[Milsurplus] Re: SCR-274-N Transmitter Dial Etc.

[J Forster]

There may be other reasons for not transmitting in hangers.

These planes were fueled by gasoline and a spark could ignite it. Before jets,
when a ground crew came out to refuel a plane, the first thing they did was
attach a grounding lead. Enclosed spaces, like a hanger or hanger deck could well
have gas fumes.

Another reason not to transmit is ordinance. Some explosives are set off by
electrically fired blasting caps. Remember those signs near construction sites,
saying "Turn Off Two-Way Radios"? A blanket no transmitting in hangers makes
sense in this regard too.

As to the detuning issue, any fixed (non-trailing) antenna is far closer to the
plane than any hanger structure,  (C=eA/d) so I think the hanger effects would be
second order, and only a touchup of the roller-ductor would be needed once air
born.

FWIW,
-John

=============

Hue Miller wrote:

> ----- Original Message -----
> From: <WA5CAB at cs.com>
>
> > Why not?
> >
> > In a message dated 7/6/2008 4:06:50 PM Central Daylight Time,
> > kargo_cult at msn.com writes:
> > > And i have wondered how on flattops, the transmitters were set up before
> > > a flight.  Let's say, a patrol plane going out. You cannot tune up the
> > > transmitter
> > > below the flight deck.
>
> Somewhere here i have instructions for tuning up a civilian HF aircraft
> radio. The instructions direct not to tune up in hangar. I assume, don't
> recall if the instructions specifically explained this, that capacity effect
> of hangar to wire antenna threw off the antenna resonance, compared
> to the open air situation.  If the antenna is naturally resonant, this effect
> isn't so strong, but if you have an electrically short antenna resonated
> with external inductance, i suppose so. Possibly this applies even more
> so below on a service deck, besides the caution to not operate any
> transmitter that might cause sparking from the antenna HV.
> So - i wonder: on the flight deck before scout flight, you could tune up
> the transmitter oscillator using the LM freq meter. You do not want to
> actually radiate from the aircraft's antenna because who knows how
> far that might go. ( I am thinking i recall reading of Japanese aircraft
> being heard on runway, preparing....don't know where i read of this
> however....)  Also there's no way to tune up on deck, to simulate the
> trail antenna, which i suppose would have been more likely to be used
> on scout patrol missions, than the fore&aft wire. However, on the SBD,
> the receiver certainly wasn't accurate enuff to use it to calibrate the
> transmitter. Loading the transmitter might throw the transmitter VFO off
> a few kHz. The ship would not transmit or respond in any case, under
> strict radio silence. I am just wondering how the patrol plane would come
> up on frequency, close enuff that the transmission would not be missed
> by the ship station. I don't think every SBD or TBM carried the LM freq
> meter, did they? Not shown in any photo i have seen. Also, if the
> carrier's fighters were still using only HF gear, such as RUGF, how did
> they tune up before take off? I suppose "radio silence" would have to go
> out the door. -Hue  K7HUE
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