[ARC5] ATA/ARA?ARC5 compatablity

[Mike Everette]

    I meant to share this summary with the list last night.
73MikeWA4DLF


 From: Mike Everette <radiocompass at yahoo.com>
 To: J Mcvey <ac2eu at yahoo.com> 
 Sent: Sunday, April 2, 2017 11:47 PM
 Subject: Re: [ARC5] ATA/ARA?ARC5 compatablity
   
The ATA/ARA and SCR-274N are pretty much identical.  The chief exception is the 1.5-3 mc ARA receiver and the 2.1-3 mc ATA transmitter, neither of which are found in the SCR-274N equipment; but even those units are completely electrically compatible with the 274N.  Both the 274N and ATA use screen modulation and the ATA modulator is identical with the BC-456.  The ATA and 274N control boxes, antenna relays and racks are electrically and mechanically identical.  The ARA receivers are identical to the 274N equivalents, as are the racks.
There are audio impedance differences between the A and B models of the 274N receivers; the A models are 8000 ohm output while the Bs are 8000 and 300 ohms.  The ARC-5 receivers are low impedance only.
The ARC-5 receivers are slightly different from the 274N and ARA, in that the ARC-5s contain an AVC circuit (hence the 12SF7 2nd IF tube in the ARC-5s).  I haven't studied the control circuitry for the receivers, but there may be minor differences.  However the ARC-5 receivers will plug directly into the ARA or 274N racks.
ARC-5 transmitters are plate modulated, and use shunt feed for the plate B plus as opposed to series feed in the 274N and ATA transmitters.  There is also a resistor in the screen circuit of the ARC-5 transmitters which is of a different value from the 274N and ATA; and this must be changed to the value in the 274N transmitters if one plans to screen-modulate the ARC-5 units.
The transmitter control circuitry for the ARC-5 transmitters contains numerous differences from the 274N and ATA control circuitry.  The transmitter control box for the ARC-5 is therefore somewhat different from the 274N and ATA equivalent.  
Functionally, the systems operate the same even though the control circuits differ; the ARC-5 circuitry is a bit more sophisticated and therefore complicated.  For one thing, the ARC-5 transmitter racks contain a "test key" function not found in the 274N and ATA.
ARC-5 transmitters are of the same physical dimensions as the 274N and ATA, but the power connectors on the transmitter racks are different.  The ATA and 274N transmitters will not plug into the ARC-5 racks, and vice versa.
The connector plugs on the 274N and ATA modulator, control box and transmitter racks are identical; but their functional equivalewnts in the ARC-5 system are slightly different in pin arrangement.  This is to help prevent the intermixing of components particularly from the ATA and ARC-5 transmitter systems.
All in all, the ARC-5 is a more versatile system with many possible installation options and variations depending upon what auxiliary equipment and what other systems may be interconnected with the ARC-5.  The ATA and SCR-274N are more basic, with far fewer variations in the installation.
In summation: You can freely intermix ATA/ARA with the SCR-274N to make up a system.  It is also indeed possible to cobble together a "complete system" using both ATC-5 and ATA or SCR-274N transmitting components, but changes are necessary in the transmitter circuitry as well as the control circuitry to make things work.  It's definitely not rocket science but does require attention to details; copies of BOTH the ARC-5 and SCR-274N manuals are necessary to do this (I have never seen an ATA/ARA manual!).
Hope this helps.
73
MikeWA4DLF

      From: J Mcvey via ARC5 <arc5 at mailman.qth.net>
 To: "ARC5 at mailman.qth.net" <ARC5 at mailman.qth.net> 
 Sent: Sunday, April 2, 2017 9:44 PM
 Subject: [ARC5] ATA/ARA?ARC5 compatablity
  
As far as I know the ATA/ARA stuff is more like or compatible to SCR274 than ARC 5.There is a guy on Ebay parting out a cobbled together system that uses an MD-7 hooked up to a CBY-52212 tx rack. How's that gonna work?I guess it didn't, and that's why he's selling- or the tx units were modified.?To paraphrase Forrest Gump: Ebay is like a box of chocolates-you never know what you're going to get...!
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