Hi Markus,
Well, the waveforms snapshots were taken right after the prototype was
fired up for the first time on the bench. I have updated the drain
waveform with what it looks like now, in fact it is transmitting WSPR
as we speak :-)
73, Dimitris
2013/2/5 Markus Vester <[email protected]>:
> Dimitrios,
>
> in your screenshot, the duty cycle seems to be already very close to 50% but
> the drain voltage is alrady rising again at turn on. This might be caused by
> a load impedance which is lower than the design value. I think the point
> Eike was trying to make is that it you could intentionally reduce the duty
> cycle a bit to compensate for some degree of mismatch.
>
> Best wishes,
> Markus (DF6NM)
>
> -----Ursprüngliche Mitteilung-----
> Von: Dimitrios Tsifakis <[email protected]>
> An: rsgb_lf_group <[email protected]>
> Verschickt: Di, 5 Feb 2013 10:30 am
> Betreff: Re: Re: LF: My transmit converter description
>
>
>
> Hi Eike,
>
>
>
> you are right, the drain voltage waveform is not perfect! I have since
>
> corrected the duty cycle on the gate to be exactly 50%. I have also
>
> added two 200 V zener diodes from the drain to the source. This will
>
> clamp the voltage to 400 V which is quite safe for a 500 V FET. The
>
> zener diodes together with the fuses, I think, make this design pretty
>
> bullet proof.
>
>
>
> 73, Dimitris
>
>
>
> PS Nothing wrong with your english :-)
>
>
>
>
>
> 2013/2/5 Eike Katzera <[email protected]>:
>
>> Hi Dimitros,
>
>> the pulse shape in this picture does not look good:
>
>> http://people.physics.anu.edu.au/~dxt103/472/nltt/vk1sv-drain.jpg
>
>> The reason seams to be the duty cycle at the gate. Please try to change R5
>
>> to a 100k potentiometer and trim it to a clean single Pilse an the drain.
>> I
>
>> solved the same problem tha way in my PA, wich killed my IRF540.
>
>> Kind regards
>
>> Eike DL3IKE
>
>> PS: sorry for my english ;)
>
>> Gesendet: Dienstag, 05. Februar 2013 um 08:45 Uhr
>
>> Von: "Victor van Kooten" <[email protected]>
>
>> An: [email protected]
>
>> Betreff: Re: LF: My transmit converter description
>
>> Looks very nice Dimitris,hope to see/hear you soon,
>
>>
>
>> 73
>
>>
>
>> Victor
>
>>
>
>>>>> Dimitrios Tsifakis <[email protected]> 05/02/2013 01:50 >>>
>
>> Hello group,
>
>>
>
>> My transmit converter is now finished and tested - it survived two
>
>> sessions of 50% duty cycle WSPR transmissions on 475 kHz and the
>
>> results are great. I thought others may find this useful, so I have
>
>> put a write-up on my web page:
>
>>
>
>> http://people.physics.anu.edu.au/~dxt103/472/nltt/
>
>>
>
>> It is a 50 W class-e PA designed for 50 ohm impedance, so there is no
>
>> need for an impedance transformer. Doesn't get simpler than that :-)
>
>> The driving circuit is based on G3XBM Roger's design with the
>
>> difference of a 10 MHz OCXO LO and the addition of a beefy MOSFET
>
>> driver.
>
>>
>
>> 73, Dimitris VK1SV
>
>>
>
>>
>
>>
>
>>
>
>
>
>
>
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