Re: Tests of variable capacitors using Q meter including latest "0219" version Oren Elliott cap

Tom Crosbie G6PZZ <tom@...>

An extremely enlightening discussion. It reminds me of customers trading in gear who handed over a box with nicotine stained fingers and you just dreaded taking the kit out. White lettering turned yellow by heavy smoking and fans in the back dragging the same in through every vent slot. We cleaned it all off as best we could, but it was a lot of man-hours making it ready for sale…


As a DXer keenly awaiting delivery of a baby FSL, it has certainly given me food for thought when I visit costal locations. I recall Paul Blundell’s efforts in operating his inside a plastic tote box. From photographs taken at Rockworks etc., I see the FSL’s are covered in what I presume to be some kind of waterproof fabric. It seems this is not as waterproof as one might think. I would have thought that’s a bit high up for direct saltwater spray but with cars and truck roaring past creating wind that blows exhaust fumes, road debris, rain and who knows what in all directions.  Down on the beach it’s a similar story. More at risk of sea spray, even a gentle breeze can blow sand, pollen from grasses and other vegetation.


Perhaps this calls for a holistic approach to mitigate the problem.

Gary, would it be possible to mount the 384P inside a small watertight plastic box? A clear box to see the vanes.  I’m thinking a small hole drilled to take the Litz wire could be sealed with hotmelt glue. The shaft could be fed through a tightly fitting grommet in another hole. This might mean the supporting PVC pipe needs to be an inch or so longer, but I suspect Gary has shares in his supplier 😊


Just an idea from someone with zero field experience of FSL’s – yet!


73 Tom G6PZZ

Nr Chesterfield | NE Derbyshire | UK | IO93he

HF250 | Sentinel 4 | RSPdx | RM50 | TR2 | ATS 808

15m MLB | MTA | D707


From: <> On Behalf Of Gary DeBock via
Sent: 10 July 2020 10:56
Subject: Re: [UltralightDX] Tests of variable capacitors using Q meter including latest "0219" version Oren Elliott cap


Thanks Steve (and Dave),

The possibility that the "Q" of older variable caps degrades over time because of environmental factors is interesting, and I appreciate your experimentation regarding this. That would certainly explain why the brand new variable caps from Mike's Electronic Parts always seem like hot performers out of the box, while the older ones installed years ago seem like duds by comparison. By coincidence I had replaced all of the variable caps in the larger Rockwork Cliff "DXpedition" FSL antennas prior to last year's trip, and did notice improved tuning performance.

<<<   This is beginning to lend credence to Dave Aichelman's comments about these caps seem to deteriorate in selectivity/Q when used in FSLs that are exposed to cruddy conditions such as coastal salt air, and that cleaning the cap can restore it to "as-new" condition.   >>>

I should thank Dave personally for this information, since during the past week I've had several requests from DXers who want me to replace the variable caps in their FSL's with the latest models, and now it seems that this type of work can be done by the DXer himself, without any effort on my part :-)

As for the "cruddy conditions" such as coastal salt air, Steve, I can certainly appreciate how that would accelerate the degradation of a variable cap. But in reality those kind of coastal locations frequently are ideal DXing venues for the compact FSL antennas, such as the wacky Rockwork Cliff in Oregon, where Tom R. has completely shattered the west coast record for South Pacific NDB's received during a DXpedition. Overseas salt water beaches are also prime FSL DXing venues, and they frequently combine extreme heat and humidity along with their salt air corrosion. I suppose it's a situation similar to pushing a race car constantly for top performance-- before you show up at a challenging race track, you need to "pay the piper" with new tires, new brakes and a perfectly tuned engine in order to be competitive. Before using FSL antennas at an exotic beach involving some serious travel $$, installing a brand new variable cap (or detailed cleaning of an old one) should be considered mandatory.

73, Gary



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