Re: Build Your Own (Reasonably Priced) FSL Antenna

Gary DeBock

Hello Chris and Ian,

Chris, thanks for your suggestion. I agree with you that the best
option for supporting all the fragile ferrite rods throughout their
length would be to have a longer rubber plumbing coupler, but
unfortunately such an animal doesn't exist. The issue with splicing two
rubber couplers together is that the 7-pound weight of the ferrite rods
would probably not be supported very well in a fall, since the splice
would not absorb the shock and flex, like solid rubber. In addition, a
splice would create a ridge around the flat surface of the rubber
couplers, making it tough to get all of the rods to lay completely flat
on the rubber coupler (which is essential for its intended purpose of
shock absorption).

There has been only one actual unplanned FSL "drop test," to my
knowledge. A 6" diameter Longwave-design FSL composed of 35 Amidon
(type 33) 4" x 1/2 ferrite rods was accidentally dropped off of a 5'
PVC stand onto the ground during my July Lincoln City, Oregon
DXpedtion, and all the ferrite rods survived without any damage. The
design of that FSL was very similar to the 7" Medium Wave FSL as far as
the Funnoodle inner core and pipe insulation padding, but it had a
rubber plumbing coupler of exactly the same length as the ferrite rods
(4") supporting the rods, which of course was ideal. Essentially, the
science of shock-proofing an FSL's fragile ferrite rods is based on
designing in as much protection as possible, since nobody wishes to try
an actual drop test on hundred of dollars of ferrite. Fortunately that
6" Longwave FSL not only survived the "drop test," but received its
best DX of the trip (a 1,000 watt NDB beacon at over 5,000 miles) about
10 minutes later.

Ian, the issue with simply using a plastic tube for a ferrite rod
support system is that the heavy weight of the ferrite rods (7 pounds)
would probably make the plastic tube sag, and if the antenna was ever
accidentally dropped, the 7 pound ferrite weight would probably flatten
the plastic tube out along the ground. Whether the ferrite rods would
survive such an adventure is of course unclear, but it wouldn't be my
first choice to risk hundreds of dollars of ferrite to find out :-)

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

-----Original Message-----
From: G3ROO <ian.g3roo@...>
To: ultralightdx <ultralightdx@...>
Sent: Tue, Oct 18, 2011 8:31 am
Subject: Re: [ultralightdx] Re: Build Your Own (Reasonably Priced) FSL

I am at a bit of a loss why use a foam core...... it's only to support
the rods so any large diameter plastic tube will be fine.... and
protect the rods to agreater degree

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