Friday, July 24, 2009

RX Experiments

As a regular observer of my grabber, you may have seen two drastically different levels of noise with some very sharp crackle inbetween. Well, apart from the recent electric storms we had, that was some testing/comparing different aerials on the subharmonic receiver. Since this receiver is actually a DC-RX with no AGC, comparison between the different aerials is pretty streight forward.

The aerial producing more noise is hidden the G5RV-jr. Signal levels are slightly stronger, depending on the direction to the signal source.

The second aerial, the one that abviously produced less noise, is an indoors "rockloop". Here, additional experiments were performed to see the influence of directivity of the aerial on the signalstrength and on the level of the noise floor.

Results and Conclusions:
I found the direction of the very strong and annoying pattern often visible in my grabber. Seems to be an appliance of one of my neighbors. The G5RV-jr, as an electric dipole, picked up that noise brilliantly, often completely drawning everything else. The rockloop, as magnetic loop, also sees it, but by far less prominent. Since a portion of the magntic component is present, it seems that the source of that noise is just something like 30-60m off my house (edge of the nearfield). In Holland, that's far enough to exclude my immediate neighbors. Anyway, the difference is dramatic, thus, I decided to further investigate in the design of a shielded magnetic loop, preferably water proof.

See my next post for the plan....