Dxers Unlimited
Dxers Unlimited mid week edition for June 3-4 2003

By Arnie Coro

radio amateur CO2KK




Hi amigos radioaficionados and TV aficionados !!! Welcome to the mid week edition of your favorite
radio hobby program coming to you from Havana. I am Arnie Coro, radio amateur CO2KK , and as always
it is my pleasure to share with you all about eighteen minutes of on the air and on the web time..
You can also read the scripts of this show by visiting www.radiohc.cu, going then to English, and
there you will find the Dxers Unlimited's scripts... Now here is item one: HF propagation conditions
continue to be in very poor shape to say the least, as the Earth is constantly receiving the solar
wind blasts and radiation that have caused so many interesting events during the last few days.
Monday morning here in Havana , I got a call on the metropolitan area primary 2 meter band repeater
from a local radio amateur.. Arnie, he said, just take a listen to the short wave bands... they are
totally dead ... I can hear nothing with my two radios... What's happening Arnie ?, he said.. I then
moved from my desk, and went to the main operating position at CO2KK my ham radio station, connected
the antennas, and started to scan from 5 megaHertz up, only to confirm what the local operator was
saying

Nothing heard from 5 megaHertz all the way up to 30 megaHertz... nothing at all, and when I say
nothing, I mean it amigos, the whole HF spectrum was totally dead, like if it was a microwave band
!!!. Obviously some kind of total ionospheric absorption event was in progress, the so called
Moss-Dillinger effect or total short-wave black out... Several other local radio amateurs, that are
new to our hobby listened to the QSO between CM2OP Olimpio and myself, and immediately started to
explore the short-wave spectrum, witnessing for the first time this interesting phenomenon that can
completely wipe out HF reception due to a tremendous increase in free electron concentration at the
D layer of the ionosphere that effectivly blocks all signals going up or down !!! Item two: Ask
Arnie , the questions and answers section of Dxers Unlimited is becoming so popular that it's
keeping yours truly pretty busy , but I must say that it brings in a lot of satisfaction, because
those who ask radio hobby related questions and solve their problems with my answers become more and
more interested and motivated to learn more about radio !!! Today I will answer two questions, one
is antenna related and the other one is related to television interference produced by short-wave
amateur radio transmitting equipment. Item three : You can certaily use the so called PLENNUM
coaxial cable, a type of cable that is now becoming available at very low cost or just for the
asking from computer network engineers.. networks using coaxial cables to link up computers are now
obsolete, and so many miles of excellent quality 50 ohm coaxial cable are waiting to be pulled out
and giving a second chance to be useful at your radio receiving or transmitting station amigos !!!
Item four, as always at the end of the show , will bring you the most up to date information about
HF propagation conditions and then Arnie Coro's forecast that will help you decide if its time to
listen to the radio , or , as it has happened during the past several days, your time will be much
better spend soldering parts to the circuit board of a new QRP transceiver kit !!! Margarita Delgado
is my sound engineer and producer, stay with us here on this same frequency or web streaming
audio... We will be back in just a few seconds...




............

Si amigos, this is the mid week edition of Dxers Unlimited, the radio hobby program with that
special accent on the technical aspects of our wonderful passtime: RADIO.. And here is item two ,
part one...Ask Arnie part one today's topic is answering a question sent in by a listener in Iowa,
who lives in an apartment building, and is having problems whenever he operates even with just

5 Watts on the 40 and 30 meter bands that are his favorites... Well amigo George, here is my
advice... Instead of using a commercially built television interference filter, make your own , and
much better one, with a cut-off frequency set for around 13 megaHertz... In actual practice, the
homebrew filter will have its minus three decibels attenuation point at 13 megaHertz, and that will
be almost transparent for the 10 megaHertz or 30 meter band signals, and totally transparent to the
7 megaHertz or 40 meter transmissions. The LOW PASS FILTER using what is known as a Butterworth
configuration , is very easy to homebrew and all I can say is that it is tremendously effective .
Commercial low pass filters for TVI prevention start their cut-off frequency around 35 or 40
megaHertz, and are not as effective as the Butterworth 7 section filter that I am recommending to
you amigo George !!! There is an excellent amateur radio freeware program , the brainchild of my
good Canadian friend George Murphy, VE3ERP, that will help you design your own highly effective
Butterworth type low pass filter... And Murph's program HAMCALC can be downloaded from the world
wide web, just run a search using one of the popular search engines and type VE3ERP... If you are
not able to find it, I do have it here, but sending it by e-mail may take some time to transmit and
receive, as the zipped HAMCALC file is a bit more than one megabyte.. Anyway, if you can't download
HAMCALC, just send me an e-mail and I will send the zipped file to you... Send mail to arnie@rhc.cu,
again, my compact easy to remember e-mail address arnie@rhc.cu... So amigo George, I must add that
building your own homebrew low pass filter requires a 60 watt or so soldering iron, so that you can
make the shielded compartments using double sided printed circuit board. The filter needs two female
coaxial connectors, 4 mica capacitors and three homebrew coils that are easily made using copper
enamelled wire.

Building low pass filters like the one just described will help you learn more about radio , will
cost little, and the filters are really very effective if constructed properly !!!

Now, here is Ask Arnie,part two... I received an e-mail from Don, KB5UVM a radio amateur operator,
regarding a multi band antenna design... Here is what he tells me and I quote from the e-mail:

Hi Arnie, I saw you latest article on the DXers website about ..." ask Arnie".... concerning ham
radio related questions. So, I have a question for you concerning off center-fed antennas. I
recently found instructions on how to build one using coax feed line and a 4:1 balun. The formula
given for the long and short

sides of the antenna is: for 80 thru 10 meters.....

Long section; 468/3.8 mhz = 123 x .66 = 81.5 feet

Short section; 468/3.8 mhz = 123 x .33 = 40.5 feet.

I built the antenna as per instructions and use Rg8x feedline to the 4:1 balun, and it is hanging at
35 between some trees.

Now I realize I shouldn't expect perfect results, because different installations

will get different results because of nearby objects, ground effects, etc. However, while the
antenna is usable at 3.5 mhz, the swr is greater than 2.5:1 on 40m and worse on all the other bands.

My question is....Since this antenna is supposed to be a multi-band antenna that DOES NOT NEED A
TUNER....and the author of the article says it works great on 80, 40, 20, 15, 10, and even 2 meters,
and that the vswr that he experienced was better (less) than 2 to 1. And in most bands it is less
than

1.5:1, (he says), why doesn't it work like that for me? I have more than 40 years experience in
electronics and building antennas, and I know how to solder and build antennas, but this one does
not work as advertised for me....what do you think I am doing wrong? The feedline is approx. 80'
long, RG8x, and

the elements are #14awg stranded copper, (insulated). It is suspended between two trees and the
height is 35' from ground to the feed point on the balun.

What do you think? Any ideas or suggestions will be deeply appreciated! I need a multiband antenna
that is simple and useable without the need of a tuner.

I enjoy listening to your show and I try to tune you in every chance I get....keep up the good work
Arnie.

Any help or suggestions will be deeply appreciated.

Thank you in advance.

Don, KB5UVM

OK amigo Don, first things first... after modelling the antenna you described very well in your
e-mail, using one of the most up to date antenna modelling software, I found out that the results
you are obtaining are exactly what to expect from such a design... In other words, the excellent
antenna modelling software shows that what you are seeing there is exactly correct... SO, here is
your friend Arnie Coro's advice... Number one: Use bare copper wire for your HF antennas, because
plastic insulation does change the velocity factor of the wire !!! Number two: If you really need a
multi-band antenna that works without an antenna tuner, you have only one choice... and that's
building the NEW TTFD, still a compromise antenna, but one that will offer much better performance
that the strange assymetric dipole you have built. Number three: If you really want to have an
efficient multi band antenna, and can afford a simple antenna tuner, then a fan dipole will give you
excellent results... My FAN DIPOLE design, using just three wires on each leg of the dipole,
provides 80 meters to 10 meters coverage with a leg length of just 13.4 meters or 44 feet... The
antenna is fed using 400 ohm homebrew open wire line that is then connected to a 4 to 1 balun, and
then coaxial cable is used to reach the shack... The length of the open wire line has to be no less
than a certain minimum in order for this antenna to work properly, and you will still need an
antenna tuner, but in this design the tuner can be located right next to your transceiver.

The NEW TTFD as per W4RNL design, requires the use of a 900 ohm or so non inductive terminating
resistor and a 12 to 1 balun. The NEW TTFD can be used without a tuner , but again, my advice is to
use a simple homebrew PI network antenna tuner. One additional solid reason for using a PI network
tuner is to avoid the radiation of harmonics from your transmitter, a problem that has to be taken
into consideration when using multi-band antennas !!! So amigo Don, if you need any more information
, just send an e-mail again to Ask Arnie.... mail to: arnie@rhc.cu

And now as always at the end of the show,here is Arnie Coro's Dxers Unlimited's HF plus low band VHF
propagation forecast... Sporadic E events now in full swing, with the Maximum Useable Frequency
curve reaching as high as the FM broadcast band several times last week, and more similar events are
expected. HF propagation conditions are rather poor due to the effects of recent solar activity
specifically from solar active region 10365, soon to turn around and dissapear from sight... Solar
flux is now going to start moving down, and hopefully the A and K indexes will be also coming down
to more HF propagation friendly figures during the next 3 to 5 days... See you all at the weekend
edition of the show, and don't forget to send your QSL requests and radio hobby related questions
via air mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba, and use the fast e-mail by sending to
arnie@rhc.cu