Converting CB Antenna to HF Bands
When I was looking for an antenna to use for my holidays abroad, I found a CB antenna (DV27) in a local store that could be converted to the HF bands. The center coil was removable so it could be rewind or replaced as shown in Figure 1.
When you remove the cover from the coil you see a coil with 10 windings. I removed the coil and rewound it with 0.45 mm wire. Then I measured the resonant frequency, which can be done as follows:
- Connect 1 winding to the underside of the antenna
- Connect the antenna on a metal surface (for example the car)
- Place the grid dipmeter near to the coil (or use an antennascope)
- Measure the resonant frequency
Then add or remove windings until the desired resonant frequency is reached. You can also pull out the windings for fine tuning. Now connect the transmitter with low power and there you go!
After I had modified the antenna for 14 MHz (my favorite band), I have modified the antenna for the other HF bands. At the time I did not have the WARC bands on my homemade rig, so in the table only the windings for the traditional bands, but you can easily make the other coils. (see Figures 2 & 3).
For the lower bands I use a PVC pipe with a diameter of 1-1/4 inch. You must make an end and a top cap that fits on the original coil form.
| Band | Windings | Wire Diameter | Coil Form |
|---|---|---|---|
| 10m | Remove 3 | 1mm | Original |
| 15m | 30 | 0.9mm | Original |
| 17 | 2mm | 1 1/4 inch | |
| 20m | 60 | 0.45mm | Original |
| 28 | 1.35mm | 1 1/4 inch | |
| 40m | 70 | 0.9mm | 1 1/4 inch |
| 75m | 112 | 0.45mm | 1 1/4 inch |
You can also make a portable dipole if you use 2 antennas and connect them together on a waterproof plastic box as in Figure 4.
If you buy more than one antenna, you can leave the lower part of the antenna on you car and replace only the coil and top end to QSY for the different bands.
Originally posted on the AntennaX Online Magazine by Kees Wiegers, PA3BHS
Last Updated : 19th March 2024