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To the members of the LF
group ,
As suggested by Mal G3KEV
it is wise to fit a protection circuit in the modified ROPEX which
prevents keying the transmitter in case of no drive caused by a
disconnected VFO or a wrong position of the VFO-Xtal drive switch
. Normally it is difficult to modify a existing PCB so I made a small
add on in the corner of the PCB next to the oscillator HCT4060
.
You need the following
parts : one small pnp transistor type 2N2907 or equivalent , one diode type
1N4148 or equivalent ,one ceramic capacitor miniature 150pf 63 Volts and a small
multi terminal tie point strip . Proceed as follows , fasten the tie pointstrip
with the screw in the corner of the PCB next to the HCT4060
,disconnect the red wire from the soldering lug marked key on the PCB and
connect it to a lug on the tiestrip , solder the transistor with the emitter to
the lug marked key on the PCB and the collector to where the
red wire is connected to the tiestrip , solder the base to a free point on the
strip and also solder the diode between the base and the emitter ( anode to base
, cathode to emitter ) , after that connect the capacitor between the base and
the hot side of R6 ( 1K ) next to pin 8 of the 4060 . Thats all
.
How it works : From R6
comes a 274 Khz pulse train if there is drive . This pulse is fed to the base of
the transistor and rectified by the diode , the negative voltage developed over
the diode with respect to the emitter turns the transistor on and the
transmitter can be keyed if there is drive .
Beware ! This circuit
does protect against absence of drive but not against drive of a wrong frequency
or wrong level . You first have to check your VFO level(300-500 millivolts
at abt. 6.5 Mhz ) before operating this circuit
.
73,William
PAØWFO
----- Original Message -----
Sent: Monday, May 23, 2005 2:28 PM
Subject: Fw: Re: Modification of the blower circuit and VFO drive
for the ROPEX LF TRANSMITTER
To Mal and members
of the LF group
Tnx for your warning
about the protection of the finals Mal . In my case the 1010,s did not
explode without proper drive but only made a lot of noise in the receiver while
practically not taking any input current . But that propably will not be so in
all cases . So just to be sure I will make a protection circuit which prevents
the keying ( or uses the protection circuit ) of the transmitter . In my
transmitter the 1010,s are originally fitted and as far as
I can check all the late versions of the Ropex have them fitted
. Because the firm who was selling the transmitters ( maybe also producing them
) went out of business recently a lot of these sets ( 25 ) were sold for very
low prices ( less then 30 Euro,s ) . I hope to work the buyers with manual CW in
the near future .
73 to all of you
William
PAØWFO
----- Original Message -----
Sent: Sunday, May 22, 2005 5:39 PM
Subject: LF: Re: Modification of the blower circuit and VFO drive
for the ROPEX LF TRANSMITTER
William you forgot to say, the PA
explodes without drive !!!!!!!!!!!!!! not just TAKES OFF
The pa fets in my model are IRF1010N,
maybe they have already been changed before !!
A protective cct is necessary so that the
the TX cannot come on except there is already drive. I have such a cct on my
home built TX as a precautionary measure.
Ropex modification operators beware
because if the switch got moved accidentally from the Xtal position and there
was no drive via an ext VFO you will end up with a heap of
ashes!!
Beware de MAL/G3KEV
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