Posted: 10/22/2011 9:02:24 AM EDT
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This is a description of Professor Arnie Coro's (CO2KK) digital interface. Arnie is host of Radio Havana's "DX'ers Unlimited" radio show. He has several very interesting articles on the web about indoor SWL antennas and other SWL related subjects. More recently, Arnie coordinated relief into Haiti following their devastating earthquake.
I asked Arnie to do a write up of his very simple digital interface described to me during a PSK31 contact. The following is edited from two emails. OH Yes amigo ! It is very easy to assemble, and several Cuban radio amateurs use it with excellent results. Here is the full description: For receiving.... the signal from the transceiver's audio output is connected to a small loudspeaker that fits inside a length of PVC pipe of about 5 inches, that is filled with sound absorbing material... at the other end there is a small microphone that picks up that acoustic wave and is connected to the microphone input of the computer's sound card. You have two places where to regulate the input to the sound card... at the transceiver volume control , and at the computer audio control program sound level setting. That is the RECEIVING path. FULLY AND TOTALLY ISOLATES THE TRANSCEIVER AND THE COMPUTER !!!! For transmitting.... what we have been doing lately is to fit a small microphone inside one of the computer's loudspeaker.... and that microphone output is connected to the transceiver's microphone input JACK. We have also taken the sound card output signal directly to the microphone input by means of a 600 to 600 ohms transformer... but I prefer to use the ¨acoustic coupling method ¨ because the acoustic coupler avoids the possibility of having ground loops and the certainly dangerous RF feedback that can be damaging to the computer, as some people have found out the hard way!!! Here is the reply to your question about how the HF transceiver is turned on to transmit with my SIMPLE DIGITAL MODES INTERFACE ... I simply do a careful setup of the rig's VOX, so that it will turn ON and OFF the transceiver. For my FM rig , when I want to transmit the satellite photos during the hurricane season, my only choice is to turn on the transmit by pressing the PTT button using a footswitch. The reason why I do it this way is to keep the TOTAL ISOLATION, between the computer and the transceivers. In other words, if you add a circuit that receives the signal from a serial port to activate the transmission, this will require a physical connection with a cable (and of course a single transistor or better yet an optocoupler ) that links the computer with the radio. A local friend uses what he describes as a much more perfect protection by employing an optocoupler device (supposedly 5000 volts isolation ) that feeds a mechanical relay.... and then the wires that go to the rig's PTT are only connected to the contacts of the relay. I had to agree with him that it was a very clever approach... and that it indeed provides an almost perfect isolation... BUT, it your HF transceiver has VOX, then IMHO, that is the way to go!!! I use FLDIGI as my digital modes software, running on a LINUX box that runs PUPPY LINUX 5.2.8 , a very rugged and small operating system that is easy to install and runs very well in old machines with little RAM available !!! 73 and DX Your friend in Havana Arnie CO2KK |
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One of the things I truly respect about Arnie Coro is that he seems to have singlehandedly kept ham radio alive in Cuba.
He has taught countless Cuban hams how to make servicable rigs out of complete JUNK. I remember chuckling about his serious lecture on making a mobile rig hands free so the driver can keep both hands on the wheel. After he said that I visualized some of my fellow countrymen tooling along at 60 mph in heavy traffic talking on the CB while smoking a cigarette and drinking a cup of coffee with both elbows on the wheel so as to free up two fingers to squash a zit. I respect Arnie for that. |