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Another Tram D201A Question

T

troyota

W9WDX Amateur Radio Club Member
May 9, 2007
120
9
28
I am getting very close on this ole gal. I am noticing on AM may receive is about 3kc lower than it should be. Example, the frequency is 27.305, but to clear it up I have to move the vfo to 27.302, then in crystal mode the clarifier will not get there (about 27.304 or so. It is like this on all channels crystal or manual selection. AM TX is dead on frequency. I replaced the 5.8015 crystal with a spare I had (not sure if it has drifted). It did not make any difference. I have another very nice D201A that works 100% perfect. I will pull that 5.8015 crystal to check it with. When I was doing the 4mhz alignment, I noticed that my 4.4 crystal was at 4.2, all my 20mhz alignment came out fine after replacing 4 crystals. Would the 4.4 crystal cause the RX issue I am having? 1,5,9,13,17,21,26,31,and 36 all tuned to frequency. I was expecting those to be off a little due to the 4.4 crystal being off. Maybe, I am looking at that wrong. I do not have a scope or a frequency generator. But they are on the "to buy" list for sure. Anyway, any guidance to what may be the issue is greatly appreciated.
Thanks!
 

Wait! My 4mhz reading was not 4.2 for the 4.4 crystal. The reading was 4.3998. I read my notes wrong. I just ran through the 4mhz again. Ch 1 = 4.3998, Ch 2 = 4.4099, Ch 3 = 4.4199, Ch 4 = 4.4399, Ch 5 = 4.4299. This was as close as they will adjust. I don't think that is my issue, but I am not sure.
 
A difference between transmit and receive frequency on AM can sometimes be blamed on the 5.8015 MHz crystal X300 used for the 2nd conversion stage in AM. Sideband receive is single conversion, but AM gets converted down from 6.255 MHz to 455 kHz. The two tiny black 455 kHz ceramic filters can also be off frequency, but that crystal is more often to blame. Has no trimmer cap. At least it's in a socket. Barkett still sells that one if it's so far off you need to replace it. Best way to check it is with a receiver that's calibrated on frequency well enough to tune it in and tell that way. Poking a probe onto it for a frequency counter can change the frequency. The tip of the probe will add capacitance to the circuit and pull down the crystal frequency to some degree. And if all you have is a receiver that you can eavesdrop on that crystal, set it to sideband, tune in the 5.8015 and see if the tone changes when you touch a counter probe to the circuit. You'll hear the pitch change when that happens.

73
 
Thanks Nomad, I have a yaesu 990 tuned to 5.8015 LSB that I used as a sniffer. It does change when I touch the crystal with the probe. If I roll the vfo back and forth on the 990, I can hear a difference. It seemed to zero beat above 5.8015. ( i think) I was leaving for work out of town, so I was in a hurry. Wasn't sure if I could tell if the crystal was off by rolling the vfo to find what freq it was at. Didn't know if I was looking for loudest tone, highest signal, zero beat...or something else. Lol.
Thanks again
 
Maybe I'm overthinking this. There's a trimpot on the crystal board that sets the transmit frequency. The front-panel clarifier is for receive only. Might be the whole cause of the issue.

R143 is the trimpot closest to the channel selector. Probe the counter to J100B, the top RCA socket at the rear of the crystal board. Center clarifier on channel 1 should be 21.7085. Key the mike and set R143 to agree with the receive frequency.

73
 

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