I ran a Hy-Gain Penetrator 500 back in the day. I can't speak for the MFJ version, SPT-500, but I doubt it is exactly the same electrically and build quality. I know MFJ changed the beta match on their version. If you look at the description of the antenna on the MFJ website, it says it is 22' 9"' in length. The manual diagram shows it as 19' and the specs say 22'. I guess MFJ has no idea what it is... I will say that the Penetrator was a great antenna, probably as good as it gets, in respect to omni-directional antennas. I am not a fan of the ring match of the V58/W58, but it is what it is. When I tested my Workman that I built up here, it was working great. I would say my build is close in performance to a Penetrator or any of the true .625/.64 wave antennas.