[ARC5] How Edwin Armstrong invented the superhet

[William Cromwell]

Hi Chris,

Thanks for shedding even more light. The regens I have are the RAK (made 
by RCA) that you mentioned and a National SW-3 with one RF amp ahead of 
the detector. The RF amps are not needed for amplification but do offer 
some 'out-of-band selectivity and more important to isolate the detector 
from the antenna. I have used regens with no amplifier ahead of the 
detector and that isolation is *valuable*.

73,

Bill KU8H

bark less - wag more

On 1/7/23 13:04, Christopher Bowne wrote:
> Surprised that people are forgetting how relatively easy it is to 
> detect CW (and when it came along, SSB) with a regenerative detector. 
> As others has mentioned, regenerative detectors were just about 
> universally used with simple one or
> two stages of RF amplification ahead of the regenerative detector, and 
> even with no amplification stage ahead of the detector.  I was puzzled 
> by the comment that one could not DF with a TRF receiver.  Regardless 
> of whether or not an IF stage was used in
> a superheterodyne or whether the detection was performed at the signal 
> frequency, DF, at least by use of a steerable loop antenna to 
> determine the null in a signal level of a transmitter of interest can 
> either be done on a CW signal with either a regenerative detector or 
> BFO operating at either the signal frequency or an IF frequency.  Low 
> frequency radio beacons used to, and where still active, send their 
> station ID and sometimes long dashes using MCW tone modulation of a 
> steady carrier so they could be received by receivers that did not 
> have a BFO or regenerative detector.
>
> The 1930s vintage design RAK VLF/LF
> receiver is a TRF receiver with two stages of TRF amplification and a 
> regenerative detector.  It has very high selectivity over its entire 
> 15 kHz to 600 kHz, obviously hugest at the lowest frequencies, and 
> comparablen contemporary superhets using the common nominal 455 kHz IF 
> frequencies of the day.
>
> It’s follow on RBA in WW2 was also a TRF was also a TRF design, 
> although I believe it used a tracking RF oscillator at the signal 
> frequency for a BFO.  I believe the injection level of the RBA was 
> adjustable to prevent overwhelming the incoming signal that was to be 
> detected.
>
> Chris AJ1G Stonington CT
>
> Sent from my iPhone
>
>> On Jan 7, 2023, at 11:44, Al Klase <ark at ar88.net> wrote:
>>
>>  OK, let me take a whack at this.
>> We have to go back to the WWI era.  Most radio operations were taking 
>> place well below 1 MHz. Communication receivers we generally crystal 
>> sets connected to large wire antennas.  There was a need for 
>> direction-finding on enemy transmitters. That required a loop 
>> antenna, but the output was too low to work with a crystal set or 
>> even a one-tube regen.
>>
>> W-AEF-1.PNG
>> The solution was multi-tube amplifiers.  The French had a leg up here 
>> having produced the first mass produced tube, the "TM" valve. See 
>> also R. J. Round and the Brit DF "B-Stations."
>>
>> W-AEF-2.PNG
>>
>> PIC00008.jpg
>> French amp among the Armstrong artifacts at the former Ft. Monmouth 
>> museum.
>>
>> Armstrong was working at the Division of Research and Inspection in 
>> Paris.  This was in effect an AT&T laboratory.
>>
>> To get amplification at HF frequencies, where the existing tubes 
>> didn't have much gain, he leveraged his knowledge of heterodyne 
>> frequency conversion gained from his work with the regenerative 
>> receivers.  He built a tunable frequency converter to feed a French 
>> amplifier operating at about 100 KHz.   The circuit was originally 
>> called the supersonic (now we say ultrasonic) heterodyne circuit, 
>> where the incoming signal in not converted to audio, but to an 
>> intermediate RF frequency.
>>
>> Hope the pix come through.
>>
>> Al
>>
>> ARK Sig Block Al Klase - N3FRQ
>> Jersey City, NJ
>> http://www.skywaves.ar88.net/
>> On 1/7/2023 7:37 AM, releazer at earthlink.net wrote:
>>
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