[Lowfer] My variometer resistance

[PAUL DAULTON]

I  have a bucket similar to what you have, it measures 11.5inch dia.
At 88 turns I calculate you have 265 ft of wire.     At nine ohms that 
translates to 25 awg. Probably 24 awg.
Best dia to length ratio is 2/1. with any larger wire you would have
 trouble getting the turns
on the form. Plus as you increase the dia your coil becomes longer as the
 turns per inch goes down
as the insulation takes more space and you get into a less than favorable
 d/l ratio.
If you are going to spend any more on the wire I would go for litz or
 enameled wire.Check with
a local rewinding shop and see what kind of deal you can make on enamel
 wire, about 22ga.
Q of the coil can be measured by a signal gen and vtvm. Loosely coupled to
 a parallel resonant circuit
( 5pf or so) you tune for a peak on the vtvm with rf probe, then tune off
 each side for the .707 point
(3db) the center freq divided by the bandwith is the Q. I have two qmeters
 which makes the job easier
but it can be done easily. Search the net for q measurements. to compare
 apples and apples you need a base
measurement.
I recently built a bitx20 ssb tranceiver, 5wat rig designed by an Indian
 ham Ashhar Farhan. Farhan used nylon 
faucet washers for the coil forms. I couldnt find any nylon so I used
 black rubber washers from Home Depot.
Performance of the rec was dissapointing so I measured the Q of the coils.
 Mine were about 60. Replacing
the coils with coils wound on T37-2(red core) I had and Increase of 3 or 4
 s-units , not db but 3 or 4 s-units.Q of new coils
was 180 . Losses can fool you. Evidently the rubber washers contain carbon
 for pigment, very lossy. Live and learn.
Only improvement I think you could make would be to go to non pigmented
 bucket. and either litz or enamel wire.
the smaller dia of enamel would shorten the length of the coil and give a
 more favorable d/l ratio. As we discussed
there may be some loss from the pigment in the bucket.
You are doing well,I think the improvements you have made so far are great.
btw I got an Email from Charles in S Coffeyville OK(COV) he copied me
 audibly last night. Distance of 254 miles. First report
I've had this year. Charles was using HP selective voltmeter and indoor
 loop.
73 Paul K5wms
-----Original Message-----
From: Andy - KU4XR <ku4xr at yahoo.com>
Sent: Fri, 24 Oct 2008 12:45:49 -0700 (PDT)
To: lowfer at mailman.qth.net 
Subject: [Lowfer] My variometer resistance
 
 
Learning as I'm going, My variometer was the single best thing  
I have done for my beacon so far, bringing the greatest gain.  
It's a 5 gallon paint bucket, wound with very small wire. I'm  
not sure of the guage, maybe #28 to #30 ( 6 stranded solid  
burglar alarm wire ). I know small wire has higher resistance,  
So I thought it would take fewer turns for a needed inductance.  
I measure 9.0 OHMs DC resistance across the variometer, and I am  
assuming that's way too high, and have been told by others they  
thought it was pretty high. If this question can even be asked  
this way; " What is a TYPICAL DC resistance of a paint bucket  
variometer ?? " I do consider wire size, material, spacing, etc.  
In the how bad do you want it catagory, the current cost of a  
500' rool of #14 solid / insulated is around $ 45.00. That's one  
reason I used the wire I had on hand for free. Still choking on  
the $ 45.00 wire.  
 
Nutshell:: Is 9 OHMs too high ? Is there any such thing as typical ?  
 
 
Andy - KU4XR - EM75xr - Friendsville, TN.  
LOWfer Beacon " XR " @ 184.322 KHz  
 
 
 
 
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