Radio Habana Cuba: Dxers Unlimited Weekend edition for July 8, 2000
By Arnie Coro, radio amateur CO2KK
Hi, this is the weekend edition of Dxers Unlimited, your favorite wideband coverage radio hobby show on short wave. I am Arnie Coro, radio amateur CO2KK, your host here for the next sixteen minutes of air time!
Here is item one: after a few days of a very quiet Sun, solar activity has now moved to moderate, and the solar flux is moving up... Latest data showed 180 solar flux units,and climbing!!!
Item two: Several amateur radio contests this weekend, among them the International Amateur Radio Union Radiosport, and the CQ Magazine worldwideVHF contest should be well underway by the time you are hearing this... So, this is an excellent chance to log quite a few nice DX stations, especially late in the evening your local time when ionospheric absorption and atmospheric noise are expected to go through a minimum.
Item three: RS13, the Russian low orbit amateur radio satellite, is very easy to access using the 15 meter band uplink, and listening on 10 meters... the downlink on 29 megaHertz is so powerful that many radio amateurs just use a portable radio to pick it up. RS13 is a fun satellite that can be worked using very simple wire antennas, and provides an excellent opportunity to demonstrate space age communications via amateur radio.
Item four: Don't throw away those nickel cadmium battery packs that fail; most of the time it is just one or two cells that cause the failure of the battery pack, and with proper care, you can open the pack, replace the dead cells, and use the expensive batteries for much longer time.
Item five: To those of you twho asked about the dual diamond quad antenna configuration: YES, when they are connected in parallel, the feedpoint impedance is very close to 50 ohms; in fact, it is so close to 50 ohms that no matching network is needed. BUT, feeding the dual diamond quads directly with coaxial cable does require using a simple 5 to 8 turn coaxial choke balun. I have used the dual diamond quad for TV DXing with excellent results. Lightweight fiberglass spreaders and wire is all that is needed to make an excellent low band TV channels antenna that will also work very well on the FM band... somewhat large, it is true, but it costs next to nothing and provides good gain and above all much better bandwidth than a Yagi antenna.
Stay tuned for more radio hobby related information coming to you from Havana. Margarita Delgado is my sound engineer and producer... I am Arnie Coro, back with you in a few seconds.
Wire loop antennas for the upper portion of the HF spectrum and the lower VHF spectrum are easy to build, cost next to nothing, provide excellent bandwidth, and if you choose the double diamond quad configuration, there is no need for any matching devices... YES amigos, the feedpoint impedance of the two diamond quad elements when fed in parallel is so close to 50 ohms that there is no need to include any kind of matching system. You can even use 75 ohm coaxial cable for direct feed, and that will only bring up the standing wave ratio to not higher than 1.5 to 1 at the center operating frequency... No wonder experienced TV Dxers always keep two diamond quads up, optimizing their coverage to the areas of maximum DX probability. The dual diamond quads are bidirectional, they have a figure eight horizontal radiation pattern, and that's why you need two of them to provide around the compass full coverage. TV DXers run two coaxial lines to a relay, and they switch from one dual diamond to the other at the flip of a switch that is located right next to the TV set.
With eight lightweight fiberglass spreaders and household No.14 PVC insulated wire, you can build the two dual diamonds during a weekend... Installation does require using two masts, in order to reduce mutual coupling between the two antennas, but the masts need not be more than about 6 meters or 20 feet high in the case of the dual diamonds for Low Band VHF TV Dxing. And as a bonus, those two antennas when cut for TV channel 2 in the Americas, spanning from 54 to 60 megaHertz, work quite well on the 6 meter amateur band too.
You should remove the insulation from the wire with a sharp knife, and a lot of care, because the PVC insulation changes the wave velocity and for that same reason, the measurements of the antenna made with PVC insulated wire are different from the dimensions provided by the standard quad antenna one wavelength loop formula that you can find in practically all antenna handbooks!!! So, after removing the insulation, the No.14 copper wire is placed around the spreaders, held in place at the ends with nylon ties or nylon strings, plus PVC plastic tape, and that's it... You want the two diamond elements to be tied together at one of the corners, and there is where the coaxial feedline is connected.
This simple antenna for TV Dxing will also pick up local and semi-local FM band stations too, but if you want to monitor the FM band for sporadic E DX, then you must build a dual diamond quad cut for the part of the FM band that you want to monitor. My experience with the FM dual diamond quad is that they cover about a third of the 20 megaHertz wide FM band with maximum efficiency, and that's the reason why I recommend cutting the antenna for the part of the band you want to monitor, although these antennas are broadband enough to provide excellent reception during a good band opening all across the FM band.
Need more information about this easy to build antenna? Want to spend next weekend building one? Then just e-mail me at arnie@radiohc.org and I'll be very happy to send you a nice illustration of a dual diamond quad antenna, plus the formula used for calculating the elements.
You are listening to Radio Havana Cuba; the name of the show is Dxers Unlimited, and our QSL info is very easy to write down: send your QSL requests via Air Mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba, or via INTERNET e-mail to arnie@radiohc.org!
Here now is item six: Regular Dxers Unlimited listeners visit our website at www.radiohc.org and download the scripts of this show for future reference, as they tell me that there are lots of useful tips to be saved. A recent example: one of the latest editions of this show explained in detail the cause of intermittent operation and complete failure of some Kenwood receivers and transceivers due to poor contacts in plated through holes on the printed circuit boards... Well, it was nice to hear from three listeners who have already brought back to operation three rigs by following Arnie Coro's advice and soldering, with a lot of patience and a lot of care, wires through each plated hole. In the first case, the suspect board was given the treatment first, and the radio started working immediately, but the amateur doing the job decided to go through all the plated holes that connect the two sides of each circuit board anyway, because they may fail in the future...
YES, it is a lot of work, but bringing back to life a TS140 a TS430, or a TR2800 by just soldering little bits of wire in each plated through hole may prove to be a very low cost approach to obtaining one of those otherwise nice rigs.... According to what I have seen so far, no less than 50 percent of Kenwoods built between 1980 and 1990 seem to have that problem which, I repeat, causes intermittent operation first and then, after some time, a completely dead radio, especially when the microprocessor board is involved.
You have questions and Arnie has the answers, amigos!!! Here is a short question asked by a listener in Arizona: Arnie, how can I keep my antenna from charging up with static electricity during those very dry days?
Answer: install a permanent discharge path to ground via the lowest value carbon resistor that will not affect your receiver's performance... You can safely go to a 2 watt carbon resistor with two thousand ohms or so, and the antenna will not be charged anymore, as the two thousand two hundred ohm or 2.2 kiloohms resistor -- which is the standard value, two thousand two hundred ohms -- will provide a path to ground while not affecting your receiver's input circuits which are low impedance...
As a matter of fact, now that we are talking about this interesting subject, it is always a very good idea to install a 2 watt 2.2 kiloohms resistor from the antenna live terminal to ground on all receiving antenna systems, something that will prevent static electricity damage to the receiver's sensitive front end amplifier devices.
And now just before going QRT, here is a special DXers Unlimited HF plus 6 meters CONTEST propagation update and forecast:
Attention IARU and CQ contest operators... Solar activity is moving up, and we may see class C and even an isolated class M flare during the next 48 hours. Solar flux is hovering around 180 units and moving UP, there are NEW solar active regions on the solar disk NOW... Expect very good HF propagation on the 20 meter band after local sunset and until about 2 hours after local sunrise. The 21 megaHertz band, 15 meters will be the best option for contest operators all along the local daylight hours and well past sunset, too.... We may see some nice sporadic E openings related to areas of high thunderstorm activity... The lower bands from 3 to 8 megaHertz will be rather noisy during the evening, but the 6 to 8 megaHertz segment will provide good daytime high radiation angle service.
See you at the mid week edition of Dxers Unlimited, and will try to work as many of you Dxers Unlimited's listeners as possible during both contests. So be on the lookout for CO2KK on 6 and 2 meters VHF and on 40 to 10 meters on the HF bands, and don't forget to send your comments about the show to arnie@radiohc.org; they are essential to make this show really appealing and interesting to all of you!!!
prepared 8 July; received 11 July, 2000
Arnie Coro CO2KK
Havana, Cuba
July 8, 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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