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


Steve Ratzlaff
 

I received my Mike's Electronics latest version of the Oren Elliot-manufactured latest version "0219" N50-384P variable cap with vernier today.

There is a way to test the relative Q of a capacitor on the Q meter using a reference inductor. You use your best cap as the reference cap noting its Q at the various test frequencies. Then you test other caps and see how their Q's compare to the best cap. My best variable cap is the so-called "holy grail" TRW variable capacitor from the URM-25D signal generator--it has ceramic insulation, silver-plated plates, etc.  Xtal Set DXers prize this cap as the best. It has a 14-495 pF range, quite a bit higher max capacitance than the nominal 385 pF of the N50-384P. Of course one just sets the cap to the same 385 pF when testing. I have two older Oren Elliott caps, both unused, so with the latest one I have 3 of them to compare. I have a number of Russian caps with vernier tuning and ceramic insulation that used to be inexpensive and plentiful on eBay 5-10 years ago (in the $5-8 range)--now only one or two sellers offer them at much higher prices in the $25-30 range; and several unknown brand caps with ceramic insulation (no vernier). Mike's Electronics also offers a custom-made dual gang polyvaricon with about 320 pF per section; it does not have vernier tuning. (The URM-25D cap doesn't have built in vernier tuning either.)

I will say right now that the latest "0219" version cap does not test any better than the previous two Oren Elliott caps and actually tests somewhat poorer/lower Q. 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.

My tests are at three frequencies, near 540 kHz for the N50-384P max capacitance; 1000 kHz; 1700 kHz.

73,

Steve AA7U

URM-25D variable cap ("holy grail" cap)

536 kHz 816Q     996 kHz 716 Q     1698 kHz 505Q

Small Russian dual gang cap with vernier, single gang tested

537 kHz 791Q     1000 kHz 695Q     1699 kHz 495Q

Larger Russian dual gang cap with vernier, single gang tested

538 kHz 780Q     1000 kHz 678Q     1701 kHz 464Q


Unknown brand dual gang cap with ceramic, no vernier, single gang tested

539 kHz 757Q     1000 kHz 660Q     1701 kHz 455Q


Mike's Electronics custom dual gang polyvaricon (about 320 pF max per gang),1 gang

(575 kHz 561Q)     1004 kHz 536Q     1702 kHz 409Q


N50-365P Oren Elliot cap with vernier (385pF)

538 kHz 604Q     999 kHz 503Q     1701 kHz 274Q


N50-384P version 0217 cap with vernier

538 kHz 614Q     1004 kHz 499Q     1700 kHz 276Q


N50-384P version 0219 (latest) cap with vernier (395pF measured)

532 kHz 555Q     999 kHz 386Q      1698 kHz 195Q



Gary DeBock
 

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

  


 


Paul Blundell
 

Great posts and some interesting thoughts on the difference that time and use has on these. I keep mine very well protected.


On Fri, 10 Jul 2020, 7:56 p.m. Gary DeBock via groups.io, <D1028Gary=aol.com@groups.io> wrote:
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

  


 


Tom Crosbie G6PZZ
 

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: main@UltralightDX.groups.io <main@UltralightDX.groups.io> On Behalf Of Gary DeBock via groups.io
Sent: 10 July 2020 10:56
To: main@UltralightDX.groups.io
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