January 1994, Six News Issue 40
Several issues of Six News ago I wrote an article about the major problems I have had with TV masthead amplifiers. I live in a low fringe area of London and to receive reasonable snow-free pictures masthead amplifiers are usually required.
For the first few years of operation on 6m I seemed to spend all of my time answering knocks on the door (I still have them in 1996!) from concerned neighbours suffering from TVI. As I said in the article, the simple task of filtering never seemed to work for me. The reason for this is exemplified in the photograph found below. Most of the houses around are old and it seemed that most of the TV antennas were installed in the 1960s or 1970s. After a few trips up to local roof tops the reason became all too apparent. As can be seen below, many of the masthead amplifiers seemed to be first generation' devices. The one shown on the left was particularly bad in this respect as it consisted of one transistor, two resistors, a coil, and two capacitors only! The model on the right is exactly the same but is better packaged. Indeed, this German model is rated, as stated on the label, at 18dB gain at VHF and 22db gain at UHF!
Now honestly, do any of you really think that a simple low-pass filter will prevent the overload of such a device from even a low-power 6m transmitter? So if you are suffering from persistant TVI problems my advice is to get the ladder out and get busy!
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Two of the offending masthead amplifiers |
