Re: [HCDX] Dxers Unlimited's weekend edition for 20 -21 October 2007

["Prof. Arnaldo Coro Antich" <coro@xxxxxxx>]

Radio Havana Cuba

Dxers Unlimited

Dxers Unlimited's weekend edition for 20-21 October 2007

By Arnie Coro

radio amateur CO2KK

Hi amigos radioaficionados around the world and orbiting the Earth. This 
is the weekend edition of your favorite radio hobby program, the one and 
only covering all , each and every aspect, of our wonderful hobby.... 
from short wave listening as you are doing right now, to exploring the 
deep far space with a homebrew radiotelescope... from giving the 
finishing touches to a new receiver assembled from one the excellent 
kits available, to experimenting with a new antenna concept like the 
spiral loaded dipoles that are now becoming quite popular among radio 
amateurs that live in very tight quarters... Si amigos, yes my 
friends... there are more than 81 ways in my list, 81 plus ways of 
enjoying our wonderful hobby : RADIO... And here is now a nice 
example... as quartz crystal manufacturing techniques have developed at 
a fast pace during the past decade, the cost of crystals cut for some 
specific frequencies used by the computer industry has gone down 
dramatically... so now, it is not too difficult to assemble your own 
quartz crystal bandpass filter, an essential component of any receiver 
or transceiver that is going to be used for serious amateur radio work.

Recently I learned about the availability of certain specific 
frequencies , that are particulary good for homebrewing the bandpass 
crystal filters, that can be designed to provide the bandwidth required 
for operating on different transmission modes. So now not only the once 
popular color burst frequency crystals of 3579 and 4433 kiloHertz used 
by the NTSC and PAL color TV systems are available to the 
experimenter... the new computer clock frequencies crystals are more 
plentiful and cheaper...

But there is still another use for those computer crystals, and that is 
using them to provide the injection frequency for front end converters 
used ahead of regenerative receivers, turning them into a type of radio 
known as a  REGENERODYNE...

More about the low cost computer crystals and how they can be used for 
making filters and front end converters crystal oscillators in a few 
seconds, after a short break for our station ID.

I am Arnie Coro, radio amateur CO2KK and as always it is my pleasure to 
share with you about seventeen to eighteen minutes of on the air, on the 
web and on the Hispasat satellite tiem amigos... stay tuned..

........

This is Radio Havana Cuba, the name of the show is Dxers Unlimited and 
yes, we do QSL, we do verify reception reports  with a nice QSL card.... 
send your signal reports and comments about our programs to 
arnie@xxxxxx, or VIA AIR MAIL to Arnie Coro , Radio Havana Cuba, Havana, 
Cuba.

Low cost mass produced computer quartz crystals are making possible that 
radio experimenters homebrew some really excellent crystal filters. A 
recent example was brought to my attention my amigo Colbert , who lives 
near London's Gatwick International Airport. He sent me the circuit 
diagrams of several crystal ladder type filters that he has experimented 
with. The simplest one of them all used three 6000 kiloHertz crystals 
that he carefully matched using a friends digital frequency meter. 
Colbert explains in his e-mail that

he obtained information about ladder type crystals filters from several 
different sources, and decided to experiment with them. He has done a 
lot of experiments, and one of the most interesting ones is a variable 
bandwidth ladder filter that he will be using in a new project, an 
amateur radio transceiver for the 20 meters band that he is now 
planning. Colbert has built a six crystals ladder filter that according 
to him works exactly as it should... He says in his e-mail : Arnie, the 
professional engineering literature calls those ladder filters by the 
name of " Assymetrical lower sideband ladder crystal ladder filter" and 
I fully agree with the authors of the paper , because when the six 
crystals filters was tested with professional laboratory equipment, the 
shape of the frequency response curve as assymetrical and favoring the 
lower sideband, exactly as the authors of the research paper had stated 
. The most important thing about these filters is that those computer 
crystals are becoming cheaper and cheaper, so if you do have a lot of 
patience, the crystals can be tested and their poles and zeros of 
resonance plotted... Then with that precise information at hand the 
design of ladder filters is not too difficult. Well amigos, as you have 
realized, Colbert has gained a lot of experience about crystal ladder 
filters and his results are very consistent...

A high quality bandpass crystal filter can be bought , but they are not 
cheap, and besides that, if you homebrew your own filter, you learn a 
lot more about radio and electronics, and that's part of the enjoyment 
of the hobby too...

.......

ASK ARNIE, si amigos, ASK ARNIE, is the most popular section of Dxers 
Unlimited... it is la numero uno, the number one favorite of our 
worldwide audience, because as listener Gary from Florida in the USA 
writes, by listening to or reading the scripts of Dxers Unlimited, you 
can learn a lot of interesting things about radio... Today's question 
also came from Florida, listener Stewart from Clearwater wants to know 
what should the frequency response of a bandpass filter should be so 
that the best possible quality AM broadcast band reception is achieved. 
Well amigo Stew, this is a tough question, a difficult one indeed, 
because one needs to understand that AM broadcast stations transmit on 
10 or 9 kilohertz bandwith channels, depending on what  part of the 
world they are located... That  means that at either side of the 
carrier, the audio bandwidth is limited to 5 or 4.5 kiloHertz, depending 
on the part of the world where you are located. According to highly 
qualified engineers, the ideal AM broadcast band receiver filter for 
listening in the Americas, that is ITU Region II should have

a bandwidth of SIX KILOHERTZ.... and a very abrupt shape factor

between the minus six dB and the minus sixty dB points of the filter's 
response curve.  Listening trough such a six kiloHertz bandwidth filter 
will make it mandatory to tune the station so that the minus 6 dB point 
of the response curve falls about 500 Hertz to one side of the 
carrier,and then your radio will be picking up the full carrier plus one 
of the sidebands, something that is very good, because you won't have 
any distortion caused by selective fading. Your sharp cutoff filter will 
cancel one of the sidebands, and because an AM signal transmits two 
identical sidebands, your receiver will produce a high quality audio.

So amigo Stew, again, look for a SIX kiloHertz bandwidth filter if you 
want to listen to AM broadcast band stations with good quality and 
without the bad effects of selective fading distortion. But, if you

want to hunt for real DX on the AM band or for that matter in the

Long Wave AM band , then my advice is to add a second filter to your 
receiver, that will provide you with a 2.4  or 2.7 kiloHertz 
bandwidth... Such a narrow filter is used by practically all Dxers 
involved in AM broadcast band activities for a very good reason, and 
that is the fact that it can dramatically reduce the adjacent channel

interference that many times makes it impossible to obtain a clear

ID of a DX station whose operating frequency is right next to a local or 
semi local station...

AM broadcast band and Long Wave broadcast band DXing are two of the 
favorite ways of enjoying our wonderful hobby amigos, and you can log 
many DX stations using low cost receivers too... But, as expected, 
better radios will bring in many more DX stations , of course !

......

And now let's move to our next item of today's weekend edition of Dxers 
Unlimited... getting ready for the upcoming ham radio contest season... 
Radio amateur operators around the world are now getting ready for what 
is going to be a really challenging contest season. The extremely low 
solar activity will make contest operations really difficult, and long 
standing contest teams are looking for special advice from HF 
propagation experts in order to optimize their operations so as to make 
as many contacts as possible under the expected very poor band 
conditions. As one of our local contest enthusiasts told me last week, 
the time windows to areas of the world with high participation are going 
to be  of very duration, so in order to have good chances to place among 
the first in any contest, very accurate propagation forecasts are 
essential in order to make the best possible use of the very short time 
windows that are expected during the next several months due to the 
extremely low solar activity...

Having a propagation guru at hand during the contest will certainly make 
a lot of difference amigos !!!

And talking about HF propagation, having access to the on line data of 
the world's network of ionospheric vertical incidence sounders will make 
possible to produce very accurate short term forecasts, the ones that 
are required by contest operators.

......

This is the weekend edition of Dxers Unlimited and now our next item... 
a quick visit to Arnie's workshop... share with me a couple of minutes 
testing my new assymetric pulses battery charger that has

already revived several nickel cadmium rechargeable batteries that I had 
thought could not be recharged any longer. Apparently the assymetric 
pulses produced by the new battery charger design removes bad areas of 
the plates and brings the cell back to its full

capacity. The circuit is not very complicated, but of course that it

is not as simple as the typical constant current charger built around

an integrated circuit voltage regulator device....Batteries continue to

be a weak spot of the radio and electronics industry, and although many 
new concepts are now in the experimental stages, like is the case of the 
newer versions of the lithium based batteries , there is still need for 
more basic and applied research to be done in order to

increase the overall efficiency of these sources of electricity 
essential for the operation of so many of today's electronic equipment.

And now amigos , as always at the end of the program, here is

Arnie Coro's Dxers Unlimited's HF plus low band VHF 30 to 60 megaHertz 
propagation update and forecast... Solar activity has stayed at 
extremely low levels with the solar flux not even reaching 70 units, 
while the optical sunspot count has been just one zero after the other.

On Thursday the Planetary A index showed a marked increase ...

   

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