[ARC5] How Edwin Armstrong invented the superhet (according to Wikipedia)

[Mark K3MSB]

" *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> 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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