--- In loopantennas@..., Richards <jruing@...> wrote:
Can you give me an elementary explanation as to why or how
that would prevent one from replacing the wire loop with
another type or size loop? Can I not wire in, say, a bigger
loop and use it with the varactor inside the control unit?
THANKS /// RIchards ///
==============================================================
Marc wrote:
You can't . There is a varactor inside...
I beg to differ! Here's a clip from a post i made in the
ferriterodexperimenters group last may.
A picture is include in the photos section in my ferroids file.
Only difference is that it was made for the DE31:
I have performed further test on the Degen DE31 coupled to my
smallest ferrite
loop. Sensitivity is almost the same as the Palomar although the
noise rejection
isn't as good. The reason is more than likely that were dealing with
a single
ended input vs the balanced input the Palomar affords.
Here is an update of the Degen loop amplifier schematic. (courtesy of
the DRM
software radio forum)
The transistor is a 2SK544 MOSFET (Idss group E) with y21 = 11 mS,
Idss = 2.5 to
6 mA, very low Crss, get its datasheet here.
The tuning diode is a 1S149 or 1SV149 (equivalent) AM tuning diode,
get its
datasheet here.
Latest Update: Latest measurements made by our forum member Funkerberg
(thanks!), indicate that L1 = 10 uH and C2 = 10 nF which yields a low-
Q series
resonant circuit for mediumwave at the drain of the FET, more or less
shortening
mediumwave signals to ground.
C1 = 10 nF, it acts as an RF short.
Assuming a lossless RF decoupling circuit in the battery box, the RF
voltage
gain for shortwave signals with a receiver load of 500 Ohms is about
0.9, it
falls to about 0.36 if a receiver with an input impedance of 50 Ohms
is
connected. However, more signal power is transferred in case of the
50 Ohm
receiver since the impedance mismatch is smaller.
If maximum sensitivity is desired on a receiver with a 50 Ohm input,
a 2:1
impedance transformer could be used to transform the loop amplifier's
output
impedance (100 Ohms, established by R1) to the receiver's input
impedance.
Similarily, a 1:4 impedance transformer could be used to transform
the loop
amplifier's output impedance to a high impedance receiver input in
case maximum
sensitivity is desired.
Link to Schematic:
attachmentid=15616&d=1130372787
John
