[Antennas] Loading Coil Placement

Wed Jul 13 11:50:16 EDT 2005

Kevin:
I did some modeling with EZNEC about a year ago. The model was of a mobile 
vertical, attempting to resolve the question about where to locate the 
loading coil for best results. I think that it would also apply to a short 
dipole in space. Your wire antenna will be longer than the antenna I was 
modeling so the result may vary.
The conclusion was that when the Q of the loading coil was included in the 
model, that it made little difference where the loading coil was located. As 
the coil was moved up the antenna, more reactance was required for resonance 
and therefore more loss resistance. I was using coil Q's of 200 to 200 in 
the model. The efficiency and bandwidth did not change much with varying 
coil location. 
 walt, W7PRB
On Tuesday 12 July 2005 20:02, Kevin Nathan wrote:
> Hi All,
>> A couple of weeks ago I wrote to this group asking for feedback on
> shortened dipoles/inverted vee's for 160, 80 and 40. In the interim, I
> found a couple of coils I had saved from an experiment about 20 years ago
> with a shortened 160 meter inverted vee. Of course, the info on dimensions
> for that antenna are long gone. These coils are wound on what appears to
> be 2 and 3/8" OD PVC which a friend had actually turned on a lathe so that
> the wire rests in a continuous spiral around the pipe. It seems to be
> number 12 or 14 AWG about 68 turns. I am thinking of adding these to my
> existing 135' inverted vee fed with 450 ohm window line. My problem is I
> can't seem to find anything definitive as to where in the antenna to insert
> these coils. This antenna started out as an 88' doublet to which I have
> added length to bring it to the present 135" length. It would be simplest
> to insert these coils at the point where the extra wire was added.
>> I would like to get some feedback as to your thoughts concerning the
> feasibility of what I propose or where to insert loading coils such as
> these and possible overall antenna length to get the system to tune on 160.
> I need to keep it somewhere around where it is now or slightly longer--I
> can't go the full length on 160 or I wouldn't need these coils. <GRIN>
>> Thanks much in advance for your thoughts and feedback. Very 73.
>> Kevin :)
> Amateur Radio: K7RX
> Navy Marine Corps MARS: NNN0SHS
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-- 
----- Walt Jamison, wcj9996(at)comcast.net ------