Wednesday, September 12, 2018

Dxers Unlimited mid-week edition, September 11

By Arnie Coro

Hola amigos… more reasons for the very poor propagation conditions on the MF and HF bands.

Geomagnetic conditions have reached moderate storm levels on a planetary level (NOAA Kp 6 for the 6-9UT period today, 11 September 2018). The storm is due to the enhanced solar wind parameters associated with a coronal hole high speed stream, while the solar wind speed gradually increased from 370 km/s at noon 10 September to values near 610 km/s at 10UT today.

According to the AR-Cluster Network for the week of Sunday, September 2-9,  they were 206 DX countries or entities on the air on the monitored amateur bands.

I am Arnaldo, Arnie, Coro your host here at the middle of the week edition of Dxers Unlimited. Now our next news item...

A number of hand-held FM transceivers capable of transmitting on frequencies beyond the 2 meters and 70 centimeters band are being banned by several frequency management authorities around the world. The usually very low-cost dual band FM handie talkies are considered a menace because they can easily be reprogrammed to operate on the public services frequencies. Banning those radios is achieved by placing them in black lists kept by Customs on the countries were they are no longer allowed to be imported.

QSL on the air to Dxers Unlimited's. Listeners that have asked to keep the HF bands propagation updates at the end of the show on every program. Don't worry, from now on whenever possible Arnie Coro's HF plus low band, HF propagation update will be on the air at the end of the show.

Next News Item: Sponsored by the International Telecommunications Union, ITU, the specialized oldest United Nations agency, a worldwide research project that is measuring the radio frequency spectrum noise levels will provide valuable information about this severe problem that has a negative impact on the use of radio telecommunications systems that are vital in today's world.

By the way some of the worst radio broadband noise levels measured at several megalopolis, like Mexico City, New York, London, Shanghai, Tokio, Moscow and Paris are showing that the AM broadcast band services are becoming useless at the present transmitting stations power levels. The actual effective service area originally planned for many AM broadcast stations since 1959 have proven to be practically useless due to the poor signal to noise ratios prevailing on the 530 to 1700 kHz frequency range.

Hurricane Florence now is in an almost fixed track, and is going to impact the US East Coast as a category 4 or even category 5 storm. The most powerful storm to reach that part of the continental United States, in more than 60 years.

Amateur radio operators located in the affected areas as well as others around the first skip HF coverage area are already deploying their emergency communications stations. 

It is expected that the record-breaking winds will produce considerable damage to the telecommunications and broadcasting facilities. As it happened last year in Texas, the cellphones networks went down before the full blast of hurricane Harvey had hit the area, making the use of amateur radio emergency systems essential for responding to live saving operations requiring air evacuations from flooded isolated areas.

Number 94 is here. Yes amigos, the number 94 way of enjoying our spare time by means of our radio and television hobby is here: It is known as amateur digital television, capable of high definition transmissions.

For delivery of television signals, there are several methods in use that include: cable (C), satellite (S), terrestrial (T), internet streaming (www), DVD, etc.

Each delivery system has its own advantages and disadvantages. As a result, different digital encoding mechanisms are used for each method. The cable, satellite and terrestrial all use RF carriers, while satellite and terrestrial are truly over the air rf paths. As radio amateurs, we use over the air rf transmission paths.

In the early days of DTV (early 2000s), some DTV hams were experimenting with using satellite TV equipment, mainly due to the low cost (? $25) of free-to-air (FTA) satellite, L-band (1-2GHz) receivers. Their work was primarily on the 23cm (1.2GHz) band.

Other early adopter, DTV hams experimented using cable TV equipment for the same lowcost reasons. The normal amateur radio environment is really the over the air, terrestrial, rf transmission with radio waves being transmitted horizontally over the surface of the earth.

The major issues encountered with such radio waves is the presence of multi-path, RFI and weak signals. Multi-path refers to multiple rf signals bouncing off of various reflectors, such as hills, buildings, etc. and arriving at the receiving antenna with various time delays. In the days of analog TV, this was readily evidenced by the presence of "ghost" signals on the TV screen.

DTV transmission in a cable TV environment is rf transmission in an almost  perfect environment. It is almost a perfect, echo free environment due to the efforts made to maintain very low VSWR in the cable TV system.   Signal strengths can also be kept up to relatively high levels. Thus, the digital modulation method for cable TV does not need to make many corrections for its good environment.

DTV transmission from broadcast TV satellites, is again in a relatively clean  rf environment. Because of the high gain and directivity of the receive antennas, there is essentially no multi-path to contend with from satellites. The main issue for satellite rf signals is very low signal strength at the receive antennas. Terrestrial rf transmission is the worst possible rf environment. It must deal with multi-path, RFI, and weak signals and still deliver a perfect DTV picture.

Here in Cuba our national television uses the highly efficient DTMB'T that has proven to be more reliable than the ATSC systems variants used in the USA. So far, Cuban radio amateurs have used analog television transmissions using several slow scan TV modes that proved to be very effective sending still photos of hurricane affected areas to the Civil Defense command posts using both 2 meters FM and HF single side band transmissions.

This is Radio Havana Cuba, the name of the show is Dxers Unlimited. I am your host Arnaldo, Arnie Coro and here is our next radio hobby related item for is about the really amazing results achieved by minimalist amateur radio stations, using minimum parts counts receivers and transmitters.

Starting with a dual triode tubes in a glass envelope the regenerative receiver was designed to work on the 40 meters amateur band, using high impedance headphones.

The first triode is the detector and the second one works as an audio amplifier. The radio tunes from 7000 to 7150 kHz only. It has good sensitivity and uses very common electronic parts that you can find by recycling equipment. It uses a low voltage power supply that is also easy to build.

The transmitter first option uses quartz crystal control and a single power tetrode or pentode vacuum tube, that when fed from a voltage doubler power supply will easily provide between two and five watts into the simple half wave coaxial fed dipole antenna.

When a local amateur that is a QRP low power radios enthusiast saw the minimalist station he said and I agreed with him that it a simplified version of the famous World War II Paraset !!! He took the circuit diagrams and photos to duplicate the set.

And now at the end of the show.... Arnie Coro's HF propagation update.... Zero sunspots ... a blank solar disc with very low solar activity ...AND A GEOMAGNETIC STORM IN PROGRESS: As predicted, a moderately strong G2-class geomagnetic storm was underway on Sept. 11th as a stream of high-speed solar wind buffets Earth's magnetic field. This morning in Alaska, "amazing auroras covered all of the sky," reports Ayumi Bakken from just outside Fairbanks:

Send your signal reports and comments about this program to or postal mail to: Arnie Coro , Radio Havana Cuba, Havana, Cuba.
(Arnie Coro/R Havana Cuba)