RADIO HABANA CUBA
DXERS UNLIMITED
MID-WEEK EDITION
TUESDAY, JULY 17, 2001
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hi amigos! You are listening to the mid-week edition of your favorite radio hobby program coming to you from Havana, Cuba. I am Arnie Coro, radio amateur CO2KK, your friend here in the capital city of Cuba and host of this twice-weekly program, always providing you with the most up-to-date HF propagation forecasts, covering from 1.8 to 50 megaHertz, and as required I also provide Medium Wave AM Broadcast Band propagation conditions reports...
Here is now our menu for today:
ITEM ONE: AMSAT-DL President Peter Guelzow provided important information regarding the OSCAR 40 amateur satellite... Peter says that the latest modified orbit should be good for at least 20 years... BUT, here is my first question, will OSCAR 40 be operational after such a long time? And my second question is: When will the worldwide amateur radio community will finally learn about OSCAR 40's technical problems in detail? So far my personal opinion is that those in charge of the most sophisticated and costly amateur satellite to orbit the Earth have kept lots of things to themselves, and that is not helping to promote further volunteer funding for future amateur satellites at all...
More about OSCAR 40 and amateur satellites later in today's midweek edition of Dxers Unlimited. Margarita Delgado is my sound engineer and producer, I am Arnie Coro in Havana, back with you in la few seconds.
You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and if you just came across this radio hobby show while tuning around, visit our Dxers Unlimited website and send your signal reports and QSL requests to arnie@radiohc.org
Now here is item one in detail, more news about the still non-operational OSCAR 40 or AO40 radio amateur satellite:
AO40's new orbit should be good for at least the next 20 years, according to information provided by AMSAT-Germany President Peter Guelzow, DB2OS. Peter heads the satellite's ground control team.
Following maneuvers to shift the satellite's orbit at perigee -- for our non-astronomer listeners, that is the nearest distance to Earth of the satellite's orbit, AO40 perigee now is "oscillating in a safe range between 810 and 1260 km," according to DB2OS, something that after carefully reading and analyzing AMSAT's and AMSAT-DL's bulletins dealing with the damaged satellite, seems to tell us that AO40 was coming too close to Earth before the maneuvers were performed to change the orbital parameters.
AO40's height at apogee of 58,971 km was unchanged by the orbital adjustment. The satellite's transponders remain off as ground controllers reorient the spacecraft. In other words, that means that the satellite is for all practical purposes not available for radio amateur communications after the brief test period during which the transponders were activated only on the higher frequency bands.
So far OSCAR 40 or AO40 has not relayed a single amateur radio station QSO using the most popular transponder modes involving the 2 meter and 70 centimeter ham bands.
Ground controllers were able to change AO40's orbit through successive cold firings of the onboard Arcjet motor, using only ammonia gas.
The move raised AO40 higher than predicted, and apparently depleted the spacecraft's ammonia supply. As a result, AO40 likely will remain in its current orbit. Again, here we see the AMSAT style of saying things in a very peculiar and obscure way.
Stacey Mills, W4SM, of the ground team said it's "quite possible"
that an ammonia leak accounted for the unexpected loss of ammonia.
"If we did have a slow leak, it is very fortunate we did not wait any longer to use the remaining fuel," he said.
Mills said that AO40's old orbital configuration, while stable, was too close for comfort at perigee.
"I sincerely hope that nothing else malfunctions for a long, long time, but this is, after all, rocket science," Mills said. "Nothing is guaranteed."
Ground controllers plan to fully test AO40's momentum wheels prior to any decision to deploy the spacecraft's solar panels. The momentum wheels provide three-axis control of the spacecraft. If the momentum wheels are not operational, it's unlikely the solar panels will be deployed, and of course, we have yet to find out how the satellite is going to work with the solar panels in a retracted position.
As a good friend of mine told me recently, it's about time to start thinking about a NEW CONCEPT of amateur satellites that may be available to the worldwide ham radio population. Maybe OSCAR 40 has provided us with a clear lesson that should be learned... SIMPLER OUGHT TO BE BETTER!!!
This is the mid-week edition of Dxers Unlimited, and here is Item Two, our popular "YOU have questions and Arnie answers them," or at least tries to answer them, amigos!!! Today's question deals with AM medium wave band DXing, an aspect of the hobby that is enjoyed by many of us...
The question was sent in by several listeners and has to do with the design of an optimized frequency converter for the AM broadcast band, something I mentioned not too long ago here... So, amigos, answering the many requests received, here are more details of Arnie Coro's SUPER AM BROADCAST BAND CONVERTER.
Let's start with the circuit's block diagram. From the antenna connector the signal goes to a neon bulb, that will ionize at around 65 volts... this is an excellent protection used by many aircraft radios of yesteryear against static electricity building up... As your AM broadcast band converter is likely to be used on some occasions with long wire antennas, it's certainly a good idea to install the neon bulb right at the input.
I also run a pair of 100 kilo-ohm two watt carbon resistors in parallel from the center of the antenna input connector to ground, that will slowly drain to ground any static electricity building up. Then, there is rather sophisticated filter, designed so that signals picked up by the antenna on frequencies above 2 megaHertz are blocked from entering into the converter... This filter is connected to the first step attenuator, which provides up to 60 dB of attenuation.
The other side of the attenuator goes to the first HIGH Q coil that forms part of the tuner's first tuned circuit... An air spaced high quality variable capacitor tunes the coil from 500 kiloHertz all the way up to 2 megaHertz... This coil-capacitor combination is coupled using a small variable capacitor, to a second identical tuned circuit. Although a Cohn type input tuned filter would be a better choice, the bandpass dual tuned circuit used here is very effective and easier to build...
Then comes a pentode RF amplifier stage that can be switched in and out of the circuit, as required. the RF pentode I use here is the EF85, with manual gain control. The next element is the passive 4 diode broadband mixer, that is fed the local oscillator signal at a frequency between 27 and 28 megaHertz, so that low cost, easy to find 27 megaHertz citizens band crystals may be used. The mixer output is fed to a broadband amplifier that provides the output signal feeding the 10 meter band ham transceiver that I use here as the tail end of my AM Broadcast Band converter... It's an HTX100, certainly not an ideal receiver, but as many of you know well, the 10 meter band is usually dead for DX precisely when the AM band is full of DX, so that was a nice way of making good use of the HTX100 during the equinoctial DX season and long winter nights when AM DX is plentiful...
If you use a better receiver with this converter, results are going to be, as you would expect, much better. For example, the HTX100 has only upper side band available, while more sophisticated receivers or transceivers have the possibility of switching sidebands, a very desirable feature when hunting for rare AM band DX, as on many occasions, just by switching sidebands you may avoid adjacent channel QRM. I have already built two of these converters with excellent results, one without the RF amplifier stage, and the other one including the RF amplifier... Both perform nicely, because the coils are of a very high Q or factor of merit, providing razor-sharp selectivity at the converter's input....
As I said last week here at Dxers Unlimited's weekend edition, using LITZ type wire will provide the highest possible Q of the coils, but winding them using enamel wire will provide a rather nice tuned circuit performance.
If you want to get ready for the upcoming AM DX season, now just about six weeks away, send me an e-mail to arnie@radiohc.org or a postcard via Air Mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba, and I will send you the complete, detailed, description of this sophisticated AM broadcast band UP CONVERTER!!!
FM band Dx enthusiasts have enjoyed lots of sporadic E DX this season... seems like the sporadic E season took a turn for the better during the first week of July. Likewise TV DXers are having a nice time picking up low band TV channels. Here in Havana I have had good pictures on channel 2 from Chicago and Mexico City, for hours at a time when our local Channel 2 station is not on the air. Also picked up an FM broadcast band station from Venezuela while listening with my small portable radio and the telescopic whip...
YES, amigos, when the sporadic E layer is very highly ionized it is amazing what can be heard on the FM broadcast band with practically no antenna at all!!! Ham radio operators know that very well, and during this summer sporadic E season some amateurs are experimenting using ultra low power rigs. Transmitters that run just a few milliwatts are capable of amazing results when the 6 meter amateur band is open via sporadic E skip.
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 activity still moving UP during this rotation. During the last 24 hours, solar activity was moderate, and the geomagnetic field was unsettled to active. For the next 24 hours, solar activity will be low to moderate, and the geomagnetic field will be be unsettled to active.
Solar activity should remain predominantly low with isolted M flares possible from region 9539. The geomagnetic field is expected to be unsettled to active for the first two days of the period due to the effects of a recurrent coronal hole. The field should diminish to quiet to unsettled by day 3.
Prepared 17-Jul-2001; transmitted 18-Jul-2001
Arnie Coro CO2KK
Havana, Cuba
July 17, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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