[Milsurplus] Freq. Coverage of Navy Transmitters

[Rian Robison]

Hi,

Thought I might as well put my two cents into this also.

I believe the reason grid modulation was used rather than plate modulation
(except in the TBM which had either but plate modulation was used in more
setups) was because the way these transmitters were used.  Voice
communication was usually used for short haul (local) communication where
as long haul traffic was sent using CW.  Since long haul voice wasn't a
requirement, most of the time, why spend extra for high level plate
modulation when it wasn't necessary for the planned transmitter application?

The TBW setup along with the RBM setup application was to be on the beach
(or such location) and used to communicate with local ships, aircraft and
ground units most likely by voice.  It could also be used for longer haul
communications using CW when this became necessary.  However, its design
purpose was supposed to be for the beach to communicate with ships
supporting the current military operation.  The TBW had a gasoline
generator for 12 VDC and 110 VAC 800 cycles and the RBMs had a 12VDC dual
dynamotor package.  There were some (how many?) MG sets made for the TBW
using a 60 cycle AC motor belt driving an 800 cycle/12 VDC combo generator.
This generator screams very loudly at 800 cycles with or without a load.  I
don't know where this was used but I'm sure the noise drove people nuts!

Rian, W6SVU


> [Original Message]
> From: <w8au at sssnet.com>
> To: <milsurplus at mailman.qth.net>
> Date: 11/3/2004 1:16:34 PM
> Subject: Re: [Milsurplus] Freq. Coverage of Navy Transmitters
>
> At 07:53 PM 11/1/04, howard holden wrote:
> >The TBW is not, as far as I know, a shipboard transmitter, rather a beach
> >unit. Remember, it comes in the watertight cases, and is designed to be
set
> >up as a free-standing field unit. The TCS, on the other hand is a
shipboard
> >unit.
> >
> >The puzzle to me is why did the TBW have the LF unit? Any antenna they
could
> >set up on the beach would be a pretty inefficient radiator in the LF
range.
> >The upper MF and HF would be far more useful and practical for shore-ship
> >comms. Perhaps it was to be able to communicate with merchants involved
in
> >landings, who might have had only MF/LF rigs. That could explain the MCW
> >capability on many Navy transmitters.
>
> Howie:
>
> If you have the TBW manual you see the antenna setup they used for LF and
HF.
> The end fed top wire against the low counterpoise wire, although small
for 
> the wavelength,
> appears to be a good try for some sort of efficiency, at least enough to 
> communicate
> with merchant and transport ships.
>
> >The other puzzle is why the Navy used suppressor-grid modulation instead
of
> >plate  mod on some transmitters? Typical power output with suppressor
mod is
> >about 1/4 of the CW output. Granted, the weight and space savings over
plate
> >mod on the TBW might mean something to the guys who had to muscle it
ashore,
> >but with a hulk like a TBL, at 700 lbs (not including the MG set), what
> >would another 150 lbs mean, instead of the 75 lbs for the suppressor
> >modulator.
>
> The resort to efficiency modulator schemes seems to follow the size of
the rig.
> The TBK has a plate modulator (which changes the nomenclature to TBM) and
> as the power and size drops (TDE, TBL, TBW, TCM, etc) you have grid
modulation.
>
> This pattern is not consistent, tho, (TCS) and we are left wishing we
knew the
> real reasons.   Maybe parts count, maintenance and weight were factors?
>
> Perry   w8au
>
>
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