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Author Topic: Tempo One CW mode  (Read 755 times)

HAMHOCK75

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Tempo One CW mode
« on: May 07, 2021, 01:38:15 PM »

The Tempo One has a unique way of generating a CW signal. For that reason, it is also susceptible to some unique faults. The image below is a capture of a nanoSaver scan of the 9 MHz, 2.4 kHz wide crystal filter used in the Tempo One.

Marker 1 is 9000.000 kHz

Markers 2 and 3 are the standard frequencies of the two carrier crystals, 8998.500 kHz and 9001.500 kHz.

Markers 4 and 5 are at the measured 6 dB bandwidth of the filter, 8998.770 and 9001.140 kHz, respectively.

Markers 6 and 7 are the updated carrier crystals frequencies based on being 300 Hz away from the measured 6 dB bandwidth frequencies, 8998.470 and 9001.440 kHz.

Marker 8 is 200 Hz lower than the updated upper carrier frequency of marker 7 ( 9001.440 kHz ).

Marker 9 is 200 Hz lower than the standard upper carrier frequency at marker 2 ( 9001.500 kHz )

Based on the 6 dB frequencies, the current center frequency of the filter is  ( 8998.770 + 9001.140 ) / 2 =  8999.955 kHz, a small shift down of 45 Hz. This small shift will have some serious consequences for this type of carrier generation however.

The CW carrier generation method employed by Yaesu in the Tempo One uses a 5 pF capacitor switched into the 9001.500 kHz crystal oscillator to lower that oscillators frequency by 200 Hz.

According to the Tempo One instruction manual page 6, “On AM & CW, crystal 9001.5 is used and its frequency is lowered 200 cps by diode switch D104, 1S1007, bringing carrier into filter passband.”. This is not true. A filter with a center frequency of 9 MHz and a 2.4 kHz 6 dB bandwidth, the upper 6 dB frequency would be 9 MHz + 1.2 kHz = 9001.2 kHz. The carrier crystal at 9001.5 kHz is 300 Hz above that 6 dB frequency. A lowering of the carrier frequency to 9001.3 kHz leaves the carrier frequency 100 Hz above and outside the filter passband.

As shown in the scan below, if the upper carrier frequency is set to 9001.5 kHz, the loss at the down shifted frequency shown at marker 9, is 14.27 dB below that at the center of the passband. If a new upper carrier frequency is determined by adding 300 Hz to the measured upper 6 dB frequency at 9001.140 kHz it would equal the 9001.440 kHz of marker 7. A 200 Hz downward shift of marker 7 leaves marker 6 at 9001.240 kHz. The loss at 9001.240 kHz relative to the passband center is 10.62 dB. This is an improvement of 3.65 dB.

That 3.65 dB can make all the difference between having adequate drive on all bands and not.

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KF6FOH

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Re: Tempo One CW mode
« Reply #1 on: May 08, 2021, 11:24:16 AM »

so, did you implement a correction?  What is the technical solution to your findings?
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N2EY

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Re: Tempo One CW mode
« Reply #2 on: May 09, 2021, 05:46:12 AM »

The CW carrier generation method employed by Yaesu in the Tempo One uses a 5 pF capacitor switched into the 9001.500 kHz crystal oscillator to lower that oscillators frequency by 200 Hz.

According to the Tempo One instruction manual page 6, “On AM & CW, crystal 9001.5 is used and its frequency is lowered 200 cps by diode switch D104, 1S1007, bringing carrier into filter passband.”. This is not true. A filter with a center frequency of 9 MHz and a 2.4 kHz 6 dB bandwidth, the upper 6 dB frequency would be 9 MHz + 1.2 kHz = 9001.2 kHz. The carrier crystal at 9001.5 kHz is 300 Hz above that 6 dB frequency. A lowering of the carrier frequency to 9001.3 kHz leaves the carrier frequency 100 Hz above and outside the filter passband.

As shown in the scan below, if the upper carrier frequency is set to 9001.5 kHz, the loss at the down shifted frequency shown at marker 9, is 14.27 dB below that at the center of the passband. If a new upper carrier frequency is determined by adding 300 Hz to the measured upper 6 dB frequency at 9001.140 kHz it would equal the 9001.440 kHz of marker 7. A 200 Hz downward shift of marker 7 leaves marker 6 at 9001.240 kHz. The loss at 9001.240 kHz relative to the passband center is 10.62 dB. This is an improvement of 3.65 dB.

That 3.65 dB can make all the difference between having adequate drive on all bands and not.

Agree on all that.

BUT

How much does the 5 pF capacitor actually shift the 9001.5 crystal frequency?

The Tempo One manual may simply be mistaken. For example, if the shift is 300 Hz rather than 200 Hz, all would be well.

Also note this: The RIT control on the Tempo One has two markings: CW1 and CW2. I can find no explanation of what these markings mean in the manual, but from some back-of-the-envelope calculations it appears that for CW operation RIT should be turned on and the RIT set for CW1 or CW2, depending on the band, in order to hear the received CW tone at a reasonable frequency (600-800 Hz for most ops).

This indicates to me that the "200 Hz" shift of the carrier oscillator may not be accurate.

73 de Jim, N2EY

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HAMHOCK75

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Re: Tempo One CW mode
« Reply #3 on: September 18, 2022, 08:21:43 PM »

The reason for the 200 Hz shift recently became clear. The actual measured shift is 200 Hz with a non-contacting spectrum analyzer. The Tempo One does not always use the 9001.5 kHz carrier crystal for CW. The 20 and 40M bands use the 8998.5 kHz carrier crystal instead. The level of carrier leakage on the slope of the crystal filter is sufficient for CW on 20 and 40.

The purpose of the 200 Hz shift is due to the shape of the crystal filter which has a pole on the high side that creates more attenuation of the 9001.5 kHz carrier vs. the 8998.5 kHz carrier. The shift compensates for that increased attenuation by bringing the 9001.5 kHz carrier frequency a little closer to the band pass but it was never intended to bring it into the band pass as Yaesu states.
« Last Edit: September 18, 2022, 08:23:50 PM by HAMHOCK75 »
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HAMHOCK75

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Re: Tempo One CW mode
« Reply #4 on: October 03, 2022, 11:43:36 PM »

The complete explanation of CW mode is now on this thread

https://www.eham.net/community/smf/index.php/topic,137231.msg1274227.html#msg1274227
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