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Re: [HCDX] Dxers Unlimited's mid week edition 30 January 2007
Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited’s mid week edition for 30-31 January 2007
By Arnie Coro
Radio amateur CO2KK
Hi amigos radioaficionados around the world and in space ! Welcome to
the mid week edition of Dxers Unlimited that is reaching you when a
geomagnetic disturbance may be making reception of this program a bit
difficult for those of you located at latitudes above 40 degrees North
…. Yes, another high speed solar wind gust is the cause of this most
recent disturbance and scientists are learning more and more about how
to forecast the arrival of the stream of charged particles ejected from
the solar corona…. More about HF plus low band VHF propagation
conditions as always at the end of the program… Now here is item one:
At the request of many Dxers Unlimited’s listeners is the very easy to
understand description of the Inverted L antenna, and how you can
install one at almost any location . Ready to copy, here is a Dxers
Unlimited special …
THE EVER-POPULAR INVERTED 'L' ANTENNA
Have you ever wanted to install a shortwave receiving antenna FAST?!!!
Then I am almost sure that you will want to learn more about the
'Inverted L' antenna... About the easiest effective skywire that you can
try to build ...
Just two supports... they may be two masts, a mast and a tree, a mast
and a nearby building... it need not be perfectly horizontal above
ground... as a matter of fact if the inverted 'L' is installed in a
slightly tilted angle, of around 20 to 30 degrees , it seems to work
better for Dx signals.
Although strictly speaking a true inverted L has the downlead connected
to one end of the horizontal section... my version calls for connecting
the downlead (a single wire) to a point about 20 percent from one end.
So for a 20 meters long horizontal section, the down leg of the Inverted
L is connected to a point four meters from one of the two ends, the one
that is nearest to your listening post or amateur radio station.
The antenna should be connected to your receiver via an antenna tuner
with a real wide matching margin. For a 10 to 15 meter horizontal
section, strung between two masts of about 5 to 7 meters each, you may
expect very nice performance on frequencies extending from about 6 to 30
megahertz."
Don’t forget that this is an antenna that MUST, and I repeat MUST be
used with an antenna tuner and a ground connection if you are going to
transmit with it, but that will work OK when connected to a radio
without the tuner, although , the difference between not using and using
an antenna tuner is really outstanding …
Si amigos, yes my friends, the Inverted L one of the first antenas used
by radio pioneers is still a very useable system that should be
considered when you cannot access the center of a dipole for bringing
down an open wire or a coaxial transmission line…
I always keep my Inverted L antenna ready , and it has proven to be an
excellent performer and also a very sturdy system under very high wind
conditions, something that may not be said of my multiband dipole, that
has broken down twice in the middle of a storm, while the Inverted L
stood up like a champ and allowed my amateur radio station CO2KK to stay
on the air providing much needed emergency communications relays during
a hurricane several years ago.
According to good engineering practice, your inverted L antenna must be
made using at least number 12 copper wire, and care must be taken to
bring in the downlead into the shack using a well designed trough wall
insulating system. Do remember that this antenna must work against a
ground system, and the prefered option is to install several wire
radials, cut to the lowest frequency band that you want to use .
Any questions ? … Just send them to arnie at rhc dot cu, again arnie at
rhc dot cu, and I will be more than happy to answer it as soon as
possible to help you to install and begin to enjoy your Inverted L
antenna very soon…
…….
Si amigos, yes my friends…You are listening to Radio Havana Cuba, the
name of the show is Dxers Unlimited and here is our next item for today…
it’s an e-mail from a listener , pointing at the fact that during the
weekend edition of the program I said that FM broadcast stations used
horizontal polarization, while he says that in the USA and in Canada too
, FM stations use circular polarization to make reception possible for
car radios that use a vertical antenna for picking up the signals.
Well amigo, what I was trying to explain is that the YAGI antenas for
receiving FM broadcasts are usually configured to receive the
horizontally polarized component of the signal transmitted by the FM
station, and so the boom of those antennas is drilled so that the clamp
used to hold it to the mast will put the antenna with the elements
parallel to the ground…that is to receive horizontally polarized radio
waves. So, when those antennas are modified to work on the 2 meters
amateur band for operating on the FM mode , the boom must be drilled so
that the antenna will have its elements in a vertical position, in order
to be able to pick up the amateur radio signals using the FM mode that
are vertically polarized….Ham stations doing weak signal work do operate
using horizontal polarization, and they use the low edge of 2 meters for
their long haul DX operations that include Earth Moon Earth
communications, extended tropospheric propagation and sporadic E layer
contacts…
And another listener wrote also to ASK ARNIE, wanting to know how he
could at least reduce the very high noise level that he is picking up on
his short wave radio when his family is using the two desktop computers
that they have. Well amigo Erik, as you told me during our e-mail
exchange, one of the computers is located right next to your short wave
radio, and I am almost sure that the very high speed microprocessor
working in the microwave frequency range is not the cause of the
interference. I will recommend that you run a test using a liquid
crystal display connected to the computer and then observe what happens
to the noise level… In many situations like yours, the main cause of the
high noise is the cathode ray tube monitor… Once the CRT monitor is
replaced by a liquid crystal display screen, the noise level will go
down dramatically. This is why radio amateurs have prefered using laptop
or notebook computers for log keeping and the digital communications
modes, because even older machines are less noisy than very up to date
desktop ones that still use a CRT monitor…
Another very practical and easy to implement test is to homebrew a
magnetic loop antenna and use it to cancel the main noise source, a
technique that has proven to be very effective for short wave listeners
and radio amateurs living in large apartment buildings…
Do remember that higher operating frequencies will almost always be
less noisy than the lower ones… That’s why radio amateurs that are
apartment dwellers have good success operating on the VHF , UHF and
Microwave bands… The same holds for VHF-UHF scanner enthusiasts that
will be discouraged when trying to pick up DX on the AM broadcast band
or the short wave bands, because of the high noise levels prevalent in
large apartment buildings while noise in the VHF and UHF bands may be
quite acceptable .
………
And now as always at the end of the program, here is our exclusive and
not copyrighted in the public domain, so that you may reproduce it
anywhere for the benefit of the radio hobby enthusiasts… here is Arnie
Coro’s Dxers Unlimited’s HF plus low band VHF propagation update and
forecast… Solar flux around 90 units and Tuesday morning local time in
Havana, almost at noon, that is 17 hours UTC the A index was at 42, yes
42, indicating geomagnetic storm conditions that as I said at the start
of the program may be making reception of our station difficult at
latitudes above 40 degrees North. We may even see some Auroral Sporadic
E openings in Northern Canada and Europe too. But conditions will slowly
go back to normal by Wednesday. Hope to have you all listening to the
weekend edition of the program next Saturday and Sunday UTC and don’t
forget to set a little time aside to send me your signal report and
comments about Dxers Unlimited, that certainly help to make it a better
program the next time I am on the air amigos ¡
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