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Re: [HCDX] Dxers Unlimited's mid week edition script for 23-24 October 2007
Dxers Unlimited
Dxers Unlimited’s mid week edition for 23-24 October 2007
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 nice examples have
frequently appeared in SPRAT, the British QRP or Low Power Amateur radio
club’s magazine.. 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.,
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 computers has seen things just vanish without leaving trace , and
that’s what happened with the sending of the scripts to several lists
…But now after some tweaking, it’s working again.
Item four: The 13 meters long wire with a fan type counterpoise antenna,
works much better when installed 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. By adding an easy to homebrew loading coil at
the lower end of the antenna, it is possible to make it work from 80
meters all the way up to 6 meters. It is fed at the top using 50 ohms
coaxial cable with a coax balun, and one counterpoise radial, so you may
call this a dual counterpoise antenna system !.
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 !!!
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@xxxxxx, 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 each and every issue of SPRAT
brings a lot of valuable radio hobby related information …. Now , a new
offer by the G-QRP Club is making available a CD that contains all the
issues of SPRAT from number one to number 136, and that amigos is a
treasure chest of really valuable radio hobby related information.
Three different short wave receiver circuits will be the subject of my
comments here today, they are all extremely simple ones. 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 by SPRAT magazine 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. 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@xxxxxx, again, arnie@xxxxxx, 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, 46 years 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…And that was our first high
power transmitter, because when we began to operate, we started by using
a 1 kiloWatt Gates short wave rig that had a 4-1000A output tetrode,
modulated by a pair of 833 triodes. 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 have 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 now !!!
Item two: Yes, all tests done here show that the 13 meters long single
wire antenna plus end loading coil 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… Solar activity continues to be extremely low, as we are
going trough another extended period of zero sunspots… The slight
disturbances are due to coronal mass ejections, not to solar flares.
Expect rather nice conditions on the 25 meters band , that is 11.6 to
12.1 megaHertz practically all day long… as it is now the most useful
band for international short wave broadcasting , closely followed by 31
meters, spanning from 9.4 to 9.97 megaHertz. For radio amateurs, your
best band for Dxing during local evening hours will continue to be 40
meters amigos!
No signs of solar activity increasing for the moment, as the winter DX
season advances with the lowest sunspot count in the past 11 years !!!
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@xxxxxx, or VIA AIR MAIL to Arnie
Coro, Radio Havana Cuba, Havana, Cuba
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