[Milsurplus] Command Set ReceiverCoffee-Grinder

[Neil Barnett]

> The "coffee-grinder" tuning was necessary during the enroute navigation 
> and approach phase where two or three different Low Freq Nav Aids were 
> utilized and  the crew would attempt multiple bearings for a fix. 
> Obviously it was advantageous to take the bearings as close together time 
> wise so that further adjustments did not have to be made to the LOP(line 
> of positioning) due to change in the aircraft position during the process. 
> It would have been nice if we could just freeze the position or fly in a 
> circle but it was not practical.    :-)   The dreaded two beacon approach 
> was a real headache in a single receiver aircraft.  Took a lot of quick 
> tuning and identifying of the beacons. You couldn't crank it fast enough 
> and you had better be proficient with the code.


Well, yeah, but that doesn't explain why there was coffee-grinder tuning
on the 3 Mc and up Command receivers. I suggested that part of the
pre-takeoff checks required the pilots to switch to "CW" and tune for
zero-beat on a "calibrate" transmission from the flight commander or
control tower.

The process would ensure that all receivers in the flight were on the same
frequency, at least to start with. And the process could be repeated at
any time during the mission, if a pilot thought he was off-frequency.

A second notion that I put forward for frequency changing was that it
might have been for tactical reasons, ie. pilots at briefing time might be
instructed to change their receivers every 15 minutes of the flight and the
frequencies to be used would be the sequence XXXX, YYYY, ZZZZ,
and so on, so that an enemy monitoring the flight commander's orders
about compass headings and other sensitive stuff would hear at most
15 minutes worth and then would have to tune around for the new
command frequency. Its difficult for an enemy to plot your course when
you're doing that and flying a zig-zag course as well.

73 de Neil ZL1ANM