[ARC5] FM-2 Radios

[Mike Morrow]

Wayne (not Robert) wrote:

>My friend said that his Wildcat was equipped with a radio that
>required you to swap out coils to change frequencies...

>As for the difficulty with changing coils, that must have been a
>real pain.

I doubt that the RU/GF on a Wildcat could be reached by the pilot
to do any coil changing in flight.  As it turns out, there would
be no need to change out coil sets, even if the RU and GF could
easily be reached in flight.

The later RU-* sets had several dual-band coil sets available.

Coil set nt-47107 covered 540 to 830 kc AND 3000 to 4524 kc.
Coil set nt-47108 covered 540 to 830 kc AND 5200 to 7700 kc.

One might ask what is the value of that 540 to 830 kc coverage (way
outside the normally important beacon band of 200 to 400 kc).  Well,
that limited broadcast band (BCB) coverage is there to support the
ZB VHF homing adapter, whose output is a BCB signal demodulated
from a 246 mc carrier.  Thus, as long as the pilot can remotely
switch the coil set between its two bands, one dual-band coil set
would provide both the MF BCB reception needed for the ZB, and the
HF reception needed for the GF (but obviously not at the same time).
The capability to copy the normal beacon band is valueless for an
at-sea deployment, away from any such beacons, so that would not be
missed.

IMHO, anyone reproducing an accurate early-war RU/GF installation
should have a ZB mounted in place of the RU receiver's tube cover,
have the ZB control box and ZB antenna relay switch (both NOT needed
when the ZB is used with the later ARA or ARB receivers, but essential
for the RU), have a dual-band coil set such as shown above, AND 
(hardest part) come up with the special spline and remote coil switch
lever that allows the pilot to select the desired receiver band while
in flight.

Mike / KK5F