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

[J. Forster]

> 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?

My concern is not the connection as nuch as the vagueries of an open
twister pair or something to the loop.

> 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...:-)

It could well not matter, but a variation of a pF or so, might throw the
loop bearing off a few degrees. It doesn't take many pFs to cause phase
shift at a MHz or so. An MN-26 is certainly better than that.

> 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.

I think so too.

Best,

John

================
>
>   - 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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>
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