06-11-2013, 07:38 PM
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A VSWR Mystery
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06-11-2013, 09:28 PM
There were no rev counters on the fans so they fitted a thermistor with insulation tape.
The last time I watched a guy fixing an RF amplifier the coax shorted due to flash over and caused a diode to explode. It had a paddle in the air duct to verify fan operation.
06-11-2013, 09:49 PM
All very reminiscent of my last employment, working with VHF / FM transmitters with output powers up to 20 kW. During that time, the term VSWR was very rarely heard, whereas the term 'return loss' was commonplace.
It's a pity that that video was spoilt right at the start by the narrator getting the definition of VSWR wrong. VSWR is not, as he stated, the ratio of forward power to reflected power. That is very nearly the definition of the return loss, RL. If the forward power is P1 and the reflected power is P2, then RL (return loss) = 10*log(P1/P2) dB. Apart from that, yes, I found that video interesting: thanks for sending it in. Just for reference, here are a couple of extracts from Wiki.: http://en.wikipedia.org/wiki/Standing_wave_ratio http://en.wikipedia.org/wiki/Return_loss Al. / Nov. 6, '13 //
06-11-2013, 10:03 PM
He made a mistake in another video as well, nevertheless an interesting fault was the inner conductor migration due to heat.
Lawrence.
06-11-2013, 10:21 PM
Some of those low loss plastics used in RF can migrate at normal temperature.
I was told a story about a war ship where the radar scanner was mounted on the funnel and there was no signal. They had replaced wiring and the antenna and nothing. It took them a very long time to find out that a PTFE block mounting had migrated enough for the antenna to end up partly in the funnel so that the signal could not get out. It did not get spotted until a proper engineer got sent up the funnel with all his gear. |
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