- June 24, 2009 at 4:39 pm #7292Carl BlareParticipant
Total posts : 1540
Every full-power transmitter has its row of meters for reading and setting everything from voltage to power level. The idea appeals to me to match this “pro look” by installing permanent meters and settings controls in a part 15 transmitter. Some of the meters are no brainers like AC or DC volt meters.
But what about a 100 milliAmp meter permanently installed at the input to the final of an AM transmitter? Will it provide a true reading and can it be left in place permanently?June 24, 2009 at 8:05 pm #17414radio8zGuest
Total posts : 45366
I am going to guess that you meant 100 mW meter rather than 100 mA meter. For the big transmitters, it suffices to have Volts and Amps metered since they usually run under constant and consistent conditions and the person watching the transmitter is actually looking for deviations from the norm. One transmitter (330 W FM) I babysat also had a meter for grid drive current so the drive could be adjusted/monitored. Power can be measured going both ways in the transmission line and this is the output power.
I appreciate the “coolness factor” of having meters just for appearance and if they can provide something useful, so much the better. The best meter I know of to measure true DC power is the electrodynometer type which monitors both volts and amps which by vector summation of the magnetic fields gives true watts. If one wants to, one can take advantage of the fact that the voltage to the final stage is a constant and install a milliammeter to measure the current and calibrate it so it indicates DC watts. Not too hard to do and maybe this is what you had in mind.
What floats my boat is a meter that is actually doing something and a great example is a VU meter. It is more satisfying to me to see the meter moving with audio than to observe the LED type of VU indication. I have two real VU meters here that I plan to attach to the SSTRAN, one to monitor the audio in and one to monitor the audio after compression primarily for the visual impact. I have built the op-amp circuit to drive them and am just waiting until I find a box to house them before proceeding. It might be an interesting way to observe the compression.
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