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Robert Smits wrote: Large Inductors aren't a problem - keeping a tuner weathertight on BC's wet coast is, however. Understood :-) Also... I'd suggest calculating the actual "excess loss" in your coax, if you accept the mismatch at the feedpoint and match to 50 ohms at the rig. At 2 MHz I'd guess that the excess loss from even a 2:1 SWR would be quite low. How do I calculate "excess loss? http://www.qsl.net/co8tw/Coax_Calculator.htm seems to work nicely. Plug in the coax-cable type and length, the frequency, the load SWR, and your input power. It's an approximation (the actual losses depend not just on the SWR, but the actual load) but it should give you a good idea of the tradeoffs. It'll calculate: - Matched loss (what you'd lose in the coax even if you have a perfect 1:1 match at the antenna) in dB - SWR loss (what I referred to as excess loss - additional power lost in the coax due to the higher currents caused by a higher SWR) in dB - Total loss (the sum of the two) - Actual power into the antenna As an example: Belden 8237 (RG-8 type), 200 feet, at 2 MHz, into a 3:1 load. The program calculates a matched loss of .487 dB, and an SWR loss of .281 dB, for a total of .768 dB. Not a whole lot. If you had a perfect lossless match at the antenna base, you'd cut your coax loss by about 40%, and gain .281 dB of signal. Then, compare that to ground losses. Based on a cursory glance at some figures on the web, it looks as if a quarter-wave vertical monopole installation can easily lose 2-3 dB in the ground, even with as many as 24 radials. Might need up to 60 radials to get down to 1 dB of ground loss. Matching or not-matching the antenna to the feedline won't affect these losses significantly. So, it may be that SWR loss in your coax isn't the best place to spend your efforts... at least, not at first. Adding more radials, or elevating the radials above ground may have a greater payback. |
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