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"Jimmie D" wrote in
: "Owen Duffy" wrote in message ... K7ITM wrote in news:1186788470.852002.260460 @b79g2000hse.googlegroups.com: On Aug 10, 2:28 pm, Owen Duffy wrote: ... I don't think you can compensate for lack of f/b ratio in the coupler, for example because the coupled lines are too long. ... I'm curious what you mean by that, Owen... Tom, I was thinking of several instruments, all of the coupled lines type of construction, that on a s/c and o/c failed to indicate rho=1, and showed similar readings when physically reversed, suggesting it was not just a fwd / rev matching issue, there was something about the coupler that was too dependent on the location of the SWR pattern relative to the coupler. Since they worked better at lower frequencies, the length of the coupler was likely to be a contribution. Owen Would this be a problem for a directional coupler designed for a specific frequecy? Jimmie Jimmie, I am talking about the el-cheap inline SWR / Power Meter that is often sold to hams with unrealistic specs. You can / should always test the performance of the kit you are using to determine if you should have confidence in it. There are a bund of notes on testing a directional wattmeter in the article at http://www.vk1od.net/VSWR/VSWRMeter.htm . BTW, for your purposes, if you had a Bird 43 with an element that read upscale on fwd power (250W element for your application), it is all you should need to form a reasonable estimate of line loss and set the transmitter to deliver 100W to the antenna. You might need a smaller slug to make a measurement of RL on a s/c or o/c termination. Owen |
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