[Milsurplus] U.S. Army TRF LF receiver 1934

[jmfranke at cox.net]

The RBA does not have a regenerative detector. It has "a triode biased near cutoff with a large cathode resistor and uses plate rectification." Hence, there is no regeneration control. 

John  WA4WDL


---- "Kenneth G. Gordon" <kgordon2006 at frontier.com> wrote: 
> On 9 Nov 2015 at 9:04, Ian Wilson wrote:
> 
> > Hi Ken, 
> 
> Hi, Ian. :-)
>  
> > The RU is worth a look. Of note is the BFO - since there is no IF, the BFO has
> > to track the signal frequency (+/- the CW tone).
> 
> Very much like the RBA receiver: a regen detector with a separate BFO 
> which must track the main tuning. QST discussed this sort of TRF back in 
> the 1930s some time. The advantage to that setup is that in a TRF like the 
> RAK/RAL, in order to get a beat-note, the tuning must be slightly off the peak 
> of the selectivity curve. By usiing a separate BFO, the RF stage can be 
> centered in the passband, preserving maximum sensitivity.
> 
> > Compare to the RAK/RAL where
> > the regen detector serves as the BFO.
> 
> Yes. See above.
> 
> > I seem to recall reading that the RU has some regeneration (the amplifier stages
> > aren't neutralized).
> 
> Could be. I am not very familiar with the RU...yet...
> 
> > I don't know if it was well-regarded - possibly temperamental and a bit deaf :)
> 
> Well the "deaf" part is what concerns me. My RAL always "heard" everything 
> that my much-later SB-101 did.
> 
> From experiments done by Bob Keys, it can be proven that if the value of the 
> regen detector's grid leak is very high, and the value of the grid-coupling 
> capacitor is very small, (like, +20 meghoms and -20 pfd) selectivity can be 
> very high indeed, and this would compound the problem: reduced sensitivity 
> caused by the tuning being down on one side or the other of the selectivity 
> curve.
> 
> Thus a separate BFO.
> 
> However, this system would work better at VLF and LF than at HF, it seems 
> to me, since building a stable and accurate tunable BFO would be more 
> difficult at higher frequencies..
> 
> Ken W7EKB
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