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

[Kenneth G. Gordon]

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