RADIO HABANA CUBA
DXERS UNLIMITED
WEEKEND EDITION
SATURDAY, AUGUST 4, 2001
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hi, amigos radioaficionados!!! Welcome to the weekend edition of your favorite radio hobby show, I am Arnie Coro, your friend in Havana and host of this twice weekly program devoted, all 18 minutes of it, to our wonderful hobby... RADIO!!!
Here is the menu for today... Solar roller coaster now moving up!!! Friday's solar optical observations by Cuban expert Angel Gonzalez Coroas showed 9 sunspot groups, an estimated WOLF number of 158, and Angel told me in a phone call that one of the active sunspot regions may harbor enough magnetic complexity as produce powerful solar flares during the next several days... So, we may expect that the higher HF bands show a gradual recovery during the rest of this week and the next one.
Item two: Copper foil with an adhesive backing, as used by artists that do stained glass artwork makes excellent homebrew antennas... The copper foil is much better for building antennas than the aluminium foil used for protecting glass works with alarm systems, because copper is very easy to solder to the downlead, and as you know well, aluminium foil simply refuses to be soldered... More about TWO COPPER FOIL antennas later in today's edition of your favorite listener oriented radio hobby program...
Item three: More about the BEST OF BOTH WORLDS HOMEBREW RECEIVER... my pet project for the past year or so... The BOBW receiver has now reached maturity, and several Cuban radio amateurs have built it to use it both as a primary station receiver or as general coverage radio so often needed when has just a ham band transceiver.
Our Item four today will answer a listener's question regarding regenerative receiver radiation, and as always at the end of the show you are most welcome to tape Arnie Coro's HF propagation update and forecast..
Stay tuned, right on this same short wave frequency, amigos... Margarita Delgado is my sound engineer and producer here at RHC's studio 7. Back with you in a few seconds...
You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, our e-mail address is arnie@radiohc.org, and our postal mail address, also very easy to remember, is Arnie Coro, Radio Havana Cuba, Havana, Cuba...
Here is item two of today's menu in detail... Copper foil adhesive tape, that is almost pure electrolytic copper foil with an adhesive backing, is an essential element of stained glass artwork... You will find the copper foil tape in different widths at artist supply stores... Yes, it's bit expensive, but the copper foil tape makes wonderful emergency and even permanent antennas. For example, a 25-millimeter or one-inch wide copper foil tape makes excellent antennas for VHF and UHF frequencies that can be used both for receiving and transmitting... The self-adhesive copper foil tape is simply pasted on to a glass window, and that's it... you just need to solder the coaxial cable downlead and your antenna is ready for action.
For example, you may build up a half wave vertical dipole for the two meter ham band, just by taping two 19-inch or 49-centimeter long copper foil tape lengths to a glass window, and feeding it with lightweight RG174 U 52 ohm coaxial cable... The coaxial cable must go away from the vertical dipole at a 90 degree angle, and its length must be kept to less than 3 meters or around 10 feet; other than that, your window copper foil dipole taped to the glass windowpane may be adjusted to the part of the 2 meter ham band that you want to use by carefully trimming the ends and watching the Standing Wave Ratio meter.
Another nice windowpane copper foil tape antenna is a BROADBAND CONICAL DIPOLE, made using three identical lengths of copper foil tape for each leg of the dipole, and joining them together at the feedpoint... The only problem with the Broadband Conical Dipole that I have found is that the lady of the house usually objects to its presence, because indeed it stands out in the middle of the glass pane... BUT, some friends here have installed these antennas on windows that are behind a curtain!!!
Ah, before I forget, the BROADBAND VHF CONICAL DIPOLE dimensions for the 140 to 174 megaHertz range are the following... The dipole legs are made with 12.7 or 25 millimeters copper foil adhesive tape that are 60 centimeters long, that is roughly 2 feet in length... but this length is not critical, you can make the legs of the dipole just 50 centimeters long and still obtain an excellent performance. This BROADBAND VHF CONICAL COPPER FOIL TAPE DIPOLE, when installed for vertical polarization, makes an excellent antenna for your VHF scanner receiver, covering from 140 to 174 megaHertz, and tests here show that it also seems to bring in stations operating in the 420 to 512 megaHertz band too.
Amigos, nice to have you listening to the weekend edition of Dxers Unlimited, you can send a signal report and comments about this show via e-mail to arnie@radiohc.org and if not yet in the cyberworld, then send an AIRMAIL postcard to Arnie Coro, Radio Havana Cuba, Havana, Cuba...
Now here is item three in detail: An update about the REGENERODYNE experimental receiver after one year of working with it...
The BEST OF BOTH WORLDS (Best of superheterodyne + best of regenerative) receiver certainly is not a fixed tuned detector receiver!!!
The regenerative detector circuit has a very smooth bandspread and in the final version tunes a segment of exactly 1 megaHertz, although I experimented with 500 kHz tuning segment too, and found the 500 kHz approach better for calibration purposes with the type of dial that I am using here..
The use of a separate, very well-shielded BFO is also a very interesting improvement...
The INJECTION of the BFO must be controlled very carefully, but it works much better than making the detector oscillate...
You will find that the detector very close to the point of oscillation is a razor-sharp selective device in the 2.1 to 3.1 megaHertz range of coverage used in the prototype, and of course the same holds true for the 500 kiloHertz bandspread option that tunes from 2.1 to 2.6 megaHertz.
By the way, this is a region of the medium frequency spectrum that nowadays has very few high power stations that may leak through the front end of the REGENERODYNE and generate confusion by pick-up of signals within the Intermediate Frequency range, so the segment from 2.1 to3.1 megaHertz has proven to be an excellent choice for a low-cost dual conversion homebrew receiver of any type, be it a standard superheterodyne of a regenerodyne..
As someone correctly pointed out, the best way to build this SUPER GAINER type of receiver is BACKWARDS, starting with the audio amplifiers and then proceed to the 2.1 to 3.1 megaHertz detector...
Now, let me clarify for the newcomers to the hobby of homebrewing radio receivers that a SUPER GAINER is a superheterodyne receiver that does not use any intermediate frequency amplifier stages... Signals go from the output of the mixer to the detector without any IF amplification...
Also what I mean by building radios BACKWARDS is that the sequence of assembling starts with the power supply, continues with the audio amplifier stages, then you wire up and test the detector, then the mixer and local oscillator and you end up by wiring the RF amplifier stage... This approach is a very logical way of doing things, as you can proceed to test each and every building block as soon as it is finished and you are never faced with the terrible headache of having to find which of the building blocks is not working after the whole radio is assembled... Remember this sequence... the power supply goes first, la numero uno, then the audio amplifier stages, then the detector and BFO and once this is done, you wire up the rest of the radio.
My favorite "low cost" quote, unquote, test signals are harmonics of broadcast AM stations, the 2.5 mHz WWV and a broadcast station on the 90 meter band (have to tweak at the high end to pick it up). Testing the half-built radio, using it as a straightforward regenerative detector may delay your project, as I found myself searching for DX signals with the half-built radio for more than a week, amazed as I was at how sensitive and selective the Hartley tetrode regenerative detector proved to be.
With the converter for the AM broadcast band, and the detector almost oscillating the receiver picks up ground wave AM stations during the daytime that are very far away and which are not heard in other sophisticated receivers...
Now, here is our popular YOU HAVE QUESTIONS and Arnie tries to answer them fast!!! section of Dxers Unlimited...
YES amigo from Toronto, Canada, regenerative receivers, when not equipped with a radio frequency amplifier isolation stage, do radiate signals that may affect nearby receivers... Some regenerative detectors used in the past by radio amateurs radiated such strong signals that creative hams used to key their power supply and actually make local two-way contacts with the receivers!!! In an upcoming edition I will tell you more about receiver radiation and the many problems that it can generate...
And now my friends, as always at the end of the show, here is Arnie Coro's Dxers Unlimited's HF plus 6 meters propagation update and forecast...
Solar activity is MOVING UP, we have seen the Sun switch ON at last, and the latest scientific achievement that lets us see what's going on at the other side of the SUN is telling solar scientists that what seems to be a big sunspot group will be rotating into view soon. One active sunspot region now at a geoeffective position may harbor enough magnetic complexity to produce class M solar flares and according to some sources, there is even a remote chance for an X class solar flare to be erupting from the SUN during the next few days...
The higher HF bands, from 18 megaHertz all the way up to 30 megaHertz will show a definite improvement in propagation during the next several days, with the nighttime MUF enhanced by as much as 30 percent at some locations.
See you all at the mid-week edition of Dxers Unlimited, amigos!!! Remember to tune in at this same time and frequency next Tuesday and Wednesday UTC days and don't forget to send your QSL requests and comments about this show to arnie@radiohc.org! Thank you all very much for listening!!!
Arnie Coro CO2KK
Havana, Cuba
August 4, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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