Wednesday, February 27, 2019

Dxers Unlimited, Tuesday 26 February

Radio Havana Cuba
Dxers Unlimited - for Tuesday 26 February 2019 
Arnie Coro, CO2KK
The Cuban CW Group of amateur radio operators is promoting a project that will help both beginners and experts operate on CW Morse Code Radiotelegraphy mode using a simple low power transmitter... Two versions of the low power rigs are now in the early design stages, one using all solid state devices recycled from retired computer CRT monitors and TV sets, and the other a hybrid transmitter using low power transistors and a pair of also recycled vacuum tubes operating as the driver and final RF amplifier stages. 

But, Jav, CO3JK, charlie oscar three Juliet Kilo, the Secretary of the Cuban CW Group wrote an e'mail explaining that the first part of the project aims at building a rugged, reliable power supply for the transmitters.

More radio hobby related information coming direct and from the source... in a few seconds after a short break for a station ID, I am your host Arnie Coro, CO 2 KILO KILO in sunny La Habana, Cuba enjoying wonderful early spring weather...

Si amigos this is Radio Havana Cuba... the name of the show is Dxers Unlimited and here is now more radio hobby related information... a few days ago I decided to dismantle an old hybrid amateur radio transceiver that had broken down many times , making each time more and more difficult to repair. 

It was not an easy decision, but when I started to take the rig apart, it proved to be the correct thing to do, when after testing the first ten electrolytic capacitors removed from the Kenwood TS820S using an equivalent series resistance meter, they all proved to be totally out of the minimum parameters... Attempting to revive that rig without a supply of high quality fully tested electrolytic capacitors for both the high voltage and low voltages power supplies would be simply an impossible task and it will also require a tremendous amount of time. 

Another finding that came out during the first steps of the dismantling process was related to the type of wrap around solderless connections used by Kenwood, that in my opinion was a very poor choice by the designers... The rest of the story is that so far I have carefully removed the VFO assembly, and the big power transformer that will soon be used for other home brew projects... Other small parts will need to be removed by first extracting printed circuit boards where valuable parts like the single side band filter and many quartz crystals can be recovered for recycling. 

Needless to say the Kenwood TS820 S had provided a useful service life of several decades that could had extended further more  if a different method of assembly had been used...  An before I forget the radio frequency driver stage and the two beam power tubes power amplifier were also neatly removed and could be used for a simple single band rig, making good use of a power supply built using the big transformer recovered from the transceiver.

ASK ARNIE, la numero uno, the most popular section of Dxers Unlimited is now on the air... answering a question sent by listener Salvatore from Romen , Italy... Amigo Salvatoreo wants to hear my opinion about the possibility of building self excited power oscillators for CW that use the Hartley – Hull circuit... Well amigo Salvatore, all I can say is that it can be done, but it does require the use of some hard to find parts, like wide spaced air variable capacitors , that are essential to achieve the required frequency stability, and you will also need a very stable fully regulated supply to feed the power oscillator.

My very good Italian friend Cris Greggio has built a prototype Hartley Hull single stage power oscillator that sounds very good on the air and does not drift at all. I remember many years ago building a similar CW rig using a single triode connected 807 type tube , fed from a professional high voltage regulated power supply... It provided about 15 watts output on the 40 meters band and was really stable ... Keying was excellent and no chirp was heard from that rig... Using an also home brew regenerative receiver, the 807 triode connected power oscillator made possible making some very nice DX contacts, but I must add that this happened many years ago during solar cycles 20, 21. 22 and 23 that were much more active than the present very weak cycle 24...

Soon, Radio Havana Cuba will be changing to the A19 transmissions schedule... and very few changes are expected to take place... The reason for not having to change many frequencies has to do with the very low solar activity expected for this season that starts during the spring and comes to an end during October.

.You can send your signal reports and comments about our short wave broadcasts to, again, and don't forget to include details of the programs heard so that we may verify your reception reports with a nice QSL card....

More radio hobby related information coming up: Recent radio noise measurements done at several of the world's most populated cities and also done at smaller towns and villages show something in common... The general background radio frequency noise levels within the frequency range from three to thirty megaHertz has increased dramatically during the past five years where ever measurements made five years ago were available... 

The results of those carefully done bandscans measuring the background noise demonstrate that services that once where capable of providing good quality coverage like the AM medium wave broadcast band have become, at some urban locations almost useless, even when the stations are using high power transmitters .... Add also that the FM broadcast band is also suffering from many electromagnetic incompatibility problems that reduce the service area of many stations in a significant way....

And now just at the end of the show,here is Arnie Coro's Dxers Unlimited's HF propagation update and forecast, expect poor to very poor conditions during the next two days due to the likely to happen effects of a high speed solar wind stream coming from a coronal hole... All  I will recommend is to monitor the lower frequencies for possible propagation anomalies... 

Send your signal reports and comments via AIR MAIL to Arnie Coro, Radio Havana Cuba, and use our primary e'mail address .See you at the weekend edition of Dxers Unlimited on the air next Sunday and Monday UTC days,
(Arnie Coro)