Dear Daniele,
I guess the
information
You want is also contained in my email, at least indirectly.
A
german
receive-only radio amateur has built such a ferrite antenna by cut and
try only
and finally succeeded to receive VLF with a ferrite rod combined from
serveral
ferrite parts and has written an article about this in the german radio
amateur
magazine cq-DL. He described his rod according to its dimensions and
number of
turns but did not give its inductivity; at that time he could not
measure it. We
have been in email concact for some time on the subject of inductive
broadband
antennas, and I have encouraged him to buy a Rohde & Schwarz LARU
which had
been offered to him. Now he knows the inductivity of 3 mH which he
had
achieved!
Finally he has kept this ferrite antenna
and some
others for higher frequencies for portable use. But for his
home
installation he has adopted the principle of using a wire loop (even
larger than
mine) and a transformer to the 50 ohms cable. I have found my dimension
rules
for loops by using the ARRL Radio
Designer.
OK?
73 Ha-Jo, DJ1ZB
"Daniele
Tincani" <[email protected]> schrieb:
Hello Ha-Jo,
thank you for your reply, which contains many interesting
information.
However, please note that my question was specifically
about the
possibility to realize wideband rx antennas on ferrite
cores.
Best regards
Danile
From:
"[email protected]"
<[email protected]>
To:
[email protected]
Sent: Friday, August 19, 2011
11:58
PM
Subject: Re: LF:
Ferrite
wideband antennas?
Dear Daniele,
At my locaton in eastern Bavaria I
am using
such a vertical broadband loop pointing north from 10 kHz to 500 kHz
since several years and have also made experiments with a
horizontal loop
covering 1,8 to 30 MHz.
Their principle is as
follows:
A broadband transformer is needed between the
loop
and the cable going into the shack.
Without such a transformer
the
loop inductivity has to be so high when feeding usual cable
impedances
that a ferrite core will be needed to realize the inductivity needed
for
broadband performance. I have used wire loops only so far.
The
inductive reactance of the secondary of this transformer should be 4
times the
cable impedance (3.2 mH for 10 kHz). The loop
circumference should be low
in length compared to a quarter of the highest frequency (for VLF
to MF
usually no problem, for HF the circumference had been 2
meters).
The inductivity of the primary of the broadband
transformer should be equal to the inductivity of the loop (in my
case 30uH and 17 meters circumference for 10 to 500
kHz).
When
meeting these conditions, the inductive reactance of the loop itself
will always be higher by a factor of 4 at least compared
to the
cable impedance transformed down by the turns ratio. This is the
condition for the loop to operate broadband.
But the problem
for the
receiver may come in the shack: It must be capable of taking all
the power delivered by the broadband loop, including the power
received
by broadcast transmitters! Otherwise the receiver may be overloaded
and may
need a more linear frontend or has to be equipped with a good
front end
selectivity.
AT VLF to MF a long
cable into
the shack usually will be no problem because of its low attenuation at
low
frequencies, therefore all additional selectivity I can provide in the
shack.
For HF and higher the situation is different of course and may need at
least
part of selectivity and preamplification already at the loop
output.
For the time being however, I have problems using my
loop for
the reception of SAQ, since a solar panel had been installed on a roof
two
houses from here, in autumn 2010. Obviously the chopper of this
installation is generating a strong 300 Hz spectrum up to 20 kHz
in my
loop. As I could clear interference into my active antenna
completely the interfering field should be
inductive. It seems
to come from several directions (including the wiring of three houses
because
the installation is feeding three phase
current into the
mains)!
OK?
73 Ha-Jo,
DJ1ZB
"Daniele Tincani"
< [email protected]> schrieb:
Hello LF,
a very interesting discussion is in progress on the reflector
on
ferrite rx antennas. My understanding however is that until now we
have been
talking about narrow-band antennas. May I ask the experts if a
wide-band
ferrite antenna could be feasible, able to (partially)
match the
"panoramic" approach of SDR receivers, at least in the LF/NDB and/or
MW
bands? Such an "ideal" antenna would combine some advantages of
air-cored
loops with a reduced size (uhm... too "ideal" to be real
:-))
Regards
Daniele
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