[ARC5] Re: [Milsurplus] LO DF

[Mike Hanz]

Ray Fantini wrote:

>Perhaps the lack of any common multi-coupler for receivers can be
>traced to the fact that almost all of the old receivers were relatively
>high impendence on their antenna input so you can stack groups of two
>and three on the same antenna with no ill effects? Look at the group
>mounting of ARC-5 receivers as an example.
>

Well, that's a good point, though perhaps we are talking apples and 
oranges here.  The EMC environment is significantly different between an 
aircraft with four or five receivers and an ELINT ground station with 
literally dozens of them.  Interaction appears to have been well 
recognized and appreciated as far back as the 1930s.  In fact, there was 
some thought given to LO frequencies and isolation in the design of the 
ARC command receivers back in 1939 (probably prompted by having to 
address the problem in the RAV suite of eight receivers), but they 
weren't the only ones.  The RAX-1 manual specifically cites the careful 
engineering that went into keeping the RAX aircraft trio from 
interfering with each other, including good isolation in the RF 
amplifiers.  In perhaps a burst of over-engineering, the design actually 
feeds antenna signals through the primaries of the selected band antenna 
coil in each receiver to the next receiver in the chain, ending up at 
the MF receiver as the final link.  Failure to feed the antenna daisy 
chain in the right order will make at least one of the receivers deaf!  
The manual does say that there is a band of frequencies where 
interfering local oscillator signals may be observed (7.9-9.0MHz) but 
they are still proud of the fact that such a wide range was covered 
(0.2-27MHz) without significant interaction.

73,
Mike