Simple 2m PSV meter

Designing a VHF PSV meter does not have to be difficult, if we do not require top parameters and accuracy. Many times, such a measuring device comes in handy only as a check - for example, whether there is a malfunction in the final stage or on the antenna.

He published a very simple construction once Jan-Martin Noeding LA8AK (SK). The essence is, that the directional taps from the wires are inserted under the braid of the coaxial cable. This gives an assumption, that the line impedance will not change much and the PSV meter should measure correctly. This construction procedure has proven itself for me:

• we will take about 20 cm of thicker coaxial cable, e.g.. RG-213, and remove the top insulation with a knife

• we will need at least a 50 mm long thin tube, repaired with pera. The inner diameter must be sufficient, so that we can push the branch wire through it

• gently make an eye in the top of the coaxial cable braid with a small screwdriver. A suitable place is there, where the main springs intersect

• insert the tube into the loop on the cable

• about 40mm from this place, make a second eye on the top side of the braiding of the coaxial cable and push the tube through it

• thread the branch wire through the tube and pull the tube out of the mesh

• exactly on the bottom side of the braiding of the coaxial cable, make a second branch in the same way

• take a heat-shrinkable tube with a length of approx. 40mm and slide it onto the coaxial cable at the branch point

• tension the branches and the stocking of the coaxial cable and heat the tube

• if you did it right, the taps are fixed in the correct positions

• symmetrically shorten the coaxial cable to the desired length and also put a heat-shrinkable tube on the part of the stocking from the detection circuit to the connectors

• connect load resistors and detection circuits with the shortest possible leads and terminate the cable with connectors

I managed to make such a measuring line on the first try in about an hour. As a cabinet, I used an old CB PSV meter from which I also used a switch, potentiometer and measuring device. The entire construction took approx. 1,5 hours and minimum costs.

The measurement accuracy compared to the commercial MFJ instrument is very good and the measured values ​​are practically the same. In my design, the minimum detected power is approx. 1W at 144MHz.