Posted by Sean Gilbert Mon, February 21, 2011 09:59:15
The OCF was picking up more noise than I would have liked, I was not sure if this was due to the ingress of moisture or something else antenna related or whether it was an increase in background EMC levels. As it turns out, I think it was the EMC levels that increased. Upon checking the antenna I was pleased to see that all the joints had remained watertight and there was no evidence of corrosion. I wanted to upgrade the ferrite choke so the coax plug was replaced anyway. The original choke consisted of 7 turns wound over 3 ferrite rings. The improved version has 7 turns over a stake of 5 rings. This did improve the performance, but the noise also increased (due to the vertical radiating part of the antenna becoming more effective). This was not what I wanted, I was trying to reduce noise! Also the choke was much heavier than before so was putting stress on the coax and the PL259 connector. With this in mind I moved the choke from 10 feet below the feedpoint to directly under the feedpoint and used cable ties to secure it to the balun box, giving strain relief to the feeder.
This changed the resonance, obviously, but it did help with the noise pickup, some bands in particular are much better than they were. Also the 6m sloper seems to work well and provides much better signals than the OCF on my local beacons, plus it is quieter on receive.
I have put pictures and info about these antennas on my website.
Now I am waiting for the 6m sporadic E season to start!!