF bands, and also watching for those elusive but 
nice and challenging sporadic E openings that area about to begin in 
just a few weeks here in the Northern Hemisphere.
Homebrew receivers, radios that are built from electronic components and 
that you assemble yourself, bring in signals that have a special sound 
of sorts, special in the sense that when signals come out trough 
headphones or loudspeakers of those homebrew radios that started to 
operate after many hours of a unique learning experience, you feel a 
sense of accomplishment second to none. And let me add that after many 
years of homebrewing radios, from the simplest to the most 
sophisticated, by homebrew receivers keep that special sound all the 
time!!! For example, my prototype vacuum tube regenerodyne, originally 
built fifteen years ago, is still a joy to operate. All along its life, 
I have done a lot of experiments with it by changing the tuning coils, 
the values of some critical components and even vacuum tube types, so it 
has acted as a test bed of sorts... But, it still gets used , especially 
during the weekends, when on Sunday mornings I enjoy operating on the 40 
meters band using the single side band voice mode to talk to my many 
friends all along the Cuban archipelago that are active on the several 
nets operated by provincial radio clubs.. My prototype regenerodyne has 
one of the plug in coils optimized for covering just the lower 150 
kiloHertz of 40 meters, where the nets operate. For those of you that 
have sent e-mail messages, letters and postcards wanting to know more 
about the original regenerodyne prototype, it will be our number one 
feature today here at Dxers Unlimited's mid week edition...
Stay tuned, and write down my e-mail address to send your signal reports 
and comments about the program as well as any radio hobby related 
questions you may have in mind... mail to arnie@xxxxxx, again 
arnie@xxxxxx, or send your postcards and letters VIA AIR MAIL to Arnie 
Coro, Radio Havana Cuba, Havana Cuba... I'll be back in just a few 
seconds amigos !!!
.....

Si amigos, this is Radio Havana Cuba, the name of the show is Dxers 
Unlimited and today our number one most popular section ASK ARNIE , will 
be providing you with a detailed description of not one , but two 
regenerative receivers that are rather easy to homebrew and provide 
excellent performance... First you will listen to the data about the 
original version of the  KK-12 REGENERODYNE vacuum tube multi band 
receiver and then I will be describing the Desert Rat Three, a solid 
state 1996 design, that is, according to all my tests the best solid 
state simple regenerative circuit design , the brainchild of well known 
American radio amateur and short wave listener Paul Harden NA5N
Now let's start with the KK-12 Regenerodyne that so many of you have 
asked about lately. The final version of this radio receiver uses a dual 
tuned bandpass input filter and signal attenuator, that is connected to 
the grid of a radio frequency amplifier vacuum tube that provides very 
little gain, as its main function is to provide isolation to the mixer 
stage that follows it. The other signal for the mixer is provided by a 
simple quartz crystal oscillator that is capable of using many different 
types of crystals in many different types of holders... So, the front 
end of the KK-12, is conventional , but very well designed... The output 
of the mixer is fed to the variable frequency regenerative detector 
stage,that uses a Hartley type detector with screen grid voltage 
regeneration control...The audio output from the detector is fed to a 
two stage audio amplifier, that in the original prototype was made using 
two individual vacuum tubes that were at hand, a 6C5 and a 6V6. But the 
latest version , which is the one in use now uses a triode-pentode 
vacuum tube contained inside the same glass envelope. Summarizing, the 
vacuum tube line up is as follows, a 6BA6 or similar pentode RF 
amplifier stage , a 12AT7 or the equivalent ECC81 in a Pullen Mixer 
configuration , a 12AT7 crystal oscillator and cathode follower, a 6BA6 
or similar regenerative detector and a ECL82 or similar audio pre-amp 
and audio power amplifier stage. The radio uses a homebrew solid state 
power supply with some special characteristics... Its maximum B + 
voltage is 140 volts DC, it provides plus 75 volts regulated DC for 
feeding the regenerative detector stage, and 6 volts DC for the 
detector's and the audio amplifier stages filaments, in order to keep 
the presence of 120 cycle HUM really low. With today's solid state 
diodes and integrated circuit voltage regulators plus the availability 
of high values of electrolytic capacitors, this power supply is almost 
like powering the receiver from a pair of B batteries and an accumulator 
for the filaments, like in the early days of radio, but without having 
to worry about changing the B plus batteries or recharging the 
accumulator !!
The radio was built without any attempt to make it a compact or 
miniature set, plenty space was left between the parts, so as to make 
experimenting easier. The regenerative detector in this final version is 
capable of tuning to several frequency ranges... With one "bandspread 
coil" it tune from 2.0 to 2.15 megaHertz, that is from 2000 kiloHertz to 
two thousand one hundred and fifty kiloHertz, that when mixed with a 5 
megaHertz crystal provide excellent bandspread coverage of the first one 
hundred and fifty kilohertz of the 40 meters amateur band, changing the 
crystal to 8 megaHertz, that by the way is a very common computer 
surplus quartz crystal, the the radio tunes to the 30 meters band, and 
provides you with a nice propagation indicator, as you can pick up the 
time and frequency standard stations that operate on 10 megaHertz, that 
serve as a reliable calibration source...A third crystal, that 
oscillates on 12 megaHertz provides reception on the first half of 20 
meters, making reception of CW stations found at the low end of 20 very 
easy.
But the KK-12's plug in detector coils feature also gives you the 
possibility of tuning to one or two megahertz wide segments of the short 
wave spectrum. Changing the detector coil to the general coverage one, 
and using the 5 megaHertz crystal, you can tune from seven to eight 
megaHertz , or from three to four megahertz according to the setting of 
the bandpass input tuning filter... Every crystal offers the possibility 
of two tuning ranges, one that comes out when you add the frequency of 
the crystal to the frequency of the detector, and the other one, that 
appears when you subtract the frequency of the detector from the 
frequency of the quartz crystal.
Let me add, that this is a "hands on the controls" radio, that requires 
the operator to tune in the radio frequency front end filter, the 
detector's frequency and the regeneration control. In the KK-12 design 
regeneration is so smooth,that once set for CW or Single sideband 
reception you can just leave it there, and when you want to do pick up 
some international short wave broadcast stations like Radio Havana Cuba, 
the only thing you have to do is back up the regeneration control a bit 
to listen to standard AM plus carrier signals...
Si amigos, yes my friends, homebrewing the KK-12 is a very nice 
project,and when properly built, this radio has an amazing sensitivity 
and selectivity !!!, so good in fact, that one of my favorite 
demonstrations is to connect the KK12 and my Kenwood TS820 to the same 
antenna by means of a coaxial switch, and show visitors at CO2KK how the 
two radios pick up a weak signal on 40 meters... something that usually 
leads to them leaving my home with the KK-12 schematic diagram and step 
by step building instructions !!!
........
This is Radio Havana Cuba,the name of the show is Dxers Unlimited, and 
yes amigos, you can receive our nice   QSL card, just send a signal 
report and comments about this program to arnie@xxxxxx, again 
arnie@xxxxxx or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba Havana, 
Cuba, and now here is as promised, ASK ARNIE part two, a brief 
description of the Desert Rat Three, NA5N's solid state regenerative 
receiver... It uses a simple untuned RF stage for isolation, a 
regenerative RF stage , an emitter follower , a germanium diode 
detector, two audio amplifier stages and at the tail end, an integrated 
circuit audio amplifier. The original circuit is designed for tuning 
between 6 and 15 megaHertz with a single coil that is wound on a small 
length of plastic tubing, so there is no need to search for hard to find 
ferrite toroid cores.
Tests done by the author, show that the receiver is capable of picking 
up a mininimum detectable signal level of minus 105 dB referenced to one 
microvolt on CW, while on the AM mode, the sensitivity is -93 dB or 5 
microvolts...
The Desert Rat 3 uses very common transistors, nothing rare or hard to 
find here, and I have built several of them without using a single new 
from the box electronic component, in other words they were built using 
just recycled parts !!!
Ah, before I forget, the same original tuning coil, when shunted by an 
extra 100 picofarads capacitor , provides a more limited coverage tuning 
range from 5.5 to 7.5 megaHertz, so you have more bandspread when tuning 
to the 49 and 41meters international broadcast bands and the 40 meters 
ham band...
I am now working on  new easy to see schematic diagrams for both the 
KK-12 regenerodyne and the Desert Rat 3, so you can send your request 
for both of them via e-mail to arnie@xxxxxx, and I'll add you to the 
mailing list !!!

And now amigos as always at the end of Dxers Unlimited, when I am here 
in Havana, your welcome to listen to Arnie Coro's HF plus low band VHF 
propagation update and forecast .. Solar flux is at rock bottom baseline 
level of 70 flux units, and there are chances for some high latitude 
propagation disturbances to happen, The effective sunspot number is just 
17 units, so the daytimemaximum useable frequency curve keeps staying 
below the 22 or 23 megaHertz marker even at peak times... After Thursday 
HF propagation will improve a bit, with better chances for nice 
equinoctial DX on the AM broadcast and the Tropical bands... Hope to 
have you all listening to the weekend edition of the program and don't 
forget to send your signal reports, comments about theshow and radio 
hobby related questions to arnie@xxxxxx or via AIr Mail to Arnie Coro, 
Radio Havana Cuba, Havana, Cuba.
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