HF Receive Antenna
If you are only using the stock antenna that came with your SWL radio, Yaesu VX-7 or Kenwood TH-F6/TH-F7 you are missing out on a lot. This page describes a couple of parts box medicine bottle antennas that you can build. Specific values are not that important. Especially for receive only use.
In one example the coil was wound on 3/8" plastic tubing. In the big bottle example the coil was wound on ~1/2" plastic tubing.
The ground side of the capacitor is soldered to the ground of the BNC connector. The positive side of the capacitor takes 5 turns around the toroid and is soldered back to itself. The center pin of the BNC connector takes 5 turns around the toroid and then continues on to the wire wound inductor. From there the antenna continues with an attached piece of wire.
Toroid, capacitor and inductor specifics are not critical as this is intended primarily as a receive antenna. You can check your resonant frequency with a tool like the MFJ-269. This simple antenna will greatly increase your enjoyment of HF SWL with your TH-F6a.
Give this simple parts box antenna and matching unit a try and you'll be surprised. I'm only using about 6Ft of wire after the inductor. For the larger coils I used a plastic form and ~22AWG magnet wire. For the smaller coil I used a piece of tubing used on water systems with very fine magnet wire. Materials and values are NOT critical for the most part. The Important thing is to have fun!
Frequently Asked Questions
- What diameter should be the of the wire winding on the core
of a plastic tube?
22 awg the inductor. I believe I used larger for the toroid. This is enamel coated wire.
- On the steps which wire has to be wound on the first core
inductor, for how long and what section of the pipe has to be the
best on the tube diameter wound wire will also be useful to know the
total length of the wire?
The center + side of coax takes 5 turns around the core and continues on to the inductor. The ground - side of the coax goes to the capacitor. From the capacitor it takes 5 turns around the core and folds back on itself. The picture at http://www.dbbear.com/k0emt/projant/hf_rcv/mb_core2.jpg probably shows this the best. For the tubing you can use a small piece of pen or tube like you find in a water bottle straw. There is very little length of wire around the toroid.
- At which length of the section, the wire has to be wound on
the second inductor tightly wound core, same tube of the same
The only reason I had a gap in the winding is because that is the way it turned out. No technical reason.
- What value should be 1000uF capacitor in volts, I see the
picture that it has 1000uF and 85 degree Celsius?
Again, try with whatever part you have handy. The one I used was 6.3V.
- What diameter of wire wound on a core of green ferrite has
to be, and its length?
This wire looks to be about 22AWG and was very little on toroid, about 2M on coil form.
- How diameter of the copper wire must be wound on the ferrite
core, and its length?
I believe this wire is 18AWG and very short. It is also enamel coated.
- What must be the diameter of the external and internal
ferrite core and what its height?
Not critical. The one I used: ~4mm tall, OD ~12mm, ID ~7mm.
The biggest thing is to have fun and experiment.
Drop me a line and let me know how it works for you.