[ARC5] ARC-5/SCR-274 Navagation Receivers?

[Mike Hanz]

I certainly agree, John.  Even so, the balanced input of the push 
terminals would seem to be *somewhat* beneficial for CMR, despite the 
impedance mismatch caused by the abrupt physical geometry change between 
the feedline and the (very short) internal 'transmission line' to the 
L-16 RF transformer of the receiver, would it not?  It sure ain't a 
UG-971/U connector, but I'm wondering how bad could it be?  The 
capacitance is controlled to a degree by high quality parts like ceramic 
insulators, thought the large physical size of the posts do pose a 
problem, not to mention the routing of one of the wires through the 
loop/ant switch.  There is definitely not the care apportioned to 
current practice in that area, but it seems to me that it's a matter of 
degree...:-)

And you are absolutely correct - the Bendix engineers understood the 
balance problem very well!  That's one reason I think the ARC-5 loop 
option was an emergency concept that was a throwback to the early Type K 
days.

  - Mike

On 4/30/2011 4:13 PM, J. Forster wrote:
> Mike,
>
> I really wonder about loop use on ARC5s because of the antenna connections
> used- a pair of push terminals.
>
> To get good performance out of a loop, you need good common mode rejection
> at RF which means balanced wiring (and low capacitance). Terminal just
> don't provide that.
>
> If you look at other RDFs and ADFs, they all use special shielded cable
> assemblies that are premade to only one length (I think). This applies to
> the RA-10, MN-26, BC-433, ARN-6 and ARN-7.
>
> -John
>
> ==============
>
>
>
>> On 4/29/2011 12:35 PM, Leslie Smith wrote:
>>> I'd like to add to Bob's question by noting that (at least) later ARC-5
>>> sets have a two-terminal attachment for the navigational loop, including
>>> a switching mechanism whereas the earlier ARA and BC-453 sets don't.
>>> What were the circumstances that led to the change, and when was it
>>> made.
>> ARC evidently developed a prototype loop antenna for the ARC-5 but it
>> was never picked up by the Navy.  I think the loop capability was
>> designed into the R-23 and R-24 receivers because it was relatively
>> inexpensive to do so and would have provided an emergency option for
>> some aircraft.  The prototype loop apparently became the basis after the
>> war for a couple of offerings in ARC's commercial line of equipment for
>> light aircraft.
>>
>> 73,
>> Mike
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