To: rsgb_lf_group@blacksheep.org Date: Sat, 28 May 2005 10:36:38 +0200 MIME-Version: 1.0 X-Priority: 1 X-MSMail-Priority: High X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 Subject: LF: Fw: Re: Modification of the blower circuit and VFO drive and protection for drive failure of the ROPEX LF TRANSMITTER Content-Type: text/html; charset=windows-1252 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SpamFiltered: by PlusNet MXCore (v2.00) Content-transfer-encoding: 8bit

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 -----

From: PA0WFO

To: rsgb_lf_group@blacksheep.org

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 -----

From: hamilton mal

To: rsgb_lf_group@blacksheep.org

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