[ARC5] VHF set

[Michael Hanz]

Robert's question is a good one.  The two models were quite different 
sets, despite the same tail end /ARC-5 nomenclature.  The T-23/T-126 
variants were initially designed in 1943 by Western Electric as an 
SCR-274N add-on system to meet a specific set of requirements, then 
renomenclatured with some design adjustments as the T-23/ and 
R-258/ARC-5.  I won't go into the WE sets because they have been covered 
at some length elsewhere, but the ARC "continuously tunable" VHF rigs 
were a limited prototype production of perhaps 50 sets targeted to meet 
the same need.  The drawings date to 1944, so they were late in the 
game.  Perhaps because of the delay, they were never adopted for 
contract production.

There were several options proposed in these ARC sets (including a 
115vac version with ARC #9906 "power packs" in place of the dynamotors), 
all of which are shown at 
https://aafradio.org/docs/VHF_ARC-5_drawings.pdf (a 10 MB download, 
BTW).  The problem, beyond the lack of crystal control at a time that 
crystal controlled channelization of sets had finally passed an 
acceptance threshold to prevent pilots from fiddling with combat 
frequencies, was that it took two receivers and two transmitters to 
cover the same bandwidth that the SCR-522 covered in one set.  It ssems 
that it was simply a bridge too far for the combat driven requirements 
guys to buy.

And so we are left with a few exquisite jewels, as Gordon Eliot White 
aptly labeled them, of these unusual sets.  I was saddened by the 
appearance of the modified T-90 on ebay in the last couple of weeks - 
the start of yet another ham mod to "make it better"  but thankfully 
unfinished before being too badly torn up - 
https://www.ebay.com/itm/254573306270

More at https://aafradio.org/flightdeck/arc5-4.htm for any who might be 
interested in such esoteric subjects.

  - Mike  KC4TOS

On 4/26/2020 6:55 PM, Robert Downs via ARC5 wrote:
> How did the T-90/ARC-5 differ from the T-23 and T-126/ARC-5?
>
> Robert Downs
>
> -----Original Message-----
> From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On
> Behalf Of Martyn Google
>
> The late Neil ZL1ANM (SK in December, sadly, he was a good friend, got me
> started on ARC products) had one of these sets unmodified, had got xtals
> from a UK supplier and was about to go on the local vhf repeater with it.
> FMing it was easy, the mechanical switching mechanism worked, a marvel of
> radio engineering we thought!
> The set has gone to another Ham.
> 73, Martyn ZL3CK