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| To: | "LF-Group" <[email protected]> |
|---|---|
| Subject: | LF: Rope |
| From: | "Dick Rollema" <[email protected]> |
| Date: | Wed, 24 Dec 2003 12:27:01 +0100 |
| Reply-to: | [email protected] |
| Sender: | <[email protected]> |
|
To All from PA0SE, The transmitter I use on LF was constructed by Harry Grimbergen, PA0LQ. It is a semiconductor affair but with 4 valves PL519 in parallel in the PA. At an input of 0.9A at 500V it produces 300W output. At my request Harry has provided an extra input so the TX can be driven from an external frequency stable source instead of the built-in VFO. Yesterday I collected the modified transmitter. The aerial consists of a 2 x 20m dipole with 11m open line feeder without spreaders. The feeder wires are connected together in the shack and fed against earth, converting the dipole to a T-aerial.The two halves of the aerial can be hoisted separately. Starting transmitting the aerial ammeter swayed wildly and I heard a disturbing noise outside. It appeared that one half of the aerial had come down. It turned out that one hoisting rope had been burned through where it had passed the pulley. Between the pulley and the "pyrex" insulator had been some 15cm of rope. But it had been raining for several days and the rope bust have been soaking wet. See the attachments; the top end of the rope was on the pulley (sorry for the resemblance...) I intend to replace the rope and to insert extra ceramic insulators of the dog bone type as I have supplied to several British amateurs (they come from the closed down "Radio Kootwijk" commercial PTT-station). The rope was at least 10 years old and white when new. There has been some discussion on types of rope on the reflector recently but at that time I was not interested in the subject and rather clumsy deleted the messages. So may I open the subject again and kindly request your opinion as to the most suitable type for my application. As you can see in the attachment the type I used may absorb water rather easily and that obviously converted it into a conductor for a strong enough LF current to burn it. I have to wait for some better weather before tilting-over the mast and do the repairs. Perhaps I will first insert an extra insulator in the remaining half of the aerial (that can be done easily at ground level) and use it as an inverted-L aerial on LF. If that results in a reasonable aerial current I may even do some beaconing at night. 73, Dick, PA0SE.
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