[Lowfer] Pill bottles...

Tue Sep 15 21:04:59 EDT 2009

Thanks Bill - Your absolutely right.   I took the very simple view that
any change due to plastic was all bad.....certainly the "loaded"
plastics were bad/worse in my view but Red coloration was as bad as
Black (:-)

I forgot to mention I was measuring the amplitude of the
oscillator...but again that could be misleading a bit dependant on what
class I was running it in. I should have varied the osc freq a bit
either side and measured the resultant Q for materials at the same time,
trouble was, like here  Im a bit strapped for test equipment or brain
power... I did try heating the materials, offering them up and seeing
the net affect on the osc as they cooled, but here it got a bit messy
given mass dm/dt stuff, the idea here was to get a material with the min
physical thermal expansion, this changing the wound coils
characteristics  Still my clear pill bottle was the winner for this app
- I didn't have access to anything else at the time.

Laurence, smoggy China.
Cough Choke.....splutter...

-----Original Message-----
From: lowfer-bounces at mailman.qth.net
[mailto:lowfer-bounces at mailman.qth.net] On Behalf Of Bill Ashlock
Sent: Wednesday, September 16, 2009 8:36 AM
To: lowfer at mailman.qth.net
Subject: Re: [Lowfer] Pill bottles...

Hi Laurence,

Excellent reporting, below. One thing you may not be thinking about in
your detuning experiments is that a change in frequency does not
necessarily mean a lowering of Q. The capacity introduced, or dielectric
effect, that causes the observed detuning may have a range in Q from
very low to very high. How about, instead of the microwave, using a test
coil having a large 137KHz field and noting the temp rise for different
materials?

Bill

> Date: Wed, 16 Sep 2009 08:07:47 +0800
> From: L.Howell at conocophillips.com
> To: lowfer at mailman.qth.net
> Subject: [Lowfer] Pill bottles...
> 
> One of the questions Ive been mulling over is how far a screened
> "room/box" relative to the dimension of the coil and operating
frequency
> and secondly the net of having the coil too close to the ground
whereby
> the flux is either compressed, short-circuited or dumped. I think I
> remember as a ballpark least 1 x D and H...?
> 
> In large Loran and some larger ATU rooms they are screened with
> foil/copper just to stop such variations but I'm guessing there must
be
> a min dimension/space between the coil and the screening
> material.,...where my Termans/sliderool...
> 
> I do know I needed to keep my LF AtU a couple of feet off the ground
not
> to see an impact on the Q (keep it off concrete especially with
rebar!)
> , though I never got as far as screening it to stop local capacitive
> affects detune.
> 
> Not all plastics are the same - one trick I did in Singapore when
trying
> to design a stable LF oscillator was to make a free running LC coil on
> 137khz and then offer up differing types of plastic with a long non
> metallic grips to the tank coil and note the detuning affects of each
> type of plastic monitoring the freq change using a nearby loosely
couple
> SSB rx. 
> 
> I guessed the smaller the change in freq and interaction with the
> material the better it was as a coil former etc...The result was the
> choice of a strong clear plastic pill bottle which I drilled out
excess
> plastic in vertical channels, though still rigid enough for coil
> stability. There was a lot of variance - and not just the color of the
> material....
> 
> When I took all my materials under test and loaded them into a
microwave
> oven there was little to no difference after 30 secs of irradiation in
> temperature at microwave...so I don't think the microwave test is
fully
> repeatable at LF..well not with the materials I tested.
> 
> Laurence
> WE2XPQ Wasilla Alaska
> BY3A Tianjin China.
> 
> 
> 
> 
> 
> -----Original Message-----
> From: lowfer-bounces at mailman.qth.net
> [mailto:lowfer-bounces at mailman.qth.net] On Behalf Of Andy - KU4XR
> Sent: Wednesday, September 16, 2009 4:00 AM
> To: European & UK) and MedFer bandsDiscussion of the Lowfer (US
> Subject: [Lowfer] Definitely did something wrong !! But fixed it.
> 
> Hey lowFERs:
> 
> I'm posting this just for " this is what happened sake "
> I put a paperbacked book about 3" thick on top of the 
> variometer bucket. and I could then lay my hand on the book
> and the tuning would change only slightly. Remove the book,
> and place a hand within 3" from the top side ( hot end of coil ,
> or within 5" above the top, and the tuning changed dramatically.
> And just to see what would happen; I placed a sheet of aluminum
> foil over the bucket, and the output droped to ZERO, and could 
> not be tuned with the variometer.
> I am not an antenna specialist, nor a coil guru, so I'm not
> really sure that this is a higher " Q " issue or not. My thought
> would be that if the coil " Q " went up, then my tuning would
> become very sharp, and critical. After removing the bottom from
> the bucket, the tuning sharpness didn't increase nor did the
> output change when peaked. The increased proximity effect around
> the variometer was the only thing noticable.
> 
> Still having fun; 73 to all ::
> 
> 
> Andy - KU4XR - EM75xr - Friendsville, TN.
> LOWfer Beacon " XR " @ 184.322 KHz ( QRSS-60 )
> Coordinates: N: 35* 43' 54" - W: 84* 3' 16"
> http://www.myspace.com/beaconxr
> 
> 
> --- On Tue, 9/15/09, Peter Barick <pbarick at niu.edu> wrote:
> 
> > Date: Tuesday, September 15, 2009, 1:08 PM
> > Hi Mike, Andy,
> > 
> > Interesting on that bottom cutout, and surprised me. If the
> > pvc bucket is thought to be nearly RF inert then why that
> > effect? As described, it appears the Q has risen greately
> > for such effect. Mike talks to this too.
> > 
> > I believe Mitch (MP) spoke of it also, causing the need for
> > an extension rod with which to adj. the vair coil.
> > 
> > High Q is usually thought to be the goal (or bragging
> > point) and causes reactions as above. But too much can lead
> > to wx affected untuning and demands for attention to keep it
> > spot on. Ha, Teslas we are Not!
> > 
> > Just some observations -- Peter
> 
> 
> 
> 
> 
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