In a message dated 25/04/2007 06:45:18 Greenwich Standard Time,
[email protected] writes:
Hi Peter,
here also FT1000MP and also observed lower senestivity
arround 500 kc.
Wonder if you have built a preamplifier in order to overcome
this ?
Uwe, dk1kq
Hullo Uwe,
Yes, I made a simple preamplifier that solved the problem of low
sensitivity and removed the spurious signals from my local medium wave broadcast
stations.
The input circuit is a small 465 KHz I.F. transformer in a can 2 x 2 x 3.5
cm, possibly from and old transistor radio. The coils are tuned by
330pF capacitors and one of the windings has a low-Z tap. The Q of each
coil is about 75 at 500KHz. I use the low-Z tap for the aerial input and
the secondary winding feeds the gate of a BF244A FET amplifier with its
drain directly coupled to a 2N3906 transistor emitter follower. It is
actually a circuit for an LF band preselector that I published more than 25
years ago in the now defunct Short Wave Magazine. I have seen a very
similar circuit for 500 KHz somewhere on the internet but can't
remember where. However, any simple tuned preamp should work fine at
this frequency.
With the preamp in circuit I operate the FT1000MP with the IPO button 'on'
and the ATT set to give a low S-meter reading on local noise picked up by the
antenna. Sensitivity is now more than adequate and there is no trace of
spurious on the Spectran waterfall.
73 Peter, G3JFS.
