[Hallicrafters] S-53 vs S-53A

[GARDGORE at aol.com]

The introduction of the Hallicrafters S-53 in 1948 was an interesting new 
design that embodied some new technology for the time. The main feature of 
interest was the new IF frequency of 2075kc that would have improved image 
rejection on the higher frequencies for a single conversion receiver. Could 
this have been a pilot model to test the acceptance and viability of the 
2075kc IF system in a production model for the coming new dual conversion 
receivers that were on the drawing boards then? It is interesting to note 
that the 1954 SX-88 used that frequency. The S-53A was (in my opinion) a cost 
reduced version introduced in 1951 that included a change back to the more 
conventional IF frequency of 455kc. This is not to imply that it was less 
capable because in the case of single conversion receiver design the high IF 
frequency of 2075 would have made it difficult to obtain good selectivity due 
to what the engineers call percentage of frequency difference. Good IF 
passband shape factor (steep skirts) is best obtained with the use of a very 
low frequency such as 50kc. Good image rejection characteristics are obtained 
with the higher frequencies which explains the concept behind the dual 
conversion receivers. The various equipment manufacturers eventually settled 
on somewhere around 455kc as the best compromise frequency for inexpensive 
receivers. The IF transformers in the older S-53 were rather large and the 
S-53A had the small ones that you see in the other inexpensive Halli models. 
I think there was a write-up in Electric Radio a while back that gave a much 
more detailed description of the differences and compared performance between 
the S-53 and S-53A.

Regards, 
Greg Gore; WA1KBQ