My HF station is (deliberately) very simple. The monopole antenna is a 17m ‘fishing pole’ with a single wire up the middle. That is formed into a classic ground plane arrangement with 50 radials ranging from 6 to 16 metres in length buried just under the soil and paths. The ARRL Antenna Book notes that for optimum operation, the radial length should be at least 20% of the wavelength of the lowest intended operating frequency. I just about achieve that.
I’ve mounted an MFJ automatic tuner, the 998RT on the ground at the foot of the monopole. Power for the remote tuner is via the coax. The arrangement is like that discussed in Section 10.4 Multiband Vertical Antennas in the ARRL Antenna Book.
This antenna offers the match per band after tuning shown in the table below. The match is measured at the rig. The important point is that high impedances outwith the tuner capability are avoided and I’ve reduced the height from an initial 18m because that failed to tune the 10m band.
Antenna measured performance
|Band||VSWR after tune||Antenna wavelength|
The gain over a quarter wavelength monopole will likely range from zero at 80m to about +6dBi at 10m. The peak in vertical response of the radiation from the antenna will likely vary from an optimum at about 15 degrees to the horizon to maybe 30 degrees with differences and multiple lobes band by band. The horizontal response will be omni-directional.
HF station operation
I’ve a simple setup – an Icom IC-7300 driving an RM Italy BLA600 solid state PA. The combination gives 500W down the coax with about 400W to the antenna. Tune up is done by placing the amp in passthrough. Then keying a carrier and allowing the auto-tuner to do its stuff. Once the VSWR has settled, the amplifier can be switched in and operation can commence.
And on air? It works like you might expect. It’s not as good as an HF beam on the upper bands, but it’s as good as a wire dipole on the lower. DX performance is not as good as might be desired since the launch angle is quite high.