I made it without understanding, but I think I got some good results, so I’ll write a post about it for my memorandum. What is it? It is an external 1seg antenna for SC-02H. Why did I make it? Actually, I want to watch Fukuoka SoftBank Hawks games on my way to and from go swimming.
SC-02H originally has an external 1seg antenna called SC03. The antenna is good when I watch 1seg in urban area. But I go through a mountain road when go swimming, so I often have a message “Airwaves are weak”. This message sometimes appears when I watch 1seg in my house like the video below.
First, I looked for an antenna amplifier for SC-02H in a car but I only found a film-type antenna in my local neighborhood. It is expensive for its features. Next, I did the same thing on the Internet and I couldn’t find antenna amplifiers for my purpose again. Although I was able to find some antennas, I couldn’t know what goods are suitable for my need. So I gave up my first goal.
By the way, SC03 is small and I carry it in my bag at almost every moment. But I don’t have the usual bag when I go swimming. I only have a bag for swimming goods though I always carry my smartphone. So sometimes I forget to move SC03 between my usual bag and swimming one. If I have another antenna for SC-02H in a car, I think it is very convenient.
So I made a simple quad antenna for SC-02H. See the right image. I used the following things for making it.
- I listed materials and tools in order of use.
- One A3 copy sheet for a mat (or two A4 copy sheets)
- Glue stick
- 15cm or 30cm ruler
- Ballpoint pen
- Aluminium kitchen foil
- Utility Knife
- A 3.5 mm stereo phone connector with audio code (from my junk box)
- About 1.3 m long coaxial cable
- Solder and soldering iron
- Two solderless connections
- Electrical tape (I used white one, because it was at home.)
- Double-sided tape
- Fold a A3 sheet in half and glue its inside.
- Draw a 11 cm square and a 15 cm square on the sheet.
Why 11 cm and 15 cm?
I found out the information that 1seg broadcast in my local neighborhood uses from 20 ch to 43 ch. 20 ch Center frequency is 515 MHz (=5.15×108 Hz) and 43’s is 653 MHz (=6.53×108 Hz). Radio wave speed is approximately 3.00×1010 cm/s.
wavelength (λ) = speed / frequency and (a side of square) = λ /4
Round down (3.00×1010 / 6.53×108 / 4) , and I got 11 cm.
Round up (3.00×1010 / 5.15×108 / 4) , and I got 15 cm.
- Apply glue between sides of big and small squares, i.e. to the parts of 「のりしろ」.
- Cover the sheet with aluminium kitchen foil.
- Cut off aluminium kitchen foil like the right image.
Cut in the center and make a mountain fold each side.
About audio code and coaxial cable, one of audio code grounds solders to woven copper shield and another one does to copper core.
When wrapping the joints by electrical tape, I think you had better use aluminium kitchen foil for shielding each audio code ground. Because audio code grounds have nothing like inner dielectric insulator.
Crimp each solderless connector to other side of woven copper shield and copper core.
- Paste the solderless connectors to the aluminium kitchen foil on the sheet with the electric tape.
Staple each solderless connector to the sheet over the tape with several staples. After that, make the staples flat by a hammer.
See the right image.
My cable has a TRS phone plug and SC03 has a TRRS one. When I full insert the plug to SC-02H jack, the sound has gone. So I wrapped 3 mm wide tape around the plug.
By the way, as I was unable to find out SC03 inside wiring, this adjustment is empirical.
Then, I installed the quad antenna in the car.