Kevin Strom, WB4AIO

by Kevin Strom, WB4AIO

LIKE THIS SITE? Let me build one that’s just as nice for you or your organization. Since the government made me a fourth class citizen, it has become very difficult for me to support myself and my three children.

I am skilled in writing, editing, graphics, and publishing (both the print and Web varieties), and I have become quite expert at customizing WordPress to create online magazines, newspapers, and organizational Web sites. I’m also a skilled broadcast engineer. If you have any kind of paying work in these fields, no matter how small, please let me know. I’m eager to get started. Just click on the ‘contact’ link on this page.

If you don’t have any work for me now, but appreciate my past efforts, please consider making a donation.

by Kevin Strom, WB4AIO

THE SUMMER THUNDERSTORM season has made me do some reading and reasoning on the topic of protecting your amateur radio equipment from lightning.

In recent years, static dissipators on top of towers have become popular at broadcast stations — multiple sharply-pointed metal rods that supposedly draw off the static charge slowly and thus prevent a strike.

Bill, KD0HG, writes that in mountaintop broadcast installations where the rocky soil has extremely poor conductivity, they abandon the concept of “grounding” and simply concentrate on bonding the tower, the building, and the racks together with very low inductance copper strap — and surround the building with a perimeter strap too. The idea here is simply to keep everything at the same potential. Even if that potential elevates to 100,000 volts from “ground,” it won’t matter if there is no voltage difference between the bonded units. That’s a smart way to look at it.

But I have some new thoughts on the matter. Is it possible for one’s ham shack to simply “retire from the field” of ground-to-sky or sky-to-ground electron pulses?

That is, when not in use, completely disconnect from aerials — and from ground.

Sky-to-ground and ground-to-sky are just reciprocals of each other, depending on whether it’s a dearth or surfeit of electrons we’re talking about. So I think it’s useful from a safety theory standpoint to visualize all lightning strikes as energy emerging from the ground and attempting to reach a charged zone in the air.

So why not just make it (nearly) impossible for energy in the ground to pass through our ham gear? In addition to disconnecting the shack from our antennas, also disconnect it from ground — disconnect it from anything having a DC or low-impedance connection to ground, like ground radials or AC lines — and disconnect it from anything having a high capacitance to ground, like counterpoise systems.

Meanwhile, trees or a nearby grounded tower could provide a current path when a path was demanded by Mother Nature. But your gear wouldn’t be involved.

I know such near-total isolation from ground might be difficult, especially the AC mains part. It might take some creative thinking. (For example, during storm season in my old shack in Alexandria, Virginia, I used to remove the antenna’s parallel feeders from my gear and toss them out the window, many feet from the house. Could something analogous be done with the AC power feed to the shack?)

It should be possible to make our gear no more likely to get damaged by lightning than is an unplugged clock radio sitting inside a steel box which is itself sitting on a wooden pallet.

Of course, induced currents from nearby strikes would still occur. But with nothing connected to our gear except a few short wires disconnected from the outside world in every way, even that risk would be minimized.

Just food for thought.

The AM-864/U broadcast peak limiter

by Kevin Strom, WB4AIO

THE AM-864/U broadcast peak limiter, which I purchased “new surplus” from John Meshna and Company in about 1974, was my first foray into true broadcast audio processing for amateur radio. Like my TCS transmitter purchase from them, the unit was beautiful and flawless out of the box. It cost me $35. I sold it in the 90s (probably a mistake) for about $100. It now has acquired a “reputation” in the recording industry, and good ones sell for over a thousand dollars.

It’s 600 ohms transformer-coupled balanced in and out, with a simple all-vacuum-tube and all-balanced audio amplifier and peak rectification and gain reduction circuit. It was built in the 1950s by the Federal Television Corporation (some were built by other contractors, I am told) for use in AM and shortwave transmitters run by AFRTS, the Armed Forces Radio and Television Service. It came with a manual, the most hilarious aspect of which was its instructions on how to destroy it (“use axes, knives, machetes, flamethrowers, incendiary grenades” etc.) in case it fell into “enemy hands.”

AM-864/U destruction instructions, from the operator's manual (click for the full-size image). And yes, the "enemy us" typo is in the original!

I modified it for adjustable release time (a faster release was often desirable for amateur voice, even relatively high fidelity voice, to increase audio density) and improved low frequency response. The AM-864/U imparts an airy, floating quality to the audio, and gives the impression of emphasizing the upper midrange. It doesn’t control peaks as well as a CBS Labs Volumax or a Gates FET peak limiter, but it’s quite usable.

At that time, my main transmitter was a Hallicrafters BC-610E (a 250TH final modulated by a pair of 100THs).  I used a UTC Linear Standard hi-fi push-pull-plates to speaker transformer hooked up backwards to drive the grids of the 100THs and the Linear Standard was driven through a resistive loading pad by a Knight high fidelity amplifier using a pair of EL34s and negative feedback from the modulated B+ of the BC-610. It was clean audio. The AM-864 was fed by my Shure 556S microphone into a Heathkit tube-type cathode follower preamp/tone control and the AM-864 fed the Knight hi-fi amp.

I used this setup for several years and it was what I was using when I made the AM amateur bulletin transmissions in 1977 to build opposition to FCC docket 20777 (which would have effectively eliminated AM and other experimental modes). I know where some of that old gear went (everything I still had in my possession in 2006 was stolen by my then-wife in complicity with the FBI and Joint Terrorism Task Force), but I do wonder who is using my old AM-864 now.

The TCS transmitter: Notice the RF output terminals on the upper left of the front panel, right next to the "antenna coupling" control. (click for a larger image)

by Kevin Strom, WB4AIO

RECENTLY I was listening to WA1HLR use his modified Navy TCS transmitter on 75 meters, and it brought back memories of my early days on the amateur bands. In 1972 I bought a World War II surplus Navy TCS transmitter, built by Collins, from military surplus dealer John Meshna, via mail order.

The transmitter looked shiny and almost new when it came out of its thick, multi-layer wooden packing crate — which I believe was also a 1940s original. It had that odd smell that electronics of that era often had — something to do with the anti-mildew “tropicalization” coating they were given, which also gave them a vaguely green sheen when seen at certain angles.

The TCS needed a power supply and control panel, which I built myself from parts scrounged from old radios and television sets and purchased at Arcade Electronics in Annandale, Virginia. The stock audio quality was not too good — strictly carbon-mike variety — so I ventured some modifications and soon had it sounding decent into my light bulb dummy load. But that was just an experiment.

Having only a Novice license at the time, my first goal was to get it on the air on CW. It wasn’t designed well for that mode, to say the least: multiple relays keyed multiple stages at once, including the free-running oscillator, clunking loudly and clicking and chirping like crazy on the air. Ultimately it would prove to be easier to get my Viking Valiant on CW than bother with totally redesigning the TCS. So my first rig was eventually consigned to carrier-current AM duties (feeding a reduced power signal into the AC power line, like many college radio stations used to do), so I could send my shortwave receiver’s (or my Wollensak reel-to-reel deck’s) audio around the house and the neighborhood to any AM-band radio while I did chores or mowed the lawn. That was fun.

But that isn’t what I remember most about the TCS transmitter. My most lasting memory of it is the front-panel nut-and-bolt RF output terminal, which was right next to the output tank coupling knob. It was almost impossible to tune the transmitter without getting RF burns on your knuckles. That feeling — and the aroma that went with it — is something I am unlikely to forget.

by Kevin Strom, WB4AIO

I’VE JUST DISCOVERED a new and worthwhile amateur radio net, meeting Saturday mornings on or around 3872 kHz in the AM mode. It’s the Flex Radio Users Net, devoted to discussions of the software-defined transceivers manufactured by Flex Radio Systems and related topics.

This week, the group was discussing both the theoretical and practical aspects of symmetrical versus asymmetrical modulation, modulation levels generally, and audio processing for HF amplitude  modulation transmission.

The discussions included insights and opinions — and quite a bit of debate and disagreement — from AB2EZ, WB2CAU, N3WWL, N2DTS, and others.

Ever since I was the chief engineer at WEAM in Arlington, Virginia, this has been a topic of great interest to me. The 1970s and 1980s incarnation of WEAM used a 10-kilowatt RCA BTA10U2 plate-modulated transmitter with reduced B+ voltage on the final amplifier running just 5 kW output. It was capable of cleanly modulating more than 170% in the positive direction. Extensive experimentation has led me to agree with Mike Dorrough (KO6NM) on asymmetric diode-detected AM, particularly when skywave is a factor:  It is better to reduce voice asymmetry with all-pass filters and stay close to balanced positive and negative peaks in audio processing. This eliminates the inherent distortion caused by forcing positive peaks to be higher, and also causes the character of any limiter-induced distortion to be more “musical” and pleasing to the ear. It also minimizes selective fading distortion and distortion caused by detector nonlinearities at modulation extremes. And any dB or two “loudness deficit” compared to aggressively induced or natural asymmetry can easily be made up in the adjustment of the final limiter. (By the way, Inovonics is now producing broadcast audio limiters designed to force symmetry in the final audio waveform, in total contrast to the forced asymmetry that has been the prevailing paradigm up ’til now. )

You can listen to a big excerpt from the Flex Radio Users Net here, as recorded by me from an online Icom PCR-1500:

Here we see HD Radio sidebands on either side of an analogue FM broadcast signal, as shown on a spectrum analyzer.

by Kevin Strom, WB4AIO

WITH 2010 APPROACHING, CNET just released its “The Decade’s 30 Biggest Tech Flops” anti-awards, and “HD Radio” was among the “winners.”

HD Radio was not only doomed from the start, it was such a serious blunder that it may well lead to the death of thousands of radio stations and the permanent stunting of the industry itself.

There is nothing wrong with the concept of digital radio.

Using modern firmware-upgradeable codecs, orthogonal FDM transmission, and a network of community transmitters in a dedicated digital band, great things could have been done:

1. In every community, all signals would have been full-quieting with no noise or multipath distortion. There would have been no more disparity in signal or noise levels between 50-kW powerhouses and 250-Watt locals or 10-Watt student stations — all would have had perfect, full-quieting signals within the community’s coverage area.

2. There would have been no more need for any licensees to sign off or go to absurdly low power at night as obtains presently among AM stations. And former AM stations would no longer suffer from crippling skywave interference at night.

3. Depending on how much spectrum was allocated and the ratio of talk to music programming (with their different bit rates), at least four to eight times as many stations could have been allocated to each community as now exist, leaving open the possibility of free and independent public access and non-profit “free radio” style programming, greatly expanding listening choices (and points of view in news programming) for everyone.

4. As stations migrated to the new band, even more channels would become open on the existing AM and FM bands, making them more listenable and viable again and allowing even more space for non-profits and those who want to broadcast for the love of it instead of just for monetary gain.

Digital community-transmitter-based radio in a dedicated digital band thus could have been a tremendous success and a revolutionary improvement.

But we didn’t get real digital radio.

Instead we got IBOC (In-Band On-Channel, now deceptively labeled “HD Radio”), a technical turkey which delivers almost none of the benefits above and increases interference to boot.

Why did this happen?

Another radio station off the air, bankrupted by increasing monopolies in the industry and failure to meet the challenges of digital audio. "HD Radio" isn't helping -- in fact, it was designed to further marginalize small local stations like this one, stifling independent voices.

Because the money-men didn’t want the benefits of item (1) above. They already owned the 50-kW powerhouses. They didn’t want the 10-Watt student station to suddenly have an equal signal to theirs. They didn’t want the mono AM daytimer to suddenly have 20-kHz digital stereo with no audible noise and be on 24 hours a day as in item (2).

And the money-men didn’t want dozens of new independent channels to be available to listeners as in item (3) above.

So they chose IBOC, where the digital signal piggybacks on top of the existing analogue signal, right on the same frequency. IBOC gives distinctly inferior results. IBOC causes significant interference. IBOC on AM is unlistenable and very nearly useless.

But IBOC gave the money-men the one thing they wanted most of all: It preserves the inferiority of the smaller broadcasters. In fact, amid a sea of IBOC hash from the big boys, it accentuates their inferiority.

The end result of this shortsightedness will be bankruptcy for many stations, fewer and poorer choices for the listeners as conglomerates gobble up the remains, and a huge migration away from AM and FM broadcasts and to audio delivery via satellite and the Internet.