On Sat, 22 May 2004 00:46:39 +0000 (UTC), in
rec.radio.amateur.homebrew you wrote:


"Richard" wrote in message
...
Apart from Ham radio, I like DXing on many other bands, including LF and
MW.

I am looking for a circuit diagam for a MW pre selector, anything would be
of interest, bit if someohw has one of thoese super dooper ones that can
focus donw to a few khz that wold be even better, (like the palomar MW pre
selector)


Download in a few seconds program SELECT_1 from website below and run
immediately. Also includes tuning coil design. Ideal for MW.
.......

well, it is so nice to inform about my own site, although it has
nothing to do with the request, neither does your reply

A quick calculation for a tuned circuit gave the results of a single
circuitfilter covering 500-1793kHz. Not quite as sharp as requested,
the coil turn calculation might have been right, but what does it
help?

sri, OM

73
Jan-Martin

http://www.noding.com/la8ak/12345/n13.htm

On Fri, 21 May 2004 21:52:06 +0200, "Richard"
wrote:


I am looking for a circuit diagam for a MW pre selector, anything would be
of interest, bit if someohw has one of thoese super dooper ones that can
focus donw to a few khz that wold be even better, (like the palomar MW pre
selector)

I have used for LF a parallel resonant circuit followed by a
(Darlington) emitter follower driving the 50 ohm line to the receiver.
Assuming hFE=100 for each transistor, the resonant circuit loading is
about 500 kohm, thus the loading is quite small. Since the antenna was
short compared to the wavelength and thus highly capacitive, a small
10-100 pF capacitor was used to connect to the hot side of the
resonant circuit.

Although the voltage gain is only 1, it works surprisingly well due to
the large (natural and artificial) field strengths in the LF and lower
MF bands.

When using some processor controlled receiver, it is a good idea to
move the preselector (and hence the antenna connection) as far as
possible from the receiver and connect them with a shielded cable, to
prevent the receiver processor radiation from entering the high
impedance antenna connection. A 1-2 m separation helps a lot, without
making it too uncomfortable to operate.

Paul OH3LWR

On Fri, 21 May 2004 21:52:06 +0200, "Richard"
wrote:


I am looking for a circuit diagam for a MW pre selector, anything would be
of interest, bit if someohw has one of thoese super dooper ones that can
focus donw to a few khz that wold be even better, (like the palomar MW pre
selector)

I have used for LF a parallel resonant circuit followed by a
(Darlington) emitter follower driving the 50 ohm line to the receiver.
Assuming hFE=100 for each transistor, the resonant circuit loading is
about 500 kohm, thus the loading is quite small. Since the antenna was
short compared to the wavelength and thus highly capacitive, a small
10-100 pF capacitor was used to connect to the hot side of the
resonant circuit.

Although the voltage gain is only 1, it works surprisingly well due to
the large (natural and artificial) field strengths in the LF and lower
MF bands.

When using some processor controlled receiver, it is a good idea to
move the preselector (and hence the antenna connection) as far as
possible from the receiver and connect them with a shielded cable, to
prevent the receiver processor radiation from entering the high
impedance antenna connection. A 1-2 m separation helps a lot, without
making it too uncomfortable to operate.

Paul OH3LWR

I am looking for a circuit diagam for a MW pre selector, anything would be
of interest

A Cohn filter covering 1.75-7.2kHz, is shown on
http://home.online.no/~la8ak/c11.htm
some Cohn filters have been published and turned out to be extremely
difficult to copy, but LA7MI claims this is quite easy to make.
Perhaps somebody could scaLe the values down to the mediumwave band?

I've received some more requests for such construction, so I am not
worried whether this writer needed a simple filter or not, it is a lot
of demands for useful solutions

73
jm

I am looking for a circuit diagam for a MW pre selector, anything would be
of interest

A Cohn filter covering 1.75-7.2kHz, is shown on
http://home.online.no/~la8ak/c11.htm
some Cohn filters have been published and turned out to be extremely
difficult to copy, but LA7MI claims this is quite easy to make.
Perhaps somebody could scaLe the values down to the mediumwave band?

I've received some more requests for such construction, so I am not
worried whether this writer needed a simple filter or not, it is a lot
of demands for useful solutions

73
jm