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About RF Cafe
Copyright: 1996 - 2024 BSEE - KB3UON RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived... All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowl My Hobby Website: |
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National Company Advertisement: TVI
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On the page following an article titled "TVI and the Novice," the National Company ran one of its conventional full-page informational advertisements - on the subject of TVI. This is number 234, and it is the newest one I have so there likely were many more. National's suggestion for curing TVI issues was to use a shielded chassis with chokes in series and bypass capacitors in parallel with power leads. A complete list of all my National Company advertisements is at the bottom of the page. National Company Advertisement Number two hundred thirty-four of a series The problem of TVI has many phases, and relatively little has been written about receiver TVI. After spending much time and toil in TVI-proofing a transmitter, many an ardent amateur is surprised and disgusted to find that his receiver is causing interference, often of a fair magnitude. This is especially true if the receiver is of an old vintage.
The shielding of the receivers was found to be generally satisfactory. Radiation of the harmonics of the high frequency oscillator was traced to leads connected to terminals on the receiver chassis sometimes accidently resonant in one of the TV channels. Coupling from the receiver oscillator was mostly by way of the cable harness in the receiver. Additional filtering of the B plus for the oscillator generally helped but little. The best cure found was to series connect 1.5 uh chokes in the offending leads and by-pass them with 0.005 to 0.01 ceramic condensers with short leads to the receiver chassis. This is the same technique used to filter leads in a transmitter. Naturally, any choke used in the speaker lead should have low resistance to prevent loss of audio power. Shielding the B switch leads external to the receiver also prevents harmonic radiation and also helps to keep transmitter power out of the receiver. An odd twist was that radiation from leads connected to the antenna terminals was negligible, although this depends to some extent on the vintage of the receiver and the model. Bill Bartell, W1PIJ Here are all the National Company advertisements I have:
Posted October 11, 2016 |
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