Tag Archives: AM

Liberty Net: September 26, 2015

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Liberty-Net---Weston-meterby Kevin Strom, WB4AIO

AT THE BEGINNING of my involvement in amateur radio (I was first licensed in 1972), I was an advocate of AM over SSB. I didn’t even operate SSB regularly until the late 1980s. My main reason for this was the vastly inferior audio quality then prevalent on SSB. (There were rare exceptions, like old Central Electronics phasing exciters used by operators who paid exceptional care to frequency accuracy.) Of course, unmodified commercial AM gear was only a tiny bit better, but that’s a story for another time. There were several problems with SSB in those days: 1) frequency instability; 2) the lack of frequency accuracy (leading to “tuning by ear” by people with tin ears); 3) poor frequency response due to excessively narrow filters; 4) SSB filter ripple; and 5) distortion. Add all these things together, and amateur SSB audio usually sounded very mechanical, robotic, and horribly unnatural. Give me home-built, or broadcast, or modified high-fidelity AM any day!

I still love AM, but today there is great improvement in SSB: the PLL and TCXO and OCXO have made frequency accuracy and stability within ten Hertz or less routine, which by itself makes a huge improvement in how SSB sounds. Add to that the fact that AM and eSSB experimenters have encouraged manufacturers to widen frequency response and lower distortion figures, and the SSB of 2015 has the potential to sound very good indeed — especially if you use a software defined radio.

Lower distortion and wider frequency response actually lead to better communication, because the subtleties and nuances of personality and meaning come through better than they ever could with the old, low-fidelity, so-called “communications quality” audio of the past.

Listen: Liberty Net 9/26″]

Here’s my brief digest of, and comment on, just a few of the issues discussed on this week’s Liberty Net:

• More than 100 Jewish rabbis recently signed an open letter to Prime Minister Cameron calling on Britain to open its borders for even more non-White invaders, bizarrely invoking the largely-fictional “Holocaust” of Jews in WW2 as justification. (43 minutes)

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WA3VJB and W3GMS on 40 Meters

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by Kevin Strom, WB4AIO

HERE’S an mp3 of Paul, WA3VJB the other day on 7290 kHz as heard on my Racal RA6790/GM in its widest — 20 kHz — bandwidth.

Although my urban Charlottesville location adds some noise and my receive-only antenna is far from optimal, Paul’s Collins 300G still impresses with its round, dense, satisfying sound. It’s not often I get to use the 20 kHz filter. And it is great to hear a transmitter that I worked on many years ago (when it emitted 1 MHz waves instead of 7 MHz ones) on the air again and sounding better than ever.

WA3VJB on 7290 – wide bandwidth on Racal RA6790/GM”]

And here’s another recent 7290 recording — this one of Joe, W3GMS.

Although a local plasma TV created some interference, the fantastic down-to-almost-DC frequency response of Joe’s rig (that makes any speaker sound better than an original Advent) comes through great in the Racal’s 20 kHz position.

[wpaudio url=”https://3950.net/recordings/W3GMS%207290%2020kHz%20bw%2020110321.mp3″ text=”W3GMS on 7290 – wide bandwidth on Racal RA6790/GM”]

The Racal’s synchrodyne AM detector is very interesting and reasonably high fidelity (as long as the AM station being received does not hit the 100% modulation baseline). I have modified the audio and AGC circuits in the Racal for better audio quality; they are a work in progress.

Out of the Past: WB4AIO on ‘AM-ology’

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by Kevin Strom, WB4AIO

THANKS TO an anonymous listener and the Audio Vault at amfone.net, we now have a audio clip of my AM station, recorded while I was living in Rochester, Minnesota in 1996.

At the time I was running my highly modified Kenwood TS-440s on 75 meters into an Alpha 77D at about 300 Watts into a 150′ inverted L antenna that just barely fit into my small city lot. (All that gear is now gone — stolen from me along with nearly everything else I owned.)

The signal isn’t bad considering that it was presumably heard a thousand miles away on the East Coast. You can hear the recordist adjusting the bandwidth (sounds much better in the wide mode) during the segment. I’m discoursing on ‘AM-ology,’ a field which certainly deserves further study!

Listen to WB4AIO on ‘AM-ology’ (1996 from Rochester MN)”]

The AM-864U Broadcast Limiter

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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!

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Flex Radio Users Net

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Power SDR screen shotsby 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.

Flex Radio Users Net – 2 January 2010 – 3872 kHz”]

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.

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Amateur Radio Audio Recordings

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The TEAC-3340S, the model which was the main WB4AIO recording deck for many years, before it was stolen along with everything else I owned in 2006. Today I use Cool Edit Pro to make most of my recordings.

The TEAC A-3340S, the model which was the main WB4AIO recording deck for many years, before it was stolen (along with virtually everything else I owned) in 2006. Today I use Cool Edit Pro (a PC-based audio suite) to make most of my recordings.

by Kevin Strom, WB4AIO

I’VE JUST added two sections to 3950.net, one appearing in each sidebar, showcasing some interesting amateur radio audio recordings. Make sure that javascript is enabled in your browser for this site, and you’ll see a list of recordings with a small arrow on the left of each listing. Click on the title or the arrow, and a small player will open up, allowing nearly instant playback of the file. Click anywhere on the progress bar to skip around, and right-click the ‘download’ link which appears during streaming if you want to save the file to your hard drive.

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