Dxers Unlimited

Dxers Unlimited's mid week edition for 13-14 April 2004

By Arnie Coro

Radio amateur CO2KK




Hi mis amigos radioaficionados !!! Welcome to the mid week edition of your favorite radio hobby
progam, the one and only attempting to cover practically all aspects of this wonderful pastime that
was born almost two centuries ago, when experimenters began to play with spark transmitters and
coherer receivers !!! Since the early days of radio amateurs have played a very important role in
its development, making some very interesting discoveries that served to make better and better
communications. Today the radio hobby continues to bring in challenges, but of a rather different
nature. as complex electronics is very difficult to assimilate at the home workshop.nevertheless
more and more radio hobbysts are enjoying building kits that, when properly assembled provide top
notch performance. And talking about radio kits, one of my dreams is to be able to design and then
provide the parts and instructions for a simple, yet effective short wave receiver using what could
best be defined as appropriate technology, in other words, parts and components that may be easily
available and at low cost. as many of my lifetime dreams somehow have managed to become true, maybe
one day I could present to Dxers Unlimited's fans around the world Arnie Coro's DREAM SHORTWAVE
RECEIVER KIT, with a nicely written and comprehensive , fully illustrated instruction manual.
Perhaps Cuba's fast developing electronics industry could make this possible in the not too distant
future. In the meantime , I do offer you all the circuit diagram and printed circuit board layout of
the AUSTRALIAN FUN solid state regenerative receiver for which you can find the parts at electronics
stores that sell components to individual users.

Item two: I was right, and others were not !!! My observations of the SUN during Friday and
Saturday,until Dxers Unlimited script was written gave me the impression that solar activity had
taken a clear downward trend. BUT, I read at least one forecaster's prediction saying that solar
activity was going to increase this week, something that was totally wrong,as the number of sunspots
has gone down to very low figures. Monday April 12, the sunspot count went to 16, and the Sun disk
was almost spotless . Item three: ASK ARNIE today will answer questions having to do with replacing
components in broken down equipment. a topic that enters into the Frequently Asked Questions here. I
will also give you some information about a very special OLD ANTENNA, the W3EDP wire that offers an
amazingly simple and practical solution when you are operating portable, and that may be also used,
with due care, at a fixed location.At the end of the program , Dxers Unlimited's HF plus low band
VHF propagation forecast will help you plan your listening for the rest of the week . Standby now
for a few seconds, as the show continues after a short musical intercut. I am Arnie Coro in
Havana,STAY TUNED !!!

..




You are listening to Radio Havana Cuba , the name of the show is Dxers Unlimited, it's a radio hobby
program for both newcomers and experts, attempting to cover the more than 77 ways you and I enjoy
this great hobby : RADIO !!! And here is once again la numero UNO. ASK ARNIE. THE most popular
section of this program according to your e-mail messages , letters , postcards and FAX reports.By
the way, our FAX number is country code 53, area 7, and the number is 8785810. so the whole number
to dial after you gain access to the international dialing is 53-7-8785810,and for those of you
familiar with telecommunications developments the need to dial 7 numbers for reaching a telephone in
the city of Havana is clearly indicating that the number of telephones here has increased
dramatically in the past 4 years or so, after practically all the city's telephone exchanges were
upgraded to digital technology. again our FAX number is dialing from abroad , 53 which is Cuba's
country code, then dial 7 for Havana, and 8785810. But of course, if you have access to e-mail, its
much cheaper to send mail to arnie@rhc.cu... Again arnie@rhc.cu... Well back to ASK ARNIE. the
questions that I will be answering today have to do with a problem that is becoming more and more
acute every day when one is attempting to repair obsolete electronic equipment. PARTS REPLACEMENT.A
typical question was sent last week by listener Daniel in Vancouver, Canada, he ASKS ARNIE if he can
use a different output transistor to replace the one that failed in a 3 ampere power supply he uses
for his QRP or low power amateur radio transceiver. Well amigo Daniel, this is what could best be
described as a problem that you can easily solve by following this simple instructions. First, look
for the specifications of the series pass power transistor that failed in your power supply. Write
them down, and then do a search for a more modern NPN transistor of similar specifications. Or you
can simply do what I did recently when having to deal with a similar problem. I simply replaced the
whole discrete components voltage regulator with a 5 ampere Integrated Circuit Voltage Regulator,
that fitted perfectly into the heat sink that was used by the series pass transistor. One
interesting fact about this particular way of handling the problem, was that the power supply ended
up working with much better regulation and had the added feature of the so called fold back current
protection that is built in into the typical modern integrated circuit voltage regulator. And of
course that I saved all the parts replaced by the upgrade , so that they can be used for other
applications. In your case amigo Daniel you have two options, one to find a direct or near direct
replacement for the damaged power transistor, or just do what I did and upgrade your supply to the
more modern circuit.

Unfortunately not all electronic components problems can be solved as easily as Daniel's power
supply. for example, I received a post card from England, Dxers Unlimited's fan George asks if he
can replace an octal vacuum tube type 6SK7 with another more modern type, as there is no way he can
find a 6SK7. Well amigo George from Southhampton. sure, you can make an adaptor and replace the 6SK7
with a 6BA6 7 pin miniature vacuum tube or valve, as they call them in England. The 6BA6 also exists
as another vacuum tube type in the European catalogs. but at this moment I simply can't remember .
It should be an EF something, that you can look around using old vacuum tube equivalents catalogs. I
remember that not too long ago a similar problem was solved at my workshop, when a beautiful 1940's
vintage Hammarlund Super Pro SP400X receiver was revived using several 7 pin miniature vacuum tubes
that were fitted with carefully built adapters, so when and if the original octal 8 pin metal tubes
are found the radio may be restored to its original state.

...




Si amigos ! Dxers Unlimited is a unique radio hobby program , providing you with useful information,
answering your questions on the air and via our fast turnaround e-mail service. We also provide
propagation updates and forecasts too. Here is our next item for today. The W3EDP single wire
antenna.Its rougly 25 and a half meters long, or 84 feet if you are not yet into metric
measurements. It's a single wire antenna, it can be installed horizontally or sloping from a tall
mast, it does need at least one ground radial or counterpoise . and you MUST USE an antenna tuner,
BUT, you can be sure that once properly installed it will work ON ALL BANDS from 3.5 to 29
megaHertz. It is known as the W3EDP antenna, honoring the callsign of the radio amateur that created
it by running many experiments and staying with the wire length that provided the best results.

The W3EDP is typically used with at least a ground wire radial connected directly to the antenna
tuner and having a minimum length of about 6 meters, but the best possible arrangement is to install
ground wires of quarter wave length for each band that you are going to operate.

Something that one day I am going to try is the half length or 12.5 meters W3EDP , that will very
probably operate quite well from 40 meters all the way up to the high end of the 10 meters band. For
portable work, the HALF W3EDP provided with at least one 10 meters long ground radial or
counterpoise is something worth trying , and nothing could be simpler to install !!

Si amigos, yes my friends, oui mes amis, simple antenna like the W3EDP and the HALF W3EDP have
proven to work , and they offer radio amateurs and short wave listeners properly equipped with
antenna tuners the easiest and lowest cost approach to enjoying our hobby. Remember those figures.
25 and a half meters for the full size version, and 12 and a half meters for the half size version.
And don't forget that YOU MUST USE at least one counterpoise or ground wire connected to your single
wire antenna tuner ground input !!!

Any questions that you may want to ask about this ultra simple single wire antenna can be sent to
arnie@rhc.cu, again arnie@rhc.cu or VIA AIR MAIL, a postcard will be fine. send it to Arnie Coro,
Radio Havana Cuba , Havana, Cuba.

...

Yes, scientists are now pretty sure that debris from comets do have an influence in some particular
types of short wave and low band VHF propagation. According to recent research results when the
Earth travels along the debris left by certain comets, an interaction with the upper atmosphere
happens, and that in turn creates high levels of ionization at an altitude of between 90 and 150
kilometers above the surface of the Earth.

We all know that form of propagation pretty well, yes, we all have seen TV DX on the lower band
channels, worked radio amateurs on 6 meters and picked up mobile units operating on the 30 to 50
megaHertz band via SPORADIC E LAYER SKIP. and according to this recent research results , at least
one form of SPORADIC E propagation can be traced to the Earth's transit trough space debris left by
those very peculiar visitors of the Solar System. the COMETS !

And now amigos just before going QRT,here is our exclusive and not copyrighted HF and low band VHF
propagation update and forecast. Solar activity is at very low levels, expect an almost spotless Sun
for the next several days, and much lower daytime maximum useable frequencies caused by the much
lower radiation levels reaching the ionosphere. Renewed heliosysmic observations of the farside of
the Sun reveal at least one developing sunspot region, but it will take several days before this one
rotates into view. in the meantime make good use of the much lower ionospheric absorption that we
will be enjoying during the next five to seven days amigos, and that translates to excellent AM
broadcast band DX becoming available !!! See you all at the weekend edition of the program and
please do take a little time to send me an e-mail with your comments about the program. they do help
me a lot to make Dxers Unlimited better for you all amigos !!! Send mail to arnie@rhc.cu, or VIA AIR
MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba.