To the members of the rsgb LF group
Those of you who own the ROPEX TX will have
the following experience :
The blower of the set is making so much
noise that it is sometimes difficult to copy the rather weak manual CW sigs that
you hear on LF .
I made the following change : You need the
following parts 1 transistor pnp 2 N 2905 a tagstrip and a few pieces of wire .
Disconnect the black minus wire of the blower and connect it to the emitter of
the transistor , connect the collector to the chassis and the base to the
collector of the BC547 antennarelaydriver this point is also connected to
the minus connection of the transmit Led . The result of this mod is that the
blower is off during reception and on during transmit with the same delay as the
keying circuit , so you can have a quiet shack for listening to weak
signals . As the finals do not generate any heat during reception the cooling
will be ample .
The second modification is more time
The ROPEX is Xtal controlled and after a
few QSO,s you will get the urge to connect a VFO for QSY . For the modification
you will need the following parts : 1 miniature switch double pole double throw
, a BNC chassis female type plug,a 10 nf capacitor and a short
piece of RG174 miniature coax or something like it and a few pieces of hookup
Now the most difficult part follows
: in order to remove the crystal you have to remove the complete case
including the heatsink .
Carefully remove the crystal with solder
wick . Make a hole for the switch and the BNC connector on the rear of the
chassis on the right side of the blower , this completes the most difficult part
of the modification , Now the soldering work . Connect the previous connections
of the Xtal on the cicuit board to the poles of the switch by means of two
pieces RG174 and the Xtal to one side of the switch ( if you switch to this side
the original circuit comes into action and the TX is Xtal controlled as it used
to be ) . Thereafter connect the BNC with the 10 nf capacitor to
that side of the switch which switches to terminal 10 of the oscillator IC
HCT4060 . Thats all.
Requirements for the VFO : Any VFO giving
about 200 to 500 millivolts on the same frequency as the Xtal will do for
IMPORTANT! The VFO has to be on or the
switch set to Xtaldrive otherwise the TX will take off at random
You can prevent this by leaving the
switch out and just connect the VFO to terminal 10 off the oscillator ,
more or less as in Dicks PAØSE transmitter ( described in the LF experimenters
handbook ) with the slight disadvantage that you cannot use the VFO on the
Xtal frequency .