Re: QCX 40


James Daldry W4JED
 

Hi, Paul

Your radio has 2 detectors working "in parallel", either one of which will do a good job of receiving signals. There are 2 detectors because by adding the detected signals 90 degrees out of phase one sideband is canceled out - signals are all on one side of zero beat. Like a "real" radio. The 3 controls are to adjust the phase of the audio signals to exactly 90 degrees. The fact that they do nothing suggests that one of the signals is missing. Since T1 has been removed the probable cause is that one of the "little" coils has a bad connection on it. IC4 should show the same voltage on pins 7 and 9, and should show equal resistance to ground with an ohmmeter.

Jim W4JED


On 09/06/2018 06:06 AM, Paul Harrison wrote:
Hi,

I have a strange situation, after removing 5 turns from the large T1 Toriod to optimise the BPF output, I can now adjust the BPF to maximum without the Variable C being fully open. However when trying to adjust the 3 variable resistors nothing happens (cannot obtain minimums). No change whatsoever.

However, the RX seems perfectly sensitive and just the same as when I first constructed the kit. I am able to merrily make contacts no problems and having great fun.

Are the 3 variable resistors basically superfluous? I am loath to desolder the SMD
to try another IC.

Thanks in advance for any suggestions.

Paul DJ0CU.

 

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