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Re: [Antennaware] homemade coil

To: K9AY <>,
Subject: Re: [Antennaware] homemade coil
From: Jan Ditzian <>
Date: Thu, 15 Mar 2007 14:01:28 -0500
List-post: <>

Thank you for the information, and for letting me know I am on the right 
track.  I have managed to work Europe and South America on SSB, both 
with poor reports, running 600 watts.  I worked US hams at about 200 
miles with good reports.  However, I think that I can lay much of the 
blame for the reports on the fact that I have a single radial, slightly 
shorter than 1/4-wavelength.  Once I  establish a good mechanical 
connection and a reasonable  SWR, I will add radials (aiming for 60) and 
probably arrange for a way to change the inductance at the antenna with 
a relay, for a high-end, low-end antenna.   I will probably then use a 
tuner in the shack to keep the output tubes happy, but I am willing to 
operate into a 1.5:1 without a tuner.

The tower is 52-feet high, with a C-3 at the top.  I added the coil and 
got X=0 on the MFJ-259.  I am also using a 4:1 balun that I had around, 
since the R component is quite high.  I am doing this empirically: 
whatever works cheaply is what I do. 

My next step is to see if I can use the hunk of (probably 75-ohm) 
hardline that is lying in the back yard, instead of the 52-ohm coax I 
stole from my 40-meter vertical.  My only concern is that the bandwidth 
seems to be far greater, and SWR lower, in the shack, implying losses.  
However, I have not quantified this.  The coax is hardly new, and I will 
put a 50-ohm dummy load on it and see what the MFJ-259 tells me once the 
wx is improved.

Your implication that even #12 wire may be small is what I had thought.  
I will go to a home-improvement place and see what copper tubing might 
cost, now that I have an idea of length.  I would again use the 4-inch 
form, but probably remove it after winding the tubing to leave only air 

I am quite heartened by this, and I am even dreaming of home-brewing 
matching networks in the future.  With the MFJ analyzer, I could even 
match to 75-ohm coax, bring it into the shack, and then reconvert to 50 
ohms with a tuner or another fixed matching network.  I can used fixed 
capacitors when I know what values I am looking for, so those costs can 
be kept low. The wire investment was $4.00 and the coil is over twice as 
long as I needed.  The PVC is less than $10.00 for ten feet.

I suppose my next step is learning how to blow glass for amplifier tubes.

Jan, KX2A

K9AY wrote:
> Jan,
> You did the #1 best thing by using a large diameter. Any improvements 
> with a neater winding will be small. Same goes for larger wire or 
> tubing -- the theoretical improvement may be hard to see.
> The only exception would be a coil with a lot of current flowing 
> through it. In that case, a larger conductor and optimum 
> length/diameter ratio for best Q would reduce the losses.
> Actually, I'm a little surprised that you need inductance with a shunt 
> feed -- is the tower short?
> 73, Gary
> K9AY
>> I began work on shunt loading my tower for 80 and/or 160.  The initial
>> reading on my MFJ 259 showed that the antenna was too short, and it
>> needed a coil in series to get X=0.  I went to a plumbing shop and found
>> solid #12 insulated wire, wrapped it around some 4-inch diameter PVC
>> pipe, and lo and behold, I am in the ballpark.
>> My question is: I intend to re-wrap the wire so it is neat, but what
>> kind of problems should I expect from this kluge coil?  I tried moving
>> the turns around, with the ends fixed in place, and there is almost no
>> change in X on the 259.  Am I looking at low efficiency, potential
>> arcing, other problems associated with such a cavalier method of
>> creating a coil?
>> Jan, KX2A
>> _______________________________________________
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