Just a few brief notes that may be of interest . . .
Following the pruning of two trees in my neighbour's garden, the feed
impedance of my 12 m vertical (at the cold end of my loading coil) has
reduced from 130 to 100 ohms, and reports on my signal indicate an
improvement of between 2 and 4 dB (thanks to Dave G3YMC and John G4GVC
for these comparative reports). When using the additional 8 m of
balloon-supported wire, the feed impedance has changed from 100 ohms
(before pruning) to 75 ohms.
Initial results with a noise canceller on local sources of interference
have been most encouraging. Based on an idea by VK5BR (RadCom, March
1993, p34), I constructed the phase-shift network and hybrid transformer
using 3C85 toroids.
- under test conditions, a sine wave can be nulled by greater than 50
dB;
- my strongest noise source (possibly a light dimmer), which, since
mid-1998, has prevented me operating in the evenings can now be reduced
from S9 to less than S5;
- a combination of phase/amplitude settings, which take about 40 seconds
to optimise, can only null out one interfering signal at a time, for a
given receive antenna;
- the number of significant noise sources at my QTH has increased from 1
to 3 over the past 4 months;
- an untuned length of wire, about 10 m long, and located in the loft
[attic] in proximity to mains wiring seems to be make a good noise sense
antenna for nulling out interference received on my vertical antenna.
- the 10 m wire does not always provide sufficient noise to null out
interference heard while using my 60 m single-turn delta loop antenna.
I regret to report that, during a recent telephone conversation with Stu
GW3XYW, I learnt that Roy GW3ITD is now a silent key. Roy died in early
October. Many in the LF Group will know of Roy's interest in the LF
bands, either through QSOs on 136 kHz, or via the early LF nets.
Indeed, it was his enthusiasm that sparked Stu's interest in 136 kHz.
Regards to all,
Steve GW4ALG
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