Wednesday, December 9, 2009

Further thoughts on 160m with a 50' vertical

Following up on my thoughts in yesterday's posting, I should note the following. First, AD5X had success with getting an autotuner apparently to tune the range of 160 with the same coil arrangement as I have. I suspect my coil doesn't present quite enough inductance and that with some more I would have better luck.

Secondly, I guessed that an improved feedline would be a good first move. This is incorrect. Playing around with the coax calculator, I note the following losses. With 100' of RG-8 matched loss is 0.23 dB; at a 5:1 SWR, it is an additional 0.3. Changing the cable to LMR-400, we get a .16 mached loss and 5:1 SWR additional loss of 0.24.

For the same factors, this time just changing the freqency to 28 MHz, we find a LMR-400 matched loss of 0.64; and additional .811 for the 5:1 SWR. Switching back to the RG-8, matched loss is 0.95 and an additional 1.1 comes into play with a mismatch.

However, it is very easy for the tuner to match a vertical at the higher frequencies.  We can therefore ignore the mismatched losses for these, and only consider them at 160m. And at that frequency, the improvement from matching is minimal, even with a mismatch, and a higher ones the matched losses are minimal for RG-8, too.

Based on this, I'm not spending money on a better cable; that money is going into the antenna analyzer piggy bank. For now, I'm going to add turns to my coil for 160m and see if the autotuner can pull it down to a reliable 1:1 SWR across the band.

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