Friday, July 24, 2009

RX Loop Experiments

Remember, some months ago I experimented with stuff called "YMVK-as 2x2.5mm²", which is doubly shielded underground mains cable - pretty sturdy stuff (expensive too)!
To that time, I cut a length of about 1.7m, connected one blue and one brown insulated lead to form a shielded double loop. Reception results were pretty amazing (see earlier post - tagged "aerial").

Today, I gave it some more testing, replaced the capacitor with a polystyrene varicap in butterfly configuration, in order to make the spindle neutral; that makes it easier to experiment with the thing.

As mentioned in the earlier posting, seems that the natural resonance of the shielded double loop is somewhere just above 7.4MHz. The capacitor, when resonating the loop to 7.0MHz, measures (MFJ-269Pro) 28pF. Bringing the resonance all the way down to the bottom results in about 5.8MHz at 62pF. Now I've got my numbers.

So, with the numbers all collected, it's hands on a piece of paper, pencil included, and maybe, by the end of the day, there is something to report about a self-resonant shielded RX-loop for 30m band.

The actual plan for the particular, above mentioned, loop is not to cut it down, but leave it just the way it is. This RX-loop, with such a capacitor seems ideal for a 40m QRSS grabber, whenever said band will be activated (volunteers?). Next to that application, the loop also covers the 49m and 41m BC bands, a hand full of underground beacons, the 45m pirate band and the RFID "medium frequency" at 6.78MHz.