Dxers Unlimited

Dxers Unlimited’s weekend edition for 20-21 November 2004

By Arnie Coro

radio amateur CO2KK

Hi amigos radioaficionados, this is the weekend edition of your favorite
radio hobby program, coming to you from Havana. I am Arnaldo, Arnie,
Coro, radio amateur CO2KK, your host here, now ready to share with you a
bit more than a quarter of an hour of air time totally devoted to our
wonderful hobby, yours and mine: RADIO…

Here is item one… a geoeffective coronal hole sent a stream of charged
particles towards the Earth and we are seeing right now, as you listen
to the show the effects of the high speed solar wind hitting the
planet’s magnetosphere… The K index has moved up, and those of you
living at latitudes higher than 40 degrees North will be able to feel
the effects of the geomagnetic disturbance. At lower latitudes, effects
on the ionosphere are less noticeable. Item two: old radios, old vacuum
tube radios didn’t use the standard antenna input connectors that we see
today… and many times users of such so called boat anchor receivers are
unable to obtain maximum sensitivity from them, because of the
characteristics of the old receivers antenna input circuit… today I’ll
give you all a practical low cost solution that will boost reception
from old vacuum tube radios , and that can be fitted in just a few
minutes, without affecting the receiver’s eventual re-sale value as a
collectors item. The menu continues with our popular tips and techniques
section, ASK ARNIE with your questions, QSL on the air, and as always at
the end of the show, our exclusive and not copyrighted HF plus low band
30 to 60 megaHertz propagation update and forecast… Stay tuned, as Dxers
Unlimited’s weekend edition continues in just a few seconds , Jose Costa
Pupo is my sound engineer and producer, I am Arnie Coro in Havana.

…..

Si amigos, you are listening to Radio Havana Cuba, coming to you via
shortwave and also via the Internet from www.radiohc.cu
<http://www.radiohc.cu/>... Here is now how to improve old vacuum tube
receiver’s sensitivity by using a very inexpensive and almost
universally available part, the ubiquos TV 300 ohm balanced to 75
unbalanced balun.

For about $2.00 (or even less), the sensitivity of many "boat anchor"
receivers can be improved up to 20 dB (or even more!). This improvement
involves no modifications to the receiver except, possibly, to remove
the external ground jumper from the antenna terminal strip on the back
of the receiver.

Many of the older receivers were designed for balanced antenna feeds
with an impedance of from 300 to 600 ohms. Just take a look at the
service manual. For example, my HQ-140X manual states that the antenna
impedance is 400 ohms. My Collins 51J-2 has an antenna impedance of 300
ohms. The Hallicrafters S-85 manual says antenna impedances from 52 to
600 ohms, the same thing for the S-107. The list goes on.

Poor matching between the 50 ohm coaxial cable antenna downlead used
nowadays with the coaxial fed antennas simply don’t matching well into
these receivers. However,the solution is rather easy… it consists of
using those "cheap" TV baluns that can be had from all sorts of sources
(including free with video tape players, etc.).

Adapting the type "F" connector to take a PL-259, It is then very easy
to hook up the coaxial fed antenna into the receivers. Every one of them
tried with the impedance adapter showed really improved performance
after the installation of the balun.

I made some sensitivity measurements using the calibrated attenuator in
one of my workbench test instruments. Depending on the band, the signals
improved by a minimum of 10 dB to almost 20 dB when comparing the direct
50 ohm feed into the receiver as opposed to using the TV balun.
Frankly,amigos this is a pretty good improvement!

For those concerned about the bandwidth of the TV type baluns ,here is
the answer running bandwidth tests on many baluns over the years show
that they were designed to pass a minimum lower frequency of 5 MHz. This
is because of certain signals that may be present on the Cable TV
Systems. Most of these baluns made it down to the broadcast band with no
problems at all

Old radios like the Hallicrafters SX-100, S-85, and S-107 like the
baluns as well as Hammarlund’s HQ-129 and HQ140X and the classic
National NC-2-40D. The newer receivers like the Collins 75S1,
75S3A,Heathkit SB-301,or GPR90, etc. all were designed for 50 ohm coax
and definitely do not need the assistance of the TV balun.

The TV type baluns are designed to convert 300 ohms into 75 ohms. But,
they do an excellent job of matching the 50 ohms feed to the balanced
requirements of the "boat anchor" receiver. Is it exact? Of course not!
But, the nominal impedance of the receiver varies with the particular
band, and, especially on general coverage receivers, within the band itself.

Therefore, this is a "cheap", but effective, method of improving the
sensitivity of those old vacuum tube receivers without having to dig
into the antenna input circuits, as you can place the TV type balun
right next to the antenna terminals and remove it very easily too…

…..

QSL on the air, to amigo Roger Chambers in New York…

Dear amigo Roger: Hope that you are now picking up RHC both

in Spanish and English with much better signal strength and modulation  quality, as we continue to install the new transmitters and antennas.

It was sad to learn about the passing away of well known radio hobby enthusiast John Killian, of whom I have heard a lot by many of my listeners of DXers Unlimited, especially from my friends in Mexico.

 I was  invited this year to go to the Mexican DX meeting, but could not make it, and Manolo de la Rosa, the host of EN CONTACTO in Spanish,  of RHC who was also  invited could not attend either.

 

Just to remind you of our frequency changes --- 6060 kHz in Spanish to East Coast from 00 to 05, and in English from 05 to 07.

6000 kHz in Spanish from 23 to 00, in English from 00 to 07 split

between 00 to 05 to East Coast and from 05 to 07 antenna change to

Pacific Coast of North America.

9820 kHz in Spanish to Great Lakes region from 23 to 00 and will soon continue in English from 05 to 07 UTC. 73 and DX, Your friend in Havana (Arnie )

It is always nice to hear from Dxers Unlimited listeners, you can contact me directly by sending an e-mail to arnie@rhc.cu <mailto:arnie@rhc.cu>, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba…More good news a new INTERNET E-mail list devoted to regenerative receivers, it was started at YAHOO by my good friend Gary Johanson WD4NKA, and here is how to subscribe to this list, as received on a message sent to me as a reply by Gary , I told amigo Gary in my message the following:

As you know there are many homebrewers and radio experimenters

> plus tinkerers among the worldwide audience of the show, so

> expect a few people to subscribe...

> By the way , could you e-mail me the detailed correct subscribing

> procedure, so that I can read it on the air slowly, thus

> increasing the chances of listeners to pick it up correctly !!!

> 73 and DX

> Arnie Coro

> CO2KK

> AND HE ANSWERED THE FOLLOWING …