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Assembly manual Rev 1.08
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Hi George There is a description of the changes, on the last page of the manual: 1.07 17-Oct-2017 Changed Q6 transistor to MPS751 (was MPS2907 in first kit batch) Corrected typo on p83 para 3 “in the event that” 3.3K R44 was mistakenly called R34 on parts list 1.08 23-Oct-2017 Swapped R19 and R25 in parts list and sections 3.22, 3.23 to match error on silkscreen (silkscreen prints for R19 and R25 were swapped). Note in section 3.41 that C47 can be mounted vertically above SN 500. The important one, is about swapping R19 and R25.? 73 Hans G0UPL On Fri, Dec 8, 2017 at 3:56 PM, George H. Gates via Groups.Io <w2bpi1@...> wrote: I printed Rev 1.06. What has changed in the newest version (Rev 1.08)? What pages do I need to reprint? Tnx 73 Geo/W2BPI |
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George H. Gates
Tnx Hans
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Hi Dee The gain of the I side is 3x higher than it should be. But this is somewhat cancelled out by the extra resistance (3.3K instead of 1K) in series to the I-Q balance trimmer pot. The I-Q balance can usually be adjusted as normal. The net result is that there is hardly any impact. This is why it went unnoticed for so long. There would be a slight decrease in dynamic range. Unlikely to be noticeable in most cases. Generally if you have already built the radio with R19 and R25 swapped, and all is working fine, then I would suggest leaving it as it is. That's what I have done (i.e., left it alone) on both my QCX currently operational here (20m and 30m). Anybody who builds the kit using manual 1.08 will automatically get the resistors the correct way around.? There will not be any PCB revision to change the silkscreen in any future PCB manufacturing runs. The manual (1.08 and on) has already been amended to fix the issue. 73 Hans G0UPL? ? On Dec 8, 2017 6:55 PM, "QRP_nut" <raspiham1973@...> wrote: Hans, |
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Hi Hans and thanks for swift the reply,
Would R19 & R25 being reversed on the PCB possibly cause one of the I/Q trim-pots to run out of adjustment while setting-up the I/Q balance? I just checked my QCX80 and R19 & R25 are reversed. While setting-up the I/Q balance I found one of the two pots' (dont remember which one but probably R27) ran out of adjustment and became "one ended" though image rejection by this time was allready excellent so I left it as it was. But looking at the schematic again in light of the revalation regarding R19 & R25 it would seem that those two resistors being reversed in position might account for one of the adjustment pots being at the end of its adjustment range? 73,s Des (M0AYF) |
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Hi Des? Yes I think it is possible. If the I-Q pot has to compensate for usual amplitude imbalances but additionally has the trauma of having to deal with the additional imbalance caused by the R19/R25 reversal then it could run out of trimmer adjustment range. I think it's quite possible.? Still, if your unwanted sideband is already excellent I think I'd be inclined to leave it as is! 73 Hans G0UPL? ? On Dec 9, 2017 1:56 PM, "QRP_nut" <raspiham1973@...> wrote: Hi Hans and thanks for swift the reply, |
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