7.5” Loopstick LW antenna


igvitk
 
Edited

Hi all! 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?


Gary DeBock
 

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)
 


igvitk
 

Thanks, Steve and Gary. I will follow your advice and add extra turns to Amidon rod to increase the inductance. Gary, where can I find information about your 12" Longwave FSL? I like LW DXing and would like to make more powerful antenna than 7.5" FSL.


Gary DeBock
 

Hello Igvitk,

My current 12" Longwave FSL antenna is a slightly more sensitive version of the 2015 model 12" Longwave FSL, the design photo for which is attached.

The ferrite rods, frame components and size of variable cap are all the same, although the 660/46 Litz wire has been replaced by 1162/46 Litz wire, which provided a sensitivity boost. Because the 1162/46 Litz wire has a larger diameter than 660/46 wire, though, I was not able to fit enough coil turns on the ferrite sleeve in order to get the start frequency down to 153 kHz. This didn't bother me, though, since the start frequency is now around 195 kHz, which is fine for chasing long range South Pacific and Asian NDB's during a DXpedition.

The variable cap has also been replaced with the razor-sharp tuning "384P" type from Oren Elliot Products, which improved the overall performance of all of the FSL antennas used during the recent Rockwork Cliff DXpedition. That type of variable cap is also now the tuner for the "Frequent Flyer" FSL antennas, three of which we plan to use this November in Poipu, Hawaii.

73, Gary DeBock (in Puyallup, WA, USA)