Jerry, The reason, I believe that made the 75A4, with 500hz Collins mechanical
Filters, such a fine 160 meter receiver in its time was the fact that on that
band the design used single conversion rather than the double conversion it used
on the other bands. I think this was the key to lower IMD. There was one
drawback. On 160, if I remember correctly, the pto and vernier dial went higher
in frequency as you turn it to the left. This was due to the choice of single
conversion on 160. I have heard some of the pros say that for the 160 meter
weak signal circumstances that a single conversion beats double in theory. I
just wonder if there are any well designed professional single conversion
receivers since the 75A4?
73
Herb (KV4FZ)
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