X510 Colinear Repair
Two common issues with these colinears are :
1. Water gets in causing corrosion to connections in the matching network and high SWR.
2. The capacitors in the matching network aren't high enough voltage and can blow if too much power is put through the antenna. this problem is worsened if the SWR goes high as a consequence of number 1. above
These capacitors are hard to find. You ideally need 1kv versions so instead I made one out of RG174 coax...
Matching unit at base of antenna
Simple tuned circuit consiting of a coil tapped off via two capcitors. The value of these isnt always clear as it seems to differ. Mine had 6.5pF (blue) and 4pF
4pF faulty Cap
This was causing terrible SWR so needed replacing, however sourcing one with the correct voltage (ideally a 1KV) is hard.
Temporary Variable cap installed
I tried this to find the correct capcitance in order to get a good match, however its so tight in there it was hard to test while the antenna was in situ. I got a figure using my LCR meter of approx 3.5pF, but there is lots of stray capacitance doing it this way making it hard to measure.
Coax used as capacitors
A more simple way of getting the correct capacitance with good power characteristics is to use a small length of coax (i used RG174). The idea is that a length of open ended coax has a certain capacitance, by using your LCR meter you simply trim the length until it reads the right figure. Attach the centre core as one leg and the braid as another leg of the original capacitor then allow the rest of the length (open ended) to extend, that length will determine the capacitance figure. These easily fit into the space once the antenna is back together. Job done!