Saturday, March 19, 2016

The three vertical elements Bobtail Antenna for a single band
use... The element lengths are approximate, and the antenna
should be carefully adjusted for minimum standing wave ratio at the center of the operating band...
For example... if the antenna is to be used on the 20 meters
amateur band, then it must be cut for minimum Standing
Wave Ratio at 14.15 megaHertz ...

Friday, March 18, 2016

Beautiful combination of rugged CPVC High Pressure 150 psi
pipes and fittings, plus six vertical elements arranged as
a three elements Bobtail vertical array, with a three elements reflectors at about 0.18 wavelength separation.
Few with 50 ohms coaxial cable, using a 6 turns RF choke made of RG59U coax cable wound on a small length of 50 mm or
2 inches diameter CPVC pipe....

The SWR is carefully set to the center of the 2 meters band
that you use most... This is an ideal home built antenna that
can be made at low cost and using readily available materials...
The vertical elements can be made from aluminum tubing
of about 10 millimeters diameter to make it enjoy the
benefits of a large diameter pipe that provides wider bandwidth...



Hola amigos of Dxers Unlimited....
Lost in cyberspace... was this blog... Now I will try to keep it up to date, by the simple expedient of, among other things uploading the actual scripts of the two weekly editions of Dxers Unlimited, the radio hobby show soon to be celebrating its 25th year on the air...
So here we go:

Radio Havana Cuba
Dxers Unlimited middle of the week edition for
Tuesday 15 March 2016
By Arnie Coro
radio amateur CO2KK

Hola amigos radioaficionados all around the world now starting to enjoy the equinoctial propagation conditions despite several solar related disruptions during the past two days.... 

The daily solar flux continues to be holding below 100 units, and that is an indication that the solar cycle continues its slow but continuos downward trend.
 
By the middle of the A'16 broadcast period of the ITU in July we are expecting an effective sunspot number of around 40.... In the meantime we are now also approaching the spring and summer sporadic E season, that according to my own forecast should provide us this year with more openings and longer lasting events... something that is connected with the lower solar activity without doubts...
 
I am your host here in hot, sunny and dry La Habana Cuba, my name is Arnaldo, but everyone involved in radio knows me as Arnie.... well actually as Arnie Coro, the long time host of Dxers Unlimited... 

Now here is item two.... in the field of electronics technologies something new happens every day, and that is why developments are so fast... take for example the Software Defined Radios technologies that are making possible to create radio receivers, transmitters and transceivers that provide amazing performance, and as a matter of fact, performance parameters that can be tailored to exactly what is required... 

Also I just saw a new model of the Raspberry Pi ultra small computer, that when associated with Software Defined Radios programs are making possible to provide radio amateurs and short wave listeners with radios that match and exceed in many aspects the performance of analog classic radios that cost several thousand dollars... 

So here is my advice, if you really want to improve your monitoring post and your amateur radio station if you happen to have one, NOW is the moment to start learning about Software Defined Radio or SDR technologies , you will not regret all the time devoted to learning about what is going on in the SDR world...
 
Item three: several amateur radio contests during the upcoming weekends will provide you with opportunities to work many DX entities, and thanks to the electronic certified QSL cards, you can claim having worked them much sooner than when one has to wait for a hard copy air mail QSL card to reach the post office box.
 
Ham radio contests in my opinion are seeing some changes, like practically eliminating competitors that do not have access to the Internet and can send their logs electronically..
 
And that amigos , again in my personal opinion is not fair at all.... I wish that contests organizers should think about the fact that although connectivity to the Internet is increasing , there are still billions of people that do not have access to the Internet services, while in many countries the quality of service is very low, having to deal poor bandwidth connections....
 
Now more about contests.... as a good friend of mine that has participated in many contests both as an individual station and forming part of a group effort has underscored, ham radio contests seem to produce a unique effect on the ionosphere.... 

One day before the contest, just to give you an example, the 10 meters band was practically dead... with maybe one or two CW beacons heard at the peak of the propagation curve.... then the next day, same time, same solar flux, same A index , same K index... you find the SSB segment of 10 meters full of stations working the contest...
 
This is something that is really hard to explain, and some experts say that especially 15, 12 and 10 meters are open for DX during the local daily hours much more than one may believe... This is why I insist on calling CQ DX many times around the spot frequencies used by DX expeditions...
 
Just to give you an example... calling CQ DX on SSB on
28495 on 10 meters or 21295 on 15 meters has made possible for my QRP or low power station to establish many very good two way contacts at times when scanning the first 500 kiloHertz of 10 meters or the first 300 kiloHertz of 15 meters brought no signals at all.... 

Then after several CQ DX calls of those two frequencies , I find that there are people monitoring them and ready to come back to my call... Although a CO station is no longer considered DX, there are many radio amateurs that do need Cuba confirmed for their DXCC Award request...
 
By the way, there is an ongoing debate as regards of the SSB calling frequency for DX on the 12 meters band... so if you know about this topic please write to inforhc at enet dot cu , again inforhc at enet dot cu and tell me what frequency of the 12 meters band you consider to be the SSB calling spot. 

For those of you not familiar with the 12 meters band it is an allocation won by the amateur radio service back in 1979 and it spans from 24890 to 24990 kiloHertz, but do not ask me why the International Telecommunications Union Conference did not allocated the band from the much more logical 24900 to 25000 megaHertz.... 

Someone told me that this not so logical frequency assignment had to do with spot frequencies assigned for radio astronomy use....
 
Stay here , in a few seconds I will be back with more
radio hobby related information...

................................ musical intercut

This is Radio Havana Cuba, the name of the show is Dxers Unlimited, and here is item four of this middle of the week edition of this program... Outstanding results on the two meters amateur band using a very simple three elements vertical antenna made with very low cost and easy to find materials... 

This version of the BOBTAIL VERTICAL adapted for the 2 meters band FM segment is really easy to build and matching it to the 50 ohms coaxial cable is done by cutting bits from the three vertical elements until the one to one or near one to one standing wave ratio is achieved...
 
It uses a simple choke made from coaxial cable as an effective decoupling between the antenna and the long 50 ohms feedline. I have also built the two elements version of this antenna, knows as the HALF SQUARE, but the three elements version is certainly better at the expense of just a longer center boom support and one additional vertical element. 

This same type of antenna can be built for 6 meters and you may want to install it to provide a North to South and South to North coverage.... Its low vertical departure angle will make possible many DX contacts too.
 
If you want to learn more about the BOBTAIL Three Elements vertical array , just send an e'mail to inforhc at enet dot cu, again inforhc at enet dot cu, and I will send you the schematic diagrams and photos of this BOBTAIL three elements beam without reflectors, and I will also add a nice photo of the BOBTAIL with reflectors that provides a very clean unidirectional antenna pattern, very useful to reach distant FM repeaters....
 
Item six: Also connected with antennas... Recently I was invited to visit the amateur radio station of a friend that lives in a 12 floors high apartment building... when he showed to me the noise level that he has to deal with on the 20 meters band I was really impacted... 

I told amigo Peter, that we should try a folded dipole to replace his 20 meters ground plane quarter wave vertical... So we made the design , went for the materials and the next week end we proceeded to build and install the folded dipole antenna , feeding it with a four to one balun.... The antenna was tuned nicely for minimum standing waves , and we found out that the noise level had dropped significantly... A similar result was experienced at the apartment building in Ciego de Avila province of central Cuba where my good friend Pedro Rodriguez CO7PR has his ham radio station installed. 

Pedro commented that the 40 meters band folded dipole was easy to build and install. Also he said that no traces of TVI on his TV were seen and so far no complaints from any ot the more than 90 apartments in the building were registered,something that has made possible for him to enjoy his retirement a lot more by going on the air on 40 meters much more often...
 
Now pretty fast , at the end of the show... solar activity continues to be very low with the solar flux around 90 units, but we will be still receiving the impact from a solar particles event that will soon fade out....Send your signal reports and comments to inforhc at enet dot cu or Via Air Mail... a postcard will be OK sent to Arnie Coro, Radio Havana Cuba, Havana, Cuba
 

Monday, November 16, 2015

With room for introducing many improvements, especially a better audio section, this is the most basic REGENERODYNE radio receiver circuit. A simple mixer  stage, the regenerative detector and a one stage audio amplifier triode...
In my latest version the audio module consists of a triode followed by a tetrode... in actual practice a ECL82 or 6BM8.... The power supply is on a separate chassis, and provides regulated DC to the filaments of the regenerative detector. The regenerative detector in the prototype tunes from 2.5 to 4..5 megaHertz.... With a 4 megahertz
crystal in the oscillator feeding the mixer stage, the receiver
tunes from 6.5 to 8.5 mega Hertz. Using a 6 mega Hertz
crystal the radio tunes from 8,5 to 10.5 megaHertz.
The experimental regenerative detector has to be well shielded to avoid picking up direct signals leaking from the antenna into its
basic 2.5 to 4.5 mHz tuning range.... something that can be noticed
at night... Testing many crystals to check other tuning ranges is
a lot of fun.... You may want to add an RF amplifier stage and a dual tuned bandpass input filter to further improve this marvelous little radio....

Sunday, November 15, 2015

Back on line

Please report if you can read this revived old BLOG 

send mail to

arnaldo.coro at gmail dot com


Just checking if this old BLOG was still on line !
Please report if any of you can see this post
send mail to
arnaldo.coro@gmail.com
Maybe it can be put back to work !!!
73 and DX
Arnie Coro
CO2KK
Host of Dxers Unlimited
Radio Havana Cuba