[Milsurplus] More Earhart scenarios

[Bob Camp]

Hi

About all I can contribute is this:

If you have two antennas that close and transmit into one while  
receiving on the same frequency with the other you have a problem.  
The front end tube in the receiver arcs over. That's not a good thing  
for the tube long term. If the system was set up to work that way  
then the receiver would not last very long.

I can't site a reference. It's just something you only do once and  
then don't do again....

Bob

On Apr 28, 2007, at 7:09 PM, Hue Miller wrote:

> I am a subscriber to the TIGHAR list. This is "The International
> Group for Historic Aircraft Recovery". This group believes
> Amelia Earhart after missing the Howland field, came down
> on Gardner Island (Nikumaroro).  In looking at the record of
> supposed signals received after her nonappearance, one
> particular signal which i questioned, is explained with the claim
> that well, why couldn't she receive and transmit at the same time.
> My statement that this was not possible, nonstandard is dismissed
> as not dealing with all cases, hers being maybe an exception.
> Unfortunately i have no radio texts on hand.
> So if you are at all interested in WW2 and pre-WW2 aviation, i
> pose these questions. If you can quote chapter and verse, not
> just off the top of your head, so much the better. Or even from
> experience.
>
> 1. Many 2-way HF systems ground the receiver antenna during
> transmit. For medium power, is this necessary?
>
> 2. If you have separate aircraft R and T antennas, T on top
> the plane in the usual fore-and-aft wire, and receive antenna
> on the belly, with 50W transmit power, does the receiver input
> circuit need to be protected, or can it handle the voltages
> developed? About 8 - 10 foot separation between the two
> horizontal wires, frequencies 3-6 MHz, and antenna less than
> 1/4w on the lower frequency.
>
> 3. If you do not at least switch off the B+ to the receiver front
> end, then you would have to either turn off the receiver, or
> manually retard the gain control before, and advance it after,
> each transmission, right?  Also, if i recall, if not done, the
> receiver's AVC charges up enuff that it takes some seconds
> to discharge, is this correct?
>
> 4. I don't particularly recall the texts, when i had them, addressing
> the control and switchover topics. Do you know if the Army's
> "AM Transmitters and Receivers" TM, or if some USAF or
> USN Electronic or radio text addresses this specific issue, that
> i could locate and quote?
>
> 5. The WE Co. type 13 transmitter carried on the plane does have
> an antenna T/R relay, and it does ground the receiver antenna post
> during transmit. However on this plane, the topside antenna was not
> used for receive. I imagine this was to minimize the antenna wire
> running internal thru the plane to under the pilot seat, where the  
> receiver
> was. Sound logical?
>
> Yes, some of this seems self-evident, but my word alone is
> not good enough!  Thanks- Hue Miller
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