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.
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.
When tuning, start at the bottom and work your way up. Tune the 70cm section first.
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. This antenna performs best for 2m VHF.
The tiny little offshoot antenna is for the 6-meter band.
The top setscrew is for 10-meter. Achieving a 1:5:1 SWR is likely the best you will achieve on 10-meter.
For each section there are Allen screws on the top and bottom. Sometimes you will see a single Allen on one end and dual Allens on the other. Always tune the end with the single Allen. For the 70cm section tune at the bottom even though there are dual Allens there.
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.
The next 2m VHF section could be added for a dual band configuration.
The tuning is impacted by omitting sections as it has to do with loading and any additional length added by metal in the isolator.
It might be desirable to operate at times with only one or two sections to prevent damage to the antenna where there might be trees or conditions hazardous to the antenna. This is a bit of a top heavy antenna that is not going to take much abuse from trees or excessive forces. Folding it down is fine except you cannot operate while it is folded down. Removing the top allows limited operation in the most critical bands.
In the two section dual band configuration the 70cm resonance tend to go back to a lower frequency better suited for ham operation rather than GMRS operation. This is desirable for true dual band ham use. The VHF side then becomes the portion of antenna slightly too short for optimal resonance on 2m ham. This can be corrected by a simple lengthening of the second, or in this case, top segment. The correct length can be obtained within the distance permitted and with the setscrew tightened the antenna is correctly tuned for true dual band 2m / 70cm ham operation.
This antenna works great as a dual band 2m/70cm antenna. With the entire antenna assembled 10-meter operation is acceptable but not stellar. Without going through extensive testing it seemed difficult to tune for 50Mhz operation. Further testing for 50Mhz is required to determine the antenna performance on this band.