Wednesday, March 31, 2010


The AN-100 dropped in today. TECSUN produces two slightly different MF multi-turn loop aerials for BC-receivers, the AN-100 and the more popular AN-200. My impression, it's just a matter of design. The AN-200 rests on a stylish arc-like stand, while the AN-100 is held by a rather non-stylish foot.

AN-100 from below

My preference was the AN-100, since I believed that the foot could be opened by a bottom plate, it seemed better suited for modifications. And, the dear reader may have a guess... I was guessing correctly. Underneath 4 rubber-foam pads, 4 screws allow access to the inside of the AN-100's stand.

screws underneath pads
Surprise surprise, the foot contains a polyvaricon, actually one of the type that is found in any random cheap broadcast receiver. The trick with those is, they employ little trimmers for basic frequency setting.

tuning capacitor
The modification to resonate the loop at 500kHz was consequently a simple one. One of the polyvaricon's trimmers was not set to maximum but rather to some odd looking position. Obviously that's the one to change. Well, guess what, I did just that, and the lowest resonance of the loop dropped to 494kHz.

Now, that was a simple one, no solder molten.
To drop the frequency even lower, solder needs to be molten. I figure a high quality, e.g. polystyrene, 47pF capacitor parallel to the tuning capacitor will do the trick.

The most upper resonance frequency is now 1330kHz.
The combination AN-100 & ATS-909 let me presently listen regular CW-QSOs.

inside the foot
Plenty of space in the compartment. Here are some ideas of what could be fit into this space:
  • a preamp
  • an I/Q-SDR receiver
  • a (subharmonic) grabber receiver w/ a USB sound-device, USB powered