RADIO HABANA CUBA
DXERS UNLIMITED
MID-WEEK EDITION
TUESDAY, JULY 31, 2001
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hi, amigos RADIOAFICIONADOS!!!... Welcome to the mid-week edition of your favorite radio hobby program, coming to you via short wave and on the world wide web. I am Arnie Coro, radio amateur CO2KK, your friend in Havana, and host of this twice-weekly program, devoted to both beginners and experts who enjoy our wonderful hobby, yours and mine... RADIO!!! Headlines for today's show:
ITEM ONE: Solar activity continues to move DOWN,so propagation conditions on the lower HF frequencies is showing a significant enhancement!
ITEM TWO: The HENTENNA, a Japanese-designed type of loop is easy to design for any frequency between 15 and 150 megaHertz, and it is also very easy to build using standard home workshop tools... More about the HENTENNA later in today's edition of DXERS UNLIMITED...
ITEM THREE: Our technical topics section will deal today with Part Two of low voltage operation of vacuum tube receivers, at the request of many listeners who wrote e-mail messages to arnie@radiohc.org asking for more information on how to actually implement this rather simple and very effective modification for vacuum tube radios...
ITEM FOUR: The ever-popular YOU have questions and Arnie tries to answer them FAST!!! Today I'll be answering a question from a listener in Ohio about regenerative receiver radiation...
All this and maybe a bit more if time permits, and as always at the end of the show, you are invited to listen to Arnie Coro's exclusive and not copyrighted HF plus 6 meters propagation update and forecast.. Margarita Delgado is my sound engineer and producer here at RHC's studio 7... stay tuned, I'll be back with you in a few seconds, amigos!!!
You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and if you are picking up this show for the first time, I invite you to send me a signal report and comments about the program to arnie@radiohc.org, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
Now here is item two in detail: The HENTENNA is yet another way of designing a loop antenna. This particular design originated in Japan a number of years ago, and among its advantages I can certainly tell you that it is a very easy to match antenna system. I have built several HENTENNAS, for frequencies between 28 megaHertz and 160 megaHertz, with excellent results.
The HENTENNA is a single band antenna system, but it does have a great advantage over a half-wave dipole or a quarter-wave vertical, two of the standard single band antennas... The HENTENNA needs only one mast, and it has a very small footprint. It does not -- and this is important -- it does not require ground radials or a counterpoise, and with the appropriate instruments, it is a delight to match for a one-to-one standing wave ratio at your favorite operating spot in the band. The HENTENNA is also a rather wideband system too, so once you match it to the center of the band for which it was designed, your SWR will stay way down from the lower to the top end of the band.
There is another interesting advantage about the HENTENNA that is often overlooked by antenna GURUS who have written articles about it, and that is the fact that the antenna radiates a horizontally polarized signal when the longest sides of the HENTENNA are in a vertical position. In other words, with a single insulated mast you can install a HENTENNA for your favorite amateur radio band between 14 and 29 megaHertz, and the system will use very little horizontal space, something that may be very useful when your location does not allow the installation of two masts to erect a horizontal dipole, or it does not provide enough room at the base of a vertical antenna to install enough ground radials, or a ground matt.
The HENTENNA's configuration is very easy to understand... It is actually formed by TWO LOOPS that are connected together; the horizontal sides of both loops are 1/6 of a wavelength long at the operating frequency, and the vertical sides of the larger loop are 1/3 of a wavelength long at the operating frequency. The smaller loop is a square loop with three of its sides 1/6 of a wavelength long.
Now pay attention to this, because the 4th side of the small square loop is actually formed by the feeder matching system. In practice, matching is achieved by moving the matching line up and down along between the large and the small loop. With a carefully done adjustment, it is possible to achieve a very low standing wave ratio, but proper matching does require the use of a one-to-one balun, or the use of a choke type coaxial cable balun, if the HENTENNA is fed directly with a coaxial line of either 50 o5 75 ohms impedance.
One of my favorite applications for the HENTENNA is to use it as a TV antenna for the VHF-HI and the UHF band, because its performance is much better than the standard indoor rabbit ears or closed circular loop antennas used by TV sets.
If you want to learn more about the HENTENNA, you can visit the following website, maintained by L.B. Cebik, W4RNL, which has a lot of very valuable information available for downloading... the URL for Dr. Cebik's site is http://www.cebik.com/
This is the mid-week edition of Dxers Unlimited, and now, here is item three of today's program, low voltage operation for vacuum tube receiver's plate and screen electrodes, a topic that generated a lot of interest among owners of the so-called boat anchor radios, as the old vacuum tube receivers are affectionally known among the ever-growing ranks of hobbyists who enjoy owning and operating those sets, and even building new ones from scratch too...
Well amigos, I was surprised by how many e-mail messages reached me about the use of voltages of 100 volts and lower to feed the plate and screen electrodes of vacuum tube receivers... Someone mentioned that Collins Radio had adopted the low voltage approach for its famous S series of receivers, which ran a lot cooler than their predecessors, and showed excellent frequency stability after a very short warm-up period. Then a Cuban radio amateur, who listens to this show via ground-wave, called on the phone to remind me that the Russian R-250M receiver also used the same approach of running the whole radio at voltages of less than 160 volts... Among the e-mail messages received was a very interesting one from an old-timer who has experimented running the ARC-5 aircraft receivers with 28 volts applied to both the filaments and the plate and screen of the tubes, something that has one only drawback: when using 28 volts on the plate and screen of the audio output stage, audio volume level is much lower, but still more than enough for headphone operation when using 600 ohms impedance headphones...
As I said during the weekend edition of Dxers Unlimited, building a voltage-regulated and well-filtered power supply that will run between 25 and 30 volts is a rather easy thing to do, by using the LM317 type integrated circuit voltage regulator and high capacity electrolytics. That's how I am now running my R-403 Chinese-built 1963 vintage communications receiver, and amigos, reception is excellent when using the radio with the outboard regulated 30 volts DC supply....
Sure, you can do all this in a way that the changes can be reversed, in the unlikely event that you may want to sell the radio, something I am sure is not going to happen, as everyone who happens to own one of those vintage boat anchor vacuum tube radios simply loves them for their nice performance and the great appeal that they do have... Believe me, those oldies have a great personality -- you can tell that when visitors enter your shack and ask... "What's that HUGE thing at the end of the operating table?" Then you will proudly reply, for example, "AH...!!! That's a 1948 vintage National NC183D receiver," or maybe "That's a 1961 vintage Russian Volna K communications receiver covering from 15 kiloHertz all the way up to 25 megaHertz!"
Collecting vintage radio equipment is one of the more than 50 ways of enjoying this wonderful hobby of ours, and experimenting with such gear is always fun, too... BUT, remember to be real careful while working with the old rigs, as they do use high voltages that can be lethal!!!
Send your signal reports, comments about the show, and radio hobby-related questions to arnie@radiohc.org, and if you are not yet in cyberspace, send them VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba...
The new MT63 digital communications mode is making headway... 14109.5 -- again, 14109.5 -- is the calling frequency that is used by the pioneers of the MT63 digital keyboard-to-keyboard mode... According to my monitoring, MT63 seems to be a very rugged communications mode, very immune to fading and interference, but I see a minor disadvantage in the fact that it tends to print in blocks, not the usual letter by letter sequence typical of radioteletype systems...
Anyway, MT63 in my opinion does have a bright future, especially during the years of lower solar activity. MT63 software is very easy to download and to install... it uses the computer soundcard, and with a very simple computer-to-transceiver interface your amateur radio station can be activated using MT63 in just a few hours...
Item four: Yes! This is one of the favorite sections of Dxers Unlimited... YOU have questions and Arnie tries to answer them... fast! Today I'll answer a question sent in by a listener in Ohio, USA...
YES amigo, sure, all regenerative detectors will radiate a signal if not properly isolated from the antenna by means of a radio frequency amplifier stage. Regenerative receiver radiation can be really annoying to nearby listeners, as it is heard as a constant carrier on the same frequency as the station that the person using the regenerative detector is tuned to. And let me tell you that there some funny and some not-so-funny anecdotes about regenerative receivers radiating a signal... in an upcoming edition of Dxers Unlimited I'll tell you a couple of them....
And now amigos, as always at the end of the show, here is Arnie Coro's Dxers Unlimited HF plus 6 meters propagation update and forecast...
Solar flux moving down, and we may see a rather low sunspot count during this solar rotation... Ionospheric absorption is also down, something that is good news for those of you who like to listen to Tropical Band stations, especially the ones still operating between 4.7 and 5.1 megaHertz, that is the 60 meter band...
For amateur radio operators the good news is that 20 meters will be open until very late in the evening local time, and 20 meters will show three very clearly marked propagation peaks from local sunrise until well past midnight local time...
TV DXers will need to start getting ready for the yearly Perseids Meteor Shower, the year's most important event for low band TV Dxing... Also amateur radio operators now using the WSJT High Speed Meteor Scatter Software should be getting ready for what may well be a record breaking Meteor Shower, not from the point of view of how many meteors per hour will be burning into the Earth's upper atmosphere, but from the point of view of the tremendous effectiveness so far demonstrated by the WSJT Software for meteor scatter communications...
Join me next Saturday and Sunday UTC when Dxers Unlimited's weekend edition will be on the air with the most up-to-date HF plus 6 meters propagation updates and forecasts, and many more interesting radio hobby related topics... See you then, amigos!!!
Arnie Coro CO2KK
Havana, Cuba
July 31, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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