Topband: R-390 rcvrs.....

[Donald Chester]

>From: "billandjosi" <billandjosi@earthlink.net>
>
>I've been stationed with the Collins 51J4...the "offical" Collins version 
>of the '390.  In my opinion, the J4 is not nearly as rugged and 
>'functional' as the  390...

The '390/390A and the 51J4 have little in common, except for the general 
coverage feature and Collins PTO/tuneable i.f. scheme.  The J4 looks like a 
general coverage version of a 75A4, but the conversion scheme is completely 
different. The J4 uses 500 kHz i.f.'s, whereas the '390 (and 75A series) use 
455 kHz if's.  One problem with the J4 is that the 500 kHz mechanical 
filters are hard to find and expensive.

I think the J4 is more user friendly, but the '390 is a better performer, 
even with all the cog wheels and bicycle chains.  It is built like a 
battleship and weighs almost as much.

The '390 with L-C if filters has much better audio than the '390A with 
mechanical filters, even though the latter give sharper skirt selectivity.  
Both receivers use xtal filters for the sharp CW selectivity mode.  Despite 
multiple conversion stages before the i.f. selectivity filters, the '390 
series has a reputation for being good performers in the presence of strong 
rf fields from nearby transmitters.

Don K4KYV

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