Barry, The Collins 75A4 with a 500 hz mechanical filter is hard to beat for
weak signal reception on 1.8 Mhz even today with all the technology that has
come along in the last 50 years since it was designed. (I am not saying this
because I used to work for Collins selling BC equipment in Latin America) The
reason for the wonderful performance on top band, I believe, is due to the
design of a high quality communications receiver with single conversion on the
160 meter band. I have used one for years next to a Sherwood mod R4C which is
also a fine unit when modified. However sometimes the 75A4 side by side on
very weak signals was noticeably better. The sharp edge of the mechanical
filter and listening to 300 Hz CW note rather than the traditional 800 hz
seemed to enhance the superiority of the 75A4.
My suggestion is to buy both. Put them side by side hooked to different RX
antennas such as a K6SE pennant and a Beverage with the audio from each split to
each ear. It creates a tunnel effect and some interesting spatial selectivity
allowing the reception of weak signals on Topband assuming the levels are set
correctly and the antennas are comparable. (I have never written anything about
this because discussing the matter with an EE he erupted in laughter and
dismissed the idea as nonsense.)
Try both and if you don't like the 75A4 better I will pay you any reasonable
price for it. I really miss mine and plan to do a lot of SWL'ing in the future.
(dit dit dit dit didit)
73
Herb (KV4FZ)
P.S. Listening at 300 HZ instead of 800 Hz helps for ANY receiver...it's due
to your ears having better S/N discrimination at that frequency...de W4ZV.
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