[ARC5] YG/ZB Demo

[Mike Morrow]

Mike wrote of the YE/ZB:

> The sector edge characteristics are not formed by narrow beam width,
> but by precisely switching the audio coding at each angle desired.

Still, Mike, if the YE beam is too wide, or the ZB is too close to the
YE, multiple sector IDs would be received at the ZB.  In that case
discrimination for the correct sector can take place only by selecting
the sector ID that's in the center of the sequence of the several IDs
that are being received.  The 246 MHz RF gain of the ZB could be 
decreased to help somewhat, but only if the ZB control box was being
used (it has a switch for that purpose).  But I doubt that any ZB 
installations whose associated BCB receiver is the ARA, or even the RU,
used the ZB control box.  Eventually as one neared the YE/YG, all 12
sector IDs must have come in clearly, making choice of the correct 
sector very problematic at that point if the pilot can not yet see
his carrier.  

>There is *no* discussion in the literature about these systems that 
>suggest you could *only* find the general vicinity of the battle group - 
>it was always about finding your particular *carrier*.

But...it appears that the specific individual YE beacons of the carriers
in a battle group were discriminated only by FREQUENCY in the 234 to 258
MHz YE/ZB operating band.

There's a pilot's report of YE/ZB use during the battle of Midway at:

  http://www.cv6.org/company/accounts/jmccarthy/

In it, Enterpsise SBD Pilot John McCarthy, working with his Radioman Howell, 
describes how the ZB was used to find the Yorktown when the Enterprise's
YE could not be received:

  "On our last homing efforts, all three contingents climbed slowly 
   - my highest altitude 3500 feet - to tune in on the ZB-YE VHF homing
   beacon. ...No signal yet - no word from the Enterprise. I had run 
   completely out of fuel on the two outboard tanks and was working on
   two low inboards, with no fuel indication on the gauges. ...Still no
   signal from the ZB. At this point, we had been away from launch five
   hours, and a lot can happen to home base in that time in a carrier duel.

  "I asked Howell if by some chance he could retune our receiver for the
   Yorktown ZB. In about three minutes he had the signal from the Yorktown
   coming in "Loud and Clear" not too far away from our position. This hadn't
   been practiced much prior to this as it was possible not to be able to 
   retune to the original frequency. What a radioman I had on board. Once 
   we had made contact, we started to lower our altitude on the line of
   sight principle, maintaining a clear signal from York's ZB. At the point
   when all sectors could be received, the rear of the Task Force was visible.
   A TBD was in the water to our left, and finally the Yorktown was sighted."

These statements indicate some intersting details of YE/ZB use:

(1)  YE/ZB frequency was DIFFERENT for each carrier in the task group.
(2)  YE/ZB sector IDs were IDENTICAL for each carrier in the task group.
(3)  YE signal strength was controlled (reduced) on approach to reduce
     multiple sector ID reception by lowering aircraft altitude.
(4)  When the YE was very close on approach, all sectors were received
     at the ZB.

I think it is doubtful that a demo setup where the ZB antenna is physically
close to the simulated YE, that one could avoid the situation described at
the end of the quote above, where are sectors are received.  And it is
essentially impossible to discriminate at the ZB and its BCB receiver on
the basis of signal strength, except that as the signal grows stronger,
more sector IDs are received.

I'm not sure there's really any disagreements about this process.  Perhaps
there are misunderstandings of the points being made.

Mike / KK5F