[BC] Re: SUPER MODULATION & AM STANDARDS

[Lamar Owen]

On Thursday 12 May 2005 17:15, Gary Blau wrote:
> I'm sorry to hear about John's passing, he was a very civilized, kindly
> gent.

He certainly taught me much, particularly about how To Make It Work.  The old 
transmitter at WKJV 1380 is an RCA BTA-5T (they had a 5F, which was a 
throttled 10kW in that only one PA tube was present, but it was replaced with 
the current Harris DX-25U).  The 5T was put in to replace the 5F; it was a 
'junkyard dog' 5T that John lovingly restored from absolute ruin.  Put many 
of his own vacuum variables, glass windows, tubes, etc, in the beast, and 
brought it up from ruin in two days.  He showed me how to properly align the 
3rd harmonic resonator on the beast; that's how the 5T got away with a single 
5762 unlike the 5R which had a pair.  With the 3rd harmonic resonator out of 
alignment, the box would do only 3300 watts; the 3rd harmonic resonators 
(plate and grid) basically put the 5762 into a pseudo squarewave mode that 
brought efficiency way up and got it up to 5500 watts.  Then of course you 
had to align the 3rd harmonic trap in the plate output network.....  Good 
memories from back in my less experienced days.

The 4 tower inline at WKJV (call sign history: WLOS, WKKE, WRAQ, WTOO, WKJV) 
is still running with the original equipment EF Johnson phasor put in in 
1946, and John gave me all kinds of useful information on the proper care and 
feeding of that phasor and the ATU's that go with it. He also showed me how 
he got seven augmentations (he didn't use that term; he said it was how he 
'got the nulls let out') that made it actually possible to operate the array 
in specs more than six months out of the year.  One null on the 302 radial 
had been so deep that the MP max was 1.2mV/m; getting it down that low is 
extraordinarily difficult; the phasor is much happier and more stable with 
that MP at 1.8mV/m.  The new MP max is 2.4mV/m, which is achievable.  This 
was done in 1981.

John was also the first person to show me how useful an AM trapezoid plot can 
be for troubleshooting modulator problems in high-level modulation systems.

I really missed him while I was installing the DX-25U in 2001.

> Back in the early/mid 70's he was the DOE for the company which owned
> WEAM 1390 Arlington, VA, to which you refer, as well as a couple other
> Carolina stations.

Yeah, Soundex same, different letter.

> They had a 10KW RCA throttled back to 5kw.  And it did indeed
> supermodulate.  The 'secret switch' on the Gates limiter would open up
> the positives all the way and the mod monitor would pin, and stay that
> way.  Used to drive WPGC crazy back when AM was a big deal in DC
> Top-40.  Very loud.

Yeah, John spoke with some pride about that beast.  I wish I had had more time 
with him, as he was a goldmine of information.  I do have some of his old 
equipment from his estate sale, though.

Hmmm, anyone want a real boatanchor?  It's a Subraco AM SW transmitter with 
coils for 160, 80, 40, 20, and 10 meters and does a good 125W AM.  You'll 
need to arrange pickup, as it's about 100 pounds and would probably not 
survive shipping.
-- 
Lamar Owen
Director of Information Technology
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772
(828)862-5554
www.pari.edu