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Hi Daniele,
according to your description your magnetic loop
has an inductively coupled secondary coil,
the pickup coil as you call it,
which presumably performs a step-down transformation
of around 10:1.
Therefore -because of the inductive coupling -
you can operate unbalanced on the
secondary,i.e. rx side ,without disturbing the receiving
loop's
balance itself.
As to mismatch losses you need not worry at
all.
If the rx had 50 Ohm and the antenna output 1000
Ohm you would just loose 7,4dB,
with 2500 Ohm it would be 8,3dB.
If your rx had say 10 kOhm and the antenna 500Ohm
you would loose again 7,4dB.
This is of *any* importance for SNR on MW/LW
because of the high atmsopheric noise.
Probably your low cost RX even will benefit from
this small signal attenuation in terms of less
overloading.
73
Clemens
DL4RAJ
----- Original Message -----
Sent: Sunday, March 28, 2010 8:08
PM
Subject: LF: Balun for tuned loop
antenna
Hi all,
I'm new to the LF and just starting to play with
an homebrew tuned magloop and my small portable (Tecsun PL-600).
I managed to enable (by means of the soldering
iron :-)) the external antenna jack also for MF and LF on PL-600 (normally it
only works in HF). Now I can connect the pick-up turn of my magloop directly
to the radio but I know it would be better to try to keep it balanced by means
of a balun. Here my problem: magloop simulation (with rjeloop3.exe)
tells the antenna has an impedance of between 500 and 2500 ohms (on
the frequencies it covers, from 280KHz up to 1000KHz). On the other hand, I
don't think the receiver have a 50ohm input. In fact, it is designed typically
for HF random wires and has a JFET input buffer stage that should ensure an
high impedance. Given these conditions, does it still make sense to build a
balun? If yes, how could it be designed in terms of number of turns (primary
side and secondary side), etc.?
Many thanks for any feedback.
Reg's
Daniele
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