Dxers Unlimited
Dxers Unlimited's mid week edition for 20-21 April 2004

By Arnie Coro

Radio Amateur CO2KK

Hi amigos radioaficionados around the world and in space !!! This is the mid week edition of your
favorite radio hobby program, Dxers Unlimited . the one and only dealing with practically all
aspects of our wonderful way of properly spending part of our spare time: RADIO !!! Here is now item
one: Amazing as it may sound, designers continue to produce very simple radios that work quite well.
several recent examples appeared in the latest edition of SPRAT, the British QRP or Low Power
Amateur radio club.. I'll describe two of them for you here later into the program. Item two: Dxers
Unlimited's fans continue to enjoy the use of our exclusive and not copyrighted, in the public
domain, HF plus low band VHF propagation updates and forecasts, and you are telling me about how
useful they are for Dxing. as always , the propagation forecast will be available at the end of the
program, Item three: Apologies to those who are used to reading the scripts of Dxers Unlimited on
several Internet distribution lists. I have had to do some computer hardware work, and in the
process, the automated resending of the scripts software somehow was lost. sounds familiar ? Sure,
anyone using computes has seen things just vanish without leaving trace , and that's what happened
with the sending of the scripts to several lists . Item four: The 13 meters long wire with
counterpoise antenna, also known as the HALF W3EDP seems to work much better as a sloper, with the
sloping angle between 20 and 45 degrees providing the best signals. It is certainly an ideal antenna
for portable work, that can also be installed as a standby system at your home QTH. Item five: ASK
ARNIE, continues to be THE most popular section of the program , closely followed by the HF plus low
band VHF propagation forecasts, and at a not too distant third place, I found ARNIE's WORKSHOP,
after receiving several kind complaints from listeners that told me to include Arnie's workshop more
often into the menu. So, I will do it today, as this program is yours amigos !!! Jose Costa Pupo is
my sound engineer and producer here today, and for those of you that miss Margarita. she is now
enjoying her retirement after 35 years of continued work as sound engineer. Standby now for more
radio hobby related information coming to you from Havana with love. I am Arnie Coro, radio amateur
CO2KK.

..

This is Radio Havana Cuba, the name of the program is Dxers Unlimited, and YES amigos, we do QSL, we
do verify reception reports, and with a fast turnaround too.. send your signal reports and comments
about our programs to arnie@rhc.cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana , Cuba.
now, here is item one. SPRAT, the British G QRP Club magazine happens to be a treasure chest of
fascinating radio circuits and projects.. each issue of SPRAT is full of very interesting
information for the radio hobbyst, and the SPRING of 2004 edition of SPRAT is no exception .. Three
different short wave receiver circuits are part of ths issue, and two of them are extremely simple
ones, so easy to build that I started to collect the parts as soon as the magazine reached my post
office box on Monday. An experimental direct conversion receiver designed by Rudi Burse, radio
amateur DK2RS from Konstanz , Germany uses four green light emitting diodes or LED's for the
detector. The GREEN LED receiver simply consists of a tuned circuit for the band you want to
receive, link coupled to the antenna, and to the detector that is made using two series connected
green LED on each leg of the product detector. The injection oscillator has to deliver 6 volts peak
to peak to the detector diodes, and the audio recovered is sent to a standard high gain audio
amplifier .Why Rudi used green light emitting diodes for the detector of his direct conversion 80
meters receiver, I can't tell, but you can be sure that as soon as I finish wiring up and testing
mine, you will certainly learn about how it worked in an upcoming edition of this program !!!

The other ultra simple receiver published in SPRAT's Spring 2004 edition uses the well known
POLYAKOV direct conversion circuit. The POLYAKOV detector uses the injection oscillator at half the
operating frequency , in this particular case, the VFO uses just one NPN small signal transistor
connected to a quartz crystal, operating at half the frequency you want to receive. Oleg Borodin,
radio amateur RV3GM from Lipetsk , Russia was the designer of this 20 meter band direct conversion
receiver that the G-QRP Club Magazine published in its Spring 2004 issue. The radio uses two
anti-parallel connected silicon diodes for the detector, a single Russian KT315 NPN small signal
transistor and the audio amplifier is an LM386 integrated circuit running from a 9 volts battery.

I have already scanned both ultra simple receiver circuits, and have them ready for e-mailing them
to Dxers Unlimited's fans around the world that may like to experiment with such simple, yet
effective receivers. My own personal experience with the original JAGUEY direct conversion
transceiver, designed way back in 1982, is that when used with a well designed front end input
circuit, those receivers provide amazing sensitivity, with signals as low as 1 microvolt easily
detected. but, they do have one drawback, their selectivity or ability to separated between stations
is very poor. The direct conversion radio receivers are used for picking up CW Morse Code Signals ,
Digital Modes and Single Side Band,but they are not good for receiving AM signals, and can't pick up
FM modulated signals at all.

Direct conversion receivers are also known by two other names. SINCHRODYNE and HOMODYNE . in the
first case, SYNCHRODYNE comes from the fact that the local oscillator operates at the same frequency
of the station that you want to receive, and for that reason the receiver's output is the audio
carried by the station. The exception to this rule is the POLYAKOV synchronous receiver, that uses
the local oscillator at half the received frequency. The HOMODYNE name comes from the fact that the
direct conversion receiver uses the local oscillator at the same frequency as the one you want to
receive. Greek prefix for same, is of course HOMO,so this radios are also known as HOMODYNE
receivers !!!And after this complex lexical explanation, let me add something.The original JAGUEY 82
Cuban designed single band amateur transceiver, was tested against a sophisticated and really
expensive factory built transceiver. The tests showed that our design was at least as sensitive as
the very expensive professional equipment , registering a measured sensitivity of less than one
microvolt per meter, producing perfect CW Morse Code copy of such a signal. Adding well engineered
audio filtering to a direct conversion receiver can turn it into a really wonderful radio by all
standards amigos. NOW, here is my special offer for today: TWO SIMPLE DIRECT CONVERSION RECIEVERS
DIAGRAMS and building instructions available to all Dxers Unlimited's listeners that request them to
my e-mail address: send your request for the DIRECT CONVERSION RECEIVERS INFO PACKAGE to
arnie@rhc.cu, again, arnie@rhc.cu, and I will send it to you via e-mail as a graphics attachment.
For those of you without e-mail capability, just send a postcard to Arnie Coro, Radio Havana Cuba,
Havana, Cuba, and Irma , from our correspondence department will send you a printed version of the
circuit diagrams and building instructions !!!

Radio is a fun hobby, and believe me amigos, there is nothing more magical than listening to a radio
receiver you have just finished building !!!

.




Si amigos ! Your radio is tuned to Radio Havana Cuba, soon to celebrate its 43rd year on the air at
your service. I still remember when our first 10 kiloWatt Swiss built Brown Boveri transmitter went
on the air as an experimental station on the 24th of February of 1961. As the steel towers for the
antennas had not arrived yet from Switzerland, and we needed to put the station on the air, we made
our first two antennas using wooden poles from the local power company !!! Today, at the Bauta
transmitting station West of Havana, we are installing new 100 kW transmitters, that have already
replaced the original ones !!! So I am sure that you will be picking up our station in a much better
way by now !!!

Item two: Yes, all tests done here show that the 13 meters long single wire antenna plus
counterpoise works better as a sloper !!! As a matter of fact, I already installed one permanently
sloping down from one of my towers at CO2KK. The 13 meters wire sloper is working nicely on the 20
meters band with my 2 Watt QRP or low power transceiver that I enjoy using around 14060 kiloHertz,
the international QRP calling frequency.

Item three: Short visit to Arnie's Workshop. that by the way needs a full clean up and organizing to
take place as soon as possible !!! At a corner of one of the two workbenches, I am giving the
finishing touch to a homebrew antenna tuner.This one is rather unusual because it was designed for
portable operation and fits into a very small case. It uses two compact air spaced variable
capacitors and a homebrew coil fitted with 15 taps, that will give a very wide range of tuning
possibilities. As soon as the project is completed, I will make start testing it with my new QRP
multi-band rig, that operates from 160 to 10 meters providing 5 Watts on all modes !!!

You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and amigos, as
always at the end of the show,here is our exclusive and not copyrighted HF plus low band VHF
propagation update and forecast. New sunspot region is growing and should be kept under close watch
as a possible source of solar flares during the next few days. Solar flux is moving slowly up,
getting now near to a nice 120 units count, while the A index, the all important geomagnetic
disturbance indicator was at a nice and low 5 units Tuesday at around 15 hours UTC. The effective
sunspot number SSN has climbed to 63, and that , together with the still prevailing equinoctial
propagation conditions is providing maximum useable frequencies as high as almost 40 megaHertz in
areas of the Earth under full sunlight. So, expect a nice peak in propagation to be enjoyed during
the next two to three days !!! See you all at the weekend edition of Dxers Unlimited, and don't
forget to send me your comments about the program, radio hobby related questions and QSL requests to
arnie@rhc.cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba