Tuesday, 4 March 2014

Cables

Whilst waiting for the transverter PCBs to arrive I thought I would have a break from building stuff and do some maintenance on my mast and cables.
I am trying to rationalise the antennas on my mast so that I have just the 6/4m dual band yagi, 2m/70cm dual band vertical, 23cm yagi, 13cm yagi and 3cm band dish.
Other bands can be added as and when required.
I initially counted 13 individual cables ( coax and wire) dangling from the mast. Once I started to untangle the cables from each other, cut tapes etc I found there were actually 16 cables in the bundle! This is a large and heavy weight to be suspended from a small Versatower mast.
So began the journey...........
Several cables have not been used for sometime and were pulled from the under-lawn duct to make way for some other cables. Others were far too long ( and hence lossy), so they were shortened.
I had thought that the pair of LMR400 cables intended to be used on 13cm, as previously, were likely to be in excellent condition. Not so. One was acceptable, the loss being within a dB or so of the expected value. The second one was very lossy for reasons that are not yet obvious. I have pulled this cable out and I am now going to replace it with a length of lower loss LMR600. This will be the 13cm transmit cable. The lossy cable certainly explains the lack of contacts on that band for some time!
The Ecoflex10 23cm receive coax also turned out to have a slightly higher loss than expected, but now I know that I can probably allow for that by increasing the gain of the masthead preamp.
I had been using a length of FSJ4/50 joined to an equal length of Ecoflx 15 as the old 9cm transmit feeder. As this measured spot on for loss, and I'm not using 9cm at present, this coax has been allocated to 23cm transmit.
Similarly, the RG213 coax connected to the 6/4m yagi was showing signs of aging with longitudinal cracks beginning to appear in the jacket. This feeder has also been pulled out and a length of Ecoflex 10, that was spare, turned over to use on this yagi.
Interestingly I discovered an unscreened Multicore cable that was not being used for anything, but which was coiled up in the masthead power feed and control box. Again this was pulled out. The screened 4 wire will provide all the control circuits I am likely to need for now.

I am beginning to think that the problem of increased loss with the EF10 and LMR400 is due to the duct being extremely wet this winter and these cables have suffered water damage by osmosis. I am going to have to rethink how I get my cables across from the outdoor shack to the mast. Maybe an open trench with removable cover might be a better solution.

I have at least one more day's work to do to reinstall all the cables and connect everything back up. Once that is done I should be back on 23 and 13cm with a better signal and able to hear signals again!

Sam




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