Dxers Unlimited

Dxers Unlimited's mid week edition for 30-31 December 2003

By Arnie Coro

radio amateur CO2KK

Hi amigos radioaficionados, welcome to the mid week edition of your favorite radio hobby program !!!
Yes, this is Dxers Unlimited coming to you from Havana with love !!! And by the way, this happens to
be the last program of the year 2003 my friends !!! Seasons Greetings to you all and I wish a very
happy and prosperous year 2004 to all Radio Havana Cuba listeners around the world.

Talking about the new year, 2004 is going to see a lower level of solar activity, so the higher
short wave bands will not be as active as they have been for the past five years now... Both the
number of solar active sunspot regions and their average size is expected to take a downturn,
sending the daily sunspot count way down as the cycle continues towards its minimum expected to
happen sometime between 2006 and 2007... Item two: A bit more about solar activity, the number of
sunspots now around 55 and the solar flux will be reaching below one hundred levels soon... But at
the same time we are going trough a period of diminished geomagnetic activity, so now ionospheric
absorption is going to go trough a nice minimum ideal for AM medium wave broadcast band and amateur
160 and 80 meter bands Dxing during your local evening hours... Item three: DRM digital radio
mondiale systems tests continue but they seem to be targeted not to the general audience of short
wave listeners at all, as the actual number of radios and adapters able to pick up the DRM digital
broadcasts is extremely low... In order to pick up the DRM transmissions you will need either a
special receiver or a combination of a digitally tuned very stable receiver and a computer program
that will decode the DRM into analog audio output from your computer's soundcard. It is remarkeable
that so far the DRM consortium has not offered a freeware version of the software required to be
able to listen to such experimental transmissions that are supposedly the begining of a new era in
short wave broacasting... Beginnings that only a very selected few engineers at the properly
equipped monitoring stations can listen to. Seems like marketing is definetely not the strong side
of the DRM consortium !!! Item four today ... YOU HAVE QUESTIONS and Arnie tries to answer them the
most popular section of Dxers Unlimited, and then if time permits the technical topics and at the
end of the show I will be presenting the year's end HF plus low band VHF propagation update and
forecast amigos !!!

Stay tuned and continue to enjoy short wave listening during the holidays...

I am Arnie Coro in Havana back in a few seconds

......

You are listening to the mid week edition of Dxers Unlimited and for those of you that tuned in
late, again Seasons Greetings from sunny and beautiful Cuba. Here is now item four in detail: The
question, send in by no less than six , ah, here is another one, so seven Dxers Unlimited fans had
the same question... They all want to know what is the minimum transmitter power requirement for an
amateur radio station to really get trough most of the time, and the question is obviously related
to buying equipment for their ham stations. Well amigos, everyone knows I am a QRP or low power
operation fan, but you should understand that running QRP is quite a challenge, so I will set up for
the compromise power of a minimum of 20 Watts output... but there seems to be a problem, there are
very few factory built amateur radio transceivers in that power category, so , you must all go for
what the market is offering.... the so called 100 watt class transceiver that in most cases is
really a 50 to 70 Watt real radio frequency output set... With the nowadays standard 100 Watt class
ham radio rig and even the most simple antennas, like a half wave wire dipole, or a quarter wave
vertical you can work the world when conditions are right, and at least make some two way contacts
when propagation is not all that good. Of course that you all must be aware that under poor
propagation conditions, even professional super power HF communications stations equipped with huge
antennas have a hard time ... So, again, here is Arnie Coro's advice if you are contemplating a nice
little present to give to yourself in the form of a brand new amateur radio transceiver... go for
the 100 Watt class radios and forget about higher power ... as you won't need it 90 percent of the
time !!! Use your hard earned money to install higher and better antennas !!!

.....

>From Havana , this is the mid week edition of Dxers Unlimited, you can send your signal reports and
comments easily via e-mail... send mail to arnie@rhc.cu again, arnie@rhc.cu, and you will get a
really fast reply, as I check personally that mailbox several times each day... Now item five, the
technical topics section of the program, another one many of you like a lot.. Today's topic: design
a simple receiver for homebrewing ... that's a request that I have received here from many RHC
listeners that have shown an interest in building their own radios. After working on that project
for several weeks, I think that I just came out with a nice little solid state receiver that can be
built by someone with a little experiene in electronics. The project is certainly not for beginners
as is... but could be adapted for newcomers if it could be made available in the form of a kit.

This receiver is quite sensitive, and has good overall selectivity, although it will not match an
expensive professional radio... Anyway, here is the lineup, and don't be surprise with what you are
going to hear...

First of all , as expected, it is a fully solid state radio that operates from a 12 volts DC power
supply or a 12 volts accumulator or battery. The lineup starts with an overvoltage protection module
for the front end that includes a static electricity discharge path, something very important with
solid state radios if you are planning on using long wire antennas !! This is followed by a radio
frequency signal attenuator, then a band pass two section filter that feeds the radio frequency
amplifier stage. The active components used for the RF amplifier are two common NPN transistors in a
cascode configuration that feed a very conventional broad band diode mixer. The local oscillator is
crystal controlled and the crystals are changed in order to switch bands. The output of the mixer
goes to an intermediate frequency amplifier variable gain stage than feeds a rather unconventional
tuneable regenerative detector stage that uses a dual gate MOSFET device... Audio recovered from the
detector is then fed to a rather conventional integrated circuit audio amplifier ... SO this is , as
some of you have already noticed, a solid state regenerodyne receiver , that in this particular case
is capable of tuning from five to thirty megahertz, depending on the way you arrange the front end
converter. The dual gate MOSFET detector tunes from 2 to 4 megaHertz, so that each band is exactly
two megahertz wide . For example, if we use

a five megahertz quartz crystal to control the frequency of the local oscillator, the tuning range
of the receiver will be from seven to nine megaHertz, giving you the possibility of listening to the
40 meters amateur band, the 41 meters international short wave broadcast band and all of the
utilities that can be still be found all the way up to nine megahertz. Changing the crystal to 9
megahertz rock will allow you to tune from eleven megahertz all the way up to thirteen megahertz, so
you can listen to that very interesting segment of the short wave spectrum that includes the 25
meters international broadcast band and again lots of long range utilities like the operating
frequencies used by the aviation long distance operating centers to control oceanic areas out of
reach of the normal VHF coverage. The new design uses common parts, common resistors and capacitors
values, and the only components that may be a little hard to find are the twin gang variable
capacitor required for the bandpass input filter tuning, and the variable capacitor and dial mechani
sm that are needed for the

regenerative detector stage frequency tuning.

The rest of all the parts are even obtainable from recycling old electronics like TV sets, VCR's FAX
machines and early computers...

As the project advances I will have available the circuit diagrams and building instructions, so you
can e-mail your request for the NEW SOLID STATE RADIO FOR HOMEBREWERS... send mail to arnie@rhc.cu,
and as soon as the diagrams are finished and the text file with the detailed instructions ir
reviewed I'll start mailing them to those of you who may want to build this modular radio to
experiment with, and also as a nice addition to your shack,where, as always, having more than one
receiver at hand is really good when looking for DX !!

.....

Amigos , this is the mid week edition of Dxers Unlimited coming to you from Havana, and here is item
six: a short tip regarding the use of surge protectors... YES, you can install them all by yourself
by connecting them across a power strip's input. The surge supressors especially made for 115 volts
AC power lines are no larger than some disk ceramic capacitors, and they do add a lot of overvoltage
protection to the equipment connected to the power strip to which they are attached. Surprisingly
they don't cost much and are available from most mail order electronic supply dealers under the name
of VARISTORS, SURGE SUPPRESSORS or similar names. It won't take too much time to solder a couple of
them in pararell with the power line, and enjoy that extra bit of protection from power line
transients that are so damaging to modern electronics !

And now, just before going QRT, here is Arnie Coro's Dxers Unlimited's HF plus low band VHF
propagation update and forecast... Solar sunspot count around 55 and moving down,solar flux will be
reaching the below 100 units mark really soon, and the A index, or planetary geomagnetic disturbance
indicator will be also down below 8 units... but not for long, as scientists are forecasting yet
another coronal hole related increase in solar wind speed and particle count.. There are some
probabilities of sporadic E openings for the frequency range between 20 and 100 megaHertz, as the
winter E skip season is now on its way. Expect still rather high maximum useable frequencies on some
paths during your local daylight hours, so call CQ from time to time on 10 and 12 meters and you may
be pleasently surprised with a DX station or two answering... See you all next year amigos, hope you
keep listening to Dxers Unlimited during all of 2004 too !!!