[ARC5] How Edwin Armstrong invented the superhet (according to Wikipedia)
MICHAEL BITTNER
mmab at cox.net
Sat Jan 7 10:06:27 EST 2023
In Armstrong's day, I doubt anyone was measuring time between transmitted and received pulses for any practical purpose. The key word in RDF is Direction, and direction is measured in degrees, not microseconds. And at that time, navies were operating mostly on long waves (below the broadcast band), and their principle concern was locating the positions of ships at sea based on bearings measured at multiple shore based RDF stations. Also, ships determining their positions based on bearings to multiple shore based beacons. The Loop Antenna was the key instrument used in these bearing measurements. Besides bearing information, variations in signal strength could determine whether a ship was advancing or retreating on a measured bearing.
As a former Naval Aviator, I did plenty of direction finding on low frequency beacons and 4-Course range stations. The loop antenna was used for DF on the beacons. For the 4-Course range stations, no loop was necessary. It all depended on measuring signal strength both audibly and with an S-meter. I won't go into the procedures for getting oneself "on the beam" of a 4-course range station as there is plenty of information on the internet, but old-time pilots will surely remember the "fade ninety" procedure.
In my day, there were two pulse systems, besides RADAR, used for navigation; LORAN A, an MF hyperbolic position fixing system, and DME, a UHF transponder-based Distance Measuring Equipment. DME was often combined with VOR, and was part of TACAN.
My two cents worth. Mike, W6MAB
> On January 7, 2023 at 8:38 AM Mark K3MSB <mark.k3msb at gmail.com> wrote:
>
> " In RDF, the strength of the signal is used to determine the location of the transmitter"
>
> No. In RDF (or radar) it is the time delay between the transmitted pulse and the returned echo that determines the range to the transmitter, not the returned signal strength.
>
> Last year I enjoyed reading several books on the development of radar by the British ( the best was "Most Secret War" by R. V. Jones") and I don't recall anything such as " tens or even hundreds of triodes had to be used, connected together anode-to-grid. These amplifiers drew enormous amounts of power and required a team of maintenance engineers to keep them running" during the (pre cavity magnetron) initial testing performed in the mid to late 1930's.
>
> " The regenerative system was highly non-linear, amplifying any signal above a certain threshold by a huge amount, sometimes so large it caused it to turn into a transmitter (which was the entire concept behind IFF)."
>
> The early British IFF sets used this principle when a radar pulse from the Chain Home radar was received.
>
> I've found that many people do not realize the level of radio-related technology that was already in use when WW II started (radar, IFF etc). I was surprised to raed the Germans used one of their beam systems (I believe it was Knickebein) when they invaded Poland in 1939.
>
> 73 Mark K3MSB
>
>
> On Sat, Jan 7, 2023 at 2:22 AM Leslie Smith <lnsmith99 at gmail.com mailto:lnsmith99 at gmail.com > wrote:
>
> > > Hello All:
> >
> > When the Aircraft Radio Corporation built the superhets we call SCR-274 (or ARC-5) it was all because the British Admiralty felt the high cost of RDF (etc) was justified. Read all about it below.
> >
> > From Wikipedia: https://en.wikipedia.org/wiki/Superheterodyne_receiver#RDF
> >
> > "RDF
> > There was one role where the regenerative system was not suitable, even for Morse code sources, and that was the task of radio direction finding, or RDF."
> >
> > "The regenerative system was highly non-linear, amplifying any signal above a certain threshold by a huge amount, sometimes so large it caused it to turn into a transmitter (which was the entire concept behind IFF). In RDF, the strength of the signal is used to determine the location of the transmitter, so one requires linear amplification to allow the strength of the original signal, often very weak, to be accurately measured."
> >
> > "To address this need, RDF systems of the era used triodes operating below unity. To get a usable signal from such a system, tens or even hundreds of triodes had to be used, connected together anode-to-grid. These amplifiers drew enormous amounts of power and required a team of maintenance engineers to keep them running. Nevertheless, the strategic value of direction finding on weak signals was so high that the British Admiralty felt the high cost was justified."
> >
> > I found the above when hunting for a little history of the development of the superhet. My first reaction was to send it to "our" resident historian (Hue). I admire his extensive knowledge of radio history and enjoy reading his postings here. Then I thought others may find the role of the British Admiralty "interesting" and so I sent it here instead.
> >
> > I must seek information about the development of the superhet elsewhere, it seems.
> >
> > Best 2023 to all
> >
> > Leslie
> >
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