"March Madness" Project-- A 14.5 inch Loopstick Transplant for the SRF-39FP
Welcome to all ultralight DX enthusiasts! We are all especially happy to have a growing ULR fan base in Europe and South America, and feel honored to have you as part of our enthusiastic team.
In search of the ultimate DX portable, a 14.5" loopstick was successfully transplanted into an SRF-39FP "Prison Radio," by use of an LCR meter, and two 7.25" ferrite bars tightly wound with heavy-duty tape. After full alignment, the sensitivity apparently exceeds any stock portable in sight (ICF-2010, E1, ICF-S5W, etc.).
The most exciting point is that the loopstick was constructed of readily available parts, and the entire experiment cost less than $60 US. A full article on this "Super Prison Radio 3" will be available shortly, documenting all the steps and part sources.
Three photos of this DX Monster have been uploaded to the Ultralightdx Yahoo Group site, and it is rumored that this ultimate Ultralight may soon haunt the shores of Grayland, Washington. This radio is so much DX fun, it should be illegal!
73, Gary DeBock
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John H. Bryant <bjohnorcas@...>
Gary!toggle quoted messageShow quoted text
Great transplant operation!!! Several questions:
1. Where did you get the Litz wire that you are using to wind the coils? What size is it?
2. Are you following the L values from that one-page paper of the Bryant/Hall-Patch tests of the SRF-39FP ferrite antenna (in our Files section)?? If you are, are you still getting great results "right out of the box" using those "L" values to wind the coils???
3. What determines the distance between the ferrite new bar and the top of the SRF-39??
4. Have you tried running the connecting wires parallel to the bar (as they run in the stock unit) and then vertically down the ruler, rather than diagonally? Is their a measurable loss?
A couple of suggestions for further experimentation: When Bill Bowers and I were building the 8'-0" Monster Ferrite bar antenna, Bill did a good bit of careful experimentation with the 3/4" x 12" bars from which the Monster was constructed. He found that there was a significant reduction in gain if the butt ends of the bars were not PERFECTLY flat together. He proved that finding in the field when our 4"x 4" redwood support beam under the bundle of ferrite bars started sagging (yes!) That slight sag plus changes in temperature (the Monster was mounted outside) opened up tiny wedge-shaped spaces between the flat bar ends and there was quite a loss of gain. Bill ended up putting a cap over each end of the monster and then putting bolts in threaded holes in the caps to put each line of ferrite bars in serious compression. In your photos, it appears that the two bars are sagging a bit. Maybe the ends that you are working with are not perfectly square and you are getting good contact, despite the apparent sag.
Another thing that Bill learned is that even with perfect contact between the ends of two bars, laying in a third bar that overlaps the joint of the first two by at least 1/3 of its length made a very measurable increase in gain.... more than could be accounted for just by the additional mass of ferrite. So, you might want to try adding a third bar in close contact with and overlapping the first two..... sort of magnetically reinforcing that center joint.... I wonder if you would increase gain even further???
In the third bar approach, Bill said that it was as if the magnetic lines of force flowed through that third bar, bypassing the joint between the first two.... might be worth a try?
Anyway, Gary, great transplant operation.... let us know how it goes at Grayland!