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Amateur Band Shortwave Receiver Project Overview in English
Page 1 : Overview |
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The receiver was dirty, but began working after cleaned the contacts of terminals and switches. The page also offers Japanese translation of the HQ-170 operation manual.Page 2: Restoration
One of the IFTs caused short circuit while cleaning the chassis. Its built-in capacitor, consists of three thin film, cracked. The plate voltage supply to the 1st mixer shorted to the ground and the film burnt. All the films was removed from the IFT and added an external capacitors. The capacity may not be optimal, but it regained the performance same as before.Page 3: Controls
The diagram in the audio stage circuit part explains how the unique feature of HQ-170, the variable NFB circuit, works. It's not a modification or improvement idea. I did not see a problem in audio section; just checked.
I also tried the realignment of the fabulous IF block. No big problem observed here.
Explains how each control works.Page 4: Tweaking and Playing
AGC time-constant capacitor was changed so that the AGC decay became my preference.
Frequency drift measurement result. Apparently it's not normal; too drifty. Supposedly the drift is caused by the age of the temperature compensation capacitors, but not sure. It will be a time consuming job to find out the best matching.
Another headache was slight frequency drift caused by the signal strength. Because of this, CW reception was quite chirpy. Test revealed that the AGC voltage to the 3rd mixer V5-6BE6 caused the frequency drift of the 3rd LO. I could not find the true reason. As a tentative solution, the AGC voltage was removed from the 6BE6. It made CW reception very crisp. On the other hand the S meter reading sky rocketed (because 3rd converter is always in full gain), needed to readjust the S meter.
One of the future plan for HQ-170 is to modify the clock. Here in Eastern Japan the electric power frequency is 50Hz, so the clock cannot be used. Putting a battery operated movement will give a trick.
Copyright(C) NoobowSystems Lab. San Jose, California 1999
Copyright(C) NoobowSystems Lab. Tomioka, Japan 1999, 2000, 2002