28 May 2013

W1FB DC Receiver experiments 5

This morning I was listening on my receiver at 6:45am - 8am. This was interesting. When I started listening I could hear DX stations from the USA coming through although not strong. By 7am the band was shorter and I could hear Capetown stations working into Joburg. By 7:30 I was hearing loud BCI. I don't have a shortwave general coverage receiver but I got the impression that these were not mediumwave AM stations but rather shortwave stations perhaps on the 41m and 49m bands. My BCI filter was not filtering out these stations obviously due to the fact that this is designed for filtering BCI below the shortwave band. The stations were not tunable except that by adjusting the input circuit I could definitely significantly affect the loudness of this BCI when compared to ham stations. The BCI was indeed coupling through the antenna (I think). When I disconnected the antenna the BCI went away.

I could also hear band conditions changing over this period with QSB on local stations and also the CapeTown stations. Based on the content of the BCI I was hearing southern african broadcasts in addition to local south african shortwave stations.

By 8:10am I was hearing BCI only from a local South African station and the african stations had gone.

So in conclusion I have 2 different kinds of BCI to contend with. The AM medium wave is sorted by using the BCI SW bandpass filter. The shortwave BCI probably needs better front-end filtering to eliminate?

However at this time of year all BCI disappears by 9am.

Superglue on toroids

Last night I decided to put superglue on the oscillator toroid to see if I could stabilize it mechanically. What I found was interesting. It is easy to apply it to the windings and to the area between the core and the underneath copper....no problem. It is very runny and tends to run a bit. However it dries very slowly when not under pressure. By this morning it was dry and appears to have worked. The toroid is now stable to mechanical vibration. The glue seems to be dry. The inductance of the toroid appears to be unaffected. Not too sure if the Q has been affected however.

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