Nanovna

I’ve been thinking of ways to get more power to W3GMS, and coax might be the weakest link. I have about 75ft of RG-58 outside and maybe 8 ft of RG-174 inside. I took down the flag pole Yagi to replace the coax.

I learned how to measure loss with a “through measurement” on the nanoVNA watching Youtube:

• The old coax run measured at least -6.5dB loss total
  • -4.5dB for the RG-58 by itself
  • -2.0dB for the RG-174 by itself
• The new coax, 100ft of KMR-400, by itself measured -1.5dB, and -3.3dB with the patch of RG-174
• SWR sweep of antenna on old coax showed lots of wiggles and hung generally low, because of all the loss.
• SWR sweep of the antenna with the new coax runs much higher on the 100MHz side, and takes a nice dip at the resonant frequency.
• Incoming signals look good and strong by the S-meter on the TYT-9800

I had a bit of bad coax on the most recent POTA, so I set out to test and repair it. I saw no damage to the cable or connectors, but there wasn’t continuity across the middle wire.

Which end is likely bad? I connected each end to the nanovna with a Smith Chart. I found on one end, the smith chart traced a spiral around the outside of the circle. The other side did not react at all, like I hadn’t connected anything. For comparison, I tried another cable I figured was good. That other cable had continuity to each end, and both ends each traced a spiral on the smith chart. The length of the spiral seemed to be related directly to the length of the coax: shorter traced shorter and longer traced longer.

So with that, I replaced the one end that didn’t react, and now the cable looks good.