I have finished all the archived forum topics from 1998 to present.
Just one minor point that I can supply information on (to confirm that Ric's understanding was correct):
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Date: Fri, 27 Apr 2007 12:38:34
From: Ric Gillespie
Subject: Re: Betty's notebook
> From Hue Miller
>
>> From Ric
>> As far as we can tell from the available photos, the transmitter and
>> receiver in NR16020 were completely independent systems. The
>> transmitter had the capability of using the same antenna as the
>> receiver but there is nothing connected to that terminal. The lead
>> from the transmitter in the cabin goes to the dorsal vee antenna.
>> The lead from the belly wire antenna goes into the bottom of the
>> fuselage under the copilot's seat where the receiver is mounted.
>>
>>> If you accept that AE was listening at the same time the
>>> transmitter was
>>> on, you have no choice but to accept that there was a second
>>> receiver
>>> onboard.
>>
>> If it works for a second receiver it seems to me that it would work
>> for an independent single receiver.
>
> Well, it's time for me to dig out the schematics again. Every other aircraft
> had some way to ground the receiver antenna and switch off the receiver
> power, but AE's ship did not?
I'm a bit surprised that you've checked every other aircraft.
> When you have a wire antenna for receiver in proximity to a transmit
> antenna, this receiver wire picks up a LOT of voltage when the
> transmitter
> is on.
How close is "proximity." The Electra's transmit antenna was
ballpark 8 feet from the receiving antenna.
> The circuit in the receiver steps this up - even without the amplifiers
> working in it - to hundreds of volts. The solution is a relay contact that
> grounds the receiver input circuit when the transmitter is on. This control
> wiring is controlled from the transmitter. If you lack this feature, you risk
> damaging the receiver, and you're treated to a blast in the earphones
> that will be like a slap to your ears. Also, how would the "transmit sidetone"
> work ( this is a little bit of your speech into transmitter fed into
> earphones, so you can hear what's being sent out - explanation for some of the
> readers ), work with the receiver being blasted by the transmitter?
I think we need to figure out how much "blasting" there would
actually be. Perhaps Bob Brandenburg could offer an opinion.
> There's no avoiding this fact: AE did NOT receive anything when her
> radio transmitter was ON.
I think I'd like a second opinion.
> It doesn't matter if in the receiver - transmitter pair, the receiver is in
> the same box in your car's CB, or it's an Army receiver in a dugout a
> quarter mile away from the transmitter: the receiver antenna is grounded,
> audio is removed during transmit.
So "proximity" is within a quarter mile? No receiver is going to be
able to receive if there's a transmitter functioning on the same
frequency within a quarter mile?
I fly a Conquest with the factory Collins Radio package, the only nav/com modification has been replacement of Collins Com 1 and Nav 1 with a Garmin 530PW Nav/Com.
Two Audio Panels and two microphones are installed and either left or right Audio Panel's can feed their audio from either com, but the left and right microphones/mike jacks and control wheel ptt's are isolated to their Audio Panels. Each Audio Panel can use any com for selecting its mike to transmit.
As a 'single-pilot' I will often have my headset listening to both coms, and the boom mike for com 1 while the second Audio Panel has its mike set for com 2.
This way I can monitor and speak to Air Traffic Control on com 1 while using the com 2's hand mike to call arinc or unicom. This transmission will block reception from com 2 but will not effect com 1.
The antenna for com 1 is on top of the cabin while com 2's antenna is below the cabin, transmitting on one will not affect the other (unless they were tuned to the same frequency and then it would be received by the other com).
This is not to say that there can be any comparison between the 1936-7 Electra (no Audio Panels needed) installation and my 1985-'05 avionics package, but to say that
you can transmit with one radio without interfering with reception on a second receiver in the same aircraft. This had held true using two Collins Com's prior to the the Garmin 530PW install as well and the 'split' between LF/MW/HF simultaneous frequency's would usually be greater than frequency's within today's VHF range.
I would expect this capability to be common in any aircraft set up for two pilots (with two Audio Panels), to allow for simultaneous communications using com 1 and com 2 on different frequency's.
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In the case of Electra #1055 with the one transmitter and the one seperate receiver, they would have logically been able to operate simultaneousely without interference on different frequencies. As I understand the aircraft radio methods of that era, it was common to transmit to a ground station on a 'calling' frequency and receive a reply on their (different) assigned frequency.
On that unfortunate morning of July 2nd, the ideal would have been to tune the receiver to Itasca's 425KHz CW/MCW LF Transmiter using Electra's Loop for direction (and a 90° heading change for a brief period would confirm the direction and supply a good distance estimate). Using the transmitter on 3105KHz would have allowed two way communications without having to retune the receiver, just by turning the loop 90° out of null point. Less ideal, but if you wanted to accomplish a DF Approach, you could transmit continuous 'A's on 500KHz and listen for Heading Corrections on Itasca's 3105KHz MCW Channel.
So close and yet so far away; for the lack of a Current IFR Ticket and perhaps an ATC/RDF Specialist in the Radio Room (and, of course that missing primary receiver antenna).
Art