[Lowfer] SW4A & Mag Loop

[Michael Sapp]

Hi All:

Craig, N6IO wrote.....

>Note the hole in the top of the case.  It's for the loop antenna which
>I have - and it works extremely well even though it is indoors.  Great
>null for pulling out the DX station from under the local.  But the
>loop only works up to 1.6 MHz.  You could probably rig one up - it's
>just an aluminum frame with a single loop of RG-174 strung around it
>to a 1/4 inch plug.  Single turn loop with the shield open at the top.
> Preamp is built into the radio and activated when you plug in the
>loop antenna.    Yes, one reason I decided to take a chance on the SW4A was the loop input option for LW & MW reception.The SW4A manual describes the loop similarly, but not how the coax from the 1/4 inch jack is connected or coupled to the loop----just that the shield is split at the top like a standard mag loop.  From the jack the loopcenter conductor couples to the S1B wafer switch with series capacitors either 3000pf (MW?) or .015uf (LW?) to the 6HS6 preamp input LC circuit.  I have to take some time to draw that cirucit out minus the band-switching complexity to understand how the circuit tunes. Then it will become clear to me as to how the loop connections or coupling is made to the loop feed point for the SW4A.    One other point of interest is this SW4A has an "ACCY" jack on the chassis but no mention of it's functionin the manual.  It appears to be identical to the accy jack configuration used in the 2C receiver for an xtal calibrator and the signal line couples to the output side of the 6HS6 preamp tube---which is consistent withan xtal cal function.    I'll have to find a matching MS-4 speaker to get the entire Drake experience---the local antique radio club here in EN90 is having a swap meet this Sunday so I might get lucky and find one....    I'm still uncertain if I like the time delayed AGC function fixed the way it is, but I understandthe design philosophy.....unfortuneately the strong BC siganls have that late night "Crazy Eddie" commercialhard compression sound---the obvious solution is to just listen to weak signals :) ...or throw my stepattenuator in the antenna line...    Thanks for your insights Craig, and to others on the list thank you for the bandwidth....   73  Mike wa3tts