Re: 7.5” Loopstick LW antenna
Hello Igvitk (and Steve),
<<< I’m trying to make the 7.5” loopstick LW antenna according to the instructions. I used the Amidon R33-050-750 rod, 100/44 litz wire, made 122 turns of the coil, which is located exactly in the center of the rod and which length is 106,5 mm. However, the output inductance measured by the multimeter is only 1432 uh instead of 1700 uh. The similar result was shown by another multimeter VICY DM4070. I think that is a strong deviation. Can anybody explain how to solve this problem? >>>
As Steve has explained, the specified 1700 uH is not an essential inductance value, and there are variations in the inductance of ferrite rods and Liz wire, even among the same manufacturer. The important thing is to have enough inductance to make your loopstick provide good sensitivity on your chosen Longwave frequencies, and in order to do this you need a lot more inductance than what SiLabs recommends for Medium Wave (180-450 uH). Your 1432 uH inductance should be fine for most of the Longwave frequencies, unless you wish to concentrate on chasing the LWBC stations from Europe and Africa on the lower edge of the band, in which case you may wish to add a few more coil turns to raise the inductance up a little. For NDB chasing you should already be OK with the 1432 uH.
Originally five test models were made up for the Longwave loopstick design project, and they were all compared on different Longwave frequencies using a Tecsun PL-360 plug-in system. Full details are contained in the article posted at http://www.mediafire.com/file/845snah2h4ek9z9/7.5inLWLS.doc/file
73, Gary DeBock (in Puyallup, WA, USA)