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

[John Franke]

My Model GF-12 and Model RU-17 manual states:

" If a fixed antenna is used the Transmitter should be tuned over dry soil; 
if circumstances render it necessary to tune it with the airplane on a wet 
surface the antenna tuning should be readjusted, if possible, after the 
plane is in the air.  The airplane antenna cannot be properly tuned inside a 
hanger."

The last sentence was italicized.

By the way, even with jets, a grounding wire is still used during fueling. 
I attached many a grounding wire to Navy jets.

John  WA4WDL

----- Original Message ----- 
From: "J Forster" <jfor at quik.com>
To: "Hue Miller" <kargo_cult at msn.com>
Cc: <milsurplus at mailman.qth.net>
Sent: Monday, July 07, 2008 9:45 AM
Subject: Re: [Milsurplus] Re: SCR-274-N Transmitter Dial Etc.


> 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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