[TenTec] Century 21 Frequency counter

[Dukes HiFi]

The Century 21 uses a 500 KHz wide 1st IF that is produced by heterodyning the desired signal with a crystal oscillator for each band. 

This 5.0 to 5.5 MHz IF signal is amplified via a broad band IF stage, then mixed with the PTO via the product detector to produce the detected signal.

When Ten Tec put counters in most of these early radios, all they did was to count the PTO frequency and add (or subtract) that count from a preset for each band as determined by the oscillator crystal in use and whether the PTO is added to or subtracted from the crystal frequency to get the detected signal. The internal Ten Tec counters got this band crystal and add subtract information directly from the band switch.

If you use a simple external frequency counter connected via loose coupling to the PTO output line, you will only get an indication of the PTO frequency. While you COULD simply start from the low end of a given band as indicated by the band switch, then mentally add the reading to get actual operating frequencies, this would only work on SOME bands. On the other bands, the low end of the band is at the high end of the PTO frequency range.

That’s why people seldom try to use external counters with early Ten Tec radios.

A simpler alternative is a small counter that I have. This goes into the antenna line and counts the carrier frequency in transmit TUNE mode. This gives you a direct readout of actual transmitting frequency, but only when transmitting.

Sorry I couldn’t make it easier…

Gary


W0DVN


> On Apr 12, 2017, at 11:31 AM, J. Fielden <gijoe1644 at gmail.com> wrote:
> 
> Where could I attach a freq counter to the C21?
> -- 
> 72/73, Jim - wa4ar
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