TENNA DIPPER
Here is
a useful
project from Steve
Weber, KD1JV
The project / schematic can be found here:
HENDRICKS QRP KITS
Steve 'Melt Solder' site: KD1JV
Designs
Please see all the projects on this great site.
You may purchase the Tenna Dipper kit from QRP KITS,
or homebrew it as I did, with some modifications.
It is used to
analyze either:
1) what frequency is at 50 OHMS on your antenna
or
2) assist in trimming the length your antenna for a given frequency.
It is a Wheatstone bridge where the antenna is one leg. No current will
flow past the bridge when the antenna leg is 50 OHMs. This 'dips' the
LED.
My modifications include:
1) building in my own homebrew 5 digit frequency counter instead
of the one designed on
the schematic.
2) including a 10 mA meter to watch the needle dip along with the LED
dip.
From the Hendricks QRP KITS WEBSITE:
Wide
tuning range: ~3 MHz to ~30 MHz in two ranges
Four digit digital display with
display shift down to 100Hz
Eliminates the need for a
transmitter and SWR bridge when:
Trimming length of resonate
dipole, and portable vertical antennas
QRM free adjusting of antenna
tuners and antennas
Quickly adjust short, portable
vertical antennas, eg. PAC-12 &
Screwdriver antennas, etc.
Current draw is approximately 50mA
My Completed Dipper
A) The schematic and
boards were layed out using EAGLE CAD
5.11,
the board
patterns were then laser printed onto acetate.
B) The PCB patterns on the acetate
were heat transfered to the copper boards,
and the
boards were then etched with ferric
sulfate.
C) The same acetate / heat process transfers the silkscreen to the top
of the boards after drilling
D) The led / meter cutouts on
the metal case were done with a homebrew
CNC milling machine.
(But thats
another story, for another page, for another day.....)