Dxers Unlimited
Dxers Unlimited's mid week edition for 30 Sept and 1 October 2003

By Arnie Coro

Radio amateur CO2KK




Hi amigos radioaficionados around the world !, you are now listening to Radio Havana Cuba's twice
weekly radio hobby program, Dxers Unlimited that comes to you on Tuesdays and Wednesdays UTC days
for the mid week edition and Saturdays and Sundays UTC days for the weekend edition. I am Arnie
Coro, radio amateur CO2KK , your host here in Havana and here is item one... what a nice HF
propagation we all enjoyed during the weekend.... The 10 meters amateur band came back to life after
a terrible summer season, and it was really a joy to hear stations from all over Europe, South
America, and the Asia Pacific region for what may be the last 10 meter Dx season of this solar
cycle... I also heard several South American stations on the 50 megaHertz band , but could not work
them because my 5 element 6 meter band Yagi is down for repairs... The ionospheric absorption was at
quite a low level for most of the weekend, so many signals usually buried by the local noise level
came out in the clear, making reception of several 60 meter tropical band stations possible...It
seems like we may continue to enjoy good HF propagation during the next several days, because there
are no signs of really significant solar coronal holes or large active sunspot regions.... Item two:
Radio is a lot of fun, because you can play with your radios in many different ways... for example,
a very interesting challenge for medium wave AM broadcast band Dxers is often overlooked... that
challenge is simply testing your receiving setup capability to pick up stations during the local
daylight hours, from two hours after local sunrise to about an hour before local sunset... The only
propagation mode available during those hours is the so called ground or surface wave, and it is
really amazing how a good AM band Dxing setup can bring in stations from very far away via the
ground wave mode... More about surface wave or ground wave AM band dxing later in the show... Item
three: Breadboard construction " a la antique ", like our grandfathers and great grandfathers
assembled their radios is also a lot of fun... You can test many circuits, rewire them to a new
configuration in a few minutes, and after you are sure that everything is working properly, then you
can simply make the breadboard radio look better by placing the wiring in such a way that it will be
appealing to the eyes of those you are going to show the receiver... More about breadboard
construction and all its possibilities later... Item four: No, I can't miss it , its going to be
always here by popular demand, YES, I am talking about the very popular YOU HAVE QUESTIONS section
of Dxers Unlimited. Today I will be answering a question sent in by a listener in Hong Kong, who
picks up the show via the INTERNET live audio feed... And as always at the end of the show, I will
be presenting Arnie Coro's HF plus low band VHF propagation update and forecast...with the most
recent data available about the behavior of the ionosphere... Stay tuned for more radio hobby
related information , direct and from the source... I'll be back with you in a few seconds...




.......

This is Dxers Unlimited's mid week edition amigos, and now here is item two in detail...When
everyone thinks about AM medium wave broadcast band Dxing, the mind goes immediately to the local
night hours... As many of you familiar with AM band Dxing know, the existence of the highly
absorptive D layer during the local daylight hours, blocks the frequencies below about 2 megahertz
or so from reaching the E layer of the ionosphere.

Then the only available service from the AM stations operating from about 530 kiloHertz to 1710
kiloHertz is provided by the surface or ground wave, that propagates along the surface of the Earth,
and the attenuation of those ground wave signals is very significant, so to explain it in simple
language, the distance that AM stations may reach during the local daylight hours is limited, and
the lower the frequency that the station uses , the greatest distance that it can reach via ground
wave. In other words, Am stations using frequencies between 530 and 800 kiloHertz will be heard at
much farther distances during the daytime daylight hours than those using frequencies above 800
kiloHertz. As a matter of fact, experts split the AM broadcast band into three frequency ranges...
from the above mentioned 530 to 800 kiloHertz that provides the best ground wave signals, from 800
to 1200 kiloHertz that have a more limited range during daytime, and the frequencies between 1200
and 1700 kiloHertz that are limited to much shorter daytime coverage. Daytime AM dxing is also
dependent on another very important key element... ground conductivity, and that explains why
daytime reception of some stations is possible at impressive far away distances when between the
transmitter and the receiver the only the ocean is present. Sea water has a very high conductivity,
when compared to any type of land, so AM signals traveling over the ocean suffer very little
attenuation amigos ! AM broadcast band daytime Dxing is one of the more than 70 ways you and I enjoy
this wonderful hobby, and you can be sure that by carefully tuning the range from 530 to 1710
kiloHertz during the local daylight hours you will be able to log in several stations that are
really far from your location... Log them in, and send their chief engineers a daytime report... I
can assure you that response to your QSL request is going to be much faster than when you report AM
band skywave DX at night !. Want to know why ? .... The answer is very logical , AM stations are
designed for local ground wave coverage, and those are the reports that they can show to their
advertisers in the case of commercial stations or to those that provide the operating budget in the
case of non-commercial broadcasters !




.......




Si amigos, this is Dxers Unlimited's mid week edition reaching you from Havana, and here is the URL
for our streaming audio, so that you can type it directly into your Internet browser... , well I
think I'll better wait a bit before giving the direct URL for the audio, so that you can reach your
notepad and pencil or pen to write it down...Now here is item three... My most recent radio project
is a breadboard version of the simple three vacuum tubes regenerative receiver... It is mounted on a
piece of half inch plywood to which I attached an aluminum panel. The power supply providing 150
volts D.C. for the plates and screen electrodes and 6.3 volts DC for the filaments is also built
using a smaller breadboard.

The three tube sockets and the two coil sockets were mounted using long bolts , to that the socket's
connecting points may be easily reached for soldering. The receiver uses a 6SK7 Radio frequency
amplifier stage, a 6SK7 regenerative detector and a more modern triode-pentode ECL-82 audio
pre-amplifier and output stage. The coils were wound to cover from the AM broadcast band up to
almost 16 megaHertz, giving me the possibility of listening to the most popular short-wave
international broadcast bands and also to the 160,80,40,30 and 20 meters amateur bands.

I did enjoyed assembling this radio because there was almost no need to drill holes trough metal,
except for the ones that I had to made to the aluminum front panel in order to install the main
tuning and bandspread capacitors dials, the regeneration and the audio gain control.

This is , like all straight regenerative receivers , a radio that does require an operator right at
the controls, but , I can assure you that it has amazing sensitivity and when taken to the point of
the edge of regeneration, selectivity is also extremely good. The use of DC regulated voltage on the
filaments of the detector and audio tubes also helps to reduce background hum, often present in
tuned radio frequency and regenerative receivers that are powered from the AC house power lines
instead of from batteries.

Breadboard construction is excellent also for teaching , as one can follow the wiring from the
schematic diagram very easily... so it is difficult to make wiring mistakes during construction.

You can provide very nice finnishing to the breadboard radios by learning from old radio handbooks
and magazines, the ones that our grandfathers and even great grandfathers used to learn about the
hobby during the early days of this wonderful hobby.......

.......

Well, I hope you have now your notepad ready, so here is the direct URL for the streaming audio ...
it starts with mms, not with the more common http... so here it goes:

mms://tvinternet.icrt.cu/rc4

again, now in phonetics..

mike mike sierra, colon, slash, slash, tango victor india nancy tango echo romeo nancy echo tango,
symbol for period india charlie romeo uniform

slash romeo charlie 4...

mms://tvinternet.icrt.cu/rc4




Now here is today's radio hobby question, sent in by listener Mike in Hong Kong.. Dear Arnie, I pick
up RHC via Internet... my question is if you think that there is a short-wave receiving antenna that
can be useful here in Hong Kong, where space is really at a premium. Dear amigo Mike, the antenna
that I will strongly recommend you is the MAGNETIC LOOP, of no less than one meter diameter, and if
you want to tune stations on frequencies below 10 megaHertz better, then go for a two meters
diameter magnetic loop. These loops have to be constantly retuned when you change frequencies, but
they have three distinctive advantages over long wires, inverted L's or dipoles. First they are more
much more compact and may fit almost anywhere... You can even keep them in storage and unpack them
just for the time you are listening. Secondly , they offer a very high Q, so that adjacent channels
interference is less noticeable, and in the third place, the magnetic loops offer the unique
advantage of ground wave signals cancellation by turning the loop around, so at locations like yours
with many noise sources and a high background noise level, you can turn the loop around to obtain
the minimum possible noise level and achieve a significant improvement in front to back ratio.

Search the INTERNET using the words MAGNETIC LOOP ANTENNAS and placing a plus sign in between the
words on the search engine... You will be suprised by the hard work done by radio amateurs in order
to develop this unique antenna system... !

And now as always at the end of the program, here is Arnie Coro's HF plus low band VHF propagation
update and forecast... Solar activity will continue to move from low to moderate according to
scientists, the effective sunspot number is around 90, while the A and K indexes are going to be
nice and low, enhancing the equinoctial propagation conditions. The 3000 kilometers maximum useable
frequency worldwide map shows some paths with the MUF reaching figures not seen for many months now,
and 6 meter band openings are possible on North-South paths across the equator. AM medium wave band
and Tropical Bands DX conditions are certainly going to be good during the next 72 hours if no big
solar flare erupts to change the propagation. See you all at the weekend edition of the program and
don't forget to send directly to me your signal reports and comments about the program... Send mail
to: arnie@rhc.cu, and VIA AIR MAIL, a postcard will be nice sent to Arnie Coro, Radio Havana Cuba ,
Havana , Cuba.