Re: [HCDX] Dxers Unlimited's mid week edition 27-28 November 2006

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

Radio Havana Cuba

Dxers Unlimited's mid week edition for 28-29 November 2006

By Arnie Coro

radio amateur CO2KK

Hi amigos de la radio !!! In Spanish in means  Hello friends of radio 
... and yes you are surely one of those people that enjoys this 
wonderful hobby in its many different forms, from listening to natural 
radio noise generated by thunderstorms in an attempt to correlate it 
with possible sporadic E layer formation, to just talking across town 
with your best friend using a simplex two meter band frequency ... And 
there are 78 other ways of having a nice time playing with our radios, 
including the ultra sophisticated Earth Moon Earth or EME amateur radio 
contacts to spending a whole evening hunting for weak DX stations on the 
AM broadcast band as I did on Monday, when it was possible to pick up 
here in Havana AM stations from sixteen different nations amigos !!!

Now here is item one of today's program... an update about solar cycle 
23... Yes my friends , we just saw anotther three days in a row of zero 
sunspots, and this according to scientists is a good indicator that the 
solar cycle is still traveling towards its minimum , expected to be 
happening by the end of next year, 2007... So, be prepared to watch many 
days of incredibly low maximum useable frequencies that will come 
associated with very low ionospheric absorption as the D layer becomes 
almost transparent to lower frequency radio waves because of the very 
little solar radiation impacting on it.

Item two: Listener Gabriel wants to know if he can replace the output 
transistor of his 5 Watt QRP transceiver with another type that has more 
gain... And here at our popular ASK ARNIE section of Dxers Unlimited my 
answer is the following: amigo Gabriel it won't be an easy job, because 
NPN power transistors designed for radio frequency amplifier service 
have to be replaced by almost identical ones, if you don't want to 
retune the amplifier , something that may require changing the bias 
resistors to other values.

As a good friend of mine likes to say, vacuum tubes are much more 
forgiving to homebrewers that solid state devices !!!

Stay tuned for more radio hobby related information, coming to you in a 
few seconds, when Dxers Unlimited's mid week edition continues... I am 
Arnie Coro in Havana.

.......

You are listening to Radio Havana Cuba, the name of the show is Dxers 
Unlimited and here is item three of today's show: Part two of ASK ARNIE, 
answering a question sent in by long time listener Fred from , I hope to 
pronounce this OK, Missisauga , Ontario , Canada. Amigo Fred wants to 
obtain a design for a compact wire antenna for the 40 meters band, as he 
has space only for an antenna about the size of a 20 meters band half 
wave dipole...

NO PROBLEM amigo Fred... you can homebrew and install a dual band, 
actually a tri-band antenna that will operate on 40, 20 and also on 15 
meters , by following these instructions.

First, build an half wave 20 meters band dipole, and feed it by means of 
one to one balun with 50 ohms coaxial cable.

After tuning up this antenna for minimum standing wave ratio on 14.15 
megaHertz, proceed to install in parallel with the 20 meter band dipole 
an antenna that has exactly the same length but that in the middle of 
each wire element has a loading coil that I will describe right now. The 
loading coil is made using two inch or 50 millimeters diameter white PVC 
pipe , but if you can't find that diameter locally, a one an half inch 
diameter, that is almost 38 millimeters diameter pipe will do OK.

For the two inch or 50 millimeters coil form, you must wind 
------------------- turns of number 18 or 1.2 millimeters diameter 
copper enamelled wire... The turns are close wound and protected from 
the weather by applying two layers of PVC electricians tape. After 
wrapping the coils withthe PVC tape, you apply several coats of enamel 
paint to provide further protection to the winding.

As you may realize, the two antennas are effectively in parallel, but 
they will sort of disconnect themselves automaticall when the wrong 
frequency is reaching them.

For example, if you feed 14 megaHertz or 20meters ham band 
radiofrequency to the pair of paralleled dipoles, the 20 meter antenna 
will accept power and radiate it, while the 40 meter band antenna simple 
disconnects itself because it shows a very high impedance at the center 
insulator.

Likewise if you feed 40 meters band energy to the system, the 20 meters 
band antenna will behave as a very high impedance load, and will take 
practically no power to be radiated.

We have tested here the efficiency of this tri-band system and to our 
amazement, losses on 40 meters are pretty low, in the less than 2 
decibels from a full size antenna range.

Now let me add that this is a triband antenna, because the 40 meters 
center loaded dipole will behave as a three and half waves center fed 
dipole antenna, a very effective multi-lobe radiator by all standards. 
Of course that for running this antenna on 15 meters using a solid state 
transmitter or transceiver, you will certainly need to feed the radio by 
means of an antenna tuner, as the standing wave ratio that can be 
expected will very probaly exceed the maximum admitted by the 
transmitter before starting the power cut back feature due to high SWR, 
in the fortunate case that your set has this additional circuit.

Anyway, this is a very compact tri-band antenna that has a very high 
radiating efficiency on 15 meters, and also on 20 meters, and it is 
about minus 3 dB or half of an S unit down as compared to a full size 40 
meters band antenna , something that is really not significant at all.

Adjusting this antenna system will require the use of a good , reliable, 
standing wave ratio meter, and some patience, especially for tuning up 
the 40 meters band shortened dipole element to the part of the band 
where you want it to resonate. I had installed an identical antenna as a 
sloper on one of my towers, and started to compare results with the full 
size 40 meters band dipole fed with 350 ohms open wire line, and found 
out that on 20 meters and 15 meters there was practically no difference 
at all between the two antennas when switching back and forth between 
them, and on the 40 meters band reports from stations located up to 
about a thousand miles away were almost identical, but at longer 
distances the full size antenna did show an advantage , something to be 
expected.

Don't forget to weather proof the loading coils properly and that the 40 
meters antenna resonance is achieved by shortening or extending a length 
of wire hanging from that antenna's end insulators...

........

QSL , QSL , QSL on the air to the many Dxers Unlimited listeners that 
are reporting our new 6180 kiloHertz frequency ... your QSL cards are 
now on the way for all of you that sent e-mail reports and included the 
postal mailing address. Be aware that we are also using 9505, 9550, and 
11760 kiloHertz at different times of the day for our English language 
program to North America and the Caribbean, that sometimes can also be 
heard in Southern Europe and even as far away as Australia, New Zealand, 
Japan and India, according to reports received at my e-mail address: 
arnie@xxxxxx, again it's arnie@xxxxxx and VIA AIR MAIL it is Arnie Coro, 
Radio Havana Cuba, Havana, Cuba...

Now the next section of this mid week edition of Dxers Unlimited... a 
quick glance at Arnie's workshop, where sitting atop the workbench there 
is the latest hybrid REGENERODYNE receiver, now under test on several 
bands. I am quite pleased with the performance of the receiver's front 
end... it uses a time proven circuit arrangement that starts with input 
protection for the solid state radio frequency cascode amplifier, and 
continues with a signal attenuator and a dual tuned bandpass input 
filter. The RF stage uses two NPN silicon transistors with a transition 
frequency of 500 megaHertz, so in theory at least, they should be able 
to provide good amplification up to 50 megaHertz . The RF stage is 
followed by a broadband double balanced mixer using four silicon diodes 
and two ferrite transformers. The mixer has a broadband output feeding 
the vacuum tube regenerative's detector antenna input.

The frequency range of this REGENERODYNE depends on the injection 
oscillator's output frequency. Two options are available, one is a 
classic transistorized crystal oscillator, and the other is using 
computer clock oscillator modules that run on 5 volts DC and generate an 
ideal square waveform . With the 8 megaHertz computer clock oscillator 
the radio tunes to ten megaHertz , when the regenerative detector is 
tuned to two megaHertz, and when the detector is set to four megaHertz 
the radio tunes to twelve megaHertz providing good coverage , in this 
case of the 30 meters amateur band and practicall all of the 25 meters 
international short wave broadcast band. A four megaHertz crystal 
provides coverage from six megaHertz to 8 megaHertz, and that's the one 
I am using at this moment , because most of my tests are done in the 
evening local time, when the 49 meters  band and the 40 meters amateur 
band , plus the 41 meters international broadcast band are wide open. 
The sensitivity and selectivity of this receiver is simply amazing, 
connecting a short length of wire to the antenna input fills the dial 
with strong signals, and stability is also very good. I am using a 
Hartley regenerative detector circuit with screen grid regeneration 
control that has proven to be very smooth and easy to set... By 
advancing this control just above the point of oscillation of the 
detector , excellent CW and single side band reception is possible. The 
power supply is on a separate chassis housed at the loudspeaker cabinet 
and amigos, the radio has a beautiful sounding audio too.

I am still giving the finishing touches to this new version of the 
Regenerodyne that combines the best of features of solid state and 
vacuum tubes !!!

And now amigos, as always when I am here in Havana,at the end of the 
program here is Arnie Coro's Dxers Unlimited's HF plus low band VHF 
propagation update and forecast... Solar activity continues at very low 
levels with several days of zero sunspot count , and then a slow rise to 
a count of about 12, with the microwave 10.7 centimeters solar flux 
hovering around 80 units. We also felt the effects of a high speed solar 
wind gust, but that is over now, and you should expect propagation 
conditions that are typical for periods of very low solar activity and 
very quiet geomagnetic field, so I think that the higher end of the HF 
spectrum from about 22 to 30 megaHertz should be performing just like 
another VHF band amigos...Hope to have you all listening to the weekend 
edition of the program next Saturday and Sunday UTC days... Don't forget 
to send your signal reports and comments about today's program to my 
e-mail address arnie@xxxxxx, or VIA AIR MAIL send a postcard or letter 
to Arnie Coro, Radio Havana Cuba, Havana , Cuba.  

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