Dear LF group,
Transmitted the usual beacon signal on 135.923kHz from 2000 until
0305 last night, apart from a period from 2205 - 2220 when I was
making an adjustment to the antenna.
For the record, my 136kHz rig details for these tests are:
TX output - 1200W, 6A antenna current.
Antenna - inverted 'V' single wire, fed at one end. Total length of
wire 50m, about 16m high in the middle and 9m at the ends.
ERP - (estimate based on old measurements - antenna changed
slightly since then) approx. 1W.
Location - IO91VR; near Hatfield, about 25km north of london,
adjacent to the Brookmans Park BBC MF transmission site.
I also monitored VA3LK's frequency from 0310 - 0900, but only
saw a single 'K' at about 0720. The noise level dropped abruptly at
0600. I don't think the street lights switch off this early, anyway
there aren't any down my road. It would certainly be interesting if
VE1ZZ could run some signals in the early morning; I don't recall
him ever being QRV at this time of day, and VA3LK's signal is on
the whole best at this time.
3C85 ferrite has an initial permeability around 2200 as I recall -
this is typical for a 'power' grade ferrite. The very high permeability
ferrites are intended for small-signal, wide band transformer
applications usually. Lower permeability ferrites such as 4C65 (mu
= 125) are well suited to HF transformer applications. Iron dust
cores, like the Micrometals -2 and -6 grades have much lower
permeability, and are intended for 'energy storage' applications
(resonant circuits and filter components in this context). Philips
seems to have sold it's ferrite components buisness to a
Taiwanese company called Yageo - oh dear..... But fortunately,
Ferroxcube seem to have reappeared in the meantime -
http://www.ferroxcube.com/ has data sheets.
Cheers, Jim Moritz
73 de M0BMU
|
