One of the shortcomings of the superhetrodyne is images. When you go to double conversion to suppress the images of the primary frequency you can then get images of the second conversion plus effects of its harmonics. If you make a chart of all the spurious responses of a receiver you will find that the more conversions you have the worse the spurious situation becomes. Its a very difficult design problem. The ability to have narrow filters at high frequencies now allows receivers to be built that have a single conversion but above the highest frequency they receive. So, one image but so far from the desired one that its essentially not there. Same thing in transmitting where you have several hetrodynes to get the final frequency.
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On 2/20/2024 8:37 PM, Gary WB6OGD wrote:
On Tue, Feb 20, 2024 at 06:47 PM, Yuichi DL1FYM wrote:
By slightly adjusting the preselector away from the usual setting
Well, don't do that.?? Hi Hi...
You are probably using the PTO signal (or its harmonics) as the 1st mixer signal to actually receive on some frequency.
With the proper crystal engaged and the Preselector set where it should be these extra signals should be pretty weak but if the signals are strong enough,
they will come thorough.?? The problems of superhet radios in this class.
By misadjusting the Preselector, you can receive WWV (US standard freq/time station) on both 5 and 10MHz without buying? more crystals, somewhat handy.
Other frequencies can be received as you have found.
73,
Gary
WB6OGD
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
