Wednesday, May 6, 2015

Battleship Iowa Transmitter Progress **We're Getting There!**




Well, good news!

I took my accurate, calibrated, LP-100A Digital Vector RF Wattmeter in today, and we re-ran the tests on the transmitters today using the LP-100A rather than the built-in panel meters.

We also wanted to make sure each exciter was outputting its 100 milliwatts (+20dBm) of rated power.

First, a little background....

The Iowa originally had 11 transmitters; 10 on shock mounts in a racked arrangement, two high and 5 wide, "odd" units on the top, and the "even" units below them, with #11 sitting by itself at the far left end of the rack mounts.

Numbers 2 and 8 were missing from the ship when she came out of the reserve fleet, leaving us with nine units. Three of the nine were stripped of usable parts in the PA (Power Amplifier) assemblies, leaving us with six more-or-less intact units. We might be able to "mix-and-match"  the three partially stripped ones to make a seventh unit, or just keep them "As Is", or as a possible source of "spares", as we really don't have any reason in the world to have seven functioning transmitters!

Originally the "need" was to have two, fully function transmitters, one being the primary unit, and the other being it's back-up, for "Special Event" use, such as the Military/Amateur Crossband Event, or perhaps Museum Ships Weekend.

As of today, two of the units has an exciter with 100mW (+20dBm) or more (+23dBm) of drive power, and one exciter is low on output, only doing 50 mW (+17dBm).

The two with the "good" exciters easily exceeded 1200 Watts output ( ! ), while the one with the "low" exciter did about 800 Watts output.

This is significantly different that what the panel meters read, by a factor of 2 to 3!

And we have another transmitter that appears to be good, as far as the PA Plate Voltage and Current go, but with a dead exciter that only puts out about .5dBm, a little over a milliwatt.

And it took quite a load off us as to trying to figure out where the "missing" RF Power was going. It wasn't "missing", it just wasn't being measured!


And on the Ham Radio side, I installed, and got operational, a Signalink USB interface box on our Kenwood TS-850 HF radio. As soon as I finish my homebrew soundcard interface, we'll have two stations capable of digital operation on such modes as SSTV, PSK31, RTTY, and other modes.

5 comments:

  1. I love a story with a happy ending - or even a happy middle. :)

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  2. Nice work! And glad you 'found' that missing RF... :-)

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  3. Now I'm working on a "Two Tone" generator to feed into the microphone input.

    This will give us a known level of audio so we can see if the exciters/transmitters meet their specs.

    I might be pretty good at saying "FOOOOOOUR!" into the microphone (it really is a "standard" test!), but I'm not sure my "Repeatability Of Level" is very accurate!

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Keep it civil, please....