OT Mitsubishi Monitor Weirdness

As an example, I use to work on some navigational transmitters with power output of a few hundred watts. There was a test jack for sampling the RF output and you hooked a scope to the jack. The gotcha was when you hooked the coax cable to the transmitter first instead of the scope. If you did that, the transmitter went down within seconds. This is rot! On a transmitter with even a few watts output the RF probe coupling would be -10dB or more, so even an open or short on this would give a return of -20dB. This is so small it can be ignored, in fact many antenna systems aren't that good. As a termination a scope is a very poor match for any low Z RF source it's impedance being 1Mohm or more so it wouldn't matter if you plugged it in or not. Also most test gear can't absorb any ammount of watts for any length of time, so if the port was a high power snif it would have to be terminated at the port with a high power attenuator which gives a good match regardless of it's terminating Z. The open circuit at the other end of the coax got reflected back to the transmitter as a low impedance and detuned it, and the monitoring circuits would detect the detuning and pull the plug. This depends entirely on the wavelength length of the coax. Did you use an exact odd multiple of 1/4 wavelength coax every time? can you remember the make/model of these transmitters? Lee. ---------------------------------------------------------------------------- ---- This email is intended only for the above named addressee(s). The information contained in this email may contain information which is confidential. The views expressed in this email are personal to the sender and do not in any way reflect the views of the company. If you have received this email and you are not a named addressee please delete it from your system and contact Merlin Communications International IT Department on +44 20 7344 5888. ________________________________________________________________________ This e-mail has been scanned for all viruses by Star Internet. The service is powered by MessageLabs. For more information on a proactive anti-virus service working around the clock, around the globe, visit: http://www.star.net.uk ________________________________________________________________________