[Amps] placement of RF choke bypass cap. (Results of experiment)

[K1TTT]

Sounds reasonable.  But it doesn't show that current flows through the
center of the disk.  There are capacitive paths between the wire on each
side and the disk surface that provides a shorter path than going radially
out and back in on the disk surface.


David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
 

> -----Original Message-----
> From: Larry Benko [mailto:xxw0qe at comcast.net]
> Sent: Saturday, March 20, 2010 16:21
> To: dezrat1242 at yahoo.com
> Cc: amps at contesting.com
> Subject: Re: [Amps] placement of RF choke bypass cap. (Results of
> experiment)
> 
> Here are the results of the experiment:
> 
> 1.) Dipole was made with #10 bare copper wire each side 12.0" long.
> 2.) Disks are 2.02" diameter x 0.01: thick copper with hole in center
> for #10 wire.
> 3.) 8ft. of RG-316 coax with 3 common mode chokes (Z>300 ohms at 200
> MHz)was calibrated at the far end in order to measure actual dipole feed
> point impedance.
> 4.) Tests were done in my basement with at dipole height of about 3.5'
> and 4-5' of clearance to other objects.
> 
> Test #1: Bare dipole
>     Fres = 236.20 MHz,  Z = 71.5 + j0  (468/length = 234MHz)
> 
> Test #2: Dipole going thru center of disks and soldered with disks
> placed 4.0" both sides of the center of the dipole.
>     Fres = 223.55 MHz,  Z = 65.7 + j0
> 
> Test #3: Dipole going thru center of disks and soldered with disks
> placed 8.0" both sides of the center of the dipole.
>     Fres = 199.01 MHz,  Z = 44.3 + j0
> 
> Test #4: Dipole soldered to top edge of each disk with disks placed 8.0"
> both sides of the center of the dipole.
>     Fres = 196.89 MHz,  Z = 43.9 + j0
> 
> Conclusions:
> 1.) The difference in frequency between tests #1 and #2 or #3 and #4 do
> NOT allow for the dipole length to be increased by the extra 4" it would
> take if the current went around the disks.
> 
> I have pictures if anyone questions my setup etc.
> 
> 73,
> Larry, W0QE
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps