Radio Habana Cuba: Dxers Unlimited mid-week edition for June 20, 2000
By Arnie Coro, radio amateur CO2KK
Hi amigos, mes amis, my friends around the world, welcome to the mid week edition of your favorite radio hobby show on short wave. I am Arnie Coro your friend here in Havana, and here is our show's menu for today...
Item one: Evenings and late evenings continue to be the best times for listening to short wave or, if you are an amateur radio operator, work a lot -- and I mean it, a lot -- of DX, as we are just at the summer solstice, the ionosphere contracts during the hours of darkness, giving us a very unsual and interesting phenomenon, of which you will learn more by staying here on this frequency for a few more minutes.
Item two: coaxial cables are an essential part of our radio hobby installations, be they amateur radio, FM or TV Dxing, Citizens Band -- you name it -- so today I'll describe a very easy, almost foolproof way of testing coaxial cables at specific operating frequencies, so be ready with your notepad and pen or pencil, or better yet, visit our website where the script will be posted, and available for downloading.
No, I did not forgot about it! Solar flux is hovering between 190 and 200 units, and YES, there are some interesting events going on 93 million kilometers away from Earth, at our nearest star: the Sun.... stand by now for a brief musical interval and station id. I'll be back in a few seconds.
You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited and here is the expansion of item one: During the summer months the ionosphere -- in fact, the whole atmosphere of which the ionosphere forms part -- receives a lot of thermal energy from the Sun. This causes thermal expansion of the plasma; in other words, the ionized gas molecules separate from each other, and the different layers are not so well defined... Now, here is what happens after the sun sets: The ionosphere's temperature goes down dramatically, causing a contraction of the plasma... so free electrons are literally packed more tightly, to put this in an easy-to-understand form.
Now, you know that the more free electrons per cubic millimeter that we have, the higher the maximum useable frequency that will be sent back to Earth by the ionosphere, so, that's it -- as the period of darkness begins, the ionosphere contracts, and there are more free electrons per cubic millimeter available, and although the recombination process is taking place, there is a delicate dynamic balance that sends the MUF, or maximum useable frequency UP, even after the SUN is not sending any ionizing ultraviolet rays anymore over that region of the Earth's atmosphere, because the Sun has set.
OK, it is a bit complicated, but if you read it carefully, you will understand, and the higher nighttime MUF phenomenon is like many other physical events: You really don't need to understand them to use them. In other words, follow Arnie Coro's HF propagation advice, and spend more time looking for DX from your local sunset until very late in the evening... I'm sure that you are going to pick up some very nice DX on the higher bands, even up to the 13 meter or 21 megahertz international broadcast band, and its nearby neighbor, the amateur 15 meters band, that spans from 21.000 to 21.450 kiloHertz...
Our e-mail address is arnie@radiohc.org Now Item two at Dxers Unlimited's mid week edition, but before I start with item two, QSL on the air to two of our regular listeners whose comments, ideas and suggestions have helped this show win your acceptance over the years... Bob Chandler VE3SRE from Toronto, Ontario, Canada, and Paul Harden NA5N from New Mexico, to both of you, my good friends, thanks for those nice comments about the program.
And now item two: Coaxial cables are an essential item in today's radio hobbyist's inventory of equipment and accessories... a little 60-centimeter or two-foot length of coaxial cable that connects a transceiver with an antenna tuner just gave a good friend of mine one of the worst headaches that one can think of... UNTIL I told him, "Listen Sergio, I think that your problem is not at the antenna," and asked the classic question: "Have you tested the short length of cable that connects your transceiver to the antenna tuner?" Well, Sergio had not tested it, and I lent him an almost identical cable with two PL259 connectors, one at each end. Well, the intermittent problem that he had, the big headache, went away after the cable was changed. A close inspection of the section of coax showed that the braid was badly corroded, causing an intermittent contact, which in turn kept those meters jumping around. The funny thing was that the problem was happening only on transmit, obviously when radio frequency energy was trying to make its way through a poor connection... SO, this is why today I'll describe an easy and foolproof method for testing coaxial cables, which will tell you, without any doubt when a cable is in good shape, and when it can be sent to the recycling bin.
You will need a dummy load resistor capable of operating at 100 watts level for at least 20 seconds or maybe a bit more, a good quality standing wave ratio meter, a wattmeter, and an RF signal source; that's a transmitter capable of at lest 50 watts output on HF. If you are a Short Wave Listener, you can test your coaxial cables with the help of a local radio amateur... NOW, here is the how-to of the easy, foolproof coaxial cable testing procedure:
Connect your SWR meter at the output of the transmitter, and BYPASS your antenna tuner if you have one installed, connect the coaxial cable you want to test to the antenna side of the SWR meter. Connect your dummy load and wattmeter to the other end of the coaxial cable. Run the transmitter at the highest possible frequency that it can operate, which typically for an HF rig will be somewhere around 29.6 megaHertz. Check how much power you read at the end of the cable. If your power measures much less than the transmitter's power output, then just stop the tests, and send the coaxial cable to the recycling bin. This test is one of the most foolproof ways of knowing how a coaxial cable passes RF currents. If you happen to have a 2 meter rig, a good dummy load that works properly at 2 meters and a wattmeter, then by all means perform the tests for your HF cables using 2 meters as the RF source.
Here is an example of a recent test: A 50-foot-long section of RG58U was tested at 145 megaHertz, feeding 25 watts of RF from an FM rig at the end of the 50-foot section; at the other end, only 2 watts made their way to the antenna. So, amigos, no doubts about this section of coax, it was in pretty bad shape, just ready to be sent to the recycling yard. In contrast, an identical section of RG58U showed 20 watts at the end of the run, quite reasonable for the frequency range and the type of cable involved.
So, before installing your coaxial cable runs, test them with radio frequency energy applied, and avoid headaches. Testing coaxial cables for losses is particularly important above 50 megaHertz, as VHF and UHF enthusiasts know very well... It may take a little time, but time spent testing the coaxial cables is well worth every second of it!!! If you have any questions about this easy to implement testing technnique, just e-mail me at arnie@radiohc.org, and I'll be more than happy to clarify any details that may have escaped due to fading on the short wave signals!!!
And now, as always, at the end of the show, here is Arnie Coro's HF plus 6 meters propagation update and forecast. Solar flares, even an X type solar flare, have erupted from the Sun's surface during the last 72 hours; every time there is an X type event, solar activity that day is described as HIGH by scientists... There are at least two solar active regions with the potential to generate both class C and class X flares during the next several days. The daytime maximum useable frequencies are now barely reaching 25 megaHertz, but at around sunset your local time, you may see the MUF go up briefly to the 10 meter amateur band... Nighttime Dxing is at its best in the range from 10 to 15 or even 18 megaHertz, with occasional periods of openings on the 21 megaHertz band. Solar flux is expected to follow a downward trend for the next several days.
According to very recent reports, HF radio users should be on the alert for possible geomagnetic disturbances, caused by streams of charged particles from recent coronal mass ejections that may reach the Earth. Sporadic E events will continue to bring lots of TV DX on the low band channels 48 to 88 megaHertz, while FM band Dx will be less frequent. 6 and 10 meter band amateur radio operators may be working some DX via sporadic E during the next several days.
See you at the weekend edition of Dxers Unlimited, next Saturday and Sunday UTC days!
Arnie Coro CO2KK
Havana, Cuba
June 20, 2000Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba
PO Box 6240, Havana, CUBA 10600
phone: 53-7-814243
phone res: 53-7-301794
e-mail: arnie@radiohc.org
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