Opek HVU-200
Opek mobile antenna 4-band HF / VHF / UHF.
- FREQUENCY RANGE: 28-29MHz/ 50MHz/ 144MHz/ 430 ~ 440MHz
- GAIN: 1.8 dBi(144MHz) / 4.5 dBi (430 ~ 440MHz)
- POLARIZATION: Vertical
- IMPEDANCE: 50 Ohm
- POWER CAPACITY: 200 Watts (144 / 430 ~440 MHz SSB), 120 Watts (28-29 / 50 MHz SSB)
- CONNECTOR: PL-259
Each section is adjustable to tune in the associated band. Adjustments are made by loosening an Allen screw and moving a section up or down guided by your SWR meter.
SWR Tuning
Standing Wave Ratio - SWR is a measure of a transceiver’s output power (Pf) verses the portion of that power reflected by the antenna system (Pr). Reflected power, the result of a poor SWR ratio, will destroy your transceiver.
The bottom section, or section A as we will refer to it here, is for 70cm band. It is slightly on the long side. Shortened all the way is typically the best possible match at 1.5:1 SWR. It might be possible to cut 1/4" inch off to better improve SWR on 70cm depending on if you operate on the low end or upper end of the range.
The middle section for 2m VHF is typically set pretty good factory, with a near 1:1 SWR.
Experimenting
The first isolator which looks like a black plastic load separating the bottom 70cm portion from the middle 2m portion can be removed leaving only the bottom 70cm portion allowing the antenna to function as a 70cm UHF only antenna. Doing this shortens the wave ratio to match it up perfectly with GMRS frequencies.
