Re: Backup 3" FSL Tecsun PL-380 Design (with 62mm ferrite bars)


Gary DeBock
 

Hi Guy,
 
<<<   Around the same time I also experimented with the nulling ability of ferrite rod antennas using a 3/4" X 18" commercial Stormwise ferrite rod. I'm sure Gary must have tried various length-to-diameter ratios, too. The diminutive Sony SRF-T615 receiver was presumed to have excellent nulling due to its skinny (albeit small) antenna; we were just trying replicate or improve upon the length-vs-diameter ratio of our antennas in larger sizes for better sensitivity.   >>>
 
Yes, I recall John's experiments, and your 18" Stormwise bar transplants for the PL-380. John even turned his 4 foot long solid-ferrite monster over to me shortly before his accident, but unfortunately there were too many other hobby projects going on here at the time to have any chance to test it out (I guess some things never change). There never was much experimentation done here with super-long loopsticks, although a 30" composite loopstick for the ICF-2010 was made by placing 4 Amidon 7.5" ferrite rods together. To me there seemed to be a point of diminishing returns with the Stormwise and longer ferrite rods, which made the attached portables very awkward to carry around. On the other hand the 7.5" loopstick transplant has always seemed to provide a lot of "bang for the buck."
 
<<<    Now with this talk about the benefits of "stubby" Ferrite Sleeve Loop antennas, it makes me wonder if the preferred ratio works in the opposite direction if the ferrite is a hollow cylinder? Gary, can you chime in with your thoughts here?   >>>
 
Well, for some reason the hard-wired FSL's do seem to have made a breakthrough in nulling performance, possibly because they can be made extremely "short and stubby," whereas loopstick coils can never get too large in diameter because of the practical need to fit inside of a radio cabinet. In comparison to the famous SRF-T615 the 3" hard-wired FSL can get deeper nulls on pest stations, even though it was never specifically designed for this capability. The real fun will start when hard-wired FSL's are purposely created with sizes and shapes to emphasize this advantage-- at which time the design principles should be clarified. 1450-KSUH may be the final victim of this ultimate "pest control."
 
73, Gary
 
           
 
     
 
 

-----Original Message-----
From: dx@... [ultralightdx]
To: ultralightdx
Sent: Mon, Jan 18, 2016 2:31 pm
Subject: [ultralightdx] Re: Backup 3" FSL Tecsun PL-380 Design (with 62mm ferrite bars)

 
Hi Nick,

With regard to nulling ability, I wonder if the optimum length-vs-diameter ratio for FSLs is different than for standard (solid, non-hollow) ferrite rod antennas. In the early days of the UltralightDX Yahoo Group there was some experimentation with very skinny, long ferrite antennas. In fact, group co-founder John Bryant created an unusually skinny antenna composed of six or seven 1/2" X 7.5" Amidon rods in a row. The rods were cleverly compressed "on-axis" to simulate a single long rod for RF receiving purposes (did you ever know John *not* to be the King of Clever in any of his projects? :^)

Around the same time I also experimented with the nulling ability of ferrite rod antennas using a 3/4" X 18" commercial Stormwise ferrite rod. I'm sure Gary must have tried various length-to-diameter ratios, too. The diminutive Sony SRF-T615 receiver was presumed to have excellent nulling due to its skinny (albeit small) antenna; we were just trying replicate or improve upon the length-vs-diameter ratio of our antennas in larger sizes for better sensitivity.

Now with this talk about the benefits of "stubby" Ferrite Sleeve Loop antennas, it makes me wonder if the preferred ratio works in the opposite direction if the ferrite is a hollow cylinder? Gary, can you chime in with your thoughts here?

73,

Guy Atkins
Puyallup, WA



---In ultralightdx@..., wrote :

Your observation of superior nulling ability with the stubby FSL antenna is very interesting Gary.   One of the most intriguing aspects of the old SRF-59 in my recollection was that in spite of its tiny size, it had very good nulling capability.

Is it a rule of thumb that a stubby antenna has better nulling capabilities?  (though a single rod hasn't much signal pickup overall)

best wishes,

Nick



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