Garey, Thanks for the explaination! I have never heard this double hump when tuning the calibrator signal in any of my Drakes (TR-3, TR-4, 4A-line twins). I assume the null that you describe tuning through is the BFO frequency, between the two filter passbands. But it would seem to me that you would only have one passband filter active at a time (depending on the selected sideband), and so no null in the middle(between the two), but rather the signal would just fall off on either side of the single (LSB or USB) passband. This is more what I think I hear from my radios. I must be missing something or perhaps I am misunderstanding your explaination. Or perhaps I have some work to do! I can switch sidebands while tuning and get close to what you describe, but my dip in the middle is only about 20dB, not all the way to noise.
KB8BKU, Darryl in Dayton On Jan 25, 2011, at 11:12 PM, Garey Barrell wrote: > Kevin - > > A scope can be used, although I find it easier to just listen to the receiver. > > Think of the two filter passbands as the letter "M" as depicted on Page 29 of > the TR-4 Manual. The goal is to adjust C130 so that it sits in the valley > between the two filters. If you turn on the CALibrator and tune through it > in either direction in receive mode, you'll see the S-Meter go from noise > level up to 10 over S-9 or so for a couple of kHz, then down to noise again, > back up to 10 over S-9 for a couple of kHz, and then back down to noise > level. If you get this pattern, then C130 is close. Fine adjustment is to > listen to the receiver noise (no antenna, high band, no signals) and switch > back and forth between USB and LSB. The 'pitch' of sound should be similar > in both positions. If one sounds low or 'bassy' and the other side sounds > high and 'hissy', then adjust C130 slightly until they sound about the same. > They will NOT sound EXACTLY the same due to anomalies in the filter > passbands, but they should sound similar. > > Just in case you are 'really' asking about nulling the Carrier in the > Balanced Modulator, in this case you can clip the ground lead of the scope to > the chassis and then just lay the probe tip near the Driver tube socket. Set > the SIDEBAND switch to "X", key the transmitter in X-CW with the GAIN at full > CCW, and adjust C127 and R85 for MINIMUM signal. Again, it's easier to > listen on an external receiver if you have one available, and do the above, > adjusting for minimum signal in the receiver. > > 73, Garey - K4OAH > Glen Allen, VA > > Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line > and TR-4/C Service Supplement CDs > <www.k4oah.com> > > > Kevin Elliott wrote: >> I have been reading all of the posts in the new Drake archive and the old >> Drake archive trying to learn as much as I can about my TR4. To you old >> pros this will be a rookie question, but I am of the belief that if you >> don't ask you don't learn. Okay I have read where it has been said that you >> can use a couple of different ways to set C130 correctly. One being use a >> digital receiver and listening for the matching null and the one that I want >> to ask about is using a scope to adjust them. Where will the scope probe be >> connected to read this information or is it indirectly connected with a loop >> of wire around the oscillator tube to see the nulls. >> I got the Great service CD and I love it and will be going through it and >> digesting all I can. >> Thanks >> Kevin _ KG0MN >> >> > > _______________________________________________ > Drakelist mailing list > Drakelist@zerobeat.net > http://mailman.zerobeat.net/mailman/listinfo/drakelist _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
