[Lowfer] Definitely did something wrong !! But fixed it.

[Paul Daulton]

Q can be easily determined with out a Q meter by loosely coupling a signal gen to the coil and measureing the voltage across the coil with a rf probe or scope. At the peak record the frequency and then move the generator off the coil to the -3db point or 0.707 voltage point. the center frequency divided by the bandwidth is the Q. ( Q=fc/bw ). 

putting the hand nearby or laying a book on the coil is just detuning the resonance. It is not suprising the book insulates the coil. I have a regen rec with a masonite front panel that is immune to hand capacitance, normally pronounced in regens. 

By the way Q for my loading coil is 302 at 1.968mh and 457 at3.185 mh. Those measurements were taken before I trimmed the coil. Nominal inductance at resonance is now 2.2 mh , but I have lost the q measurements after I trimmed the coil. Next time the beacon is down for maintenance I will measure it . 
I trimmed the coil until the variometer is nearly meshed. When I started the antenna current was 10% deflection on a current meter consisting of a 40 turns on a ft50 torroid inseries with a 1n914 diode and a 50ua meter. The primary of the pick up is the antenna lead. As I trimmed the coil I had to remove turns from the pick up. I now have 90% deflection on the meter with 19 turns. When I got it to that point I started to get out of state reports. 

I have two q meters. A Boonton 260 a very expensive and delicate machine. And a Heathkit QM-1 I picked up at a Hamfest for $15. I really prefer the Heathkit. It is very simple, an oscillator and an rf vtvm
and capacitor. There are a lot of sites on the internet that describe homebuilt qmeters. I wouldn't be without mine. 

73 Paul

Quoting Andy - KU4XR <ku4xr at yahoo.com>:
> 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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Paul Daulton K5WMS
beacon WMS 187.492 khz qrss30/slow 24/7
Jacksonville,Ar 72076
em34wu