Dear ODXA members:
Greetings from sunny Havana !
You are kindly invited to send your comments, suggestions and radio hobby
related questions to
inforhc@enet.cu
73 and DX
Arnie Coro
CO2KK
Host of Dxers Unlimited
Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited weekend edition 8-9 July 2006
By Arnie Coro
radio amateur CO2KK
Hi amigos,welcome to the weekend edition of this radio hobby program that is
broadcast twice weekly . I am Arnie Coro , radio amateur CO2KK, your amigo here
in Havana,
the capital city of Cuba, and I have just now completed a typical reverse HF
band-scan... Now, do you know what I am talking about... do you really know how
useful a reverse band scan is for both short wave listeners and amateur radio
operators ? Are you aware that a reverse band scan done by an experienced
operator can help to win ham radio contests like this weekend's IARU Radio Sport
contest ? Stay here on this frequency , or if listening via the world wide web,
keep your computer connected to our streaming audio, and in a few minutes I will
tell you about the very useful and easy to
do "reverse band-scan method" to provide you with a very accurate picture of how
HF propagation is behaving at a given moment... Item two: Homebrewing radios and
accessories is a lot of fun, and sure,there is no match to the unique feeling of
listening to a station using a receiver that you have built yourself... It
doesn't matter if the radio is just
a simple tuned circuit and a diode detector or a sophisticated quadruple
conversion, digital signal processing set... if they both were the product of
your hard work, then they will sound better than any commercially built
equivalent...
Take for example the many variations that are possible when you start by
homebrewing a very well designed regenerative receiver... Of course that you can
use it as a direct on frequency receiver as soon as it starts working... but the
best will come when you add a crystal controlled converter ahead of your
homebrew regenerative radio, to create a receiver known as a REGENERODYNE...
More about the REGENERODYNES and several other more radio hobby related topics
when Dxers Unlimited's weekend edition continues in just a few seconds. I am
your amigo Arnie Coro, radio amateur CO2KK in Havana, stay right here on this
frequency...
.......
Si amigos , this is Radio Havana Cuba's Dxers Unlimited's weekend edition ,and
here , as promised earlier is more information about the " reverse band-scan
monitoring technique"... Listen carefully... every time you connect the antenna
to your receiver or ham transceiver, my advise is to tune the radio to the
highest band of frequencies that it can be set... for example, a typical good
quality table top receiver will tune up to 29,999 or almost 30 megaHertz, so
when you begin your listening, set the radio to this frequency and start slowly
scanning down,until you hear the first signal ...
Write that frequency down, and continue scanning downwards, until you find more
signals... again write down
the frequency range where the first cluster of signals appears, and you have a
really valuable information about the actual state of the ionosphere ! For
example , Friday evening I ran the reverse band-scan procedure on my Grundig
Satellit 800 big size , not miniature portable, connected to my broadband TTFD
or Tilted Terminated Folded Dipole that provides broadband reception between
6 and 30 megaHertz.... The time was midnight local, that is
0400 UTC, and the first signals heard when tuning from my start up point that I
arbitrarily set to 25 megaHertz, considering the time of the day and the present
solar activity, came in at around 18 megaHertz... they were very weak, but
careful observation led to the conclusion that they were certainly ionospheric
propagation.... The first really strong cluster of signals came when the reverse
band scan reached 15.5 to 15.0 megaHertz, with by the way happens
to be a large part of the 19 meters international short wave broadcast band. Now,
with the already mentioned data, I just apply a very simple formula that has
given me excellent results when advising amateur radio contest participants...
Just multiply 15. times 0,75, again, the multiplying factor
is 0,75 and not 0.85 as usually recommended... Let's do it...
15 times 0.75 = equals 11.2, and sure enough from that frequency down is where
stations are heard for the next two to three hours.... Its both simple and
reliable, and you can learn how to use it by sending an e-mail to arnie@rhc.cu,
again arnie@rhc.cu , or send a postcard or letter via AIR MAIL to Arnie Coro ,
Radio Havana Cuba, and don't forget to include a line saying , reverse scan
method instructions, to which you may want also to add a reception report and
your comments about the program.
.......
This is Dxers Unlimited;s weekend edition, and now you will be listening to a
segment devoted to the practical , field testing of amateur radio antennas.
So you want to evaluate your new antenna ?
Then listen and if possible tape the program or take some notes
In order to properly evaluate the efficiency of HF Antennas is you must go
trough a very difficult and time consuming process, if you really want to do a
fruitful and useful test..
Listing of the number of contacts, signal reports, list of worked countries etc.
says nothing about the efficiency of the antenna.
Many radio hobby publications describe the quality of new antennas. But as many
of you know very well,
with just a short piece of wire connected to an antenna tuner one can perform
worldwide contacts under good conditions, while the best antenna does not allow
to reach any contact, if HF conditions are closed.
Also, the SWR of an antenna does not say anything about the efficiency of an
antenna.
The SWR only tells us, how good the transmitter is
matched to the antenna, but says nothing about the radiation of waves from the
antenna.
Based on the SWR, and following this line of thought then a Dummy Load would be
the best antenna, as it shows an SWR of 1.0 on all frequencies ...
The problem arises from the very different HF wave propagation, which shows
strong variations daily, hourly, and every single minute.
A signal report of S5 may be good, while a report of S9+10 may be a bad report,
as it all depends under what propagation conditions the report is obtained.
Now here is a practical procedure on how to evaluate correctly an amateur radio
transmitting antenna system
In order to evaluate correctly an HF antenna, this evaluation has to be done by
actually contacting distant stations.
The contact to a distant or DX station is by means of so called sky waves
signals, waves that come back to Earth reflected by the ionosphere.
To make a valid comparison, we need a defined second antenna, or a nearby
station what could be described as a comparison or reference station, working
with the same power, and a correctly installed and adjusted antenna with defined
characteristics.
Measuring in the near field, or in the ground wave is not suitable, as remote
contacts work through the sky wave at an elevation angle of between about 5 and
up to 50, 60 or even 90 degrees .
During the contact with a Distant Station, multiple changeover between the Test
Station and the Comparing Station has to be done, to allow the Distant Station
to dynamically make many successive comparisons of the signal levels of the two
stations, and to perform an averaging of the signals if there is fading or QSB
present.
This when done many times , will certainly average the results over time as you
will always receive some "strange reports", as some operators are unable to read
correctly the signal level, or even confuse the call signs.
Furthermore, you have to be really sure that the operator at the distant station
is really reading the S meter ! YES, one has to make sure, that a real signal
report is obtained, as many stations just report 59 without observing the signal.
So forget about Contests for running serious antenna tests.
After performing 40 to 60 such correct test QSOs, one obtains the real picture
of the efficiency of an antenna.
This procedure requires a real big effort, but it seems like it is the only
valid method to evaluate the efficiency of an
HF Antenna.
And add to this that in case of directional antennas, the test antenna, as well
as the comparing antenna have to be directed towards the Distant Station or
otherwise the results will be obviously wrong !!!
By the way amigos , this the procedure that I have used for the past twenty
years or so to evaluate new antennas for the HF spectrum in the frequency range
from 1.8 megaHertz up to the top end of the 10 meters amateur band on 29.7
megaHertz, and all I can say is that it does bring very consistent and many
times quite different from what you expect results...
......
Now here is Dxers Unlimited's very popular ASK ARNIE section of the program,
devoted today to answering a question sent by a listener that is the owner of a
war surplus
RAK-7 tuned radio frequency receiver... a boat anchor by
all standards, and also a museum relic... He wants to use it more, and asks me
if it will work OK with a frequency converter, because the RAK-7 tuning range
ends around 600 kiloHertz or so... ANSWER, Yes amigo Mark, the RAK-7 with a
frequency converter ahead of it will become an excellent
dual conversion receiver... a REGENERODYNE that will amaze you with its super
selectivity so useful for picking up
amateur CW Morse Code signals... But be aware that the highest possible
frequency for a single conversion will be
at the most the 40 meters or 7 megaHertz amateur band... so if you want to pick
up signals on the higher ham bands like
10, 14,18,21, 24 or 28 megaHertz , you have no choice but to homebrew a dual
conversion converter to install ahead of your very low frequency RAK-7 receiver
that will be used
always as a tunable intermediate frequency between around 150 and 600 kiloHertz.
And please take note that the RAK-7 antenna input circuit is not 50 ohms, but a
high impedance input designed for very short wire antennas...
Hope that this answers your question, and I wish you good luck with the
frequency converter project !!!
And now amigos as always at the end of the program, here is Arnie Coro's Dxers
Unlimited HF and low band VHF propagation forecast. Some nice 6 meter band
sporadic E openings picked up here on Thursday and Friday, indicating that the E
skip season is still in progress... Solar flux around 80 units and the A index
was a at a nice low level on Friday, and should probably continue at low levels
for the next two to three days... Expect some interesting late evening
propagation to your WEST, and don't forget to set your alarm clocks as early as
possible in the morning to enjoy
the best propagation possible at this time of the year, that is happening from
about 4 o'clock in the morning local time until about an hour after local
sunrise. Hope to have you all listening to our midweek edition next Tuesday and
Wednesday UTC, and don't forget to send an e-mail or a postcard with your signal
reports and comments about the program ... send e-mail to arnie@rhc.cu, and VIA
AIR MAIL send a postcard or letter to Arnie Coro , Radio Havana Cuba,
Havana, Cuba
